DecoderAPI: add function decoder_skip()

Move code from the "mad" plugin.

src/DecoderAPI.cxx

@@ -292,6 +292,22 @@ decoder_read(Decoder *decoder,
 	return nbytes;
 }
 
+bool
+decoder_skip(Decoder *decoder, InputStream &is, size_t size)
+{
+	while (size > 0) {
+		char buffer[1024];
+		size_t nbytes = decoder_read(decoder, is, buffer,
+					     std::min(sizeof(buffer), size));
+		if (nbytes == 0)
+			return false;
+
+		size -= nbytes;
+	}
+
+	return true;
+}
+
 void
 decoder_timestamp(Decoder &decoder, double t)
 {

src/DecoderAPI.hxx

@@ -112,6 +112,14 @@ decoder_read(Decoder &decoder, InputStream &is,
 	return decoder_read(&decoder, is, buffer, length);
 }
 
+/**
+ * Skip data on the #InputStream.
+ *
+ * @return true on success, false on error or command
+ */
+bool
+decoder_skip(Decoder *decoder, InputStream &is, size_t size);
+
 /**
  * Sets the time stamp for the next data chunk [seconds].  The MPD
  * core automatically counts it up, and a decoder plugin only needs to

src/decoder/MadDecoderPlugin.cxx

@@ -413,20 +413,7 @@ MadDecoder::ParseId3(size_t tagsize, Tag **mpd_tag)
 		mad_stream_skip(&stream, tagsize);
 	} else {
 		mad_stream_skip(&stream, count);
-
-		while (count < tagsize) {
-			size_t len = tagsize - count;
-			char ignored[1024];
-			if (len > sizeof(ignored))
-				len = sizeof(ignored);
-
-			len = decoder_read(decoder, input_stream,
-					   ignored, len);
-			if (len == 0)
-				break;
-			else
-				count += len;
-		}
+		decoder_skip(decoder, input_stream, tagsize - count);
 	}
 #endif
 }

test/FakeDecoderAPI.cxx

@@ -65,6 +65,22 @@ decoder_read(gcc_unused Decoder *decoder,
 	return is.LockRead(buffer, length, IgnoreError());
 }
 
+bool
+decoder_skip(Decoder *decoder, InputStream &is, size_t size)
+{
+	while (size > 0) {
+		char buffer[1024];
+		size_t nbytes = decoder_read(decoder, is, buffer,
+					     std::min(sizeof(buffer), size));
+		if (nbytes == 0)
+			return false;
+
+		size -= nbytes;
+	}
+
+	return true;
+}
+
 void
 decoder_timestamp(gcc_unused Decoder &decoder,
 		  gcc_unused double t)

test/run_decoder.cxx

@@ -101,6 +101,22 @@ decoder_read(gcc_unused Decoder *decoder,
 	return is.LockRead(buffer, length, IgnoreError());
 }
 
+bool
+decoder_skip(Decoder *decoder, InputStream &is, size_t size)
+{
+	while (size > 0) {
+		char buffer[1024];
+		size_t nbytes = decoder_read(decoder, is, buffer,
+					     std::min(sizeof(buffer), size));
+		if (nbytes == 0)
+			return false;
+
+		size -= nbytes;
+	}
+
+	return true;
+}
+
 void
 decoder_timestamp(gcc_unused Decoder &decoder,
 		  gcc_unused double t)