use size_t and constant pointer in ao plugins

The audio output plugins should get a constant pointer, because they
must not modify the buffer.  Since the size is a non-negative buffer
size in bytes, we should change its type to size_t.

git-svn-id: https://svn.musicpd.org/mpd/trunk@7293 09075e82-0dd4-0310-85a5-a0d7c8717e4f

1 files changed, 23 insertions, 5 deletions

diff --git a/src/audioOutputs/audioOutput_ao.c b/src/audioOutputs/audioOutput_ao.c
index e7f3dcd6b..c28415410 100644
--- a/src/audioOutputs/audioOutput_ao.c
+++ b/src/audioOutputs/audioOutput_ao.c
@@ -199,19 +199,37 @@ static int audioOutputAo_openDevice(AudioOutput * audioOutput)
 	return 0;
 }
 
-static int audioOutputAo_play(AudioOutput * audioOutput, char *playChunk,
-			      int size)
+/**
+ * For whatever reason, libao wants a non-const pointer.  Let's hope
+ * it does not write to the buffer, and use the union deconst hack to
+ * work around this API misdesign.
+ */
+static int ao_play_deconst(ao_device *device, const void *output_samples,
+			   uint_32 num_bytes)
+{
+	union {
+		const void *in;
+		void *out;
+	} u;
+
+	u.in = output_samples;
+	return ao_play(device, u.out, num_bytes);
+}
+
+static int audioOutputAo_play(AudioOutput * audioOutput,
+			      const char *playChunk, size_t size)
 {
-	int send;
+	size_t send;
 	AoData *ad = (AoData *) audioOutput->data;
 
 	if (ad->device == NULL)
 		return -1;
 
 	while (size > 0) {
-		send = ad->writeSize > size ? size : ad->writeSize;
+		send = (size_t)ad->writeSize > size
+			? size : (size_t)ad->writeSize;
 
-		if (ao_play(ad->device, playChunk, send) == 0) {
+		if (ao_play_deconst(ad->device, playChunk, send) == 0) {
 			audioOutputAo_error();
 			ERROR("closing audio device due to write error\n");
 			audioOutputAo_closeDevice(audioOutput);