DecoderBuffer: add method _need()

src/decoder/DecoderBuffer.cxx

@@ -117,21 +117,40 @@ decoder_buffer_fill(DecoderBuffer *buffer)
 	return true;
 }
 
+static const void *
+decoder_buffer_head(const DecoderBuffer *buffer)
+{
+	return buffer->data + buffer->consumed;
+}
+
 size_t
 decoder_buffer_available(const DecoderBuffer *buffer)
 {
-	return buffer->length - buffer->consumed;;
+	return buffer->length - buffer->consumed;
 }
 
 ConstBuffer<void>
 decoder_buffer_read(const DecoderBuffer *buffer)
 {
 	return {
-		buffer->data + buffer->consumed,
-		buffer->length - buffer->consumed
+		decoder_buffer_head(buffer),
+		decoder_buffer_available(buffer),
 	};
 }
 
+ConstBuffer<void>
+decoder_buffer_need(DecoderBuffer *buffer, size_t min_size)
+{
+	while (true) {
+		const auto available = decoder_buffer_available(buffer);
+		if (available >= min_size)
+			return { decoder_buffer_head(buffer), available };
+
+		if (!decoder_buffer_fill(buffer))
+			return nullptr;
+	}
+}
+
 void
 decoder_buffer_consume(DecoderBuffer *buffer, size_t nbytes)
 {

src/decoder/DecoderBuffer.hxx

@@ -91,6 +91,13 @@ ConstBuffer<void>
 decoder_buffer_read(const DecoderBuffer *buffer);
 
 /**
+ * Wait until this number of bytes are available.  Returns nullptr on
+ * error.
+ */
+ConstBuffer<void>
+decoder_buffer_need(DecoderBuffer *buffer, size_t min_size);
+
+/**
  * Consume (delete, invalidate) a part of the buffer.  The "nbytes"
  * parameter must not be larger than the length returned by
  * decoder_buffer_read().

src/decoder/plugins/FaadDecoderPlugin.cxx

@@ -66,15 +66,10 @@ static size_t
 adts_find_frame(DecoderBuffer *buffer)
 {
 	while (true) {
-		auto data = ConstBuffer<uint8_t>::FromVoid(decoder_buffer_read(buffer));
-		if (data.size < 8) {
-			/* not enough data yet */
-			if (!decoder_buffer_fill(buffer))
-				/* failed */
-				return 0;
-
-			continue;
-		}
+		auto data = ConstBuffer<uint8_t>::FromVoid(decoder_buffer_need(buffer, 8));
+		if (data.IsNull())
+			/* failed */
+			return 0;
 
 		/* find the 0xff marker */
 		const uint8_t *p = (const uint8_t *)
@@ -100,17 +95,10 @@ adts_find_frame(DecoderBuffer *buffer)
 			continue;
 		}
 
-		if (data.size < frame_length) {
-			/* available buffer size is smaller than the
-			   frame will be - attempt to read more
-			   data */
-			if (!decoder_buffer_fill(buffer)) {
-				/* not enough data; discard this frame
-				   to prevent a possible buffer
-				   overflow */
-				decoder_buffer_clear(buffer);
-			}
-
+		if (decoder_buffer_need(buffer, frame_length).IsNull()) {
+			/* not enough data; discard this frame to
+			   prevent a possible buffer overflow */
+			decoder_buffer_clear(buffer);
 			continue;
 		}
 
@@ -181,9 +169,8 @@ faad_song_duration(DecoderBuffer *buffer, InputStream &is)
 	const auto size = is.GetSize();
 	const size_t fileread = size >= 0 ? size : 0;
 
-	decoder_buffer_fill(buffer);
-	auto data = ConstBuffer<uint8_t>::FromVoid(decoder_buffer_read(buffer));
-	if (data.IsEmpty())
+	auto data = ConstBuffer<uint8_t>::FromVoid(decoder_buffer_need(buffer, 5));
+	if (data.IsNull())
 		return -1;
 
 	size_t tagsize = 0;
@@ -195,13 +182,11 @@ faad_song_duration(DecoderBuffer *buffer, InputStream &is)
 
 		tagsize += 10;
 
-		const bool success = decoder_buffer_skip(buffer, tagsize) &&
-			decoder_buffer_fill(buffer);
-		if (!success)
+		if (!decoder_buffer_skip(buffer, tagsize))
 			return -1;
 
-		data = ConstBuffer<uint8_t>::FromVoid(decoder_buffer_read(buffer));
-		if (data.IsEmpty())
+		data = ConstBuffer<uint8_t>::FromVoid(decoder_buffer_need(buffer, 5));
+		if (data.IsNull())
 			return -1;
 	}