music_chunk: added music_chunk_write(), music_chunk_expand()

Moved some code from music_pipe_write() and music_pipe_expand().  Only
music_chunk.c should access the music_chunk internals.

src/chunk.h

@@ -19,13 +19,17 @@
 #ifndef MPD_CHUNK_H
 #define MPD_CHUNK_H
 
+#include <stdbool.h>
 #include <stdint.h>
+#include <stddef.h>
 
 enum {
 	/* pick 1020 since its devisible for 8,16,24, and 32-bit audio */
 	CHUNK_SIZE = 1020,
 };
 
+struct audio_format;
+
 /**
  * A chunk of music data.  Its format is defined by the
  * music_pipe_append() caller.
@@ -58,4 +62,36 @@ music_chunk_init(struct music_chunk *chunk);
 void
 music_chunk_free(struct music_chunk *chunk);
 
+/**
+ * Prepares appending to the music chunk.  Returns a buffer where you
+ * may write into.  After you are finished, call music_chunk_expand().
+ *
+ * @param chunk the music_chunk object
+ * @param audio_format the audio format for the appended data; must
+ * stay the same for the life cycle of this chunk
+ * @param data_time the time within the song
+ * @param bit_rate the current bit rate of the source file
+ * @param max_length_r the maximum write length is returned here
+ * @return a writable buffer, or NULL if the chunk is full
+ */
+void *
+music_chunk_write(struct music_chunk *chunk,
+		  const struct audio_format *audio_format,
+		  float data_time, uint16_t bit_rate,
+		  size_t *max_length_r);
+
+/**
+ * Increases the length of the chunk after the caller has written to
+ * the buffer returned by music_chunk_write().
+ *
+ * @param chunk the music_chunk object
+ * @param audio_format the audio format for the appended data; must
+ * stay the same for the life cycle of this chunk
+ * @param length the number of bytes which were appended
+ * @return true if the chunk is full
+ */
+bool
+music_chunk_expand(struct music_chunk *chunk,
+		   const struct audio_format *audio_format, size_t length);
+
 #endif