sndio: test if sndio works in sndio_init

This avoids issues when uses have libsndio installed but are not using
it, also prefer sndio devices i.e. snd/0 by default on platforms other
than OpenBSD. This way cubebs alsa backend can be used insted of using
libsndio code which will use alsa directly, but with no benefit over
cubebs implementation.

src/cubeb_sndio.c

@@ -125,6 +125,23 @@ s16_to_float(void *ptr, long nsamp)
     *(--dst) = (1. / 32768) * *(--src);
 }
 
+static const char *
+sndio_get_device()
+{
+#ifndef __OpenBSD__
+  /*
+   * On other platforms default to sndio devices,
+   * so cubebs other backends can be used instead.
+   */
+  const char *dev = getenv("AUDIODEVICE");
+  if (dev == NULL || *dev == '\0')
+	return "snd/0";
+  return dev;
+#else
+  return SIO_DEVANY;
+#endif
+}
+
 static void
 sndio_onmove(void *arg, int delta)
 {
@@ -288,6 +305,7 @@ sndio_mainloop(void *arg)
 sndio_init(cubeb **context, char const *context_name)
 {
   void * libsndio = NULL;
+  struct sio_hdl *hdl;
 
   assert(context);
 
@@ -314,6 +332,13 @@ sndio_init(cubeb **context, char const *context_name)
 #undef LOAD
 #endif
 
+  /* test if sndio works */
+  hdl = WRAP(sio_open)(sndio_get_device(), SIO_PLAY, 1);
+  if (hdl == NULL) {
+    return CUBEB_ERROR;
+  }
+  WRAP(sio_close)(hdl);
+
   DPR("sndio_init(%s)\n", context_name);
   *context = malloc(sizeof(**context));
   if (*context == NULL)
@@ -388,7 +413,7 @@ sndio_stream_init(cubeb * context,
     goto err;
   }
   s->context = context;
-  s->hdl = WRAP(sio_open)(NULL, s->mode, 1);
+  s->hdl = WRAP(sio_open)(sndio_get_device(), s->mode, 1);
   if (s->hdl == NULL) {
     DPR("sndio_stream_init(), sio_open() failed\n");
     goto err;