fix: more issue #112 follow-ups (stanza-id disco gate, account sanitizer)

- xmpp: gate XEP-0359 stanza-id dedup on disco urn:xmpp:sid:0. Before
  honoring <stanza-id by='…'/> for archive_id dedup, check that the entity
  in `by` (or its domain — that's what profanity disco's on connect)
  announces the namespace; fall back to no-dedup when caps are unknown,
  matching the XEP §6 disco-gate (#1).
- accounts: narrow group-name sanitizer to only the characters GKeyFile
  actually forbids in group headers (`[`, `]`, `\n`, `\r`); `=` and `#` are
  valid inside a header and stay (#2).
- functional tests cover both branches of the disco gate — replayed
  stanza-id is flagged as duplicate when sid:0 is announced, and not
  flagged when it isn't.

Refs #112

src/config/accounts.c

@@ -43,8 +43,8 @@ _sanitize_account_name(const char* const name)
     gchar* sanitized = g_strdup(name);
     gchar* p = sanitized;
     while (*p) {
-        // GKeyFile special characters: [ ] = # \n \r
-        if (*p == '[' || *p == ']' || *p == '=' || *p == '#' || *p == '\n' || *p == '\r') {
+        // GKeyFile group header forbids these characters.
+        if (*p == '[' || *p == ']' || *p == '\n' || *p == '\r') {
             *p = '_';
         }
         p++;

src/xmpp/message.c

@@ -65,6 +65,7 @@ static void _handle_pubsub(xmpp_stanza_t* const stanza, xmpp_stanza_t* const eve
 static gboolean _handle_form(xmpp_stanza_t* const stanza);
 static gboolean _handle_jingle_message(xmpp_stanza_t* const stanza);
 static gboolean _should_ignore_based_on_silence(xmpp_stanza_t* const stanza);
+static gboolean _stanza_id_by_trusted(const char* by);
 #ifdef HAVE_OMEMO
 static void _receive_omemo(xmpp_stanza_t* const stanza, ProfMessage* message);
 #endif
@@ -1088,7 +1089,7 @@ _handle_groupchat(xmpp_stanza_t* const stanza)
     xmpp_stanza_t* stanzaidst = xmpp_stanza_get_child_by_name_and_ns(stanza, STANZA_NAME_STANZA_ID, STANZA_NS_STABLE_ID);
     if (stanzaidst) {
         const char* by = xmpp_stanza_get_attribute(stanzaidst, "by");
-        if (by && (g_strcmp0(by, from_jid->barejid) == 0)) {
+        if (by && g_strcmp0(by, from_jid->barejid) == 0 && _stanza_id_by_trusted(by)) {
             stanzaid = (char*)xmpp_stanza_get_attribute(stanzaidst, STANZA_ATTR_ID);
             if (stanzaid) {
                 message->stanzaid = strdup(stanzaid);
@@ -1397,7 +1398,7 @@ _handle_chat(xmpp_stanza_t* const stanza, gboolean is_mam, gboolean is_carbon, c
         xmpp_stanza_t* stanzaidst = xmpp_stanza_get_child_by_name_and_ns(stanza, STANZA_NAME_STANZA_ID, STANZA_NS_STABLE_ID);
         if (stanzaidst) {
             const char* by = xmpp_stanza_get_attribute(stanzaidst, "by");
-            if (by && equals_our_barejid(by)) {
+            if (by && equals_our_barejid(by) && _stanza_id_by_trusted(by)) {
                 stanzaid = (char*)xmpp_stanza_get_attribute(stanzaidst, STANZA_ATTR_ID);
                 if (stanzaid) {
                     message->stanzaid = strdup(stanzaid);
@@ -1735,3 +1736,22 @@ _should_ignore_based_on_silence(xmpp_stanza_t* const stanza)
     }
     return FALSE;
 }
+
+// XEP-0359 §6 disco-gate; falls back to domain since that's what disco is run against.
+static gboolean
+_stanza_id_by_trusted(const char* by)
+{
+    if (!by) {
+        return FALSE;
+    }
+    GHashTable* features = connection_get_features(by);
+    if (features && g_hash_table_contains(features, STANZA_NS_STABLE_ID)) {
+        return TRUE;
+    }
+    const char* at = strchr(by, '@');
+    if (!at) {
+        return FALSE;
+    }
+    features = connection_get_features(at + 1);
+    return features && g_hash_table_contains(features, STANZA_NS_STABLE_ID);
+}