Better formspec prepend hack for 0.4 clients

src/nodemetadata.cpp

@@ -51,9 +51,8 @@ void NodeMetadata::serialize(std::ostream &os, u8 version, bool disk,
 			continue;
 
 		os << serializeString16(sv.first);
-		if (!formspec_prepend.empty() && sv.first == "formspec" &&
-				sv.second.find("no_prepend[]") == std::string::npos)
-			os << serializeString32(sv.second + formspec_prepend);
+		if (!formspec_prepend.empty() && sv.first == "formspec")
+			os << serializeString32(insert_formspec_prepend(sv.second, formspec_prepend));
 		else
 			os << serializeString32(sv.second);
 		if (version >= 2)

src/server.cpp

@@ -1542,9 +1542,8 @@ void Server::SendShowFormspecMessage(session_t peer_id, const std::string &forms
 	} else {
 		m_formspec_state_data[peer_id] = formname;
 		RemotePlayer *player = m_env->getPlayer(peer_id);
-		if (player && player->protocol_version < 37 &&
-				formspec.find("no_prepend[]") == std::string::npos)
-			pkt.putLongString(formspec + player->formspec_prepend);
+		if (player && player->protocol_version < 37)
+			pkt.putLongString(insert_formspec_prepend(formspec, player->formspec_prepend));
 		else
 			pkt.putLongString(formspec);
 	}
@@ -1935,10 +1934,9 @@ void Server::SendPlayerInventoryFormspec(session_t peer_id)
 		return;
 
 	NetworkPacket pkt(TOCLIENT_INVENTORY_FORMSPEC, 0, peer_id);
-	if (player->protocol_version < 37 && player->inventory_formspec.find(
-			"no_prepend[]") == std::string::npos)
-		pkt.putLongString(player->inventory_formspec +
-			player->formspec_prepend);
+	if (player->protocol_version < 37)
+		pkt.putLongString(insert_formspec_prepend(player->inventory_formspec,
+			player->formspec_prepend));
 	else
 		pkt.putLongString(player->inventory_formspec);
 

src/util/string.cpp

@@ -894,3 +894,36 @@ std::string sanitizeDirName(const std::string &str, const std::string &optional_
 
 	return wide_to_utf8(safe_name);
 }
+
+std::string insert_formspec_prepend(const std::string &formspec, const std::string &prepend) {
+	size_t pos = 0;
+	size_t pos2;
+	while ((pos2 = formspec.find('[', pos)) != std::string::npos) {
+		const std::string element_type = trim(formspec.substr(pos, pos2 - pos));
+
+		// If a no_prepend[] is found then don't insert the prepend
+		if (element_type == "no_prepend")
+			return formspec;
+
+		// Insert the prepend before this element if it isn't size, position,
+		// or anchor.
+		if (element_type != "size" && element_type != "position" &&
+				element_type != "anchor") {
+			break;
+		}
+
+		// Search for the closing ] and continue iterating
+		// Valid size, position, and anchor elements only have numbers so
+		// escaping doesn't have to be accounted for here.
+		pos = formspec.find(']', pos2);
+		if (pos == std::string::npos)
+			return formspec;
+		pos++;
+	}
+
+	// Make a copy of the const string and insert the formspec prepend in the
+	// correct location.
+	std::string prepended_fs = formspec;
+	prepended_fs.insert(pos, prepend);
+	return prepended_fs;
+}

src/util/string.h

@@ -728,3 +728,11 @@ inline irr::core::stringw utf8_to_stringw(const std::string &input)
  * 2. Remove 'unsafe' characters from the name by replacing them with '_'
  */
 std::string sanitizeDirName(const std::string &str, const std::string &optional_prefix);
+
+
+/**
+* @param formspec The version 1 formspec string
+ * @param prepend The formspec prepend
+ * @return A copy of \p formspec with \p prepend added if possible.
+ */
+std::string insert_formspec_prepend(const std::string &formspec, const std::string &prepend);