transform: Add struct sr_transform and struct sr_transform_module.

include/libsigrok/libsigrok.h

@@ -515,6 +515,8 @@ struct sr_input;
 struct sr_input_module;
 struct sr_output;
 struct sr_output_module;
+struct sr_transform;
+struct sr_transform_module;
 
 /** Constants for channel type. */
 enum sr_channeltype {

src/libsigrok-internal.h

@@ -433,6 +433,93 @@ struct sr_output_module {
 	int (*cleanup) (struct sr_output *o);
 };
 
+/** Transform module instance. */
+struct sr_transform {
+	/** A pointer to this transform's module.  */
+	const struct sr_transform_module *module;
+
+	/**
+	 * The device for which this transform module is used. This
+	 * can be used by the module to find out channel names and numbers.
+	 */
+	const struct sr_dev_inst *sdi;
+
+	/**
+	 * A generic pointer which can be used by the module to keep internal
+	 * state between calls into its callback functions.
+	 */
+	void *priv;
+};
+
+struct sr_transform_module {
+	/**
+	 * A unique ID for this transform module, suitable for use in
+	 * command-line clients, [a-z0-9-]. Must not be NULL.
+	 */
+	char *id;
+
+	/**
+	 * A unique name for this transform module, suitable for use in GUI
+	 * clients, can contain UTF-8. Must not be NULL.
+	 */
+	const char *name;
+
+	/**
+	 * A short description of the transform module. Must not be NULL.
+	 *
+	 * This can be displayed by frontends, e.g. when selecting
+	 * which transform module(s) to add.
+	 */
+	char *desc;
+
+	/**
+	 * Returns a NULL-terminated list of options this transform module
+	 * can take. Can be NULL, if the transform module has no options.
+	 */
+	const struct sr_option *(*options) (void);
+
+	/**
+	 * This function is called once, at the beginning of a stream.
+	 *
+	 * @param t Pointer to the respective 'struct sr_transform'.
+	 * @param options Hash table of options for this transform module.
+	 *                Can be NULL if no options are to be used.
+	 *
+	 * @retval SR_OK Success
+	 * @retval other Negative error code.
+	 */
+	int (*init) (struct sr_transform *t, GHashTable *options);
+
+	/**
+	 * This function is passed a pointer to every packet in the data feed.
+	 *
+	 * It can either return (in packet_out) a pointer to another packet
+	 * (possibly the exact same packet it got as input), or NULL.
+	 *
+	 * @param t Pointer to the respective 'struct sr_transform'.
+	 * @param packet_in Pointer to a datafeed packet.
+	 * @param packet_out Pointer to the resulting datafeed packet after
+	 *                   this function was run. If NULL, the transform
+	 *                   module intentionally didn't output a new packet.
+	 *
+	 * @retval SR_OK Success
+	 * @retval other Negative error code.
+	 */
+	int (*receive) (const struct sr_transform *t,
+			struct sr_datafeed_packet *packet_in,
+			struct sr_datafeed_packet **packet_out);
+
+	/**
+	 * This function is called after the caller is finished using
+	 * the transform module, and can be used to free any internal
+	 * resources the module may keep.
+	 *
+	 * @retval SR_OK Success
+	 * @retval other Negative error code.
+	 */
+	int (*cleanup) (struct sr_transform *t);
+};
+
 #ifdef HAVE_LIBUSB_1_0
 /** USB device instance */
 struct sr_usb_dev_inst {