res_remb_modifier: Add module for controlling REMB from CLI.

This adds a module which registers a CLI command that can set the
REMB bitrate value for REMB as it enters or exits Asterisk. This
allows you to ignore what Asterisk or a client produces and is
useful for demonstrations.

This does not generate REMB frames, however, but just modifies
them as they flow to or from a channel.

Change-Id: Ib089427c46a4a36d645cecfe02406adb38c17bec

res/res_remb_modifier.c

@@ -0,0 +1,225 @@
+/*
+ * Asterisk -- An open source telephony toolkit.
+ *
+ * Copyright (C) 2018, Digium, Inc.
+ *
+ * Joshua Colp <jcolp@digium.com>
+ *
+ * See http://www.asterisk.org for more information about
+ * the Asterisk project. Please do not directly contact
+ * any of the maintainers of this project for assistance;
+ * the project provides a web site, mailing lists and IRC
+ * channels for your use.
+ *
+ * This program is free software, distributed under the terms of
+ * the GNU General Public License Version 2. See the LICENSE file
+ * at the top of the source tree.
+ */
+
+/*!
+ * \file
+ *
+ * \brief REMB Modifier Module
+ *
+ * \author Joshua Colp <jcolp@digium.com>
+ */
+
+/*** MODULEINFO
+	<support_level>extended</support_level>
+	<defaultenabled>no</defaultenabled>
+ ***/
+
+#include "asterisk.h"
+
+#include "asterisk/module.h"
+#include "asterisk/cli.h"
+#include "asterisk/channel.h"
+#include "asterisk/framehook.h"
+#include "asterisk/rtp_engine.h"
+
+struct remb_values {
+	/*! \brief The amount of bitrate to use for REMB received from the channel */
+	unsigned int receive_bitrate;
+	/*! \brief The amount of bitrate to use for REMB sent to the channel */
+	unsigned int send_bitrate;
+};
+
+static void remb_values_free(void *data)
+{
+	ast_free(data);
+}
+
+static const struct ast_datastore_info remb_info = {
+	.type = "REMB Values",
+	.destroy = remb_values_free,
+};
+
+static struct ast_frame *remb_hook_event_cb(struct ast_channel *chan, struct ast_frame *frame, enum ast_framehook_event event, void *data)
+{
+	struct ast_rtp_rtcp_feedback *feedback;
+	struct ast_datastore *remb_store;
+	struct remb_values *remb_values;
+
+	if (!frame) {
+		return NULL;
+	}
+
+	switch (event) {
+	case AST_FRAMEHOOK_EVENT_READ:
+	case AST_FRAMEHOOK_EVENT_WRITE:
+		break;
+	case AST_FRAMEHOOK_EVENT_ATTACHED:
+	case AST_FRAMEHOOK_EVENT_DETACHED:
+		return frame;
+	}
+
+	/* We only care about REMB frames, all others will be unmodified */
+	if (frame->subclass.integer != AST_RTP_RTCP_PSFB) {
+		return frame;
+	}
+
+	feedback = frame->data.ptr;
+	if (feedback->fmt != AST_RTP_RTCP_FMT_REMB) {
+		return frame;
+	}
+
+	remb_store = ast_channel_datastore_find(chan, &remb_info, NULL);
+	if (!remb_store) {
+		return frame;
+	}
+	remb_values = remb_store->data;
+
+	/* If a bitrate override has been set apply it to the REMB Frame */
+	if (event == AST_FRAMEHOOK_EVENT_READ && remb_values->receive_bitrate) {
+		feedback->remb.br_mantissa = remb_values->receive_bitrate;
+		feedback->remb.br_exp = 0;
+	} else if (event == AST_FRAMEHOOK_EVENT_WRITE && remb_values->send_bitrate) {
+		feedback->remb.br_mantissa = remb_values->send_bitrate;
+		feedback->remb.br_exp = 0;
+	}
+
+	/* The mantissa only has 18 bits available, so while it exceeds them we bump
+	 * up the exp.
+	 */
+	while (feedback->remb.br_mantissa > 0x3ffff) {
+		feedback->remb.br_mantissa = feedback->remb.br_mantissa >> 1;
+		feedback->remb.br_exp++;
+	}
+
+	return frame;
+}
+
+static char *handle_remb_set(struct ast_cli_entry *e, int cmd, struct ast_cli_args *a)
+{
+	struct ast_channel *chan;
+	unsigned int bitrate;
+	struct ast_datastore *remb_store;
+	struct remb_values *remb_values;
+	struct ast_framehook_interface interface = {
+		.version = AST_FRAMEHOOK_INTERFACE_VERSION,
+		.event_cb = remb_hook_event_cb,
+	};
+
+	switch(cmd) {
+	case CLI_INIT:
+		e->command = "remb set {send|receive}";
+		e->usage =
+			"Usage: remb set {send|receive} <channel> <bitrate in bits>\n"
+			"       Set the REMB value which overwrites what we send or receive\n";
+		return NULL;
+	case CLI_GENERATE:
+		return ast_complete_channels(a->line, a->word, a->pos, a->n, 3);
+	}
+
+	if (a->argc != 5) {
+		return CLI_SHOWUSAGE;
+	}
+
+	if (sscanf(a->argv[4], "%30d", &bitrate) != 1) {
+		ast_cli(a->fd, "%s is not a valid bitrate in bits\n", a->argv[4]);
+		return CLI_SUCCESS;
+	} else if (strcasecmp(a->argv[2], "send") && strcasecmp(a->argv[2], "receive")) {
+		ast_cli(a->fd, "%s is not a valid direction for REMB\n", a->argv[2]);
+		return CLI_SUCCESS;
+	}
+
+	chan = ast_channel_get_by_name(a->argv[3]);
+	if (!chan) {
+		ast_cli(a->fd, "%s is not a known channel\n", a->argv[3]);
+		return CLI_SUCCESS;
+	}
+
+	ast_channel_lock(chan);
+
+	remb_store = ast_channel_datastore_find(chan, &remb_info, NULL);
+	if (!remb_store) {
+		int framehook_id;
+
+		framehook_id = ast_framehook_attach(chan, &interface);
+		if (framehook_id < 0) {
+			ast_cli(a->fd, "Could not attach framehook for modifying REMB\n");
+			ast_channel_unlock(chan);
+			ast_channel_unref(chan);
+			return CLI_SUCCESS;
+		}
+
+		remb_values = ast_calloc(1, sizeof(*remb_values));
+		if (!remb_values) {
+			ast_cli(a->fd, "Could not create a place to store provided REMB value\n");
+			ast_framehook_detach(chan, framehook_id);
+			ast_channel_unlock(chan);
+			ast_channel_unref(chan);
+			return CLI_SUCCESS;
+		}
+
+		remb_store = ast_datastore_alloc(&remb_info, NULL);
+		if (!remb_store) {
+			ast_cli(a->fd, "Could not create a place to store provided REMB value\n");
+			ast_framehook_detach(chan, framehook_id);
+			ast_channel_unlock(chan);
+			ast_channel_unref(chan);
+			ast_free(remb_values);
+			return CLI_SUCCESS;
+		}
+
+		remb_store->data = remb_values;
+		ast_channel_datastore_add(chan, remb_store);
+	} else {
+		remb_values = remb_store->data;
+	}
+
+	if (!strcasecmp(a->argv[2], "send")) {
+		remb_values->send_bitrate = bitrate;
+	} else if (!strcasecmp(a->argv[2], "receive")) {
+		remb_values->receive_bitrate = bitrate;
+	}
+
+	ast_channel_unlock(chan);
+	ast_channel_unref(chan);
+
+	ast_cli(a->fd, "Set REMB %s override to a bitrate of %s on %s\n", a->argv[2], a->argv[3], a->argv[4]);
+
+	return CLI_SUCCESS;
+}
+
+static struct ast_cli_entry remb_cli[] = {
+	AST_CLI_DEFINE(handle_remb_set, "Set the REMB value which overwrites what is sent or received"),
+};
+
+static int load_module(void)
+{
+	ast_cli_register_multiple(remb_cli, ARRAY_LEN(remb_cli));
+	return AST_MODULE_LOAD_SUCCESS;
+}
+
+static int unload_module(void)
+{
+	ast_cli_unregister_multiple(remb_cli, ARRAY_LEN(remb_cli));
+	return 0;
+}
+
+AST_MODULE_INFO(ASTERISK_GPL_KEY, AST_MODFLAG_DEFAULT, "REMB Modifier Module",
+	.support_level = AST_MODULE_SUPPORT_EXTENDED,
+	.load = load_module,
+	.unload = unload_module,
+);