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* Copyright 2019 The WebRTC project authors. All Rights Reserved.
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
#ifndef PC_USED_IDS_H_
#define PC_USED_IDS_H_
#include <set>
#include <vector>
#include "api/rtp_parameters.h"
#include "media/base/codec.h"
#include "rtc_base/checks.h"
#include "rtc_base/logging.h"
namespace cricket {
template <typename IdStruct>
class UsedIds {
UsedIds(int min_allowed_id, int max_allowed_id)
: min_allowed_id_(min_allowed_id),
next_id_(max_allowed_id) {}
virtual ~UsedIds() {}
// Loops through all Id in `ids` and changes its id if it is
// already in use by another IdStruct. Call this methods with all Id
// in a session description to make sure no duplicate ids exists.
// Note that typename Id must be a type of IdStruct.
template <typename Id>
void FindAndSetIdUsed(std::vector<Id>* ids) {
for (const Id& id : *ids) {
// Finds and sets an unused id if the `idstruct` id is already in use.
void FindAndSetIdUsed(IdStruct* idstruct) {
const int original_id = idstruct->id;
int new_id = idstruct->id;
if (original_id > max_allowed_id_ || original_id < min_allowed_id_) {
// If the original id is not in range - this is an id that can't be
// dynamically changed.
if (IsIdUsed(original_id)) {
new_id = FindUnusedId();
// Duplicate id found. Reassign from the original id to the new.
idstruct->id = new_id;
virtual bool IsIdUsed(int new_id) {
return id_set_.find(new_id) != id_set_.end();
const int min_allowed_id_;
const int max_allowed_id_;
// Returns the first unused id in reverse order.
// This hopefully reduces the risk of more collisions. We want to change the
// default ids as little as possible. This function is virtual and can be
// overriden if the search for unused IDs should follow a specific pattern.
virtual int FindUnusedId() {
while (IsIdUsed(next_id_) && next_id_ >= min_allowed_id_) {
RTC_DCHECK(next_id_ >= min_allowed_id_);
return next_id_;
void SetIdUsed(int new_id) {
RTC_DCHECK(new_id >= min_allowed_id_);
RTC_DCHECK(new_id <= max_allowed_id_);
int next_id_;
std::set<int> id_set_;
// Helper class used for finding duplicate RTP payload types among audio, video
// and data codecs. When bundle is used the payload types may not collide.
class UsedPayloadTypes : public UsedIds<Codec> {
: UsedIds<Codec>(kFirstDynamicPayloadTypeLowerRange,
kLastDynamicPayloadTypeUpperRange) {}
bool IsIdUsed(int new_id) override {
// Range marked for RTCP avoidance is "used".
if (new_id > kLastDynamicPayloadTypeLowerRange &&
new_id < kFirstDynamicPayloadTypeUpperRange)
return true;
return UsedIds<Codec>::IsIdUsed(new_id);
static const int kFirstDynamicPayloadTypeLowerRange = 35;
static const int kLastDynamicPayloadTypeLowerRange = 63;
static const int kFirstDynamicPayloadTypeUpperRange = 96;
static const int kLastDynamicPayloadTypeUpperRange = 127;
// Helper class used for finding duplicate RTP Header extension ids among
// audio and video extensions.
class UsedRtpHeaderExtensionIds : public UsedIds<webrtc::RtpExtension> {
enum class IdDomain {
// Only allocate IDs that fit in one-byte header extensions.
// Prefer to allocate one-byte header extension IDs, but overflow to
// two-byte if none are left.
explicit UsedRtpHeaderExtensionIds(IdDomain id_domain)
: UsedIds<webrtc::RtpExtension>(
id_domain == IdDomain::kTwoByteAllowed
? webrtc::RtpExtension::kMaxId
: webrtc::RtpExtension::kOneByteHeaderExtensionMaxId),
next_extension_id_(webrtc::RtpExtension::kOneByteHeaderExtensionMaxId) {
// Returns the first unused id in reverse order from the max id of one byte
// header extensions. This hopefully reduce the risk of more collisions. We
// want to change the default ids as little as possible. If no unused id is
// found and two byte header extensions are enabled (i.e.,
// `extmap_allow_mixed_` is true), search for unused ids from 15 to 255.
int FindUnusedId() override {
if (next_extension_id_ <=
webrtc::RtpExtension::kOneByteHeaderExtensionMaxId) {
// First search in reverse order from the max id of one byte header
// extensions.
while (IsIdUsed(next_extension_id_) &&
next_extension_id_ >= min_allowed_id_) {
if (id_domain_ == IdDomain::kTwoByteAllowed) {
if (next_extension_id_ < min_allowed_id_) {
// We have searched among all one-byte IDs without finding an unused ID,
// continue at the first two-byte ID.
next_extension_id_ =
webrtc::RtpExtension::kOneByteHeaderExtensionMaxId + 1;
if (next_extension_id_ >
webrtc::RtpExtension::kOneByteHeaderExtensionMaxId) {
while (IsIdUsed(next_extension_id_) &&
next_extension_id_ <= max_allowed_id_) {
RTC_DCHECK(next_extension_id_ >= min_allowed_id_);
RTC_DCHECK(next_extension_id_ <= max_allowed_id_);
return next_extension_id_;
const IdDomain id_domain_;
int next_extension_id_;
} // namespace cricket
#endif // PC_USED_IDS_H_