DecoderAPI: add function decoder_read_full()

Move code from the "mad" plugin.

src/DecoderAPI.cxx

@@ -292,6 +292,24 @@ decoder_read(Decoder *decoder,
 	return nbytes;
 }
 
+bool
+decoder_read_full(Decoder *decoder, InputStream &is,
+		  void *_buffer, size_t size)
+{
+	uint8_t *buffer = (uint8_t *)_buffer;
+
+	while (size > 0) {
+		size_t nbytes = decoder_read(decoder, is, buffer, size);
+		if (nbytes == 0)
+			return false;
+
+		buffer += nbytes;
+		size -= nbytes;
+	}
+
+	return true;
+}
+
 bool
 decoder_skip(Decoder *decoder, InputStream &is, size_t size)
 {

src/DecoderAPI.hxx

@@ -112,6 +112,17 @@ decoder_read(Decoder &decoder, InputStream &is,
 	return decoder_read(&decoder, is, buffer, length);
 }
 
+/**
+ * Blocking read from the input stream.  Attempts to fill the buffer
+ * completely; there is no partial result.
+ *
+ * @return true on success, false on error or command or not enough
+ * data
+ */
+bool
+decoder_read_full(Decoder *decoder, InputStream &is,
+		  void *buffer, size_t size);
+
 /**
  * Skip data on the #InputStream.
  *

src/decoder/MadDecoderPlugin.cxx

@@ -353,18 +353,8 @@ MadDecoder::ParseId3(size_t tagsize, Tag **mpd_tag)
 		memcpy(allocated, stream.this_frame, count);
 		mad_stream_skip(&(stream), count);
 
-		while (count < tagsize) {
-			size_t len;
-
-			len = decoder_read(decoder, input_stream,
-					   allocated + count, tagsize - count);
-			if (len == 0)
-				break;
-			else
-				count += len;
-		}
-
-		if (count != tagsize) {
+		if (!decoder_read_full(decoder, input_stream,
+				       allocated + count, tagsize - count)) {
 			LogDebug(mad_domain, "error parsing ID3 tag");
 			g_free(allocated);
 			return;

test/FakeDecoderAPI.cxx

@@ -65,6 +65,24 @@ decoder_read(gcc_unused Decoder *decoder,
 	return is.LockRead(buffer, length, IgnoreError());
 }
 
+bool
+decoder_read_full(Decoder *decoder, InputStream &is,
+		  void *_buffer, size_t size)
+{
+	uint8_t *buffer = (uint8_t *)_buffer;
+
+	while (size > 0) {
+		size_t nbytes = decoder_read(decoder, is, buffer, size);
+		if (nbytes == 0)
+			return false;
+
+		buffer += nbytes;
+		size -= nbytes;
+	}
+
+	return true;
+}
+
 bool
 decoder_skip(Decoder *decoder, InputStream &is, size_t size)
 {

test/run_decoder.cxx

@@ -101,6 +101,24 @@ decoder_read(gcc_unused Decoder *decoder,
 	return is.LockRead(buffer, length, IgnoreError());
 }
 
+bool
+decoder_read_full(Decoder *decoder, InputStream &is,
+		  void *_buffer, size_t size)
+{
+	uint8_t *buffer = (uint8_t *)_buffer;
+
+	while (size > 0) {
+		size_t nbytes = decoder_read(decoder, is, buffer, size);
+		if (nbytes == 0)
+			return false;
+
+		buffer += nbytes;
+		size -= nbytes;
+	}
+
+	return true;
+}
+
 bool
 decoder_skip(Decoder *decoder, InputStream &is, size_t size)
 {