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

7 files changed, 44 insertions, 19 deletions

diff --git a/src/client/Client.hxx b/src/client/Client.hxx
index d19d08760..deb4b8caa 100644
--- a/src/client/Client.hxx
+++ b/src/client/Client.hxx
@@ -84,6 +84,12 @@ public:
 	 */
 	TagMask tag_mask = TagMask::All();
 
+	/**
+	 * The maximum number of bytes transmitted in a binary
+	 * response.  Can be changed with the "binarylimit" command.
+	 */
+	size_t binary_limit = 8192;
+
 private:
 	static constexpr size_t MAX_SUBSCRIPTIONS = 16;
 
@@ -122,6 +128,7 @@ public:
 	~Client() noexcept;
 
 	using FullyBufferedSocket::GetEventLoop;
+	using FullyBufferedSocket::GetOutputMaxSize;
 
 	gcc_pure
 	bool IsExpired() const noexcept {
diff --git a/src/client/Response.cxx b/src/client/Response.cxx
index 3900df75e..0c9145a50 100644
--- a/src/client/Response.cxx
+++ b/src/client/Response.cxx
@@ -59,7 +59,7 @@ Response::Format(const char *fmt, ...) noexcept
 bool
 Response::WriteBinary(ConstBuffer<void> payload) noexcept
 {
-	assert(payload.size <= MAX_BINARY_SIZE);
+	assert(payload.size <= client.binary_limit);
 
 	return Format("binary: %zu\n", payload.size) &&
 		Write(payload.data, payload.size) &&
diff --git a/src/client/Response.hxx b/src/client/Response.hxx
index 00c1566fc..4c7e40e8a 100644
--- a/src/client/Response.hxx
+++ b/src/client/Response.hxx
@@ -79,8 +79,6 @@ public:
 	gcc_printf(2,3)
 	bool Format(const char *fmt, ...) noexcept;
 
-	static constexpr size_t MAX_BINARY_SIZE = 8192;
-
 	/**
 	 * Write a binary chunk; this writes the "binary" line, the
 	 * given chunk and the trailing newline.
diff --git a/src/command/AllCommands.cxx b/src/command/AllCommands.cxx
index 96ae21e42..4508fa92f 100644
--- a/src/command/AllCommands.cxx
+++ b/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 },
diff --git a/src/command/ClientCommands.cxx b/src/command/ClientCommands.cxx
index f0e3470be..01bd462f2 100644
--- a/src/command/ClientCommands.cxx
+++ b/src/command/ClientCommands.cxx
@@ -41,6 +41,21 @@ handle_ping([[maybe_unused]] Client &client, [[maybe_unused]] Request args,
 }
 
 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)
 {
 	unsigned permission = 0;
diff --git a/src/command/ClientCommands.hxx b/src/command/ClientCommands.hxx
index fc0dc42e1..de766e802 100644
--- a/src/command/ClientCommands.hxx
+++ b/src/command/ClientCommands.hxx
@@ -33,6 +33,9 @@ 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);
 
 CommandResult
diff --git a/src/command/FileCommands.cxx b/src/command/FileCommands.cxx
index 4ac239646..7efbb211c 100644
--- a/src/command/FileCommands.cxx
+++ b/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);