[ADD/WIP] Bridging Matrix redacts

I'll still need to consider making redacts from other people count as
"moderations", whatever that is to Gajim, instead of a "self-redact".

Also, _please_, support it if you _ever_ wish adoption, XMPP users!

README.MD

@@ -35,6 +35,8 @@ TODO
 TODO
 
 ## TODOS
+- Mess with Cytoplasm to make it have support for something like Berkeley DB as 
+an *optional* dependency. This should increase reliability and speed for anyone.
 - PROPER FUCKING AVATARS
     XEP-0084 IS THE WORST PIECE OF SHIT KNOWN TO MAN. If any Jabberbros want to 
     look at terrible code/XML and suggest things to have *proper* avatar support,

src/MatrixEventHandler.c

@@ -149,6 +149,77 @@ ParseeBotHandler(ParseeData *data, HashMap *event)
     Free(profile);
     CommandFree(cmd);
 }
+
+static const char *
+GetXMPPInformation(ParseeData *data, HashMap *event, char **from, char **to)
+{
+    const char *type = NULL;
+
+    char *room_id = GrabString(event, 1, "room_id");
+    char *matrix_sender = GrabString(event, 1, "sender");
+    char *chat_id = NULL, *muc_id = NULL;
+    char *user;
+
+    DbRef *room_data;
+    HashMap *data_json;
+
+    XMPPComponent *jabber = data ? data->jabber : NULL;
+
+    bool direct = false;
+    if (!data || !event || !from || !to)
+    {
+        return NULL;
+    }
+
+    *from   = NULL;
+    *to     = NULL;
+
+    chat_id = ParseeGetFromRoomID(data, room_id);
+
+    room_data = DbLock(data->db, 3, "rooms", room_id, "data");
+    data_json = DbJson(room_data);
+    direct = GrabBoolean(data_json, 1, "is_direct");
+    type = direct ? "chat" : "groupchat";
+
+    user = GrabString(data_json, 1, "xmpp_user");
+
+    *from = ParseeEncodeMXID(matrix_sender);
+
+    if (direct)
+    {
+        *to = StrDuplicate(user);
+        Free(chat_id);
+    }
+    else
+    {
+        char *matrix_name, *muc_join_as;
+        
+        muc_id = ParseeGetMUCID(data, chat_id);
+        if (!chat_id)
+        {
+            /* muc_id is already implied to be freed by this point */
+
+            Free(*from);
+            *from = NULL;
+            DbUnlock(data->db, room_data);
+            return NULL;
+        }
+
+        matrix_name = ASGetName(data->config, room_id, matrix_sender);
+        muc_join_as = StrConcat(4, muc_id, "/", matrix_name, "[p]");
+
+        XMPPJoinMUC(jabber, *from, muc_join_as);
+
+        *to = muc_id;
+
+        Free(matrix_name);
+        Free(muc_join_as);
+    }
+
+    Free(chat_id);
+    DbUnlock(data->db, room_data);
+    return type;
+}
 static void
 ParseeMessageHandler(ParseeData *data, HashMap *event)
 {
@@ -316,9 +387,37 @@ ParseeEventHandler(ParseeData *data, HashMap *event)
     }
     else if (StrEquals(event_type, "m.room.redaction"))
     {
-        Log(LOG_WARNING, "Unsupported event redaction %s", event_id);
-        /* TODO: Implement Matrix->XMPP redactions. */
+        char *from, *to;
+        char *redacted = GrabString(event, 1, "redacts");
+        char *redacted_stanza = NULL;
+        char *chat_id;
+        XMPPComponent *jabber = data->jabber;
+
+        const char *type = GetXMPPInformation(data, event, &from, &to);
+
+        chat_id = ParseeGetFromRoomID(data, room_id);
+
+        if (!ParseeGetOrigin(data, chat_id, redacted, &redacted_stanza))
+        {
+            ParseeGetDMOrigin(data, room_id, redacted, &redacted_stanza);
         }
 
+        /* Some clients don't support retractions *at all*, which smell.
+         * This therefore serves as a fallback, just in case that fails. */
+        XMPPSendPlain(
+            jabber, from, to, 
+            "[EDIT REDACT FROM PARSEE]", 
+            (char *) type, 
+            NULL, NULL, redacted, 
+            NULL, redacted_stanza
+        );
+        XMPPRetract(jabber, from, to, (char *) type, redacted_stanza);
+
+        Free(redacted_stanza);
+        Free(chat_id);
+        Free(from);
+        Free(to);
+        /* TODO: Implement Matrix->XMPP redactions. */
+    }
 }
 

src/XMPP/Stanza.c

@@ -15,6 +15,74 @@ XMPPSendPlain(XMPPComponent *comp, char *fr, char *to, char *msg, char *type, ch
     Free(ident);
 }
 
+void
+XMPPRetract(XMPPComponent *comp, char *fr, char *to, char *type, char *redact)
+{
+    XMLElement *message;
+    char *ident = StrRandom(32), *from;
+    if (!comp || !fr || !to || !type || !redact)
+    {
+        Free(ident);
+        return;
+    }
+
+    message = XMLCreateTag("message");
+    XMLAddAttr(message, "from", (from = StrConcat(3, fr, "@", comp->host)));
+    XMLAddAttr(message, "to", to);
+    XMLAddAttr(message, "type", type);
+    XMLAddAttr(message, "id", ident);
+
+    {
+        XMLElement *apply_to, *retract, *body, *txt, *fallback;
+
+        apply_to = XMLCreateTag("apply-to");
+        XMLAddAttr(apply_to, "xmlns", "urn:xmpp:fasten:0");
+        XMLAddAttr(apply_to, "id", redact);
+        {
+            retract = XMLCreateTag("retract");
+            XMLAddAttr(retract, "xmlns", "urn:xmpp:message-retract:0");
+            XMLAddChild(apply_to, retract);
+        }
+        XMLAddChild(message, apply_to);
+
+        retract = XMLCreateTag("retract");
+        XMLAddAttr(retract, "xmlns", "urn:xmpp:message-retract:1");
+        XMLAddAttr(retract, "id", redact);
+        XMLAddChild(message, retract);
+
+        fallback = XMLCreateTag("fallback");
+        XMLAddAttr(fallback, "xmlns", "urn:xmpp:fallback:0");
+        XMLAddAttr(fallback, "for", "urn:xmpp:message-retract:0");
+        XMLAddChild(message, fallback);
+
+        fallback = XMLCreateTag("fallback");
+        XMLAddAttr(fallback, "xmlns", "urn:xmpp:fallback:0");
+        XMLAddAttr(fallback, "for", "urn:xmpp:message-retract:1");
+        XMLAddChild(message, fallback);
+
+        body = XMLCreateTag("body");
+        txt = XMLCreateText(
+            "This person attempted to retract a previous message, "
+            "but your client does not yet support the 0.4.1 version of "
+            "XEP-0424.\n\n"
+
+            "(_Parsee is jealous of being able to read such messages._)"
+        );
+        XMLAddChild(body, txt);
+        XMLAddChild(message, body);
+
+    }
+
+    pthread_mutex_lock(&comp->write_lock);
+    XMLEncode(comp->stream, message);
+    StreamFlush(comp->stream);
+    XMLFreeElement(message);
+
+    pthread_mutex_unlock(&comp->write_lock);
+
+    Free(from);
+    Free(ident);
+}
 void
 XMPPSendPlainID(XMPPComponent *comp, char *fr, char *to, char *msg, char *type, char *rst, char *rse, char *event_id, char *oob, char *edit, char *ident)
 {

src/XMPPThread.c

@@ -48,6 +48,7 @@ typedef struct XMPPIdentity {
     char *category, *type, *lang, *name;
 } XMPPIdentity;
 
+/* Generates the JID of the Parsee bridge user. */
 static char *
 ParseeJID(ParseeData *data)
 {
@@ -548,6 +549,7 @@ MessageStanza(ParseeData *args, XMLElement *stanza, XMPPThread *thr)
         {
             char *parsee = ParseeJID(args);
 
+            /* Subscribe to the sender's metadata node. */
             XMLElement *ps = CreatePubsubRequest(
                 parsee, decode_from, "urn:xmpp:avatar:metadata"
             );

src/include/XMPP.h

@@ -31,6 +31,7 @@ extern void XMPPLeaveMUC(XMPPComponent *comp, char *fr, char *muc, char *r);
 /* TODO: XMPP stuff, I don't fucking know, I'm not a Jabbernerd. */
 extern void XMPPSendPlain(XMPPComponent *comp, char *fr, char *to, char *msg, char *type, char *rst, char *rse, char *event_id, char *oob, char *id);
 extern void XMPPSendPlainID(XMPPComponent *comp, char *fr, char *to, char *msg, char *type, char *rst, char *rse, char *event_id, char *oob, char *id, char *sid);
+extern void XMPPRetract(XMPPComponent *comp, char *fr, char *to, char *type, char *redact);
 
 /* Finishes a component stream, and doesn't free it. */
 extern void XMPPFinishCompStream(XMPPComponent *stream);