Make @ and ! work as webfinger prefixes

client/client.go

@@ -108,11 +108,6 @@ converts a webfinger identifier to a url
 see: https://datatracker.ietf.org/doc/html/rfc7033
 */
 func ResolveWebfinger(username string) (string, error) {
-	if len(username) == 0 || username[0] != '@' {
-		panic("webfinger usernames must begin with @")
-	}
-
-	username = username[1:]
 	split := strings.SplitN(username, "@", 2)
 	var account, domain string
 	if len(split) != 2 {

pub/user-input.go

@@ -6,8 +6,8 @@ import (
 )
 
 func FetchUserInput(text string) Any {
-	if strings.HasPrefix(text, "@") {
-		link, err := client.ResolveWebfinger(text)
+	if strings.HasPrefix(text, "@") || strings.HasPrefix(text, "!") {
+		link, err := client.ResolveWebfinger(text[1:])
 		if err != nil {
 			return NewFailure(err)
 		}