tinycompress: Add support for getting list of supported codecs

Right now, there is no way to expose a list of codecs from tinycompress. While
one could theoretically call is_codec_supported multiple times in an application
to check against a list of codecs, an API would make it easy to enumerate supported
codecs. The IOCTL SNDRV_COMPRESS_GET_CAPS after all already exists.

The use case is Pipewire where we would like the compressed sink Pipewire node to
advertise only codecs supported by the underlying hardware.

Signed-off-by: Sanchayan Maity <sanchayan@asymptotic.io>

include/tinycompress/compress_ops.h

@@ -42,6 +42,7 @@ struct compress_ops {
 	int (*is_compress_running)(void *compress_data);
 	int (*is_compress_ready)(void *compress_data);
 	const char *(*get_error)(void *compress_data);
+	int (*get_supported_codecs_by_name)(const char *name, unsigned int flags, void *codecs, int size);
 };
 
 #endif /* end of __COMPRESS_OPS_H__ */

include/tinycompress/tinycompress.h

@@ -307,6 +307,37 @@ int is_compress_ready(struct compress *compress);
 /* Returns a human readable reason for the last error */
 const char *compress_get_error(struct compress *compress);
 
+/*
+ * compress_get_supported_codecs: gets the list of supported codecs
+ *
+ * returns number of codecs on success, negative on error
+ *
+ * @card: sound card number
+ * @device: device number
+ * @flags: stream flags
+ * @codecs: Pointer to an array which will hold the list of codecs
+ * @size: Size of the codecs array. Must be sized to hold 32 integers.
+ */
+int compress_get_supported_codecs(unsigned int card, unsigned int device,
+		unsigned int flags, int *codecs, int size);
+
+/*
+ * compress_get_supported_codecs_by_name: gets the list of supported codecs
+ *
+ * returns number of codecs on success, negative on error
+ *
+ * format of name is :
+ *    hw:<card>,<device> for real hw compress node
+ *    <plugin_libname>:<custom string> for virtual compress node
+ *
+ * @name: name of the compress node
+ * @flags: stream flags
+ * @codecs: Pointer to an array which will hold the list of codecs
+ * @size: Size of the codecs array. Must be sized to hold 32 integers.
+ */
+int compress_get_supported_codecs_by_name(const char *name, unsigned int flags,
+		int *codecs, int size);
+
 #if defined(__cplusplus)
 } // extern "C"
 #endif

src/lib/compress.c

@@ -310,3 +310,40 @@ int compress_wait(struct compress *compress, int timeout_ms)
 	return compress->ops->wait(compress->data, timeout_ms);
 }
 
+int compress_get_supported_codecs(unsigned int card, unsigned int device,
+		unsigned int flags, int *codecs, int size)
+{
+	struct compress_ops *ops = &compress_hw_ops;
+	char name[128];
+
+	snprintf(name, sizeof(name), "hw:%u,%u", card, device);
+
+	return ops->get_supported_codecs_by_name(name, flags, codecs, size);
+}
+
+int compress_get_supported_codecs_by_name(const char *name, unsigned int flags, int *codecs, int size)
+{
+	struct compress *compress;
+	int ret = -1;
+
+	compress = calloc(1, sizeof(struct compress));
+	if (!compress)
+		return ret;
+
+	if ((name[0] == 'h') || (name[1] == 'w') || (name[2] == ':')) {
+		compress->ops = &compress_hw_ops;
+	} else {
+		if (populate_compress_plugin_ops(compress, name)) {
+			free(compress);
+			return ret;
+		}
+	}
+
+	ret = compress->ops->get_supported_codecs_by_name(name, flags, codecs, size);
+
+	if (compress->dl_hdl)
+		dlclose(compress->dl_hdl);
+	free(compress);
+
+	return ret;
+}

src/lib/compress_hw.c

@@ -119,6 +119,48 @@ static bool _is_codec_type_supported(int fd, struct snd_codec *codec)
 	return found;
 }
 
+static int compress_hw_get_supported_codecs_by_name(const char *name, unsigned int flags, void *codecs, int size)
+{
+	struct snd_compr_caps caps;
+	unsigned int *codecs_buf = (unsigned int *)codecs;
+	unsigned int card, device;
+	unsigned int dev_flag;
+	unsigned int num_codecs, i;
+	int fd, ret;
+	char fn[256];
+
+	if (size < MAX_NUM_CODECS)
+		return oops(&bad_compress, EINVAL, "Input not big enough to hold list of available codecs");
+
+	if (sscanf(&name[3], "%u,%u", &card, &device) != 2)
+		return -EINVAL;
+
+	snprintf(fn, sizeof(fn), "/dev/snd/comprC%uD%u", card, device);
+
+	if (flags & COMPRESS_OUT)
+		dev_flag = O_RDONLY;
+	else
+		dev_flag = O_WRONLY;
+
+	fd = open(fn, dev_flag);
+	if (fd < 0)
+		return oops(&bad_compress, errno, "cannot open device '%s'", fn);
+
+	if (ioctl(fd, SNDRV_COMPRESS_GET_CAPS, &caps)) {
+		close(fd);
+		return oops(&bad_compress, errno, "cannot get device caps");
+	}
+
+	close(fd);
+
+	num_codecs = caps.num_codecs;
+	for (i = 0; i < num_codecs; i++) {
+		codecs_buf[i] = caps.codecs[i];
+	}
+
+	return num_codecs;
+}
+
 static inline void
 fill_compress_hw_params(struct compr_config *config, struct snd_compr_params *params)
 {
@@ -595,5 +637,6 @@ struct compress_ops compress_hw_ops = {
 	.is_compress_running = is_compress_hw_running,
 	.is_compress_ready = is_compress_hw_ready,
 	.get_error = compress_hw_get_error,
+	.get_supported_codecs_by_name = compress_hw_get_supported_codecs_by_name,
 };