Bug 1816160: Warn (and no-op) on setParameters with empty encodings if the compat mode is enabled. r=jib

Also add some wpt for this (invalid) case.

Differential Revision: https://phabricator.services.mozilla.com/D169505

dom/media/webrtc/jsapi/RTCRtpSender.cpp

@@ -621,15 +621,21 @@ already_AddRefed<Promise> RTCRtpSender::SetParameters(
   // This could conceivably happen if we are allowing the old setParameters
   // behavior.
   if (!paramsCopy.mEncodings.Length()) {
-    if (!mHaveFailedBecauseNoEncodings) {
-      mHaveFailedBecauseNoEncodings = true;
-      mozilla::glean::rtcrtpsender_setparameters::fail_no_encodings
-          .AddToNumerator(1);
-    }
+    nsCString error("Cannot set an empty encodings array");
+    if (!mAllowOldSetParameters) {
+      if (!mHaveFailedBecauseNoEncodings) {
+        mHaveFailedBecauseNoEncodings = true;
+        mozilla::glean::rtcrtpsender_setparameters::fail_no_encodings
+            .AddToNumerator(1);
+      }
 
-    p->MaybeRejectWithInvalidModificationError(
-        "Cannot set an empty encodings array");
-    return p.forget();
+      p->MaybeRejectWithInvalidModificationError(error);
+      return p.forget();
+    }
+    // TODO: Add some warning telemetry here
+    WarnAboutBadSetParameters(error);
+    // Just don't do this; it's stupid.
+    paramsCopy.mEncodings = oldParams->mEncodings;
   }
 
   // TODO: Verify remaining read-only parameters

dom/media/webrtc/tests/mochitests/test_peerConnection_glean.html

@@ -313,7 +313,7 @@ const tests = [
     } catch (e) {
     }
     let newRate = await GleanTest.rtcrtpsenderSetparameters.failNoEncodings.testGetValue();
-    is(newRate.numerator, oldRate.numerator + 1, "Glean should have recorded an error due to stale transactionId in setParameters");
+    is(newRate.numerator, oldRate.numerator, "Glean should not have recorded an error due to empty encodings in setParameters");
 
     // Glean should only record the error once per sender!
     oldRate = newRate;
@@ -324,7 +324,7 @@ const tests = [
     } catch (e) {
     }
     newRate = await GleanTest.rtcrtpsenderSetparameters.failNoEncodings.testGetValue();
-    is(newRate.numerator, oldRate.numerator, "Glean should not have recorded another error due to stale transactionId in setParameters");
+    is(newRate.numerator, oldRate.numerator, "Glean should not have recorded an error due empty encodings in setParameters");
   },
 
   async function checkBadSetParametersOtherError() {

testing/web-platform/tests/webrtc/RTCRtpParameters-encodings.html

@@ -422,6 +422,32 @@
       sender.setParameters(param));
   }, `sender.setParameters() with encodings unset should reject with TypeError`);
 
+  promise_test(async t => {
+    const pc = new RTCPeerConnection();
+    t.add_cleanup(() => pc.close());
+    const { sender } = pc.addTransceiver('video');
+
+    const param = sender.getParameters();
+
+    param.encodings = [];
+
+    return promise_rejects_dom(t, 'InvalidModificationError',
+      sender.setParameters(param));
+  }, `sender.setParameters() with empty encodings should reject with InvalidModificationError (video)`);
+
+  promise_test(async t => {
+    const pc = new RTCPeerConnection();
+    t.add_cleanup(() => pc.close());
+    const { sender } = pc.addTransceiver('audio');
+
+    const param = sender.getParameters();
+
+    param.encodings = [];
+
+    return promise_rejects_dom(t, 'InvalidModificationError',
+      sender.setParameters(param));
+  }, `sender.setParameters() with empty encodings should reject with InvalidModificationError (audio)`);
+
   promise_test(async t => {
     const pc = new RTCPeerConnection();
     t.add_cleanup(() => pc.close());