From 8a4a7897a0d2902b83a22a0e01080a7d3294c32c Mon Sep 17 00:00:00 2001
From: John Preston <johnprestonmail@gmail.com>
Date: Wed, 10 May 2017 10:58:02 +0300
Subject: [PATCH] Fix contract violation in Call::startIncoming.

Also fix call answer while dhConfig is not received yet.
---
 Telegram/SourceFiles/calls/calls_call.cpp | 17 ++++++++++++++---
 Telegram/SourceFiles/calls/calls_call.h   |  1 +
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/Telegram/SourceFiles/calls/calls_call.cpp b/Telegram/SourceFiles/calls/calls_call.cpp
index be264ba26d..72e2ddb33b 100644
--- a/Telegram/SourceFiles/calls/calls_call.cpp
+++ b/Telegram/SourceFiles/calls/calls_call.cpp
@@ -121,19 +121,21 @@ void Call::start(base::const_byte_span random) {
 	t_assert(!_dhConfig.p.empty());
 
 	generateModExpFirst(random);
-	if (_state != State::Failed && _state != State::FailedHangingUp) {
+	if (_state == State::Starting || _state == State::Requesting) {
 		if (_type == Type::Outgoing) {
 			startOutgoing();
 		} else {
 			startIncoming();
 		}
+	} else if (_state == State::ExchangingKeys && _answerAfterDhConfigReceived) {
+		answer();
 	}
 }
 
 void Call::startOutgoing() {
 	Expects(_type == Type::Outgoing);
+	Expects(_state == State::Requesting);
 
-	setState(State::Requesting);
 	request(MTPphone_RequestCall(_user->inputUser, MTP_int(rand_value<int32>()), MTP_bytes(_gaHash), MTP_phoneCallProtocol(MTP_flags(MTPDphoneCallProtocol::Flag::f_udp_p2p | MTPDphoneCallProtocol::Flag::f_udp_reflector), MTP_int(kMinLayer), MTP_int(kMaxLayer)))).done([this](const MTPphone_PhoneCall &result) {
 		Expects(result.type() == mtpc_phone_phoneCall);
 
@@ -184,9 +186,17 @@ void Call::answer() {
 	Expects(_type == Type::Incoming);
 
 	if (_state != State::Starting && _state != State::WaitingIncoming) {
-		return;
+		if (_state != State::ExchangingKeys || !_answerAfterDhConfigReceived) {
+			return;
+		}
 	}
 	setState(State::ExchangingKeys);
+	if (_gb.empty()) {
+		_answerAfterDhConfigReceived = true;
+		return;
+	} else {
+		_answerAfterDhConfigReceived = false;
+	}
 	request(MTPphone_AcceptCall(MTP_inputPhoneCall(MTP_long(_id), MTP_long(_accessHash)), MTP_bytes(_gb), _protocol)).done([this](const MTPphone_PhoneCall &result) {
 		Expects(result.type() == mtpc_phone_phoneCall);
 		auto &call = result.c_phone_phoneCall();
@@ -234,6 +244,7 @@ void Call::redial() {
 	t_assert(_controller == nullptr);
 	_type = Type::Outgoing;
 	setState(State::Requesting);
+	_answerAfterDhConfigReceived = false;
 	startWaitingTrack();
 	_delegate->callRedial(this);
 }
diff --git a/Telegram/SourceFiles/calls/calls_call.h b/Telegram/SourceFiles/calls/calls_call.h
index 1045bf626e..958421e11f 100644
--- a/Telegram/SourceFiles/calls/calls_call.h
+++ b/Telegram/SourceFiles/calls/calls_call.h
@@ -161,6 +161,7 @@ private:
 	Type _type = Type::Outgoing;
 	State _state = State::Starting;
 	FinishType _finishAfterRequestingCall = FinishType::None;
+	bool _answerAfterDhConfigReceived = false;
 	base::Observable<State> _stateChanged;
 	TimeMs _startTime = 0;
 	base::DelayedCallTimer _finishByTimeoutTimer;