snac2/activitypub.c

/* snac - A simple, minimalistic ActivityPub instance */
/* copyright (c) 2022 - 2024 grunfink et al. / MIT license */

#include "xs.h"
#include "xs_json.h"
#include "xs_curl.h"
#include "xs_mime.h"
#include "xs_openssl.h"
#include "xs_regex.h"
#include "xs_time.h"
#include "xs_set.h"
#include "xs_match.h"
#include "xs_unicode.h"

#include "snac.h"

#include <sys/wait.h>

const char *public_address = "https:/" "/www.w3.org/ns/activitystreams#Public";

/* susie.png */

const char *susie =
    "iVBORw0KGgoAAAANSUhEUgAAAEAAAABAAQAAAAC"
    "CEkxzAAAAUUlEQVQoz43R0QkAMQwCUDdw/y3dwE"
    "vsvzlL4X1IoQkAisKmwfAFT3RgJHbQezpSRoXEq"
    "eqCL9BJBf7h3QbOCCxV5EVWMEMwG7K1/WODtlvx"
    "AYTtEsDU9F34AAAAAElFTkSuQmCC";

const char *susie_cool =
    "iVBORw0KGgoAAAANSUhEUgAAAEAAAABAAQAAAAC"
    "CEkxzAAAAV0lEQVQoz43RwQ3AMAwCQDZg/y3ZgN"
    "qo3+JaedwDOUQBQFHYaTB8wTM6sGl2cMPu+DFzn"
    "+ZcgN7wF7ZVihXkfSlWIVzIA6dbQzaygllpNuTX"
    "ZmmFNlvxADX1+o0cUPMbAAAAAElFTkSuQmCC";

const char *susie_muertos = 
    "iVBORw0KGgoAAAANSUhEUgAAAEAAAABAAQAAAAC"
    "CEkxzAAAAV0lEQVQoz4XQsQ0AMQxCUW/A/lv+DT"
    "ic6zGRolekIMyMELNp8PiCEw6Q4w4NoAt53IH5m"
    "xXksrZYgZwJrIox+Z8vJAfe2lCxG6AK7eKkWcEb"
    "QHbF617xAQatAAD7jJHUAAAAAElFTkSuQmCC";


const char *default_avatar_base64(void)
/* returns the default avatar in base64 */
{
    time_t t = time(NULL);
    struct tm tm;
    const char *p = susie;

    gmtime_r(&t, &tm);

    if (tm.tm_mon == 10 && tm.tm_mday == 2)
        p = susie_muertos;
    else
    if (tm.tm_wday == 0 || tm.tm_wday == 6)
        p = susie_cool;

    return p;
}


int activitypub_request(snac *user, const char *url, xs_dict **data)
/* request an object */
{
    int status = 0;
    xs *response = NULL;
    xs *payload = NULL;
    int p_size;
    const char *ctype;

    *data = NULL;

    if (user != NULL) {
        /* get from the net */
        response = http_signed_request(user, "GET", url,
            NULL, NULL, 0, &status, &payload, &p_size, 0);
    }

    if (status == 0 || (status >= 500 && status <= 599)) {
        /* I found an instance running Misskey that returned
           500 on signed messages but returned the object
           perfectly without signing (?), so why not try */
        xs_free(response);

        xs *hdrs = xs_dict_new();
        hdrs = xs_dict_append(hdrs, "accept",     "application/activity+json");
        hdrs = xs_dict_append(hdrs, "user-agent", USER_AGENT);

        response = xs_http_request("GET", url, hdrs,
            NULL, 0, &status, &payload, &p_size, 0);
    }

    if (valid_status(status)) {
        /* ensure it's ActivityPub data */
        ctype = xs_dict_get(response, "content-type");

        if (xs_is_null(ctype))
            status = HTTP_STATUS_BAD_REQUEST;
        else
        if (xs_str_in(ctype, "application/activity+json") != -1 ||
            xs_str_in(ctype, "application/ld+json") != -1) {

            /* if there is no payload, fail */
            if (xs_is_null(payload))
                status = HTTP_STATUS_BAD_REQUEST;
            else
                *data = xs_json_loads(payload);
        }
        else
            status = HTTP_STATUS_INTERNAL_SERVER_ERROR;
    }

    return status;
}


int actor_request(snac *user, const char *actor, xs_dict **data)
/* request an actor */
{
    int status;
    xs *payload = NULL;

    if (data)
        *data = NULL;

    /* get from disk first */
    status = actor_get_refresh(user, actor, data);

    if (!valid_status(status)) {
        /* actor data non-existent: get from the net */
        status = activitypub_request(user, actor, &payload);

        if (valid_status(status)) {
            /* renew data */
            status = actor_add(actor, payload);

            if (data != NULL) {
                *data   = payload;
                payload = NULL;
            }
        }
        else
            srv_debug(1, xs_fmt("actor_request error %s %d", actor, status));
    }

    /* collect the (presumed) shared inbox in this actor */
    if (xs_type(xs_dict_get(srv_config, "disable_inbox_collection")) != XSTYPE_TRUE) {
        if (valid_status(status) && data && *data)
            inbox_add_by_actor(*data);
    }

    return status;
}


const char *get_atto(const xs_dict *msg)
/* gets the attributedTo field (an actor) */
{
    const xs_val *actor = xs_dict_get(msg, "attributedTo");

    /* if the actor is a list of objects (like on Peertube videos), pick the Person */
    if (xs_type(actor) == XSTYPE_LIST) {
        const xs_list *p = actor;
        int c = 0;
        const xs_dict *v;
        actor = NULL;

        while (actor == NULL && xs_list_next(p, &v, &c)) {
            if (xs_type(v) == XSTYPE_DICT) {
                const char *type = xs_dict_get(v, "type");
                if (xs_type(type) == XSTYPE_STRING && strcmp(type, "Person") == 0) {
                    actor = xs_dict_get(v, "id");

                    if (xs_type(actor) != XSTYPE_STRING)
                        actor = NULL;
                }
            }
        }
    }
    else
    if (xs_type(actor) == XSTYPE_DICT) {
        /* bandwagon.fm returns this */
        actor = xs_dict_get(actor, "id");
    }

    return actor;
}


const char *get_in_reply_to(const xs_dict *msg)
/* gets the inReplyTo id */
{
    const xs_val *in_reply_to = xs_dict_get(msg, "inReplyTo");

    if (xs_type(in_reply_to) == XSTYPE_DICT)
        in_reply_to = xs_dict_get(in_reply_to, "id");

    return in_reply_to;
}


xs_list *get_attachments(const xs_dict *msg)
/* unify the garbage fire that are the attachments */
{
    xs_list *l = xs_list_new();
    const xs_list *p;

    /* try first the attachments list */
    if (!xs_is_null(p = xs_dict_get(msg, "attachment"))) {
        xs *attach = NULL;
        const xs_val *v;

        /* ensure it's a list */
        if (xs_type(p) == XSTYPE_DICT) {
            attach = xs_list_new();
            attach = xs_list_append(attach, p);
        }
        else
            attach = xs_dup(p);

        if (xs_type(attach) == XSTYPE_LIST && xs_list_len(attach) == 0) {
            /* does the message have an image? */
            const xs_dict *d = xs_dict_get(msg, "image");
            if (xs_type(d) == XSTYPE_DICT) {
                /* add it to the attachment list */
                attach = xs_list_append(attach, d);
            }
        }

        /* now iterate the list */
        int c = 0;
        while (xs_list_next(attach, &v, &c)) {
            const char *type = xs_dict_get(v, "mediaType");
            if (xs_is_null(type))
                type = xs_dict_get(v, "type");

            if (xs_is_null(type))
                continue;

            const char *href = xs_dict_get(v, "url");
            if (xs_is_null(href))
                href = xs_dict_get(v, "href");
            if (xs_is_null(href))
                continue;

            /* infer MIME type from non-specific attachments */
            if (xs_list_len(attach) < 2 && xs_match(type, "Link|Document")) {
                char *mt = (char *)xs_mime_by_ext(href);

                if (xs_match(mt, "image/*|audio/*|video/*")) /* */
                    type = mt;
            }

            const char *name = xs_dict_get(v, "name");
            if (xs_is_null(name))
                name = xs_dict_get(msg, "name");
            if (xs_is_null(name))
                name = "";

            xs *d = xs_dict_new();
            d = xs_dict_append(d, "type", type);
            d = xs_dict_append(d, "href", href);
            d = xs_dict_append(d, "name", name);

            const xs_dict *icon = xs_dict_get(v, "icon");
            if (xs_type(icon) == XSTYPE_DICT)
                d = xs_dict_append(d, "icon", icon);

            l = xs_list_append(l, d);
        }
    }

    /** urls (attachments from Peertube) **/
    p = xs_dict_get(msg, "url");

    if (xs_type(p) == XSTYPE_LIST) {
        const char *href = NULL;
        const char *type = NULL;
        int c = 0;
        const xs_val *v;

        while (href == NULL && xs_list_next(p, &v, &c)) {
            if (xs_type(v) == XSTYPE_DICT) {
                const char *mtype = xs_dict_get(v, "type");

                if (xs_type(mtype) == XSTYPE_STRING && strcmp(mtype, "Link") == 0) {
                    mtype = xs_dict_get(v, "mediaType");
                    const xs_list *tag = xs_dict_get(v, "tag");

                    if (xs_type(mtype) == XSTYPE_STRING &&
                        strcmp(mtype, "application/x-mpegURL") == 0 &&
                        xs_type(tag) == XSTYPE_LIST) {
                        /* now iterate the tag list, looking for a video URL */
                        const xs_dict *d;
                        int c = 0;

                        while (href == NULL && xs_list_next(tag, &d, &c)) {
                            if (xs_type(d) == XSTYPE_DICT) {
                                if (xs_type(mtype = xs_dict_get(d, "mediaType")) == XSTYPE_STRING &&
                                    xs_startswith(mtype, "video/")) {
                                    const char *h = xs_dict_get(d, "href");

                                    /* this is probably it */
                                    if (xs_type(h) == XSTYPE_STRING) {
                                        href = h;
                                        type = mtype;
                                    }
                                }
                            }
                        }
                    }
                }
            }
        }

        if (href && type) {
            xs *d = xs_dict_new();
            d = xs_dict_append(d, "href", href);
            d = xs_dict_append(d, "type", type);
            d = xs_dict_append(d, "name", "---");

            l = xs_list_append(l, d);
        }
    }

    return l;
}


int timeline_request(snac *snac, const char **id, xs_str **wrk, int level)
/* ensures that an entry and its ancestors are in the timeline */
{
    int status = 0;

    if (level < MAX_CONVERSATION_LEVELS && !xs_is_null(*id)) {
        xs *msg = NULL;

        /* from a blocked instance? discard and break */
        if (is_instance_blocked(*id)) {
            snac_debug(snac, 1, xs_fmt("timeline_request blocked instance %s", *id));
            return status;
        }

        /* is the object already there? */
        if (!valid_status(object_get(*id, &msg))) {
            /* no; download it */
            status = activitypub_request(snac, *id, &msg);

            if (valid_status(status)) {
                const xs_dict *object = msg;
                const char *type = xs_dict_get(object, "type");

                /* get the id again from the object, as it may be different */
                const char *nid = xs_dict_get(object, "id");

                if (xs_type(nid) != XSTYPE_STRING)
                    return 0;

                if (wrk && strcmp(nid, *id) != 0) {
                    snac_debug(snac, 1,
                        xs_fmt("timeline_request canonical id for %s is %s", *id, nid));

                    *wrk = xs_dup(nid);
                    *id  = *wrk;
                }

                if (xs_is_null(type))
                    type = "(null)";

                srv_debug(2, xs_fmt("timeline_request type %s '%s'", nid, type));

                if (strcmp(type, "Create") == 0) {
                    /* some software like lemmy nest Announce + Create + Note */
                    if (!xs_is_null(object = xs_dict_get(object, "object"))) {
                        type = xs_dict_get(object, "type");
                        nid  = xs_dict_get(object, "id");
                    }
                    else
                        type = "(null)";
                }

                if (xs_match(type, POSTLIKE_OBJECT_TYPE)) {
                    if (content_match("filter_reject.txt", object))
                        snac_log(snac, xs_fmt("timeline_request rejected by content %s", nid));
                    else {
                        const char *actor = get_atto(object);

                        if (!xs_is_null(actor)) {
                            /* request (and drop) the actor for this entry */
                            if (!valid_status(actor_request(snac, actor, NULL))) {
                                /* failed? retry later */
                                enqueue_actor_refresh(snac, actor, 60);
                            }

                            /* does it have an ancestor? */
                            const char *in_reply_to = get_in_reply_to(object);

                            /* store */
                            timeline_add(snac, nid, object);

                            /* redistribute to lists for this user */
                            list_distribute(snac, actor, object);

                            /* recurse! */
                            timeline_request(snac, &in_reply_to, NULL, level + 1);
                        }
                    }
                }
            }
        }
    }

    return status;
}


int send_to_inbox_raw(const char *keyid, const char *seckey,
                  const xs_str *inbox, const xs_dict *msg,
                  xs_val **payload, int *p_size, int timeout)
/* sends a message to an Inbox */
{
    int status;
    xs_dict *response;
    xs *j_msg = xs_json_dumps((xs_dict *)msg, 4);

    response = http_signed_request_raw(keyid, seckey, "POST", inbox,
        NULL, j_msg, strlen(j_msg), &status, payload, p_size, timeout);

    xs_free(response);

    return status;
}


int send_to_inbox(snac *snac, const xs_str *inbox, const xs_dict *msg,
                  xs_val **payload, int *p_size, int timeout)
/* sends a message to an Inbox */
{
    const char *seckey = xs_dict_get(snac->key, "secret");

    return send_to_inbox_raw(snac->actor, seckey, inbox, msg, payload, p_size, timeout);
}


xs_str *get_actor_inbox(const char *actor, int shared)
/* gets an actor's inbox */
{
    xs *data = NULL;
    const char *v = NULL;

    if (valid_status(actor_request(NULL, actor, &data))) {
        /* try first endpoints/sharedInbox */
        if (shared && (v = xs_dict_get(data, "endpoints")))
            v = xs_dict_get(v, "sharedInbox");

        /* try then the regular inbox */
        if (xs_is_null(v))
            v = xs_dict_get(data, "inbox");
    }

    return xs_is_null(v) ? NULL : xs_dup(v);
}


int send_to_actor(snac *snac, const char *actor, const xs_dict *msg,
                  xs_val **payload, int *p_size, int timeout)
/* sends a message to an actor */
{
    int status = HTTP_STATUS_BAD_REQUEST;
    xs *inbox = get_actor_inbox(actor, 1);

    if (!xs_is_null(inbox))
        status = send_to_inbox(snac, inbox, msg, payload, p_size, timeout);

    return status;
}


void post_message(snac *snac, const char *actor, const xs_dict *msg)
/* posts a message immediately (bypassing the output queues) */
{
    xs *payload = NULL;
    int p_size;

    int status = send_to_actor(snac, actor, msg, &payload, &p_size, 3);

    srv_log(xs_fmt("post_message to actor %s %d", actor, status));

    if (!valid_status(status))
        /* cannot send right now, enqueue */
        enqueue_message(snac, msg);
}


xs_list *recipient_list(snac *snac, const xs_dict *msg, int expand_public)
/* returns the list of recipients for a message */
{
    const xs_val *to = xs_dict_get(msg, "to");
    const xs_val *cc = xs_dict_get(msg, "cc");
    xs_set rcpts;
    int n;

    xs_set_init(&rcpts);

    const xs_list *lists[] = { to, cc, NULL };
    for (n = 0; lists[n]; n++) {
        xs_list *l = (xs_list *)lists[n];
        const char *v;
        xs *tl = NULL;

        /* if it's a string, create a list with only one element */
        if (xs_type(l) == XSTYPE_STRING) {
            tl = xs_list_new();
            tl = xs_list_append(tl, l);

            l = tl;
        }

        while (xs_list_iter(&l, &v)) {
            if (expand_public && strcmp(v, public_address) == 0) {
                /* iterate the followers and add them */
                xs *fwers = follower_list(snac);
                const char *actor;

                char *p = fwers;
                while (xs_list_iter(&p, &actor))
                    xs_set_add(&rcpts, actor);
            }
            else
                xs_set_add(&rcpts, v);
        }
    }

    return xs_set_result(&rcpts);
}


int is_msg_public(const xs_dict *msg)
/* checks if a message is public */
{
    const char *to = xs_dict_get(msg, "to");
    const char *cc = xs_dict_get(msg, "cc");
    int n;

    const char *lists[] = { to, cc, NULL };
    for (n = 0; lists[n]; n++) {
        const xs_val *l = lists[n];

        if (xs_type(l) == XSTYPE_STRING) {
            if (strcmp(l, public_address) == 0)
                return 1;
        }
        else
        if (xs_type(l) == XSTYPE_LIST) {
            if (xs_list_in(l, public_address) != -1)
                return 1;
        }
    }

    return 0;
}


int is_msg_from_private_user(const xs_dict *msg)
/* checks if a message is from a local, private user */
{
    int ret = 0;

    /* is this message from a local user? */
    if (xs_startswith(xs_dict_get(msg, "id"), srv_baseurl)) {
        const char *atto = get_atto(msg);
        xs *l = xs_split(atto, "/");
        const char *uid = xs_list_get(l, -1);
        snac user;

        if (uid && user_open(&user, uid)) {
            if (xs_type(xs_dict_get(user.config, "private")) == XSTYPE_TRUE)
                ret = 1;

            user_free(&user);
        }
    }

    return ret;
}


int is_msg_for_me(snac *snac, const xs_dict *c_msg)
/* checks if this message is for me */
{
    const char *type  = xs_dict_get(c_msg, "type");
    const char *actor = xs_dict_get(c_msg, "actor");

    if (strcmp(actor, snac->actor) == 0) {
        /* message by myself? (most probably via the shared-inbox) reject */
        snac_debug(snac, 1, xs_fmt("ignoring message by myself"));
        return 0;
    }

    if (xs_match(type, "Like|Announce|EmojiReact")) {
        const char *object = xs_dict_get(c_msg, "object");

        if (xs_type(object) == XSTYPE_DICT)
            object = xs_dict_get(object, "id");

        /* bad object id? reject */
        if (xs_type(object) != XSTYPE_STRING)
            return 0;

        /* if it's about one of our posts, accept it */
        if (xs_startswith(object, snac->actor))
            return 2;

        /* if it's by someone we don't follow, reject */
        return following_check(snac, actor);
    }

    /* if it's an Undo, it must be from someone related to us */
    if (xs_match(type, "Undo")) {
        return follower_check(snac, actor) || following_check(snac, actor);
    }

    /* if it's an Accept + Follow, it must be for a Follow we created */
    if (xs_match(type, "Accept")) {
        return following_check(snac, actor);
    }

    /* if it's a Follow, it must be explicitly for us */
    if (xs_match(type, "Follow")) {
        const char *object = xs_dict_get(c_msg, "object");
        return !xs_is_null(object) && strcmp(snac->actor, object) == 0;
    }

    /* only accept Ping directed to us */
    if (xs_match(type, "Ping")) {
        const char *dest = xs_dict_get(c_msg, "to");
        return !xs_is_null(dest) && strcmp(snac->actor, dest) == 0;
    }

    /* if it's not a Create or Update, allow as is */
    if (!xs_match(type, "Create|Update")) {
        return 1;
    }

    int pub_msg = is_msg_public(c_msg);

    /* if this message is public and we follow the actor of this post, allow */
    if (pub_msg && following_check(snac, actor))
        return 1;

    const xs_dict *msg = xs_dict_get(c_msg, "object");
    xs *rcpts = recipient_list(snac, msg, 0);
    xs_list *p = rcpts;
    const xs_str *v;

    xs *actor_followers = NULL;

    if (!pub_msg) {
        /* not a public message; get the actor and its followers list */
        xs *actor_obj = NULL;

        if (valid_status(object_get(actor, &actor_obj))) {
            const xs_val *fw = xs_dict_get(actor_obj, "followers");
            if (fw)
                actor_followers = xs_dup(fw);
        }
    }

    while(xs_list_iter(&p, &v)) {
        /* explicitly for me? accept */
        if (strcmp(v, snac->actor) == 0)
            return 2;

        if (pub_msg) {
            /* a public message for someone we follow? (probably cc'ed) accept */
            if (following_check(snac, v))
                return 5;
        }
        else
        if (actor_followers && strcmp(v, actor_followers) == 0) {
            /* if this message is for this actor's followers, are we one of them? */
            if (following_check(snac, actor))
                return 6;
        }
    }

    /* accept if it's by someone we follow */
    const char *atto = get_atto(msg);

    if (pub_msg && !xs_is_null(atto) && following_check(snac, atto))
        return 3;

    /* is this message a reply to another? */
    const char *irt = get_in_reply_to(msg);
    if (!xs_is_null(irt)) {
        xs *r_msg = NULL;

        /* try to get the replied message */
        if (valid_status(object_get(irt, &r_msg))) {
            atto = get_atto(r_msg);

            /* accept if the replied message is from someone we follow */
            if (pub_msg && !xs_is_null(atto) && following_check(snac, atto))
                return 4;
        }
    }

    /* does this message contain a tag we are following? */
    const xs_list *fw_tags = xs_dict_get(snac->config, "followed_hashtags");
    if (pub_msg && xs_type(fw_tags) == XSTYPE_LIST) {
        const xs_list *tags_in_msg = xs_dict_get(msg, "tag");
        if (xs_type(tags_in_msg) == XSTYPE_LIST) {
            const xs_dict *te;

            /* iterate the tags in the message */
            xs_list_foreach(tags_in_msg, te) {
                if (xs_type(te) == XSTYPE_DICT) {
                    const char *type = xs_dict_get(te, "type");
                    const char *name = xs_dict_get(te, "name");

                    if (xs_type(type) == XSTYPE_STRING && xs_type(name) == XSTYPE_STRING) {
                        if (strcmp(type, "Hashtag") == 0) {
                            xs *lc_name = xs_utf8_to_lower(name);

                            if (xs_list_in(fw_tags, lc_name) != -1)
                                return 7;
                        }
                    }
                }
            }
        }
    }

    return 0;
}


xs_str *process_tags(snac *snac, const char *content, xs_list **tag)
/* parses mentions and tags from content */
{
    xs_str *nc  = xs_str_new(NULL);
    xs_list *tl = *tag;
    xs *split;
    xs_list *p;
    const xs_val *v;
    int n = 0;

    /* create a default server for incomplete mentions */
    xs *def_srv = NULL;

    if (xs_list_len(tl)) {
        /* if there are any mentions, get the server from
           the first one, which is the inReplyTo author */
        p = tl;
        while (xs_list_iter(&p, &v)) {
            const char *type = xs_dict_get(v, "type");
            const char *name = xs_dict_get(v, "name");

            if (type && name && strcmp(type, "Mention") == 0) {
                xs *l = xs_split(name, "@");

                def_srv = xs_dup(xs_list_get(l, -1));

                break;
            }
        }
    }

    if (xs_is_null(def_srv))
        /* use this same server */
        def_srv = xs_dup(xs_dict_get(srv_config, "host"));

    split = xs_regex_split(content, "(@[A-Za-z0-9_]+(@[A-Za-z0-9\\.-]+)?|&#[0-9]+;|#(_|[^[:punct:][:space:]])+)");

    p = split;
    while (xs_list_iter(&p, &v)) {
        if ((n & 0x1)) {
            if (*v == '@') {
                xs *link = NULL;
                xs *wuid = NULL;

                if (strchr(v + 1, '@') == NULL) {
                    /* only one @? it's a dumb Mastodon-like mention
                       without server; add the default one */
                    wuid = xs_fmt("%s@%s", v, def_srv);

                    snac_debug(snac, 2, xs_fmt("mention without server '%s' '%s'", v, wuid));
                }
                else
                    wuid = xs_dup(v);

                /* query the webfinger about this fellow */
                xs *actor = NULL;
                xs *uid   = NULL;
                int status;

                status = webfinger_request(wuid, &actor, &uid);

                if (valid_status(status) && actor && uid) {
                    xs *d = xs_dict_new();
                    xs *n = xs_fmt("@%s", uid);

                    d = xs_dict_append(d, "type",   "Mention");
                    d = xs_dict_append(d, "href",   actor);
                    d = xs_dict_append(d, "name",   n);

                    tl = xs_list_append(tl, d);

                    link = xs_fmt("<span class=\"h-card\"><a href=\"%s\" class=\"u-url mention\">%s</a></span>", actor, n);
                }

                if (!xs_is_null(link))
                    nc = xs_str_cat(nc, link);
                else
                    nc = xs_str_cat(nc, v);
            }
            else
            if (*v == '#') {
                /* hashtag */
                xs *d = xs_dict_new();
                xs *n = xs_tolower_i(xs_dup(v));
                xs *h = xs_fmt("%s?t=%s", srv_baseurl, n + 1);
                xs *l = xs_fmt("<a href=\"%s\" class=\"mention hashtag\" rel=\"tag\">%s</a>", h, v);

                d = xs_dict_append(d, "type",   "Hashtag");
                d = xs_dict_append(d, "href",   h);
                d = xs_dict_append(d, "name",   n);

                tl = xs_list_append(tl, d);

                /* add the code */
                nc = xs_str_cat(nc, l);
            }
            else
            if (*v == '&') {
                /* HTML Unicode entity, probably part of an emoji */

                /* write as is */
                nc = xs_str_cat(nc, v);
            }
        }
        else
            nc = xs_str_cat(nc, v);

        n++;
    }

    *tag = tl;

    return nc;
}


void notify(snac *snac, const char *type, const char *utype, const char *actor, const xs_dict *msg)
/* notifies the user of relevant events */
{
    /* skip our own notifications */
    if (strcmp(snac->actor, actor) == 0)
        return;

    const char *id = xs_dict_get(msg, "id");

    if (strcmp(type, "Create") == 0) {
        /* only notify of notes specifically for us */
        xs *rcpts = recipient_list(snac, msg, 0);

        if (xs_list_in(rcpts, snac->actor) == -1)
            return;

        /* discard votes */
        const xs_dict *note = xs_dict_get(msg, "object");

        if (note && !xs_is_null(xs_dict_get(note, "name")))
            return;
    }

    if (strcmp(type, "Undo") == 0 && strcmp(utype, "Follow") != 0)
        return;

    /* get the object id */
    const char *objid = xs_dict_get(msg, "object");

    if (xs_type(objid) == XSTYPE_DICT)
        objid = xs_dict_get(objid, "id");

    if (xs_match(type, "Like|Announce|EmojiReact")) {
        /* if it's not an admiration about something by us, done */
        if (xs_is_null(objid) || !xs_startswith(objid, snac->actor))
            return;
    }

    /* updated poll? */
    if (strcmp(type, "Update") == 0 && strcmp(utype, "Question") == 0) {
        const xs_dict *poll;
        const char *poll_id;

        if ((poll = xs_dict_get(msg, "object")) == NULL)
            return;

        /* if it's not closed, discard */
        if (xs_is_null(xs_dict_get(poll, "closed")))
            return;

        if ((poll_id = xs_dict_get(poll, "id")) == NULL)
            return;

        /* if it's not ours and we didn't vote, discard */
        if (!xs_startswith(poll_id, snac->actor) && !was_question_voted(snac, poll_id))
            return;
    }

    /* user will love to know about this! */

    /* prepare message body */
    xs *body = xs_fmt("User  : @%s@%s\n",
        xs_dict_get(snac->config, "uid"),
        xs_dict_get(srv_config,   "host")
    );

    if (strcmp(utype, "(null)") != 0) {
        xs *s1 = xs_fmt("Type  : %s + %s\n", type, utype);
        body = xs_str_cat(body, s1);
    }
    else {
        xs *s1 = xs_fmt("Type  : %s\n", type);
        body = xs_str_cat(body, s1);
    }

    {
        xs *s1 = xs_fmt("Actor : %s\n", actor);
        body = xs_str_cat(body, s1);
    }

    if (objid != NULL) {
        xs *s1 = xs_fmt("Object: %s\n", objid);
        body = xs_str_cat(body, s1);
    }

    /* email */

    const char *email = "[disabled by admin]";

    if (xs_type(xs_dict_get(srv_config, "disable_email_notifications")) != XSTYPE_TRUE) {
        email = xs_dict_get(snac->config_o, "email");
        if (xs_is_null(email)) {
            email = xs_dict_get(snac->config, "email");

            if (xs_is_null(email))
                email = "[empty]";
        }
    }

    if (*email != '\0' && *email != '[') {
        snac_debug(snac, 1, xs_fmt("email notify %s %s %s", type, utype, actor));

        xs *subject = xs_fmt("snac notify for @%s@%s",
                    xs_dict_get(snac->config, "uid"), xs_dict_get(srv_config, "host"));
        xs *from    = xs_fmt("snac-daemon <snac-daemon@%s>", xs_dict_get(srv_config, "host"));
        xs *header  = xs_fmt(
                    "From: %s\n"
                    "To: %s\n"
                    "Subject: %s\n"
                    "\n",
                    from, email, subject);

        xs *email_body = xs_fmt("%s%s", header, body);

        enqueue_email(email_body, 0);
    }

    /* telegram */

    const char *bot     = xs_dict_get(snac->config, "telegram_bot");
    const char *chat_id = xs_dict_get(snac->config, "telegram_chat_id");

    if (!xs_is_null(bot) && !xs_is_null(chat_id) && *bot && *chat_id)
        enqueue_telegram(body, bot, chat_id);

    /* ntfy */
    const char *ntfy_server = xs_dict_get(snac->config, "ntfy_server");
    const char *ntfy_token  = xs_dict_get(snac->config, "ntfy_token");

    if (!xs_is_null(ntfy_server) && *ntfy_server)
        enqueue_ntfy(body, ntfy_server, ntfy_token);

    /* auto boost */
    if (xs_match(type, "Create") && xs_is_true(xs_dict_get(snac->config, "auto_boost"))) {
        xs *msg = msg_admiration(snac, objid, "Announce");
        enqueue_message(snac, msg);

        snac_debug(snac, 1, xs_fmt("auto boosted %s", objid));
    }

    /* finally, store it in the notification folder */
    if (strcmp(type, "Follow") == 0)
        objid = id;
    else
    if (strcmp(utype, "Follow") == 0)
        objid = actor;

    notify_add(snac, type, utype, actor, objid != NULL ? objid : id, msg);
}

/** messages **/

xs_dict *msg_base(snac *snac, const char *type, const char *id,
                  const char *actor, const char *date, const char *object)
/* creates a base ActivityPub message */
{
    xs *did       = NULL;
    xs *published = NULL;
    xs *ntid      = tid(0);
    const char *obj_id;

    if (xs_type(object) == XSTYPE_DICT)
        obj_id = xs_dict_get(object, "id");
    else
        obj_id = object;

    /* generated values */
    if (date && strcmp(date, "@now") == 0) {
        published = xs_str_utctime(0, ISO_DATE_SPEC);
        date = published;
    }

    if (id != NULL) {
        if (strcmp(id, "@dummy") == 0) {
            did = xs_fmt("%s/d/%s/%s", snac->actor, ntid, type);

            id = did;
        }
        else
        if (strcmp(id, "@object") == 0) {
            if (obj_id != NULL) {
                did = xs_fmt("%s/%s_%s", obj_id, type, ntid);
                id = did;
            }
            else
                id = NULL;
        }
        else
        if (strcmp(id, "@wrapper") == 0) {
            /* like @object, but always generate the same id */
            if (object != NULL) {
                date = xs_dict_get(object, "published");
                did = xs_fmt("%s/%s", obj_id, type);
                id = did;
            }
            else
                id = NULL;
        }
    }

    xs_dict *msg = xs_dict_new();

    msg = xs_dict_append(msg, "@context", "https:/" "/www.w3.org/ns/activitystreams");
    msg = xs_dict_append(msg, "type",     type);

    if (id != NULL)
        msg = xs_dict_append(msg, "id", id);

    if (actor != NULL)
        msg = xs_dict_append(msg, "actor", actor);

    if (date != NULL)
        msg = xs_dict_append(msg, "published", date);

    if (object != NULL)
        msg = xs_dict_append(msg, "object", object);

    return msg;
}


xs_dict *msg_collection(snac *snac, const char *id, int items)
/* creates an empty OrderedCollection message */
{
    xs_dict *msg = msg_base(snac, "OrderedCollection", id, NULL, NULL, NULL);
    xs *n = xs_number_new(items);

    msg = xs_dict_append(msg, "attributedTo", snac->actor);
    msg = xs_dict_append(msg, "totalItems",   n);

    return msg;
}


xs_dict *msg_accept(snac *snac, const xs_val *object, const char *to)
/* creates an Accept message (as a response to a Follow) */
{
    xs_dict *msg = msg_base(snac, "Accept", "@dummy", snac->actor, NULL, object);

    msg = xs_dict_append(msg, "to", to);

    return msg;
}


xs_dict *msg_update(snac *snac, const xs_dict *object)
/* creates an Update message */
{
    xs_dict *msg = msg_base(snac, "Update", "@object", snac->actor, "@now", object);

    const char *type = xs_dict_get(object, "type");

    if (strcmp(type, "Note") == 0) {
        msg = xs_dict_append(msg, "to", xs_dict_get(object, "to"));
        msg = xs_dict_append(msg, "cc", xs_dict_get(object, "cc"));
    }
    else
    if (strcmp(type, "Person") == 0) {
        msg = xs_dict_append(msg, "to", public_address);

        /* also spam the people being followed, so that
           they have the newest information about who we are */
        xs *cc = following_list(snac);

        msg = xs_dict_append(msg, "cc", cc);
    }
    else
        msg = xs_dict_append(msg, "to", public_address);

    return msg;
}


xs_dict *msg_admiration(snac *snac, const char *object, const char *type)
/* creates a Like or Announce message */
{
    xs *a_msg    = NULL;
    xs_dict *msg = NULL;
    xs *wrk      = NULL;

    /* call the object */
    timeline_request(snac, &object, &wrk, 0);

    if (valid_status(object_get(object, &a_msg))) {
        xs *rcpts = xs_list_new();
        xs *o_md5 = xs_md5_hex(object, strlen(object));
        xs *id    = xs_fmt("%s/%s/%s", snac->actor, *type == 'L' ? "l" : "a", o_md5);

        msg = msg_base(snac, type, id, snac->actor, "@now", object);

        if (is_msg_public(a_msg))
            rcpts = xs_list_append(rcpts, public_address);

        rcpts = xs_list_append(rcpts, get_atto(a_msg));

        msg = xs_dict_append(msg, "to", rcpts);
    }
    else
        snac_log(snac, xs_fmt("msg_admiration cannot retrieve object %s", object));

    return msg;
}


xs_dict *msg_repulsion(snac *user, const char *id, const char *type)
/* creates an Undo + admiration message */
{
    xs *a_msg    = NULL;
    xs_dict *msg = NULL;

    if (valid_status(object_get(id, &a_msg))) {
        /* create a clone of the original admiration message */
        xs *object = msg_admiration(user, id, type);

        /* delete the published date */
        object = xs_dict_del(object, "published");

        /* create an undo message for this object */
        msg = msg_undo(user, object);

        /* copy the 'to' field */
        msg = xs_dict_set(msg, "to", xs_dict_get(object, "to"));
    }

    /* now we despise this */
    object_unadmire(id, user->actor, *type == 'L' ? 1 : 0);

    return msg;
}


xs_dict *msg_actor(snac *snac)
/* create a Person message for this actor */
{
    xs *ctxt     = xs_list_new();
    xs *icon     = xs_dict_new();
    xs *keys     = xs_dict_new();
    xs *tags     = xs_list_new();
    xs *avtr     = NULL;
    xs *kid      = NULL;
    xs *f_bio    = NULL;
    xs_dict *msg = msg_base(snac, "Person", snac->actor, NULL, NULL, NULL);
    const char *p;
    int n;

    /* change the @context (is this really necessary?) */
    ctxt = xs_list_append(ctxt, "https:/" "/www.w3.org/ns/activitystreams");
    ctxt = xs_list_append(ctxt, "https:/" "/w3id.org/security/v1");
    msg = xs_dict_set(msg, "@context",          ctxt);

    msg = xs_dict_set(msg, "url",               snac->actor);
    msg = xs_dict_set(msg, "name",              xs_dict_get(snac->config, "name"));
    msg = xs_dict_set(msg, "preferredUsername", snac->uid);
    msg = xs_dict_set(msg, "published",         xs_dict_get(snac->config, "published"));

    xs *f_bio_2 = not_really_markdown(xs_dict_get(snac->config, "bio"), NULL, &tags);
    f_bio = process_tags(snac, f_bio_2, &tags);
    msg = xs_dict_set(msg, "summary", f_bio);
    msg = xs_dict_set(msg, "tag", tags);

    char *folders[] = { "inbox", "outbox", "followers", "following", "featured", NULL };
    for (n = 0; folders[n]; n++) {
        xs *f = xs_fmt("%s/%s", snac->actor, folders[n]);
        msg = xs_dict_set(msg, folders[n], f);
    }

    p = xs_dict_get(snac->config, "avatar");

    if (*p == '\0')
        avtr = xs_fmt("%s/susie.png", srv_baseurl);
    else
        avtr = xs_dup(p);

    icon = xs_dict_append(icon, "type",         "Image");
    icon = xs_dict_append(icon, "mediaType",    xs_mime_by_ext(avtr));
    icon = xs_dict_append(icon, "url",          avtr);
    msg = xs_dict_set(msg, "icon", icon);

    kid = xs_fmt("%s#main-key", snac->actor);

    keys = xs_dict_append(keys, "id",           kid);
    keys = xs_dict_append(keys, "owner",        snac->actor);
    keys = xs_dict_append(keys, "publicKeyPem", xs_dict_get(snac->key, "public"));
    msg = xs_dict_set(msg, "publicKey", keys);

    /* if the "bot" config field is set to true, change type to "Service" */
    if (xs_type(xs_dict_get(snac->config, "bot")) == XSTYPE_TRUE)
        msg = xs_dict_set(msg, "type", "Service");

    /* add the header image, if there is one defined */
    const char *header = xs_dict_get(snac->config, "header");
    if (!xs_is_null(header)) {
        xs *d = xs_dict_new();
        d = xs_dict_append(d, "type",       "Image");
        d = xs_dict_append(d, "mediaType",  xs_mime_by_ext(header));
        d = xs_dict_append(d, "url",        header);
        msg = xs_dict_set(msg, "image", d);
    }

    /* add the metadata as attachments of PropertyValue */
    xs *metadata = NULL;
    const xs_dict *md = xs_dict_get(snac->config, "metadata");

    if (xs_type(md) == XSTYPE_DICT)
        metadata = xs_dup(md);
    else
    if (xs_type(md) == XSTYPE_STRING) {
        metadata = xs_dict_new();
        xs *l = xs_split(md, "\n");
        const char *ll;

        xs_list_foreach(l, ll) {
            xs *kv = xs_split_n(ll, "=", 1);
            const char *k = xs_list_get(kv, 0);
            const char *v = xs_list_get(kv, 1);

            if (k && v) {
                xs *kk = xs_strip_i(xs_dup(k));
                xs *vv = xs_strip_i(xs_dup(v));
                metadata = xs_dict_set(metadata, kk, vv);
            }
        }
    }

    if (xs_type(metadata) == XSTYPE_DICT) {
        xs *attach = xs_list_new();
        const xs_str *k;
        const xs_str *v;

        int c = 0;
        while (xs_dict_next(metadata, &k, &v, &c)) {
            xs *d = xs_dict_new();

            xs *k2 = encode_html(k);
            xs *v2 = NULL;

            if (xs_startswith(v, "https:/") || xs_startswith(v, "http:/")) {
                xs *t = encode_html(v);
                v2 = xs_fmt("<a href=\"%s\" rel=\"me\">%s</a>", t, t);
            }
            else
                v2 = encode_html(v);

            d = xs_dict_append(d, "type",  "PropertyValue");
            d = xs_dict_append(d, "name",  k2);
            d = xs_dict_append(d, "value", v2);

            attach = xs_list_append(attach, d);
        }

        msg = xs_dict_set(msg, "attachment", attach);
    }

    /* use shared inboxes? */
    if (xs_type(xs_dict_get(srv_config, "shared_inboxes")) == XSTYPE_TRUE) {
        xs *d = xs_dict_new();
        xs *si = xs_fmt("%s/shared-inbox", srv_baseurl);
        d = xs_dict_append(d, "sharedInbox", si);
        msg = xs_dict_set(msg, "endpoints", d);
    }

    /* does this user have an aka? */
    const char *aka = xs_dict_get(snac->config, "alias");
    if (xs_type(aka) == XSTYPE_STRING && *aka) {
        xs *loaka = xs_list_append(xs_list_new(), aka);

        msg = xs_dict_set(msg, "alsoKnownAs", loaka);
    }

    const xs_val *manually = xs_dict_get(snac->config, "approve_followers");
    msg = xs_dict_set(msg, "manuallyApprovesFollowers",
        xs_stock(xs_is_true(manually) ? XSTYPE_TRUE : XSTYPE_FALSE));

    return msg;
}


xs_dict *msg_create(snac *snac, const xs_dict *object)
/* creates a 'Create' message */
{
    xs_dict *msg = msg_base(snac, "Create", "@wrapper", snac->actor, NULL, object);
    const xs_val *v;

    if ((v = get_atto(object)))
        msg = xs_dict_append(msg, "attributedTo", v);

    if ((v = xs_dict_get(object, "cc")))
        msg = xs_dict_append(msg, "cc", v);

    if ((v = xs_dict_get(object, "to")))
        msg = xs_dict_append(msg, "to", v);
    else
        msg = xs_dict_append(msg, "to", public_address);

    return msg;
}


xs_dict *msg_undo(snac *snac, const xs_val *object)
/* creates an 'Undo' message */
{
    xs_dict *msg = msg_base(snac, "Undo", "@object", snac->actor, "@now", object);
    const char *to;

    if (xs_type(object) == XSTYPE_DICT && (to = xs_dict_get(object, "object")))
        msg = xs_dict_append(msg, "to", to);

    return msg;
}


xs_dict *msg_delete(snac *snac, const char *id)
/* creates a 'Delete' + 'Tombstone' for a local entry */
{
    xs *tomb = xs_dict_new();
    xs_dict *msg = NULL;

    /* sculpt the tombstone */
    tomb = xs_dict_append(tomb, "type", "Tombstone");
    tomb = xs_dict_append(tomb, "id",   id);

    /* now create the Delete */
    msg = msg_base(snac, "Delete", "@object", snac->actor, "@now", tomb);

    msg = xs_dict_append(msg, "to", public_address);

    return msg;
}


xs_dict *msg_follow(snac *snac, const char *q)
/* creates a 'Follow' message */
{
    xs *actor_o = NULL;
    xs *actor   = NULL;
    xs_dict *msg = NULL;
    int status;

    xs *url_or_uid = xs_strip_i(xs_str_new(q));

    if (xs_startswith(url_or_uid, "https:/") || xs_startswith(url_or_uid, "http:/"))
        actor = xs_dup(url_or_uid);
    else
    if (!valid_status(webfinger_request(url_or_uid, &actor, NULL)) || actor == NULL) {
        snac_log(snac, xs_fmt("cannot resolve user %s to follow", url_or_uid));
        return NULL;
    }

    /* request the actor */
    status = actor_request(snac, actor, &actor_o);

    if (valid_status(status)) {
        /* check if the actor is an alias */
        const char *r_actor = xs_dict_get(actor_o, "id");

        if (r_actor && strcmp(actor, r_actor) != 0) {
            snac_log(snac, xs_fmt("actor to follow is an alias %s -> %s", actor, r_actor));
        }

        msg = msg_base(snac, "Follow", "@dummy", snac->actor, NULL, r_actor);
    }
    else
        snac_log(snac, xs_fmt("cannot get actor to follow %s %d", actor, status));

    return msg;
}


xs_dict *msg_note(snac *snac, const xs_str *content, const xs_val *rcpts,
                  const xs_str *in_reply_to, const xs_list *attach,
                  int scope, const char *lang_str)
/* creates a 'Note' message */
/* scope: 0, public; 1, private (mentioned only); 2, "quiet public"; 3, followers only */
{
    xs *ntid = tid(0);
    xs *id   = xs_fmt("%s/p/%s", snac->actor, ntid);
    xs *ctxt = NULL;
    xs *fc2  = NULL;
    xs *fc1  = NULL;
    xs *to   = NULL;
    xs *cc   = xs_list_new();
    xs *irt  = NULL;
    xs *tag  = xs_list_new();
    xs *atls = xs_list_new();
    xs_dict *msg = msg_base(snac, "Note", id, NULL, "@now", NULL);
    xs_list *p;
    const xs_val *v;

    /* FIXME: implement scopes 2 and 3 */
    int priv = scope == 1;

    if (rcpts == NULL)
        to = xs_list_new();
    else {
        if (xs_type(rcpts) == XSTYPE_STRING) {
            to = xs_list_new();
            to = xs_list_append(to, rcpts);
        }
        else
            to = xs_dup(rcpts);
    }

    /* format the content */
    fc2 = not_really_markdown(content, &atls, &tag);

    if (in_reply_to != NULL && *in_reply_to) {
        xs *p_msg = NULL;
        xs *wrk   = NULL;

        /* demand this thing */
        timeline_request(snac, &in_reply_to, &wrk, 0);

        if (valid_status(object_get(in_reply_to, &p_msg))) {
            /* add this author as recipient */
            const char *a, *v;

            if ((a = get_atto(p_msg)) && xs_list_in(to, a) == -1)
                to = xs_list_append(to, a);

            /* add this author to the tag list as a mention */
            if (!xs_is_null(a)) {
                xs *l = xs_split(a, "/");
                xs *actor_o = NULL;

                if (xs_list_len(l) > 3 && valid_status(object_get(a, &actor_o))) {
                    const char *uname = xs_dict_get(actor_o, "preferredUsername");

                    if (!xs_is_null(uname) && *uname) {
                        xs *handle = xs_fmt("@%s@%s", uname, xs_list_get(l, 2));

                        xs *t = xs_dict_new();

                        t = xs_dict_append(t, "type", "Mention");
                        t = xs_dict_append(t, "href", a);
                        t = xs_dict_append(t, "name", handle);

                        tag = xs_list_append(tag, t);
                    }
                }
            }

            /* get the context, if there is one */
            if ((v = xs_dict_get(p_msg, "context")))
                ctxt = xs_dup(v);

            /* propagate the conversation field, if there is one */
            if ((v = xs_dict_get(p_msg, "conversation")))
                msg = xs_dict_append(msg, "conversation", v);

            /* if this message is public, ours will also be */
            if (!priv && is_msg_public(p_msg) && xs_list_in(to, public_address) == -1)
                to = xs_list_append(to, public_address);
        }

        irt = xs_dup(in_reply_to);
    }
    else
        irt = xs_val_new(XSTYPE_NULL);

    /* extract the mentions and hashtags and convert the content */
    fc1 = process_tags(snac, fc2, &tag);

    /* create the attachment list, if there are any */
    if (!xs_is_null(attach)) {
        xs_list_foreach(attach, v) {
            const char *url  = xs_list_get(v, 0);
            const char *alt  = xs_list_get(v, 1);
            const char *mime = xs_mime_by_ext(url);
            int add = 1;

            /* check if it's already here */
            const xs_dict *ad;
            xs_list_foreach(atls, ad) {
                if (strcmp(xs_dict_get_def(ad, "url", ""), url) == 0) {
                    add = 0;
                    break;
                }
            }

            if (add) {
                xs *d = xs_dict_new();
                d = xs_dict_append(d, "mediaType", mime);
                d = xs_dict_append(d, "url",       url);
                d = xs_dict_append(d, "name",      alt);
                d = xs_dict_append(d, "type",
                    xs_startswith(mime, "image/") ? "Image" : "Document");

                atls = xs_list_append(atls, d);
            }
        }
    }

    if (ctxt == NULL)
        ctxt = xs_fmt("%s#ctxt", id);

    /* add all mentions to the cc */
    p = tag;
    while (xs_list_iter(&p, &v)) {
        if (xs_type(v) == XSTYPE_DICT) {
            const char *t;

            if (!xs_is_null(t = xs_dict_get(v, "type")) && strcmp(t, "Mention") == 0) {
                if (!xs_is_null(t = xs_dict_get(v, "href")))
                    cc = xs_list_append(cc, t);
            }
        }
    }

    /* no recipients? must be for everybody */
    if (!priv && xs_list_len(to) == 0)
        to = xs_list_append(to, public_address);

    /* delete all cc recipients that also are in the to */
    p = to;
    while (xs_list_iter(&p, &v)) {
        int i;

        if ((i = xs_list_in(cc, v)) != -1)
            cc = xs_list_del(cc, i);
    }

    msg = xs_dict_append(msg, "attributedTo", snac->actor);
    msg = xs_dict_append(msg, "summary",      "");
    msg = xs_dict_append(msg, "content",      fc1);
    msg = xs_dict_append(msg, "context",      ctxt);
    msg = xs_dict_append(msg, "url",          id);
    msg = xs_dict_append(msg, "to",           to);
    msg = xs_dict_append(msg, "cc",           cc);
    msg = xs_dict_append(msg, "inReplyTo",    irt);
    msg = xs_dict_append(msg, "tag",          tag);

    msg = xs_dict_append(msg, "sourceContent", content);

    if (xs_list_len(atls))
        msg = xs_dict_append(msg, "attachment", atls);

    /* set language content map */
    if (xs_type(lang_str) == XSTYPE_STRING) {
        /* split at the first _ */
        xs *l0 = xs_split(lang_str, "_");
        const char *lang = xs_list_get(l0, 0);

        if (xs_type(lang) == XSTYPE_STRING && strlen(lang) == 2) {
            /* a valid ISO language id */
            xs *cmap = xs_dict_new();
            cmap = xs_dict_set(cmap, lang, xs_dict_get(msg, "content"));
            msg = xs_dict_set(msg, "contentMap", cmap);
        }
    }

    return msg;
}


xs_dict *msg_ping(snac *user, const char *rcpt)
/* creates a Ping message (https://humungus.tedunangst.com/r/honk/v/tip/f/docs/ping.txt) */
{
    xs_dict *msg = msg_base(user, "Ping", "@dummy", user->actor, NULL, NULL);

    msg = xs_dict_append(msg, "to", rcpt);

    return msg;
}


xs_dict *msg_pong(snac *user, const char *rcpt, const char *object)
/* creates a Pong message (https://humungus.tedunangst.com/r/honk/v/tip/f/docs/ping.txt) */
{
    xs_dict *msg = msg_base(user, "Pong", "@dummy", user->actor, NULL, object);

    msg = xs_dict_append(msg, "to", rcpt);

    return msg;
}


xs_dict *msg_move(snac *user, const char *new_account)
/* creates a Move message (to move the user to new_account) */
{
    xs_dict *msg = msg_base(user, "Move", "@dummy", user->actor, NULL, user->actor);

    msg = xs_dict_append(msg, "target", new_account);

    return msg;
}


xs_dict *msg_question(snac *user, const char *content, xs_list *attach,
                      const xs_list *opts, int multiple, int end_secs)
/* creates a Question message */
{
    xs_dict *msg = msg_note(user, content, NULL, NULL, attach, 0, NULL);
    int max      = 8;
    xs_set seen;

    msg = xs_dict_set(msg, "type", "Question");

    /* make it non-editable */
    msg = xs_dict_del(msg, "sourceContent");

    xs *o = xs_list_new();
    xs_list *p = (xs_list *)opts;
    const xs_str *v;
    xs *replies = xs_json_loads("{\"type\":\"Collection\",\"totalItems\":0}");

    xs_set_init(&seen);

    while (max && xs_list_iter(&p, &v)) {
        if (*v) {
            xs *v2 = xs_dup(v);
            xs *d  = xs_dict_new();

            if (strlen(v2) > 60) {
                v2[60] = '\0';
                v2 = xs_str_cat(v2, "...");
            }

            if (xs_set_add(&seen, v2) == 1) {
                d = xs_dict_append(d, "type",    "Note");
                d = xs_dict_append(d, "name",    v2);
                d = xs_dict_append(d, "replies", replies);
                o = xs_list_append(o, d);

                max--;
            }
        }
    }

    xs_set_free(&seen);

    msg = xs_dict_append(msg, multiple ? "anyOf" : "oneOf", o);

    /* set the end time */
    time_t t = time(NULL) + end_secs;
    xs *et = xs_str_utctime(t, ISO_DATE_SPEC);

    msg = xs_dict_append(msg, "endTime", et);

    return msg;
}


int update_question(snac *user, const char *id)
/* updates the poll counts */
{
    xs *msg   = NULL;
    xs *rcnt  = xs_dict_new();
    xs *lopts = xs_list_new();
    const xs_list *opts;
    xs_list *p;
    const xs_val *v;

    /* get the object */
    if (!valid_status(object_get(id, &msg)))
        return -1;

    /* closed? do nothing more */
    if (xs_dict_get(msg, "closed"))
        return -2;

    /* get the options */
    if ((opts = xs_dict_get(msg, "oneOf")) == NULL &&
        (opts = xs_dict_get(msg, "anyOf")) == NULL)
        return -3;

    /* fill the initial count */
    int c = 0;
    while (xs_list_next(opts, &v, &c)) {
        const char *name = xs_dict_get(v, "name");
        if (name) {
            lopts = xs_list_append(lopts, name);
            rcnt  = xs_dict_set(rcnt, name, xs_stock(0));
        }
    }

    xs_set s;
    xs_set_init(&s);

    /* iterate now the children (the votes) */
    xs *chld = object_children(id);
    p = chld;
    while (xs_list_iter(&p, &v)) {
        xs *obj = NULL;

        if (!valid_status(object_get_by_md5(v, &obj)))
            continue;

        const char *name = xs_dict_get(obj, "name");
        const char *atto = get_atto(obj);

        if (name && atto) {
            /* get the current count */
            const xs_number *cnt = xs_dict_get(rcnt, name);

            if (xs_type(cnt) == XSTYPE_NUMBER) {
                /* if it exists, increment */
                xs *ucnt = xs_number_new(xs_number_get(cnt) + 1);
                rcnt = xs_dict_set(rcnt, name, ucnt);

                xs_set_add(&s, atto);
            }
        }
    }

    xs *rcpts = xs_set_result(&s);

    /* create a new list of options with their new counts */
    xs *nopts = xs_list_new();
    p = lopts;
    while (xs_list_iter(&p, &v)) {
        const xs_number *cnt = xs_dict_get(rcnt, v);

        if (xs_type(cnt) == XSTYPE_NUMBER) {
            xs *d1 = xs_dict_new();
            xs *d2 = xs_dict_new();

            d2 = xs_dict_append(d2, "type",       "Collection");
            d2 = xs_dict_append(d2, "totalItems", cnt);

            d1 = xs_dict_append(d1, "type",    "Note");
            d1 = xs_dict_append(d1, "name",    v);
            d1 = xs_dict_append(d1, "replies", d2);

            nopts = xs_list_append(nopts, d1);
        }
    }

    /* update the list */
    msg = xs_dict_set(msg, xs_dict_get(msg, "oneOf") != NULL ? "oneOf" : "anyOf", nopts);

    /* due date? */
    int closed = 0;
    const char *end_time = xs_dict_get(msg, "endTime");
    if (!xs_is_null(end_time)) {
        xs *now = xs_str_utctime(0, ISO_DATE_SPEC);

        /* is now greater than the endTime? */
        if (strcmp(now, end_time) >= 0) {
            xs *et    = xs_dup(end_time);
            msg       = xs_dict_set(msg, "closed", et);

            closed = 1;
        }
    }

    /* update the count of voters */
    xs *vcnt = xs_number_new(xs_list_len(rcpts));
    msg = xs_dict_set(msg, "votersCount", vcnt);
    msg = xs_dict_set(msg, "cc", rcpts);

    /* store */
    object_add_ow(id, msg);

    snac_debug(user, 1, xs_fmt("recounted poll %s", id));
    timeline_touch(user);

    /* send an update message to all voters */
    xs *u_msg = msg_update(user, msg);
    u_msg = xs_dict_set(u_msg, "cc", rcpts);

    enqueue_message(user, u_msg);

    if (closed) {
        xs *c_msg = msg_update(user, msg);
        notify(user, "Update", "Question", user->actor, c_msg);
    }

    return 0;
}


/** queues **/

int process_input_message(snac *snac, const xs_dict *msg, const xs_dict *req)
/* processes an ActivityPub message from the input queue */
/* return values: -1, fatal error; 0, transient error, retry;
   1, processed and done; 2, propagate to users (only when no user is set) */
{
    const char *actor = xs_dict_get(msg, "actor");
    const char *type  = xs_dict_get(msg, "type");
    xs *actor_o = NULL;
    int a_status;
    int do_notify = 0;

    if (xs_is_null(actor) || *actor == '\0') {
        srv_debug(0, xs_fmt("malformed message (bad actor)"));
        return -1;
    }

    /* question votes may not have a type */
    if (xs_is_null(type))
        type = "Note";

    /* reject uninteresting messages right now */
    if (xs_match(type, "Add|View|Reject|Read|Remove")) {
        srv_debug(0, xs_fmt("Ignored message of type '%s'", type));
        return -1;
    }

    const char *object, *utype;

    object = xs_dict_get(msg, "object");
    if (object != NULL && xs_type(object) == XSTYPE_DICT)
        utype = xs_dict_get(object, "type");
    else
        utype = "(null)";

    /* special case for Delete messages */
    if (strcmp(type, "Delete") == 0) {
        /* if the actor is not here, do not even try */
        if (!object_here(actor)) {
            srv_debug(1, xs_fmt("dropped 'Delete' message from unknown actor '%s'", actor));
            return -1;
        }

        /* discard crap */
        if (xs_is_null(object)) {
            srv_log(xs_fmt("dropped 'Delete' message with invalid object from actor '%s'", actor));
            return -1;
        }

        /* also discard if the object to be deleted is not here */
        const char *obj_id = object;
        if (xs_type(obj_id) == XSTYPE_DICT)
            obj_id = xs_dict_get(obj_id, "id");

        if (xs_is_null(obj_id) || !object_here(obj_id)) {
            srv_debug(1, xs_fmt("dropped 'Delete' message from unknown object '%s'", obj_id));
            return -1;
        }
    }

    /* bring the actor */
    a_status = actor_request(snac, actor, &actor_o);

    /* do not retry permanent failures */
    if (a_status == HTTP_STATUS_NOT_FOUND
        || a_status == HTTP_STATUS_GONE
        || a_status < 0) {
        srv_debug(1, xs_fmt("dropping message due to actor error %s %d", actor, a_status));
        return -1;
    }

    if (!valid_status(a_status)) {
        /* do not retry 'Delete' messages */
        if (strcmp(type, "Delete") == 0) {
            srv_debug(1, xs_fmt("dropping 'Delete' message due to actor error %s %d", actor, a_status));
            return -1;
        }

        /* other actor download errors */

        /* the actor may require a signed request; propagate if no user is set */
        if (snac == NULL)
            return 2;

        /* may need a retry */
        srv_debug(0, xs_fmt("error requesting actor %s %d -- retry later", actor, a_status));
        return 0;
    }

    /* check the signature */
    xs *sig_err = NULL;

    if (!check_signature(req, &sig_err)) {
        srv_log(xs_fmt("bad signature %s (%s)", actor, sig_err));

        srv_archive_error("check_signature", sig_err, req, msg);
        return -1;
    }

    /* if no user is set, no further checks can be done; propagate */
    if (snac == NULL)
        return 2;

    /* reject messages that are not for this user */
    if (!is_msg_for_me(snac, msg)) {
        snac_debug(snac, 1, xs_fmt("message from %s of type '%s' not for us", actor, type));

        return 1;
    }

    /* if it's a DM from someone we don't follow, reject the message */
    if (xs_type(xs_dict_get(snac->config, "drop_dm_from_unknown")) == XSTYPE_TRUE) {
        if (strcmp(utype, "Note") == 0 && !is_msg_public(msg) &&
            !following_check(snac, actor)) {
            snac_log(snac, xs_fmt("DM rejected from unknown actor %s", actor));

            return 1;
        }
    }

    /* check the minimum acceptable account age */
    int min_account_age = xs_number_get(xs_dict_get(srv_config, "min_account_age"));

    if (min_account_age > 0) {
        const char *actor_date = xs_dict_get(actor_o, "published");
        if (!xs_is_null(actor_date)) {
            time_t actor_t = xs_parse_iso_date(actor_date, 0);

            if (actor_t < 950000000) {
                snac_log(snac, xs_fmt("rejected activity from %s (suspicious date, %s)",
                    actor, actor_date));

                return 1;
            }

            if (actor_t > 0) {
                int td = (int)(time(NULL) - actor_t);

                snac_debug(snac, 2, xs_fmt("actor %s age: %d seconds", actor, td));

                if (td < min_account_age) {
                    snac_log(snac, xs_fmt("rejected activity from %s (too new, %d seconds)",
                        actor, td));

                    return 1;
                }
            }
        }
        else
            snac_debug(snac, 1, xs_fmt("warning: empty or null creation date for %s", actor));
    }

    if (strcmp(type, "Follow") == 0) { /** **/
        const char *id = xs_dict_get(msg, "id");

        if (xs_is_null(id)) {
            snac_log(snac, xs_fmt("malformed message: no 'id' field"));
        }
        else
        if (!follower_check(snac, actor)) {
            /* ensure the actor object is here */
            if (!object_here(actor)) {
                xs *actor_obj = NULL;
                actor_request(snac, actor, &actor_obj);
                object_add(actor, actor_obj);
            }

            if (xs_is_true(xs_dict_get(snac->config, "approve_followers"))) {
                pending_add(snac, actor, msg);

                snac_log(snac, xs_fmt("new pending follower approval %s", actor));
            }
            else {
                /* automatic following */
                xs *f_msg = xs_dup(msg);
                xs *reply = msg_accept(snac, f_msg, actor);

                post_message(snac, actor, reply);

                if (xs_is_null(xs_dict_get(f_msg, "published"))) {
                    /* add a date if it doesn't include one (Mastodon) */
                    xs *date = xs_str_utctime(0, ISO_DATE_SPEC);
                    f_msg = xs_dict_set(f_msg, "published", date);
                }

                timeline_add(snac, id, f_msg);

                follower_add(snac, actor);

                snac_log(snac, xs_fmt("new follower %s", actor));
            }

            do_notify = 1;
        }
        else
            snac_log(snac, xs_fmt("repeated 'Follow' from %s", actor));
    }
    else
    if (strcmp(type, "Undo") == 0) { /** **/
        const char *id = xs_dict_get(object, "object");

        if (xs_type(object) != XSTYPE_DICT)
            utype = "Follow";

        if (strcmp(utype, "Follow") == 0) { /** **/
            if (id && strcmp(id, snac->actor) != 0)
                snac_debug(snac, 1, xs_fmt("Undo + Follow from %s not for us (%s)", actor, id));
            else {
                if (valid_status(follower_del(snac, actor))) {
                    snac_log(snac, xs_fmt("no longer following us %s", actor));
                    do_notify = 1;
                }
                else
                if (pending_check(snac, actor)) {
                    pending_del(snac, actor);
                    snac_log(snac, xs_fmt("cancelled pending follow from %s", actor));
                }
                else
                    snac_log(snac, xs_fmt("error deleting follower %s", actor));
            }
        }
        else
        if (strcmp(utype, "Like") == 0 || strcmp(utype, "EmojiReact") == 0) { /** **/
            int status = object_unadmire(id, actor, 1);

            snac_log(snac, xs_fmt("Undo '%s' for %s %d", utype, id, status));
        }
        else
        if (strcmp(utype, "Announce") == 0) { /** **/
            int status = HTTP_STATUS_OK;

            /* commented out: if a followed user boosts something that
               is requested and then unboosts, the post remains here,
               but with no apparent reason, and that is confusing */
            //status = object_unadmire(id, actor, 0);

            snac_log(snac, xs_fmt("Unboost for %s %d", id, status));
        }
        else
            snac_debug(snac, 1, xs_fmt("ignored 'Undo' for object type '%s'", utype));
    }
    else
    if (strcmp(type, "Create") == 0) { /** **/
        if (is_muted(snac, actor)) {
            snac_log(snac, xs_fmt("ignored 'Create' + '%s' from muted actor %s", utype, actor));
            return 1;
        }

        if (xs_match(utype, "Note|Article")) { /** **/
            const char *id          = xs_dict_get(object, "id");
            const char *in_reply_to = get_in_reply_to(object);
            const char *atto        = get_atto(object);
            xs *wrk           = NULL;

            if (xs_is_null(id))
                snac_log(snac, xs_fmt("malformed message: no 'id' field"));
            else
            if (xs_is_null(atto))
                snac_log(snac, xs_fmt("malformed message: no 'attributedTo' field"));
            else
            if (!xs_is_null(in_reply_to) && is_hidden(snac, in_reply_to)) {
                snac_debug(snac, 0, xs_fmt("dropped reply %s to hidden post %s", id, in_reply_to));
            }
            else {
                if (content_match("filter_reject.txt", object)) {
                    snac_log(snac, xs_fmt("rejected by content %s", id));
                    return 1;
                }

                if (strcmp(actor, atto) != 0)
                    snac_log(snac, xs_fmt("SUSPICIOUS: actor != atto (%s != %s)", actor, atto));

                timeline_request(snac, &in_reply_to, &wrk, 0);

                if (timeline_add(snac, id, object)) {
                    snac_log(snac, xs_fmt("new '%s' %s %s", utype, actor, id));
                    do_notify = 1;
                }

                /* if it has a "name" field, it may be a vote for a question */
                const char *name = xs_dict_get(object, "name");

                if (!xs_is_null(name) && *name && !xs_is_null(in_reply_to) && *in_reply_to)
                    update_question(snac, in_reply_to);
            }
        }
        else
        if (strcmp(utype, "Question") == 0) { /**  **/
            const char *id = xs_dict_get(object, "id");

            if (xs_is_null(id))
                snac_log(snac, xs_fmt("malformed message: no 'id' field"));
            else
            if (timeline_add(snac, id, object))
                snac_log(snac, xs_fmt("new 'Question' %s %s", actor, id));
        }
        else
        if (strcmp(utype, "Video") == 0) { /** **/
            const char *id = xs_dict_get(object, "id");

            if (xs_is_null(id))
                snac_log(snac, xs_fmt("malformed message: no 'id' field"));
            else
            if (timeline_add(snac, id, object))
                snac_log(snac, xs_fmt("new 'Video' %s %s", actor, id));
        }
        else
            snac_debug(snac, 1, xs_fmt("ignored 'Create' for object type '%s'", utype));
    }
    else
    if (strcmp(type, "Accept") == 0) { /** **/
        if (strcmp(utype, "(null)") == 0) {
            const char *obj_id = xs_dict_get(msg, "object");

            /* if the accepted object id is a string that may
               be created by us, it's a follow */
            if (xs_type(obj_id) == XSTYPE_STRING &&
                xs_startswith(obj_id, srv_baseurl) &&
                xs_endswith(obj_id, "/Follow"))
                utype = "Follow";
        }

        if (strcmp(utype, "Follow") == 0) { /** **/
            if (following_check(snac, actor)) {
                following_add(snac, actor, msg);
                snac_log(snac, xs_fmt("confirmed follow from %s", actor));
            }
            else
                snac_log(snac, xs_fmt("spurious follow accept from %s", actor));
        }
        else
        if (strcmp(utype, "Create") == 0) {
            /* some implementations send Create confirmations, go figure */
            snac_debug(snac, 1, xs_dup("ignored 'Accept' + 'Create'"));
        }
        else {
            srv_archive_error("accept", "ignored Accept", req, msg);
            snac_debug(snac, 1, xs_fmt("ignored 'Accept' for object type '%s'", utype));
        }
    }
    else
    if (strcmp(type, "Like") == 0 || strcmp(type, "EmojiReact") == 0) { /** **/
        if (xs_type(object) == XSTYPE_DICT)
            object = xs_dict_get(object, "id");

        if (xs_is_null(object))
            snac_log(snac, xs_fmt("malformed message: no 'id' field"));
        else
        if (timeline_admire(snac, object, actor, 1) == HTTP_STATUS_CREATED)
            snac_log(snac, xs_fmt("new '%s' %s %s", type, actor, object));
        else
            snac_log(snac, xs_fmt("repeated '%s' from %s to %s", type, actor, object));

        do_notify = 1;
    }
    else
    if (strcmp(type, "Announce") == 0) { /** **/
        if (xs_type(object) == XSTYPE_DICT)
            object = xs_dict_get(object, "id");

        if (xs_is_null(object))
            snac_log(snac, xs_fmt("malformed message: no 'id' field"));
        else
        if (is_muted(snac, actor) && !xs_startswith(object, snac->actor))
            snac_log(snac, xs_fmt("dropped 'Announce' from muted actor %s", actor));
        else
        if (is_limited(snac, actor) && !xs_startswith(object, snac->actor))
            snac_log(snac, xs_fmt("dropped 'Announce' from limited actor %s", actor));
        else {
            xs *a_msg = NULL;
            xs *wrk   = NULL;

            timeline_request(snac, &object, &wrk, 0);

            if (valid_status(object_get(object, &a_msg))) {
                const char *who = get_atto(a_msg);

                if (who && !is_muted(snac, who)) {
                    /* bring the actor */
                    xs *who_o = NULL;

                    if (valid_status(actor_request(snac, who, &who_o))) {
                        if (timeline_admire(snac, object, actor, 0) == HTTP_STATUS_CREATED)
                            snac_log(snac, xs_fmt("new 'Announce' %s %s", actor, object));
                        else
                            snac_log(snac, xs_fmt("repeated 'Announce' from %s to %s",
                                actor, object));

                        /* distribute the post with the actor as 'proxy' */
                        list_distribute(snac, actor, a_msg);

                        do_notify = 1;
                    }
                    else
                        snac_debug(snac, 1, xs_fmt("dropped 'Announce' on actor request error %s", who));
                }
                else
                    snac_log(snac, xs_fmt("ignored 'Announce' about muted actor %s", who));
            }
            else
                snac_debug(snac, 2, xs_fmt("error requesting 'Announce' object %s", object));
        }
    }
    else
    if (strcmp(type, "Update") == 0) { /** **/
        if (xs_match(utype, "Person|Service")) { /** **/
            actor_add(actor, xs_dict_get(msg, "object"));
            timeline_touch(snac);

            snac_log(snac, xs_fmt("updated actor %s", actor));
        }
        else
        if (xs_match(utype, "Note|Page|Article|Video")) { /** **/
            const char *id = xs_dict_get(object, "id");

            if (xs_is_null(id))
                snac_log(snac, xs_fmt("malformed message: no 'id' field"));
            else
            if (object_here(id)) {
                object_add_ow(id, object);
                timeline_touch(snac);

                snac_log(snac, xs_fmt("updated '%s' %s", utype, id));
            }
            else
                snac_log(snac, xs_fmt("dropped update for unknown '%s' %s", utype, id));
        }
        else
        if (strcmp(utype, "Question") == 0) { /** **/
            const char *id     = xs_dict_get(object, "id");
            const char *closed = xs_dict_get(object, "closed");

            if (xs_is_null(id))
                snac_log(snac, xs_fmt("malformed message: no 'id' field"));
            else {
                object_add_ow(id, object);
                timeline_touch(snac);

                snac_log(snac, xs_fmt("%s poll %s", closed == NULL ? "updated" : "closed", id));

                if (closed != NULL)
                    do_notify = 1;
            }
        }
        else {
            srv_archive_error("unsupported_update", "unsupported_update", req, msg);

            snac_log(snac, xs_fmt("ignored 'Update' for object type '%s'", utype));
        }
    }
    else
    if (strcmp(type, "Delete") == 0) { /** **/
        if (xs_type(object) == XSTYPE_DICT)
            object = xs_dict_get(object, "id");

        if (xs_is_null(object))
            snac_log(snac, xs_fmt("malformed message: no 'id' field"));
        else
        if (object_here(object)) {
            timeline_del(snac, object);
            snac_debug(snac, 1, xs_fmt("new 'Delete' %s %s", actor, object));
        }
        else
            snac_debug(snac, 1, xs_fmt("ignored 'Delete' for unknown object %s", object));
    }
    else
    if (strcmp(type, "Pong") == 0) { /** **/
        snac_log(snac, xs_fmt("'Pong' received from %s", actor));
    }
    else
    if (strcmp(type, "Ping") == 0) { /** **/
        const char *id = xs_dict_get(msg, "id");

        snac_log(snac, xs_fmt("'Ping' requested from %s", actor));

        if (!xs_is_null(id)) {
            xs *rsp = msg_pong(snac, actor, id);

            enqueue_output_by_actor(snac, rsp, actor, 0);
        }
    }
    else
    if (strcmp(type, "Block") == 0) { /** **/
        snac_debug(snac, 1, xs_fmt("'Block' received from %s", actor));

        /* should we MUTE the actor back? */
        /* mute(snac, actor); */

        if (!xs_is_true(xs_dict_get(srv_config, "disable_block_notifications")))
            do_notify = 1;
    }
    else
    if (strcmp(type, "Move") == 0) { /** **/
        do_notify = 1;

        const char *old_account = xs_dict_get(msg, "object");
        const char *new_account = xs_dict_get(msg, "target");

        if (!xs_is_null(old_account) && !xs_is_null(new_account)) {
            if (following_check(snac, old_account)) {
                xs *n_actor = NULL;

                if (valid_status(object_get(new_account, &n_actor))) {
                    const xs_list *aka = xs_dict_get(n_actor, "alsoKnownAs");

                    if (xs_type(aka) == XSTYPE_LIST) {
                        if (xs_list_in(aka, old_account) != -1) {
                            /* all conditions met! */

                            /* follow new account */
                            xs *f_msg = msg_follow(snac, new_account);

                            if (f_msg != NULL) {
                                const char *new_actor = xs_dict_get(f_msg, "object");
                                following_add(snac, new_actor, f_msg);
                                enqueue_output_by_actor(snac, f_msg, new_actor, 0);

                                snac_log(snac, xs_fmt("'Move': following %s", new_account));
                            }

                            /* unfollow old account */
                            xs *of_msg = NULL;

                            if (valid_status(following_get(snac, old_account, &of_msg))) {
                                xs *uf_msg = msg_undo(snac, xs_dict_get(of_msg, "object"));
                                following_del(snac, old_account);
                                enqueue_output_by_actor(snac, uf_msg, old_account, 0);

                                snac_log(snac, xs_fmt("'Move': unfollowing %s", old_account));
                            }
                        }
                        else
                            snac_log(snac, xs_fmt("'Move' error: old actor %s not found in %s 'alsoKnownAs'",
                                old_account, new_account));
                    }
                    else
                        snac_log(snac, xs_fmt("'Move' error: cannot get %s 'alsoKnownAs'", new_account));
                }
                else {
                    snac_log(snac, xs_fmt("'Move' error: cannot get new actor %s", new_account));

                    /* may be a server hiccup, retry later */
                    return 0;
                }
            }
            else
                snac_log(snac, xs_fmt("'Move' error: actor %s is not being followed", old_account));
        }
        else {
            snac_log(snac, xs_fmt("'Move' error: malformed message from %s", actor));
            srv_archive_error("move", "move", req, msg);
        }
    }
    else {
        srv_archive_error("unsupported_type", "unsupported_type", req, msg);

        snac_debug(snac, 1, xs_fmt("process_input_message type '%s' ignored", type));
    }

    if (do_notify) {
        notify(snac, type, utype, actor, msg);

        timeline_touch(snac);
    }

    return 1;
}


int send_email(const char *msg)
/* invoke sendmail with email headers and body in msg */
{
    FILE *f;
    int status;
    int fds[2];
    pid_t pid;
    if (pipe(fds) == -1) return -1;
    pid = vfork();
    if (pid == -1) return -1;
    else if (pid == 0) {
        dup2(fds[0], 0);
        close(fds[0]);
        close(fds[1]);
        execl("/usr/sbin/sendmail", "sendmail", "-t", (char *) NULL);
        _exit(1);
    }
    close(fds[0]);
    if ((f = fdopen(fds[1], "w")) == NULL) {
        close(fds[1]);
        return -1;
    }
    fprintf(f, "%s\n", msg);
    fclose(f);
    if (waitpid(pid, &status, 0) == -1) return -1;
    return status;
}


void process_user_queue_item(snac *snac, xs_dict *q_item)
/* processes an item from the user queue */
{
    const char *type;
    int queue_retry_max = xs_number_get(xs_dict_get(srv_config, "queue_retry_max"));

    if ((type = xs_dict_get(q_item, "type")) == NULL)
        type = "output";

    if (strcmp(type, "message") == 0) {
        const xs_dict *msg = xs_dict_get(q_item, "message");
        xs *rcpts = recipient_list(snac, msg, 1);
        xs_set inboxes;
        const xs_str *actor;

        xs_set_init(&inboxes);

        /* add this shared inbox first */
        xs *this_shared_inbox = xs_fmt("%s/shared-inbox", srv_baseurl);
        xs_set_add(&inboxes, this_shared_inbox);
        enqueue_output(snac, msg, this_shared_inbox, 0, 0);

        /* iterate the recipients */
        xs_list_foreach(rcpts, actor) {
            /* local users were served by this_shared_inbox */
            if (!xs_startswith(actor, srv_baseurl)) {
                xs *inbox = get_actor_inbox(actor, 1);

                if (inbox != NULL) {
                    /* add to the set and, if it's not there, send message */
                    if (xs_set_add(&inboxes, inbox) == 1)
                        enqueue_output(snac, msg, inbox, 0, 0);
                }
                else
                    snac_log(snac, xs_fmt("cannot find inbox for %s", actor));
            }
        }

        /* if it's a public note or question, send to the collected inboxes */
        if (xs_match(xs_dict_get_def(msg, "type", ""), "Create|Update") && is_msg_public(msg)) {
            if (xs_type(xs_dict_get(srv_config, "disable_inbox_collection")) != XSTYPE_TRUE) {
                xs *shibx = inbox_list();
                const xs_str *inbox;

                xs_list_foreach(shibx, inbox) {
                    if (xs_set_add(&inboxes, inbox) == 1)
                        enqueue_output(snac, msg, inbox, 0, 0);
                }
            }
        }

        xs_set_free(&inboxes);
    }
    else
    if (strcmp(type, "input") == 0) {
        /* process the message */
        const xs_dict *msg = xs_dict_get(q_item, "message");
        const xs_dict *req = xs_dict_get(q_item, "req");
        int retries  = xs_number_get(xs_dict_get(q_item, "retries"));

        if (xs_is_null(msg))
            return;

        if (!process_input_message(snac, msg, req)) {
            if (retries > queue_retry_max)
                snac_log(snac, xs_fmt("input giving up"));
            else {
                /* reenqueue */
                enqueue_input(snac, msg, req, retries + 1);
                snac_log(snac, xs_fmt("input requeue #%d", retries + 1));
            }
        }
    }
    else
    if (strcmp(type, "close_question") == 0) {
        /* the time for this question has ended */
        const char *id = xs_dict_get(q_item, "message");

        if (!xs_is_null(id))
            update_question(snac, id);
    }
    else
    if (strcmp(type, "object_request") == 0) {
        const char *id = xs_dict_get(q_item, "message");

        if (!xs_is_null(id)) {
            int status;
            xs *data = NULL;

            status = activitypub_request(snac, id, &data);

            if (valid_status(status))
                object_add_ow(id, data);

            snac_debug(snac, 1, xs_fmt("object_request %s %d", id, status));
        }
    }
    else
    if (strcmp(type, "verify_links") == 0) {
        verify_links(snac);
    }
    else
    if (strcmp(type, "actor_refresh") == 0) {
        const char *actor = xs_dict_get(q_item, "actor");
        double mtime = object_mtime(actor);

        /* only refresh if it was refreshed more than an hour ago */
        if (mtime + 3600.0 < (double) time(NULL)) {
            xs *actor_o = NULL;
            int status;

            if (valid_status((status = activitypub_request(snac, actor, &actor_o))))
                actor_add(actor, actor_o);
            else
                object_touch(actor);

            snac_log(snac, xs_fmt("actor_refresh %s %d", actor, status));
        }
    }
    else
        snac_log(snac, xs_fmt("unexpected user q_item type '%s'", type));
}


int process_user_queue(snac *snac)
/* processes a user's queue */
{
    int cnt = 0;
    xs *list = user_queue(snac);

    xs_list *p = list;
    const xs_str *fn;

    while (xs_list_iter(&p, &fn)) {
        xs *q_item = dequeue(fn);

        if (q_item == NULL)
            continue;

        process_user_queue_item(snac, q_item);
        cnt++;
    }

    return cnt;
}


void process_queue_item(xs_dict *q_item)
/* processes an item from the global queue */
{
    const char *type = xs_dict_get(q_item, "type");
    int queue_retry_max = xs_number_get(xs_dict_get(srv_config, "queue_retry_max"));

    if (strcmp(type, "output") == 0) {
        int status;
        const xs_str *inbox  = xs_dict_get(q_item, "inbox");
        const xs_str *keyid  = xs_dict_get(q_item, "keyid");
        const xs_str *seckey = xs_dict_get(q_item, "seckey");
        const xs_dict *msg   = xs_dict_get(q_item, "message");
        int retries    = xs_number_get(xs_dict_get(q_item, "retries"));
        int p_status   = xs_number_get(xs_dict_get(q_item, "p_status"));
        xs *payload    = NULL;
        int p_size     = 0;
        int timeout    = 0;

        if (xs_is_null(inbox) || xs_is_null(msg) || xs_is_null(keyid) || xs_is_null(seckey)) {
            srv_log(xs_fmt("output message error: missing fields"));
            return;
        }

        if (is_instance_blocked(inbox)) {
            srv_debug(0, xs_fmt("discarded output message to blocked instance %s", inbox));
            return;
        }

        /* deliver (if previous error status was a timeout, try now longer) */
        if (p_status == 599)
            timeout = xs_number_get(xs_dict_get_def(srv_config, "queue_timeout_2", "8"));
        else
            timeout = xs_number_get(xs_dict_get_def(srv_config, "queue_timeout", "6"));

        if (timeout == 0)
            timeout = 6;

        status = send_to_inbox_raw(keyid, seckey, inbox, msg, &payload, &p_size, timeout);

        if (payload) {
            if (p_size > 64) {
                /* trim the message */
                payload[64] = '\0';
                payload = xs_str_cat(payload, "...");
            }

            /* strip ugly control characters */
            payload = xs_replace_i(payload, "\n", "");
            payload = xs_replace_i(payload, "\r", "");

            if (*payload)
                payload = xs_str_wrap_i(" [", payload, "]");
        }
        else
            payload = xs_str_new(NULL);

        srv_log(xs_fmt("output message: sent to inbox %s %d%s", inbox, status, payload));

        if (!valid_status(status)) {
            retries++;

            /* if it's not the first time it fails with a timeout,
               penalize the server by skipping one retry */
            if (p_status == status && status == HTTP_STATUS_CLIENT_CLOSED_REQUEST)
                retries++;

            /* error sending; requeue? */
            if (status == HTTP_STATUS_BAD_REQUEST
                || status == HTTP_STATUS_NOT_FOUND
                || status == HTTP_STATUS_METHOD_NOT_ALLOWED
                || status == HTTP_STATUS_GONE
                || status == HTTP_STATUS_UNPROCESSABLE_CONTENT
                || status < 0)
                /* explicit error: discard */
                srv_log(xs_fmt("output message: fatal error %s %d", inbox, status));
            else
            if (retries > queue_retry_max)
                srv_log(xs_fmt("output message: giving up %s %d", inbox, status));
            else {
                /* requeue */
                enqueue_output_raw(keyid, seckey, msg, inbox, retries, status);
                srv_log(xs_fmt("output message: requeue %s #%d", inbox, retries));
            }
        }
    }
    else
    if (strcmp(type, "email") == 0) {
        /* send this email */
        const xs_str *msg = xs_dict_get(q_item, "message");
        int retries = xs_number_get(xs_dict_get(q_item, "retries"));

        if (!send_email(msg))
            srv_debug(1, xs_fmt("email message sent"));
        else {
            retries++;

            if (retries > queue_retry_max)
                srv_log(xs_fmt("email giving up (errno: %d)", errno));
            else {
                /* requeue */
                srv_log(xs_fmt(
                    "email requeue #%d (errno: %d)", retries, errno));

                enqueue_email(msg, retries);
            }
        }
    }
    else
    if (strcmp(type, "telegram") == 0) {
        /* send this via telegram */
        const char *bot   = xs_dict_get(q_item, "bot");
        const char *msg   = xs_dict_get(q_item, "message");
        xs *chat_id = xs_dup(xs_dict_get(q_item, "chat_id"));
        int status  = 0;

        /* chat_id must start with a - */
        if (!xs_startswith(chat_id, "-"))
            chat_id = xs_str_wrap_i("-", chat_id, NULL);

        xs *url  = xs_fmt("https:/" "/api.telegram.org/bot%s/sendMessage", bot);
        xs *body = xs_fmt("{\"chat_id\":%s,\"text\":\"%s\"}", chat_id, msg);

        xs *headers = xs_dict_new();
        headers = xs_dict_append(headers, "content-type", "application/json");

        xs *rsp = xs_http_request("POST", url, headers,
                                   body, strlen(body), &status, NULL, NULL, 0);
        rsp = xs_free(rsp);

        srv_debug(0, xs_fmt("telegram post %d", status));
    }
    else
    if (strcmp(type, "ntfy") == 0) {
        /* send this via ntfy */
        const char *ntfy_server   = xs_dict_get(q_item, "ntfy_server");
        const char *msg   = xs_dict_get(q_item, "message");
        const char *ntfy_token   = xs_dict_get(q_item, "ntfy_token");
        int status  = 0;

        xs *url  = xs_fmt("%s", ntfy_server);
        xs *body = xs_fmt("%s", msg);

        xs *headers = xs_dict_new();
        headers = xs_dict_append(headers, "content-type", "text/plain");
        // Append the Authorization header only if ntfy_token is not NULL
         if (ntfy_token != NULL) {
             headers = xs_dict_append(headers, "Authorization", xs_fmt("Bearer %s", ntfy_token));
             }

        xs *rsp = xs_http_request("POST", url, headers,
                                   body, strlen(body), &status, NULL, NULL, 0);
        rsp = xs_free(rsp);

        srv_debug(0, xs_fmt("ntfy post %d", status));
    }
    else
    if (strcmp(type, "purge") == 0) {
        srv_log(xs_dup("purge start"));

        purge_all();

        srv_log(xs_dup("purge end"));
    }
    else
    if (strcmp(type, "input") == 0) {
        const xs_dict *msg = xs_dict_get(q_item, "message");
        const xs_dict *req = xs_dict_get(q_item, "req");
        int retries  = xs_number_get(xs_dict_get(q_item, "retries"));

        /* do some instance-level checks */
        int r = process_input_message(NULL, msg, req);

        if (r == 0) {
            /* transient error? retry */
            if (retries > queue_retry_max)
                srv_log(xs_fmt("shared input giving up"));
            else {
                /* reenqueue */
                enqueue_shared_input(msg, req, retries + 1);
                srv_log(xs_fmt("shared input requeue #%d", retries + 1));
            }
        }
        else
        if (r == 2) {
            /* redistribute the input message to all users */
            const char *ntid = xs_dict_get(q_item, "ntid");
            xs *tmpfn  = xs_fmt("%s/tmp/%s.json", srv_basedir, ntid);
            FILE *f;

            if ((f = fopen(tmpfn, "w")) != NULL) {
                xs_json_dump(q_item, 4, f);
                fclose(f);
            }

            xs *users = user_list();
            xs_list *p = users;
            const char *v;
            int cnt = 0;

            while (xs_list_iter(&p, &v)) {
                snac user;

                if (user_open(&user, v)) {
                    if (is_msg_for_me(&user, msg)) {
                        xs *fn = xs_fmt("%s/queue/%s.json", user.basedir, ntid);

                        snac_debug(&user, 1,
                            xs_fmt("enqueue_input (from shared inbox) %s", xs_dict_get(msg, "id")));

                        if (link(tmpfn, fn) < 0)
                            srv_log(xs_fmt("link(%s, %s) error", tmpfn, fn));

                        cnt++;
                    }

                    user_free(&user);
                }
            }

            unlink(tmpfn);

            if (cnt == 0) {
                srv_debug(1, xs_fmt("no valid recipients for %s", xs_dict_get(msg, "id")));
            }
        }
    }
    else
        srv_log(xs_fmt("unexpected q_item type '%s'", type));
}


int process_queue(void)
/* processes the global queue */
{
    int cnt = 0;
    xs *list = queue();

    xs_list *p = list;
    const xs_str *fn;

    while (xs_list_iter(&p, &fn)) {
        xs *q_item = dequeue(fn);

        if (q_item != NULL) {
            job_post(q_item, 0);
            cnt++;
        }
    }

    return cnt;
}


/** account migration **/

int migrate_account(snac *user)
/* migrates this account to a new one (stored in the 'alias' user field) */
{
    const char *new_account = xs_dict_get(user->config, "alias");

    if (xs_type(new_account) != XSTYPE_STRING) {
        snac_log(user, xs_fmt("Cannot migrate: alias (destination account) not set"));
        return 1;
    }

    xs *new_actor = NULL;
    int status;

    if (!valid_status(status = activitypub_request(user, new_account, &new_actor))) {
        snac_log(user, xs_fmt("Cannot migrate: error requesting actor %s %d", new_account, status));
        return 1;
    }

    actor_add(new_account, new_actor);

    const char *loaka = xs_dict_get(new_actor, "alsoKnownAs");

    if (xs_type(loaka) != XSTYPE_LIST) {
        snac_log(user, xs_fmt("Cannot migrate: destination account doesn't have any aliases"));
        return 1;
    }

    if (xs_list_in(loaka, user->actor) == -1) {
        snac_log(user, xs_fmt("Cannot migrate: destination account doesn't have this one as an alias"));
        return 1;
    }

    xs *move = msg_move(user, new_account);
    xs *fwers = follower_list(user);

    const char *actor;
    xs_list_foreach(fwers, actor) {
        /* get the actor inbox, excluding the shared one */
        xs *inbox = get_actor_inbox(actor, 0);

        if (xs_is_null(inbox))
            snac_log(user, xs_fmt("migrate_account: cannot get inbox for actor %s", actor));
        else
            enqueue_output(user, move, inbox, 0, 0);
    }

    return 0;
}


/** HTTP handlers */

int activitypub_get_handler(const xs_dict *req, const char *q_path,
                            char **body, int *b_size, char **ctype)
{
    int status = HTTP_STATUS_OK;
    const char *accept = xs_dict_get(req, "accept");
    snac snac;
    xs *msg = NULL;

    if (accept == NULL)
        return 0;

    if (xs_str_in(accept, "application/activity+json") == -1 &&
        xs_str_in(accept, "application/ld+json") == -1)
        return 0;

    xs *l = xs_split_n(q_path, "/", 2);
    const char *uid;
    const char *p_path;

    uid = xs_list_get(l, 1);
    if (!user_open(&snac, uid)) {
        /* invalid user */
        srv_debug(1, xs_fmt("activitypub_get_handler bad user %s", uid));
        return HTTP_STATUS_NOT_FOUND;
    }

    p_path = xs_list_get(l, 2);

    *ctype  = "application/activity+json";

    int show_contact_metrics = xs_is_true(xs_dict_get(snac.config, "show_contact_metrics"));

    if (p_path == NULL) {
        /* if there was no component after the user, it's an actor request */
        msg = msg_actor(&snac);
        *ctype = "application/ld+json; profile=\"https://www.w3.org/ns/activitystreams\"";

        const char *ua = xs_dict_get(req, "user-agent");

        snac_debug(&snac, 0, xs_fmt("serving actor [%s]", ua ? ua : "No UA"));
    }
    else
    if (strcmp(p_path, "outbox") == 0 || strcmp(p_path, "featured") == 0) {
        xs *id = xs_fmt("%s/%s", snac.actor, p_path);
        xs *list = xs_list_new();
        const char *v;
        int cnt = xs_number_get(xs_dict_get_def(srv_config, "max_public_entries", "20"));

        /* get the public outbox or the pinned list */
        xs *elems = *p_path == 'o' ? timeline_simple_list(&snac, "public", 0, cnt) : pinned_list(&snac);

        xs_list_foreach(elems, v) {
            xs *i = NULL;

            if (valid_status(object_get_by_md5(v, &i))) {
                const char *type = xs_dict_get(i, "type");
                const char *id   = xs_dict_get(i, "id");

                if (type && id && strcmp(type, "Note") == 0 && xs_startswith(id, snac.actor)) {
                    xs *c_msg = msg_create(&snac, i);
                    list = xs_list_append(list, c_msg);
                }
            }
        }

        /* replace the 'orderedItems' with the latest posts */
        msg = msg_collection(&snac, id, xs_list_len(list));
        msg = xs_dict_set(msg, "orderedItems", list);
    }
    else
    if (strcmp(p_path, "followers") == 0) {
        int total = 0;

        if (show_contact_metrics) {
            xs *l = follower_list(&snac);
            total = xs_list_len(l);
        }

        xs *id = xs_fmt("%s/%s", snac.actor, p_path);
        msg = msg_collection(&snac, id, total);
    }
    else
    if (strcmp(p_path, "following") == 0) {
        int total = 0;

        if (show_contact_metrics) {
            xs *l = following_list(&snac);
            total = xs_list_len(l);
        }

        xs *id = xs_fmt("%s/%s", snac.actor, p_path);
        msg = msg_collection(&snac, id, total);
    }
    else
    if (xs_startswith(p_path, "p/")) {
        xs *id = xs_fmt("%s/%s", snac.actor, p_path);

        status = object_get(id, &msg);

        /* don't return non-public objects */
        if (valid_status(status) && !is_msg_public(msg))
            status = HTTP_STATUS_NOT_FOUND;
    }
    else
        status = HTTP_STATUS_NOT_FOUND;

    if (status == HTTP_STATUS_OK && msg != NULL) {
        *body   = xs_json_dumps(msg, 4);
        *b_size = strlen(*body);
    }

    snac_debug(&snac, 1, xs_fmt("activitypub_get_handler serving %s %d", q_path, status));

    user_free(&snac);

    return status;
}


int activitypub_post_handler(const xs_dict *req, const char *q_path,
                             char *payload, int p_size,
                             char **body, int *b_size, char **ctype)
/* processes an input message */
{
    (void)b_size;

    int status = HTTP_STATUS_ACCEPTED;
    const char *i_ctype = xs_dict_get(req, "content-type");
    snac snac;
    const char *v;

    if (i_ctype == NULL) {
        *body  = xs_str_new("no content-type");
        *ctype = "text/plain";
        return HTTP_STATUS_BAD_REQUEST;
    }

    if (xs_is_null(payload)) {
        *body  = xs_str_new("no payload");
        *ctype = "text/plain";
        return HTTP_STATUS_BAD_REQUEST;
    }

    if (xs_str_in(i_ctype, "application/activity+json") == -1 &&
        xs_str_in(i_ctype, "application/ld+json") == -1)
        return 0;

    /* decode the message */
    xs *msg = xs_json_loads(payload);
    const char *id = xs_dict_get(msg, "id");

    if (msg == NULL) {
        srv_log(xs_fmt("activitypub_post_handler JSON error %s", q_path));

        srv_archive_error("activitypub_post_handler", "JSON error", req, payload);

        *body  = xs_str_new("JSON error");
        *ctype = "text/plain";
        return HTTP_STATUS_BAD_REQUEST;
    }

    if (id && is_instance_blocked(id)) {
        srv_debug(1, xs_fmt("full instance block for %s", id));

        *body  = xs_str_new("blocked");
        *ctype = "text/plain";
        return HTTP_STATUS_FORBIDDEN;
    }

    /* get the user and path */
    xs *l = xs_split_n(q_path, "/", 2);

    if (xs_list_len(l) == 2 && strcmp(xs_list_get(l, 1), "shared-inbox") == 0) {
        enqueue_shared_input(msg, req, 0);
        return HTTP_STATUS_ACCEPTED;
    }

    if (xs_list_len(l) != 3 || strcmp(xs_list_get(l, 2), "inbox") != 0) {
        /* strange q_path */
        srv_debug(1, xs_fmt("activitypub_post_handler unsupported path %s", q_path));
        return HTTP_STATUS_NOT_FOUND;
    }

    const char *uid = xs_list_get(l, 1);
    if (!user_open(&snac, uid)) {
        /* invalid user */
        srv_debug(1, xs_fmt("activitypub_post_handler bad user %s", uid));
        return HTTP_STATUS_NOT_FOUND;
    }

    /* if it has a digest, check it now, because
       later the payload won't be exactly the same */
    if ((v = xs_dict_get(req, "digest")) != NULL) {
        xs *s1 = xs_sha256_base64(payload, p_size);
        xs *s2 = xs_fmt("SHA-256=%s", s1);

        if (strcmp(s2, v) != 0) {
            srv_log(xs_fmt("digest check FAILED"));

            *body  = xs_str_new("bad digest");
            *ctype = "text/plain";
            status = HTTP_STATUS_BAD_REQUEST;
        }
    }

    /* if the message is from a muted actor, reject it right now */
    if (!xs_is_null(v = xs_dict_get(msg, "actor")) && *v) {
        if (is_muted(&snac, v)) {
            snac_log(&snac, xs_fmt("rejected message from MUTEd actor %s", v));

            *body  = xs_str_new("rejected");
            *ctype = "text/plain";
            status = HTTP_STATUS_FORBIDDEN;
        }
    }

    if (valid_status(status)) {
        enqueue_input(&snac, msg, req, 0);
        *ctype = "application/activity+json";
    }

    user_free(&snac);

    return status;
}