util/*FifoBuffer: migrate from WritableBuffer to std::span

src/decoder/DecoderBuffer.cxx

@@ -29,7 +29,7 @@ DecoderBuffer::Fill()
 		return false;
 
 	size_t nbytes = decoder_read(client, is,
-				     w.data, w.size);
+				     w.data(), w.size());
 	if (nbytes == 0)
 		/* end of file, I/O error or decoder command
 		   received */
@@ -39,16 +39,16 @@ DecoderBuffer::Fill()
 	return true;
 }
 
-ConstBuffer<void>
+std::span<const std::byte>
 DecoderBuffer::Need(size_t min_size)
 {
 	while (true) {
 		const auto r = Read();
-		if (r.size >= min_size)
+		if (r.size() >= min_size)
 			return r;
 
 		if (!Fill())
-			return nullptr;
+			return {};
 	}
 }
 
@@ -56,13 +56,13 @@ bool
 DecoderBuffer::Skip(size_t nbytes)
 {
 	const auto r = buffer.Read();
-	if (r.size >= nbytes) {
+	if (r.size() >= nbytes) {
 		buffer.Consume(nbytes);
 		return true;
 	}
 
 	buffer.Clear();
-	nbytes -= r.size;
+	nbytes -= r.size();
 
 	return decoder_skip(client, is, nbytes);
 }

src/decoder/DecoderBuffer.hxx

@@ -21,10 +21,6 @@
 #define MPD_DECODER_BUFFER_HXX
 
 #include "util/DynamicFifoBuffer.hxx"
-#include "util/ConstBuffer.hxx"
-
-#include <cstddef>
-#include <cstdint>
 
 class DecoderClient;
 class InputStream;
@@ -38,7 +34,7 @@ class DecoderBuffer {
 	DecoderClient *const client;
 	InputStream &is;
 
-	DynamicFifoBuffer<uint8_t> buffer;
+	DynamicFifoBuffer<std::byte> buffer;
 
 public:
 	/**
@@ -83,16 +79,15 @@ public:
 	 * you have to call Consume() to do that.  The returned buffer
 	 * becomes invalid after a Fill() or a Consume() call.
 	 */
-	ConstBuffer<void> Read() const noexcept {
-		auto r = buffer.Read();
-		return { r.data, r.size };
+	std::span<const std::byte> Read() const noexcept {
+		return buffer.Read();
 	}
 
 	/**
 	 * Wait until this number of bytes are available.  Returns nullptr on
 	 * error.
 	 */
-	ConstBuffer<void> Need(size_t min_size);
+	std::span<const std::byte> Need(size_t min_size);
 
 	/**
 	 * Consume (delete, invalidate) a part of the buffer.  The

src/decoder/plugins/FaadDecoderPlugin.cxx

@@ -93,7 +93,7 @@ adts_find_frame(DecoderBuffer &buffer)
 			continue;
 		}
 
-		if (buffer.Need(frame_length).IsNull()) {
+		if (buffer.Need(frame_length).empty()) {
 			/* not enough data; discard this frame to
 			   prevent a possible buffer overflow */
 			buffer.Clear();

src/decoder/plugins/HybridDsdDecoderPlugin.cxx

@@ -237,11 +237,11 @@ HybridDsdDecode(DecoderClient &client, InputStream &input)
 		auto w = buffer.Write();
 		if (!w.empty()) {
 			if (remaining_bytes < (1<<30ULL) &&
-			    w.size > size_t(remaining_bytes))
-				w.size = remaining_bytes;
+			    w.size() > size_t(remaining_bytes))
+				w = w.first(remaining_bytes);
 
 			const size_t nbytes = client.Read(input,
-							  w.data, w.size);
+							  w.data(), w.size());
 			if (nbytes == 0)
 				return;
 
@@ -251,9 +251,9 @@ HybridDsdDecode(DecoderClient &client, InputStream &input)
 
 		/* submit the buffer to our client */
 		auto r = buffer.Read();
-		auto n_frames = r.size / frame_size;
+		auto n_frames = r.size() / frame_size;
 		if (n_frames > 0) {
-			cmd = client.SubmitData(input, r.data,
+			cmd = client.SubmitData(input, r.data(),
 						n_frames * frame_size,
 						kbit_rate);
 			buffer.Consume(n_frames * frame_size);

src/decoder/plugins/PcmDecoderPlugin.cxx

@@ -51,7 +51,7 @@ FillBuffer(DecoderClient &client, InputStream &is, B &buffer)
 	if (w.empty())
 		return true;
 
-	size_t nbytes = decoder_read(client, is, w.data, w.size);
+	size_t nbytes = decoder_read(client, is, w.data(), w.size());
 	if (nbytes == 0 && is.LockIsEOF())
 		return false;
 
@@ -188,25 +188,28 @@ pcm_stream_decode(DecoderClient &client, InputStream &is)
 		/* round down to the nearest frame size, because we
 		   must not pass partial frames to
 		   DecoderClient::SubmitData() */
-		r.size -= r.size % in_frame_size;
-		buffer.Consume(r.size);
+		r = r.first(r.size() - r.size() % in_frame_size);
+		buffer.Consume(r.size());
 
 		if (reverse_endian)
 			/* make sure we deliver samples in host byte order */
-			reverse_bytes_16((uint16_t *)r.data,
-					 (uint16_t *)r.data,
-					 (uint16_t *)(r.data + r.size));
+			reverse_bytes_16((uint16_t *)r.data(),
+					 (uint16_t *)r.data(),
+					 (uint16_t *)(r.data() + r.size()));
 		else if (l24) {
 			/* convert big-endian packed 24 bit
 			   (audio/L24) to native-endian 24 bit (in 32
 			   bit integers) */
-			pcm_unpack_24be(unpack_buffer, r.begin(), r.end());
-			r.data = (uint8_t *)&unpack_buffer[0];
-			r.size = (r.size / 3) * 4;
+			pcm_unpack_24be(unpack_buffer,
+					r.data(), r.data() + r.size());
+			r = {
+				(uint8_t *)&unpack_buffer[0],
+				(r.size() / 3) * 4,
+			};
 		}
 
 		cmd = !r.empty()
-			? client.SubmitData(is, r.data, r.size, 0)
+			? client.SubmitData(is, r.data(), r.size(), 0)
 			: client.GetCommand();
 		if (cmd == DecoderCommand::SEEK) {
 			uint64_t frame = client.GetSeekFrame();