protocol: add command "binarylimit"

Increasing the protocol version to 0.22.4 to allow clients to detect
this feature.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1038

src/command/AllCommands.cxx

@@ -87,6 +87,7 @@ static constexpr struct command commands[] = {
 	{ "addid", PERMISSION_ADD, 1, 2, handle_addid },
 	{ "addtagid", PERMISSION_ADD, 3, 3, handle_addtagid },
 	{ "albumart", PERMISSION_READ, 2, 2, handle_album_art },
+	{ "binarylimit", PERMISSION_NONE, 1, 1, handle_binary_limit },
 	{ "channels", PERMISSION_READ, 0, 0, handle_channels },
 	{ "clear", PERMISSION_CONTROL, 0, 0, handle_clear },
 	{ "clearerror", PERMISSION_CONTROL, 0, 0, handle_clearerror },

src/command/ClientCommands.cxx

@@ -40,6 +40,21 @@ handle_ping([[maybe_unused]] Client &client, [[maybe_unused]] Request args,
 	return CommandResult::OK;
 }
 
+CommandResult
+handle_binary_limit(Client &client, Request args,
+		    [[maybe_unused]] Response &r)
+{
+	size_t value = args.ParseUnsigned(0, client.GetOutputMaxSize() - 4096);
+	if (value < 64) {
+		r.Error(ACK_ERROR_ARG, "Value too small");
+		return CommandResult::ERROR;
+	}
+
+	client.binary_limit = value;
+
+	return CommandResult::OK;
+}
+
 CommandResult
 handle_password(Client &client, Request args, Response &r)
 {

src/command/ClientCommands.hxx

@@ -32,6 +32,9 @@ handle_close(Client &client, Request request, Response &response);
 CommandResult
 handle_ping(Client &client, Request request, Response &response);
 
+CommandResult
+handle_binary_limit(Client &client, Request request, Response &response);
+
 CommandResult
 handle_password(Client &client, Request request, Response &response);
 

src/command/FileCommands.cxx

@@ -43,6 +43,7 @@
 #include "thread/Mutex.hxx"
 #include "Log.hxx"
 
+#include <algorithm>
 #include <cassert>
 #include <cinttypes> /* for PRIu64 */
 
@@ -205,28 +206,26 @@ read_stream_art(Response &r, const char *uri, size_t offset)
 
 	const offset_type art_file_size = is->GetSize();
 
-	if (offset >= art_file_size) {
-		if (offset > art_file_size) {
-			r.Error(ACK_ERROR_ARG, "Offset too large");
-			return CommandResult::ERROR;
-		} else {
-			r.Format("size: %" PRIoffset "\n", art_file_size);
-			r.WriteBinary(nullptr);
-			return CommandResult::OK;
-		}
+	if (offset > art_file_size) {
+		r.Error(ACK_ERROR_ARG, "Offset too large");
+		return CommandResult::ERROR;
 	}
 
-	uint8_t buffer[Response::MAX_BINARY_SIZE];
-	size_t read_size;
+	std::size_t buffer_size =
+		std::min<offset_type>(art_file_size - offset,
+				      r.GetClient().binary_limit);
 
-	{
+	std::unique_ptr<std::byte[]> buffer(new std::byte[buffer_size]);
+
+	std::size_t read_size = 0;
+	if (buffer_size > 0) {
 		std::unique_lock<Mutex> lock(mutex);
 		is->Seek(lock, offset);
-		read_size = is->Read(lock, &buffer, sizeof(buffer));
+		read_size = is->Read(lock, buffer.get(), buffer_size);
 	}
 
 	r.Format("size: %" PRIoffset "\n", art_file_size);
-	r.WriteBinary({buffer, read_size});
+	r.WriteBinary({buffer.get(), read_size});
 
 	return CommandResult::OK;
 }
@@ -313,8 +312,10 @@ public:
 			response.Format("type: %s\n", mime_type);
 
 		buffer.size -= offset;
-		if (buffer.size > Response::MAX_BINARY_SIZE)
-			buffer.size = Response::MAX_BINARY_SIZE;
+
+		const std::size_t binary_limit = response.GetClient().binary_limit;
+		if (buffer.size > binary_limit)
+			buffer.size = binary_limit;
 		buffer.data = OffsetPointer(buffer.data, offset);
 
 		response.WriteBinary(buffer);