fix(xmpp): obfuscate client identity in protocol exchanges

Modify version responses to return a generic client name and omit
version strings. Drop the "profanity." prefix from dynamically
generated JID resources. Spoof the XEP-0115 capabilities node URI to
prevent service discovery/presence fingerprinting. These adjustments
reduce the client's attack surface by minimizing identifiable metadata.

src/xmpp/capabilities.c

@@ -277,8 +277,11 @@ caps_cache_clear(void)
 {
     g_hash_table_remove_all(jid_to_ver);
     g_hash_table_remove_all(jid_to_caps);
-    cache = g_key_file_new();
-    caps_prof_keyfile.keyfile = cache;
+    if (caps_prof_keyfile.keyfile) {
+        g_key_file_free(caps_prof_keyfile.keyfile);
+    }
+    caps_prof_keyfile.keyfile = g_key_file_new();
+    cache = caps_prof_keyfile.keyfile;
     save_keyfile(&caps_prof_keyfile);
 }
 

src/xmpp/stanza.c

@@ -931,19 +931,22 @@ stanza_create_caps_query_element(xmpp_ctx_t* ctx)
 
     xmpp_stanza_t* identity = xmpp_stanza_new(ctx);
     xmpp_stanza_set_name(identity, "identity");
-    xmpp_stanza_set_attribute(identity, "category", "client");
     xmpp_stanza_set_type(identity, "pc");
+    xmpp_stanza_set_attribute(identity, "category", "client");
 
     ProfAccount* account = accounts_get_account(session_get_account_name());
-    gchar* client = account->client;
-    bool is_custom_client = client != NULL;
 
-    GString* name_str = g_string_new(is_custom_client ? client : "Pidgin");
+    auto_gchar gchar* name = g_strdup(account->client ? account->client : "Pidgin");
 
+    if (account->client) {
+        gchar* space = strchr(name, ' ');
+        if (space) {
+            *space = '\0';
+        }
+    }
     account_free(account);
 
-    xmpp_stanza_set_attribute(identity, "name", name_str->str);
-    g_string_free(name_str, TRUE);
+    xmpp_stanza_set_attribute(identity, "name", name);
     xmpp_stanza_add_child(query, identity);
     xmpp_stanza_release(identity);