core: Fix pick_first NPE when accepting resolved addresses and in CONNECTING state

[schiemon]

This PR resolves #12796.

It makes sure that whenever PickFirstLeafLoadBalancer transitions into CONNECTING the current address in the addressIndex has a corresponding subchannel. This prevents an NPE when hitting

grpc-java/core/src/main/java/io/grpc/internal/PickFirstLeafLoadBalancer.java

Lines 143 to 154 in 86fa860

	if (rawConnectivityState == READY
	|| (rawConnectivityState == CONNECTING
	&& (!enableHappyEyeballs || addressIndex.isValid()))) {
	// If the previous ready (or connecting) subchannel exists in new address list,
	// keep this connection and don't create new subchannels. Happy Eyeballs is excluded when
	// connecting, because it allows multiple attempts simultaneously, thus is fine to start at
	// the beginning.
	SocketAddress previousAddress = addressIndex.getCurrentAddress();
	addressIndex.updateGroups(newImmutableAddressGroups);
	if (addressIndex.seekTo(previousAddress)) {
	SubchannelData subchannelData = subchannels.get(previousAddress);
	subchannelData.getSubchannel().updateAddresses(addressIndex.getCurrentEagAsList());

in acceptResolvedAddresses in some situations.

Note that for READY, a state where this path can also be entered, this is already guaranteed.

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: schiemon / name: szymon.habrainski (c76956a)

[schiemon]

If concludedState == TRANSIENT_FAILURE but rawConnectivityState != TRANSIENT_FAILURE, shouldn't we adapt our rawConnectivityState?

[schiemon]

Why not

Suggested change

	&& addressIndex.isValid())) {

? If we !enableHappyEyeballs and !addressIndex.isValid() then we get an exception when calling addressIndex.getCurrentAddress().

[schiemon]

With HE we have potentionally multiple connecting subchannels: why aren't we updating them all?