Add server side ICE consent checks to detect silent WebRTC disconnection

- Fixes #1127

### Details

- This PR provides the app with the ability to detect downed networks or silent/abrupts disconnections in client side.
- Make mediasoup send ICE consent requests every ~5 seconds once ICE is established.
- Move to 'disconnected' state (and notify the app as usual) if no ICE response is received in 30 seconds as per spec (this may change with a setting, see TODO below).
- This feature requires providing the mediasoup `WebRtcTransport` with the remote ICE username fragment and ICE password, which will be done by latest mediasoup-client once released.

### TODO

- [ ] Add a `iceConsentTimeout` parameter to `WebRtcTransportOptions` to override the default value of 30 seconds (0 means "disable the mechanism").
- [ ] Rust.
- [ ] React to 403 ICE error responses by also moving to 'disconnected' state.

node/src/WebRtcTransport.ts

@@ -150,6 +150,8 @@ export type IceCandidate = {
 export type DtlsParameters = {
 	role?: DtlsRole;
 	fingerprints: DtlsFingerprint[];
+	iceUfrag?: string;
+	icePwd?: string;
 };
 
 /**
@@ -933,6 +935,9 @@ function serializeDtlsParameters(
 			fingerprints
 		);
 
+	const iceUfragOffset = builder.createString(dtlsParameters.iceUfrag ?? '');
+	const icePwdOffset = builder.createString(dtlsParameters.icePwd ?? '');
+
 	const role =
 		dtlsParameters.role !== undefined
 			? dtlsRoleToFbs(dtlsParameters.role)
@@ -941,6 +946,8 @@ function serializeDtlsParameters(
 	return FbsWebRtcTransport.DtlsParameters.createDtlsParameters(
 		builder,
 		fingerprintsOffset,
-		role
+		role,
+		iceUfragOffset,
+		icePwdOffset
 	);
 }

worker/fbs/webRtcTransport.fbs

@@ -55,6 +55,8 @@ enum DtlsState: uint8 {
 table DtlsParameters {
     fingerprints: [Fingerprint] (required);
     role: DtlsRole = AUTO;
+    ice_ufrag: string;
+    ice_pwd: string;
 }
 
 table IceParameters {

worker/include/RTC/IceServer.hpp

@@ -2,15 +2,18 @@
 #define MS_RTC_ICE_SERVER_HPP
 
 #include "common.hpp"
+#include "Utils.hpp"
 #include "FBS/webRtcTransport.h"
 #include "RTC/StunPacket.hpp"
 #include "RTC/TransportTuple.hpp"
+#include "handles/TimerHandle.hpp"
+#include <deque>
 #include <list>
 #include <string>
 
 namespace RTC
 {
-	class IceServer
+	class IceServer : public TimerHandle::Listener
 	{
 	public:
 		enum class IceState
@@ -21,6 +24,19 @@ namespace RTC
 			DISCONNECTED,
 		};
 
+	public:
+		struct SentConsent
+		{
+			uint8_t transactionId[12];
+			uint64_t sentAtMs;
+
+			SentConsent(uint64_t transactionId, uint64_t sentAtMs) : sentAtMs(sentAtMs)
+			{
+				Utils::Byte::Set4Bytes(this->transactionId, 0, transactionId);
+				Utils::Byte::Set8Bytes(this->transactionId, 4, 0);
+			}
+		};
+
 	public:
 		static IceState RoleFromFbs(FBS::WebRtcTransport::IceState state);
 		static FBS::WebRtcTransport::IceState IceStateToFbs(IceState state);
@@ -54,7 +70,7 @@ namespace RTC
 
 	public:
 		IceServer(Listener* listener, const std::string& usernameFragment, const std::string& password);
-		~IceServer();
+		~IceServer() override;
 
 	public:
 		void ProcessStunPacket(RTC::StunPacket* packet, RTC::TransportTuple* tuple);
@@ -66,6 +82,21 @@ namespace RTC
 		{
 			return this->password;
 		}
+		void SetRemoteUsernameFragmentAndPassword(
+		  const std::string& usernameFragment, const std::string& password)
+		{
+			this->remoteUsernameFragment = usernameFragment;
+			this->remotePassword         = password;
+
+			if (AreConsentChecksEnabled())
+			{
+				MayRestartConsentChecks();
+			}
+			else
+			{
+				MayStopConsentChecks();
+			}
+		}
 		IceState GetState() const
 		{
 			return this->state;
@@ -74,28 +105,7 @@ namespace RTC
 		{
 			return this->selectedTuple;
 		}
-		void RestartIce(const std::string& usernameFragment, const std::string& password)
-		{
-			if (!this->oldUsernameFragment.empty())
-			{
-				this->listener->OnIceServerLocalUsernameFragmentRemoved(this, this->oldUsernameFragment);
-			}
-
-			this->oldUsernameFragment = this->usernameFragment;
-			this->usernameFragment    = usernameFragment;
-
-			this->oldPassword = this->password;
-			this->password    = password;
-
-			this->remoteNomination = 0u;
-
-			// Notify the listener.
-			this->listener->OnIceServerLocalUsernameFragmentAdded(this, usernameFragment);
-
-			// NOTE: Do not call listener->OnIceServerLocalUsernameFragmentRemoved()
-			// yet with old usernameFragment. Wait until we receive a STUN packet
-			// with the new one.
-		}
+		void RestartIce(const std::string& usernameFragment, const std::string& password);
 		bool IsValidTuple(const RTC::TransportTuple* tuple) const;
 		void RemoveTuple(RTC::TransportTuple* tuple);
 		/**
@@ -116,10 +126,29 @@ namespace RTC
 		 */
 		RTC::TransportTuple* HasTuple(const RTC::TransportTuple* tuple) const;
 		/**
-		 * Set the given tuple as the selected tuple.
+		 * Set the given tuple as the selected tuple. Returns true if given tuple
+		 * was not already the selected tuple, false otherwise.
 		 * NOTE: The given tuple MUST be already stored within the list.
 		 */
-		void SetSelectedTuple(RTC::TransportTuple* storedTuple);
+		bool SetSelectedTuple(RTC::TransportTuple* storedTuple);
+		bool AreConsentChecksEnabled() const
+		{
+			// TODO: We also need an API setting probably.
+			return (!this->remoteUsernameFragment.empty() && !this->remotePassword.empty());
+		}
+		bool AreConsentChecksRunning() const
+		{
+			return (this->consentCheckTimer && this->consentCheckTimer->IsActive());
+		}
+		void MayStartConsentChecks();
+		void MayStopConsentChecks();
+		void MayRestartConsentChecks();
+		void MayStartOrRestartConsentChecks();
+		void SendConsentRequest();
+
+		/* Pure virtual methods inherited from TimerHandle::Listener. */
+	public:
+		void OnTimer(TimerHandle* timer) override;
 
 	private:
 		// Passed by argument.
@@ -129,10 +158,14 @@ namespace RTC
 		std::string password;
 		std::string oldUsernameFragment;
 		std::string oldPassword;
+		std::string remoteUsernameFragment;
+		std::string remotePassword;
 		IceState state{ IceState::NEW };
 		uint32_t remoteNomination{ 0u };
 		std::list<RTC::TransportTuple> tuples;
 		RTC::TransportTuple* selectedTuple{ nullptr };
+		TimerHandle* consentCheckTimer{ nullptr };
+		std::deque<SentConsent> sentConsents;
 	};
 } // namespace RTC
 

worker/include/RTC/StunPacket.hpp

@@ -50,7 +50,7 @@ namespace RTC
 		{
 			OK           = 0,
 			UNAUTHORIZED = 1,
-			BAD_REQUEST  = 2
+			BAD_MESSAGE  = 2
 		};
 
 	public:
@@ -95,6 +95,10 @@ namespace RTC
 		{
 			return this->size;
 		}
+		const uint8_t* GetTransactionId() const
+		{
+			return this->transactionId;
+		}
 		void SetUsername(const char* username, size_t len)
 		{
 			this->username.assign(username, len);
@@ -127,6 +131,10 @@ namespace RTC
 		{
 			this->errorCode = errorCode;
 		}
+		void SetSoftware(const char* software, size_t len)
+		{
+			this->software.assign(software, len);
+		}
 		void SetMessageIntegrity(const uint8_t* messageIntegrity)
 		{
 			this->messageIntegrity = messageIntegrity;
@@ -171,6 +179,10 @@ namespace RTC
 		{
 			return this->errorCode;
 		}
+		std::string GetSoftware() const
+		{
+			return this->software;
+		}
 		bool HasMessageIntegrity() const
 		{
 			return (this->messageIntegrity != nullptr);
@@ -180,7 +192,9 @@ namespace RTC
 			return this->hasFingerprint;
 		}
 		Authentication CheckAuthentication(
-		  const std::string& localUsername, const std::string& localPassword);
+		  const std::string& usernameFragment1,
+		  const std::string& usernameFragment2,
+		  const std::string& password);
 		StunPacket* CreateSuccessResponse();
 		StunPacket* CreateErrorResponse(uint16_t errorCode);
 		void Authenticate(const std::string& password);
@@ -194,7 +208,8 @@ namespace RTC
 		uint8_t* data{ nullptr };                // Pointer to binary data.
 		size_t size{ 0u };                       // The full message size (including header).
 		// STUN attributes.
-		std::string username;          // Less than 513 bytes.
+		std::string username; // Less than 513 bytes.
+		std::string password;
 		uint32_t priority{ 0u };       // 4 bytes unsigned integer.
 		uint64_t iceControlling{ 0u }; // 8 bytes unsigned integer.
 		uint64_t iceControlled{ 0u };  // 8 bytes unsigned integer.
@@ -205,7 +220,7 @@ namespace RTC
 		bool hasFingerprint{ false };                       // 4 bytes.
 		const struct sockaddr* xorMappedAddress{ nullptr }; // 8 or 20 bytes.
 		uint16_t errorCode{ 0u };                           // 4 bytes (no reason phrase).
-		std::string password;
+		std::string software;                               // Less than 763 bytes.
 	};
 } // namespace RTC