commit f6a5e22616bee8e740d9e1fbee1129f289a73f35
author Lance Niles <lniles@google.com> Mon Aug 09 11:09:11 2021 -0600
committer Lance Niles <lniles@google.com> Mon Aug 09 11:09:11 2021 -0600
tree cd910883c9bae6fb067a5182079e151e87e5e8bd
parent ee13d71e6b017cfb50057e3e1815f7d700a03548

Only report multicast failures of none of the local interfaces send successfully.

On iOS, `sendmsg` succeeds on only one of the local interfaces when multicasting to an IPv6 address, the others fail with `EINVAL`. This **does not** address the root cause but just ignores the error if any one of the `sendmsg` calls succeed.

src/lib/core/WeaveMessageLayer.cpp

diff --git a/src/lib/core/WeaveMessageLayer.cpp b/src/lib/core/WeaveMessageLayer.cpp
index 5393077..d259978 100644
--- a/src/lib/core/WeaveMessageLayer.cpp
+++ b/src/lib/core/WeaveMessageLayer.cpp
@@ -642,7 +642,9 @@
 
     case kMulticast_AllInterfaces:
 
-        // Send the message over each local interface that supports multicast.
+        // Send the message over each local interface that supports multicast, only report an error
+        // if *none* of the interfaces succeed (b/195258416).
+        err = 0xFF;
         for (InterfaceIterator intfIter; intfIter.HasCurrent(); intfIter.Next())
         {
             if (intfIter.SupportsMulticast())
@@ -650,7 +652,7 @@
                 pktInfo.Interface = intfIter.GetInterface();
                 WEAVE_ERROR sendErr = ep->SendMsg(&pktInfo, payload, UDPEndPoint::kSendFlag_RetainBuffer);
                 CheckForceRefreshUDPEndPointsNeeded(sendErr);
-                if (err == WEAVE_NO_ERROR)
+                if (err != WEAVE_NO_ERROR)
                 {
                     err = FilterUDPSendError(sendErr, true);
                 }
@@ -664,6 +666,8 @@
         // Send the message once for each Weave Fabric ULA assigned to a local interface that supports
         // multicast/broadcast. If the caller has specified a particular interface, only send over the
         // specified interface.  For each message sent, arrange for the source address to be the Fabric ULA.
+        // Only report an error if *none* of the interfaces succeed (b/195258416).
+        err = 0xFF;
         for (InterfaceAddressIterator addrIter; addrIter.HasCurrent(); addrIter.Next())
         {
             pktInfo.SrcAddress = addrIter.GetAddress();
@@ -674,7 +678,7 @@
             {
                 WEAVE_ERROR sendErr = ep->SendMsg(&pktInfo, payload, UDPEndPoint::kSendFlag_RetainBuffer);
                 CheckForceRefreshUDPEndPointsNeeded(sendErr);
-                if (err == WEAVE_NO_ERROR)
+                if (err != WEAVE_NO_ERROR)
                 {
                     err = FilterUDPSendError(sendErr, true);
                 }