client/Response: add method WriteBinary()

Move code from read_stream_art().

src/client/Response.cxx

@@ -56,6 +56,14 @@ Response::Format(const char *fmt, ...) noexcept
 	return success;
 }
 
+bool
+Response::WriteBinary(ConstBuffer<void> payload) noexcept
+{
+	return Format("binary: %zu\n", payload.size) &&
+		Write(payload.data, payload.size) &&
+		Write("\n");
+}
+
 void
 Response::Error(enum ack code, const char *msg) noexcept
 {

src/client/Response.hxx

@@ -26,6 +26,7 @@
 #include <stddef.h>
 #include <stdarg.h>
 
+template<typename T> struct ConstBuffer;
 class Client;
 class TagMask;
 
@@ -76,6 +77,14 @@ public:
 	bool FormatV(const char *fmt, va_list args) noexcept;
 	bool Format(const char *fmt, ...) noexcept;
 
+	/**
+	 * Write a binary chunk; this writes the "binary" line, the
+	 * given chunk and the trailing newline.
+	 *
+	 * @return true on success
+	 */
+	bool WriteBinary(ConstBuffer<void> payload) noexcept;
+
 	void Error(enum ack code, const char *msg) noexcept;
 	void FormatError(enum ack code, const char *fmt, ...) noexcept;
 };

src/command/FileCommands.cxx

@@ -296,14 +296,8 @@ read_stream_art(Response &r, const char *uri, size_t offset)
 		read_size = is->Read(lock, &buffer, CHUNK_SIZE);
 	}
 
-	r.Format("size: %" PRIoffset "\n"
-			 "binary: %u\n",
-			 art_file_size,
-			 read_size
-			 );
-
-	r.Write(buffer, read_size);
-	r.Write("\n");
+	r.Format("size: %" PRIoffset "\n", art_file_size);
+	r.WriteBinary({buffer, read_size});
 
 	return CommandResult::OK;
 }