[WebRTC] WebRTCSessionID should start from 0 (project-chip#40494)

* [WebRTC] WebRTCSessionID should start from 0

* Address review comment

* Address review comments

Author: yufengwangca

src/app/clusters/webrtc-transport-provider-server/webrtc-transport-provider-server.cpp

@@ -224,25 +224,33 @@ WebRTCSessionStruct * WebRTCTransportProviderServer::CheckForMatchingSession(Han
     return session;
 }
 
-uint16_t WebRTCTransportProviderServer::GenerateSessionId()
+CHIP_ERROR WebRTCTransportProviderServer::GenerateSessionId(uint16_t & outSessionId)
 {
-    static uint16_t lastSessionId = 1;
+    static uint16_t nextSessionId = 0;
+    uint16_t candidateId          = 0;
 
-    do
+    // Try at most kMaxSessionId+1 attempts to find a free ID
+    // This ensures we never loop infinitely even if all IDs are somehow in use
+    for (uint16_t attempts = 0; attempts <= kMaxSessionId; attempts++)
     {
-        uint16_t candidateId = lastSessionId++;
+        candidateId = nextSessionId++;
 
         // Handle wrap-around per spec
-        if (lastSessionId > kMaxSessionId)
+        if (nextSessionId > kMaxSessionId)
         {
-            lastSessionId = 1;
+            nextSessionId = 0;
         }
 
         if (FindSession(candidateId) == nullptr)
         {
-            return candidateId;
+            outSessionId = candidateId;
+            return CHIP_NO_ERROR;
         }
-    } while (true);
+    }
+
+    // All session IDs are in use
+    ChipLogError(Zcl, "All session IDs are in use! Cannot generate new session ID.");
+    return CHIP_IM_GLOBAL_STATUS(ResourceExhausted);
 }
 
 // Command Handlers
@@ -337,7 +345,15 @@ void WebRTCTransportProviderServer::HandleSolicitOffer(HandlerContext & ctx, con
 
     // Prepare the arguments for the delegate.
     Delegate::OfferRequestArgs args;
-    args.sessionId             = GenerateSessionId();
+    uint16_t sessionId;
+    CHIP_ERROR err = GenerateSessionId(sessionId);
+    if (err != CHIP_NO_ERROR)
+    {
+        ChipLogError(Zcl, "HandleSolicitOffer: Cannot generate session ID: %" CHIP_ERROR_FORMAT, err.Format());
+        ctx.mCommandHandler.AddStatus(ctx.mRequestPath, Protocols::InteractionModel::ClusterStatusCode(err));
+        return;
+    }
+    args.sessionId             = sessionId;
     args.streamUsage           = req.streamUsage;
     args.videoStreamId         = req.videoStreamID;
     args.audioStreamId         = req.audioStreamID;
@@ -546,8 +562,16 @@ void WebRTCTransportProviderServer::HandleProvideOffer(HandlerContext & ctx, con
             return;
         }
 
-        // Generate new sessiond id
-        args.sessionId = GenerateSessionId();
+        // Generate new session id
+        uint16_t sessionId;
+        err = GenerateSessionId(sessionId);
+        if (err != CHIP_NO_ERROR)
+        {
+            ChipLogError(Zcl, "HandleProvideOffer: Cannot generate session ID: %" CHIP_ERROR_FORMAT, err.Format());
+            ctx.mCommandHandler.AddStatus(ctx.mRequestPath, Protocols::InteractionModel::ClusterStatusCode(err));
+            return;
+        }
+        args.sessionId = sessionId;
     }
 
     args.streamUsage           = req.streamUsage;

src/app/clusters/webrtc-transport-provider-server/webrtc-transport-provider-server.h

@@ -333,7 +333,7 @@ class WebRTCTransportProviderServer : public AttributeAccessInterface, public Co
     WebRTCSessionStruct * CheckForMatchingSession(HandlerContext & ctx, uint16_t sessionId);
     UpsertResultEnum UpsertSession(const WebRTCSessionStruct & session);
     void RemoveSession(uint16_t sessionId);
-    uint16_t GenerateSessionId();
+    CHIP_ERROR GenerateSessionId(uint16_t & outSessionId);
 
     // Command Handlers
     void HandleSolicitOffer(HandlerContext & ctx, const Commands::SolicitOffer::DecodableType & req);

src/python_testing/TC_WEBRTCP_2_1.py

@@ -162,7 +162,6 @@ async def test_TC_WebRTCProvider_2_1(self):
         resp = await self.send_single_cmd(cmd=cmd, endpoint=endpoint, payloadCapability=ChipDeviceCtrl.TransportPayloadCapability.LARGE_PAYLOAD)
         asserts.assert_equal(type(resp), Clusters.WebRTCTransportProvider.Commands.SolicitOfferResponse,
                              "Incorrect response type")
-        asserts.assert_not_equal(resp.webRTCSessionID, 0, "webrtcSessionID in SolicitOfferResponse should not be 0.")
         asserts.assert_true(resp.deferredOffer, "Expected 'deferredOffer' to be True.")
 
         self.step(7)

src/python_testing/TC_WEBRTCP_2_2.py

@@ -108,7 +108,6 @@ async def test_TC_WebRTCProvider_2_2(self):
         resp = await self.send_single_cmd(cmd=cmd, endpoint=endpoint, payloadCapability=ChipDeviceCtrl.TransportPayloadCapability.LARGE_PAYLOAD)
         asserts.assert_equal(type(resp), Clusters.WebRTCTransportProvider.Commands.SolicitOfferResponse,
                              "Incorrect response type")
-        asserts.assert_not_equal(resp.webRTCSessionID, 0, "webrtcSessionID in SolicitOfferResponse should not be 0.")
         asserts.assert_false(resp.deferredOffer, "Expected 'deferredOffer' to be False.")
 
         # TODO: Enable this check after integrating with Camera AvStreamManager

src/python_testing/TC_WEBRTCP_2_3.py

@@ -213,7 +213,6 @@ async def test_TC_WebRTCProvider_2_3(self):
         resp = await self.send_single_cmd(cmd=cmd, endpoint=endpoint, payloadCapability=ChipDeviceCtrl.TransportPayloadCapability.LARGE_PAYLOAD)
         asserts.assert_equal(type(resp), Clusters.WebRTCTransportProvider.Commands.ProvideOfferResponse,
                              "Incorrect response type")
-        asserts.assert_not_equal(resp.webRTCSessionID, 0, "webRTCSessionID in ProvideOfferResponse should not be 0.")
 
         self.step(9)
         # Verify CurrentSessions contains the new session

src/python_testing/TC_WEBRTCP_2_4.py

@@ -158,9 +158,6 @@ async def test_TC_WebRTCProvider_2_4(self):
         saved_session_id = resp.webRTCSessionID
         asserts.assert_equal(videoStreamID, resp.videoStreamID, "Video stream ID does not match that in the command")
         asserts.assert_equal(audioStreamID, resp.audioStreamID, "Audio stream ID does not match that in the command")
-        asserts.assert_not_equal(
-            saved_session_id, 0, "Allocated WebRTCSessionID must be non‑zero"
-        )
 
         self.step(5)
         current_sessions = await self.read_single_attribute_check_success(

src/python_testing/TC_WEBRTCP_2_5.py

@@ -146,7 +146,6 @@ async def test_TC_WebRTCProvider_2_5(self):
         resp = await self.send_single_cmd(cmd=cmd, endpoint=endpoint, payloadCapability=ChipDeviceCtrl.TransportPayloadCapability.LARGE_PAYLOAD)
         asserts.assert_equal(type(resp), Clusters.WebRTCTransportProvider.Commands.SolicitOfferResponse,
                              "Incorrect response type")
-        asserts.assert_not_equal(resp.webRTCSessionID, 0, "webrtcSessionID in SolicitOfferResponse should not be 0.")
         asserts.assert_false(resp.deferredOffer, "Expected 'deferredOffer' to be False.")
 
         # TODO: Enable this check after integrating with Camera AvStreamManager