Check media requests on the server more carefully

src/clientiface.h

@@ -284,10 +284,10 @@ public:
 		return m_blocks_sent.find(p) != m_blocks_sent.end();
 	}
 
-	// Increments timeouts and removes timed-out blocks from list
-	// NOTE: This doesn't fix the server-not-sending-block bug
-	//       because it is related to emerging, not sending.
-	//void RunSendingTimeouts(float dtime, float timeout);
+	bool markMediaSent(const std::string &name) {
+		auto insert_result = m_media_sent.emplace(name);
+		return insert_result.second; // true = was inserted
+	}
 
 	void PrintInfo(std::ostream &o)
 	{
@@ -310,7 +310,7 @@ public:
 
 	ClientState getState() const { return m_state; }
 
-	std::string getName() const { return m_name; }
+	const std::string &getName() const { return m_name; }
 
 	void setName(const std::string &name) { m_name = name; }
 
@@ -394,6 +394,12 @@ private:
 	const s16 m_max_gen_distance;
 	const bool m_occ_cull;
 
+	/*
+		Set of media files the client has already requested
+		We won't send the same file twice to avoid bandwidth consumption attacks.
+	*/
+	std::unordered_set<std::string> m_media_sent;
+
 	/*
 		Blocks that are currently on the line.
 		This is used for throttling the sending of blocks.

src/network/serverpackethandler.cpp

@@ -356,24 +356,24 @@ void Server::handleCommand_Init2(NetworkPacket* pkt)
 
 void Server::handleCommand_RequestMedia(NetworkPacket* pkt)
 {
-	std::vector<std::string> tosend;
+	std::unordered_set<std::string> tosend;
 	u16 numfiles;
 
 	*pkt >> numfiles;
 
 	session_t peer_id = pkt->getPeerId();
-	infostream << "Sending " << numfiles << " files to " <<
-		getPlayerName(peer_id) << std::endl;
-	verbosestream << "TOSERVER_REQUEST_MEDIA: requested file(s)" << std::endl;
+	verbosestream << "Client " << getPlayerName(peer_id)
+		<< " requested media file(s):\n";
 
 	for (u16 i = 0; i < numfiles; i++) {
 		std::string name;
 
 		*pkt >> name;
 
-		tosend.emplace_back(name);
-		verbosestream << "  " << name << std::endl;
+		tosend.emplace(name);
+		verbosestream << "  " << name << "\n";
 	}
+	verbosestream << std::flush;
 
 	sendRequestedMedia(peer_id, tosend);
 }

src/server.cpp

@@ -137,6 +137,7 @@ void *ServerThread::run()
 		} catch (con::PeerNotFoundException &e) {
 			infostream<<"Server: PeerNotFoundException"<<std::endl;
 		} catch (ClientNotFoundException &e) {
+			infostream<<"Server: ClientNotFoundException"<<std::endl;
 		} catch (con::ConnectionBindFailed &e) {
 			m_server->setAsyncFatalError(e.what());
 		} catch (LuaError &e) {
@@ -2671,15 +2672,18 @@ struct SendableMedia
 };
 
 void Server::sendRequestedMedia(session_t peer_id,
-		const std::vector<std::string> &tosend)
+		const std::unordered_set<std::string> &tosend)
 {
-	verbosestream<<"Server::sendRequestedMedia(): "
-			<<"Sending files to client"<<std::endl;
+	auto *client = getClient(peer_id, CS_DefinitionsSent);
+	assert(client);
+
+	infostream << "Server::sendRequestedMedia(): Sending "
+		<< tosend.size() << " files to " << client->getName() << std::endl;
 
 	/* Read files */
 
 	// Put 5kB in one bunch (this is not accurate)
-	u32 bytes_per_bunch = 5000;
+	const u32 bytes_per_bunch = 5000;
 
 	std::vector<std::vector<SendableMedia>> file_bunches;
 	file_bunches.emplace_back();
@@ -2687,13 +2691,25 @@ void Server::sendRequestedMedia(session_t peer_id,
 	u32 file_size_bunch_total = 0;
 
 	for (const std::string &name : tosend) {
-		if (m_media.find(name) == m_media.end()) {
+		auto it = m_media.find(name);
+
+		if (it == m_media.end()) {
 			errorstream<<"Server::sendRequestedMedia(): Client asked for "
 					<<"unknown file \""<<(name)<<"\""<<std::endl;
 			continue;
 		}
+		const auto &m = it->second;
 
-		const auto &m = m_media[name];
+		// no_announce <=> usually ephemeral dynamic media, which may
+		// have duplicate filenames. So we can't check it.
+		if (!m.no_announce) {
+			if (!client->markMediaSent(name)) {
+				infostream << "Server::sendRequestedMedia(): Client asked has "
+					"requested \"" << name << "\" before, not sending it again."
+					<< std::endl;
+				continue;
+			}
+		}
 
 		// Read data
 		std::string data;
@@ -2717,11 +2733,11 @@ void Server::sendRequestedMedia(session_t peer_id,
 
 	/* Create and send packets */
 
-	u16 num_bunches = file_bunches.size();
+	const u16 num_bunches = file_bunches.size();
 	for (u16 i = 0; i < num_bunches; i++) {
+		auto &bunch = file_bunches[i];
 		/*
-			u16 command
-			u16 total number of texture bunches
+			u16 total number of media bunches
 			u16 index of this bunch
 			u32 number of files in this bunch
 			for each file {
@@ -2735,14 +2751,14 @@ void Server::sendRequestedMedia(session_t peer_id,
 		NetworkPacket pkt(TOCLIENT_MEDIA, 4 + 0, peer_id);
 		pkt << num_bunches << i << (u32) file_bunches[i].size();
 
-		for (const SendableMedia &j : file_bunches[i]) {
+		for (auto &j : bunch) {
 			pkt << j.name;
 			pkt.putLongString(j.data);
 		}
 
 		verbosestream << "Server::sendRequestedMedia(): bunch "
 				<< i << "/" << num_bunches
-				<< " files=" << file_bunches[i].size()
+				<< " files=" << bunch.size()
 				<< " size="  << pkt.getSize() << std::endl;
 		Send(&pkt);
 	}

src/server.h

@@ -515,7 +515,7 @@ private:
 	void fillMediaCache();
 	void sendMediaAnnouncement(session_t peer_id, const std::string &lang_code);
 	void sendRequestedMedia(session_t peer_id,
-			const std::vector<std::string> &tosend);
+			const std::unordered_set<std::string> &tosend);
 	void stepPendingDynMediaCallbacks(float dtime);
 
 	// Adds a ParticleSpawner on peer with peer_id (PEER_ID_INEXISTENT == all)