music_pipe: added functions music_pipe_write() and music_pipe_expand()

This new API gives the caller a writable buffer to the music pipe
chunk.  This may allow the caller to eliminate several buffer copies,
because it may manipulate the returned buffer, until it calls
music_pipe_expand().

src/pipe.c

@@ -207,25 +207,49 @@ tail_chunk(size_t frame_size)
 	return chunk;
 }
 
-static size_t
-music_chunk_append(struct music_chunk *chunk, const void *data, size_t length,
-		   size_t frame_size)
+void *
+music_pipe_write(const struct audio_format *audio_format,
+		 float data_time, uint16_t bit_rate,
+		 size_t *max_length_r)
 {
-	size_t rest = sizeof(chunk->data) - chunk->length;
+	const size_t frame_size = audio_format_frame_size(audio_format);
+	struct music_chunk *chunk;
+	size_t num_frames;
 
-	assert(rest >= frame_size);
+	chunk = tail_chunk(frame_size);
+	if (chunk == NULL)
+		return NULL;
 
-	if (length > rest)
-		length = rest;
+	if (chunk->length == 0) {
+		/* if the chunk is empty, nobody has set bitRate and
+		   times yet */
 
-	/* don't split frames */
-	length /= frame_size;
-	length *= frame_size;
+		chunk->bit_rate = bit_rate;
+		chunk->times = data_time;
+	}
+
+	num_frames = (sizeof(chunk->data) - chunk->length) / frame_size;
+	*max_length_r = num_frames * frame_size;
+	return chunk->data + chunk->length;
+}
+
+void
+music_pipe_expand(const struct audio_format *audio_format, size_t length)
+{
+	const size_t frame_size = audio_format_frame_size(audio_format);
+	struct music_chunk *chunk;
+
+	/* no partial frames allowed */
+	assert(length % frame_size == 0);
+
+	chunk = tail_chunk(frame_size);
+	assert(chunk != NULL);
+	assert(chunk->length + length <= sizeof(chunk->data));
 
-	memcpy(chunk->data + chunk->length, data, length);
 	chunk->length += length;
 
-	return length;
+	if (chunk->length + frame_size > sizeof(chunk->data))
+		music_pipe_flush();
 }
 
 size_t music_pipe_append(const void *data0, size_t datalen,
@@ -233,38 +257,28 @@ size_t music_pipe_append(const void *data0, size_t datalen,
 			 float data_time, uint16_t bit_rate)
 {
 	const unsigned char *data = data0;
-	const size_t frame_size = audio_format_frame_size(audio_format);
 	size_t ret = 0, nbytes;
-	struct music_chunk *chunk = NULL;
-
-	/* no partial frames allowed */
-	assert((datalen % frame_size) == 0);
+	void *dest;
 
 	while (datalen) {
-		chunk = tail_chunk(frame_size);
-		if (chunk == NULL)
-			return ret;
+		dest = music_pipe_write(audio_format, data_time, bit_rate,
+					&nbytes);
+		if (dest == NULL)
+			break;
 
-		if (chunk->length == 0) {
-			/* if the chunk is empty, nobody has set bitRate and
-			   times yet */
-
-			chunk->bit_rate = bit_rate;
-			chunk->times = data_time;
-		}
-
-		nbytes = music_chunk_append(chunk, data, datalen,
-					    frame_size);
 		assert(nbytes > 0);
 
+		if (nbytes > datalen)
+			nbytes = datalen;
+
+		memcpy(dest, data, nbytes);
+		music_pipe_expand(audio_format, nbytes);
+
 		datalen -= nbytes;
 		data += nbytes;
 		ret += nbytes;
 	}
 
-	if (chunk != NULL && chunk->length == sizeof(chunk->data))
-		music_pipe_flush();
-
 	return ret;
 }
 

src/pipe.h

@@ -147,6 +147,24 @@ music_pipe_peek(void)
 	return music_pipe_get_chunk(music_pipe.begin);
 }
 
+/**
+ * Prepares appending to the music pipe.  Returns a buffer where you
+ * may write into.  After you are finished, call music_pipe_expand().
+ *
+ * @return a writable buffer
+ */
+void *
+music_pipe_write(const struct audio_format *audio_format,
+		 float data_time, uint16_t bit_rate,
+		 size_t *max_length_r);
+
+/**
+ * Tells the music pipe to move the end pointer, after you have
+ * written to the buffer returned by music_pipe_write().
+ */
+void
+music_pipe_expand(const struct audio_format *audio_format, size_t length);
+
 /**
  * Append a data block to the buffer.
  *