Make remote media exclusively use GET for hash set (#15885)

src/client/clientmedia.cpp

@@ -154,7 +154,7 @@ void ClientMediaDownloader::step(Client *client)
 			startRemoteMediaTransfers();
 
 		// Did all remote transfers end and no new ones can be started?
-		// If so, request still missing files from the minetest server
+		// If so, request still missing files from the server
 		// (Or report that we have all files.)
 		if (m_httpfetch_active == 0) {
 			if (m_uncached_received_count < m_uncached_count) {
@@ -168,6 +168,15 @@ void ClientMediaDownloader::step(Client *client)
 	}
 }
 
+std::string ClientMediaDownloader::makeReferer(Client *client)
+{
+	std::string addr = client->getAddressName();
+	if (addr.find(':') != std::string::npos)
+		addr = '[' + addr + ']';
+	return std::string("minetest://") + addr + ':' +
+		std::to_string(client->getServerAddress().getPort());
+}
+
 void ClientMediaDownloader::initialStep(Client *client)
 {
 	std::wstring loading_text = wstrgettext("Media...");
@@ -227,9 +236,14 @@ void ClientMediaDownloader::initialStep(Client *client)
 		m_httpfetch_active_limit = g_settings->getS32("curl_parallel_limit");
 		m_httpfetch_active_limit = MYMAX(m_httpfetch_active_limit, 84);
 
-		// Write a list of hashes that we need. This will be POSTed
-		// to the server using Content-Type: application/octet-stream
-		std::string required_hash_set = serializeRequiredHashSet();
+		// Note: we used to use a POST request that contained the set of
+		// hashes we needed here, but this use was discontinued in 5.12.0 as
+		// it's not CDN/static hosting-friendly.
+		// Even with a large repository of media (think 60k files), you would be
+		// looking at only 1.1 MB for the index file.
+		// If it becomes a problem we can always still introduce a v2 of the
+		// hash set format and truncate the hashes to 6 bytes -- at the cost of
+		// a false-positive rate of 2^-48 -- which is 70% less space.
 
 		// minor fixme: this loop ignores m_httpfetch_active_limit
 
@@ -251,19 +265,8 @@ void ClientMediaDownloader::initialStep(Client *client)
 				remote->baseurl + MTHASHSET_FILE_NAME;
 			fetch_request.caller = m_httpfetch_caller;
 			fetch_request.request_id = m_httpfetch_next_id; // == i
-			fetch_request.method = HTTP_POST;
-			fetch_request.raw_data = required_hash_set;
 			fetch_request.extra_headers.emplace_back(
-				"Content-Type: application/octet-stream");
-
-			// Encapsulate possible IPv6 plain address in []
-			std::string addr = client->getAddressName();
-			if (addr.find(':', 0) != std::string::npos)
-				addr = '[' + addr + ']';
-			fetch_request.extra_headers.emplace_back(
-				std::string("Referer: minetest://") +
-				addr + ":" +
-				std::to_string(client->getServerAddress().getPort()));
+				"Referer: " + makeReferer(client));
 
 			httpfetch_async(fetch_request);
 
@@ -585,25 +588,6 @@ bool IClientMediaDownloader::checkAndLoad(
 	1 - Initial version
 */
 
-std::string ClientMediaDownloader::serializeRequiredHashSet()
-{
-	std::ostringstream os(std::ios::binary);
-
-	writeU32(os, MTHASHSET_FILE_SIGNATURE); // signature
-	writeU16(os, 1);                        // version
-
-	// Write list of hashes of files that have not been
-	// received (found in cache) yet
-	for (const auto &it : m_files) {
-		if (!it.second->received) {
-			FATAL_ERROR_IF(it.second->sha1.size() != 20, "Invalid SHA1 size");
-			os << it.second->sha1;
-		}
-	}
-
-	return os.str();
-}
-
 void ClientMediaDownloader::deSerializeHashSet(const std::string &data,
 		std::set<std::string> &result)
 {

src/client/clientmedia.h

@@ -119,6 +119,8 @@ protected:
 	bool loadMedia(Client *client, const std::string &data,
 			const std::string &name) override;
 
+	static std::string makeReferer(Client *client);
+
 private:
 	struct FileStatus {
 		bool received;
@@ -142,7 +144,6 @@ private:
 
 	static void deSerializeHashSet(const std::string &data,
 			std::set<std::string> &result);
-	std::string serializeRequiredHashSet();
 
 	// Maps filename to file status
 	std::map<std::string, FileStatus*> m_files;