MultiChildLoadBalancer with EquivalentAddressGroup with multiple addresses throws NPE

[thegridman]

gRPC Java version 1.60.0

What is your environment?

This fails on all our environments, Linux, MacOS etc

What did you expect to see?

We expect the load balancer to work with a single EquivalentAddressGroup containing multiple addresses.

What did you see instead?

In our client code we receive a Runtime io.grpc.StatusRuntimeException: INTERNAL: Panic! This is a bug!

After debugging the client we tracked it down to this code in the MultiChildLoadBalancer.Endpoint constructor

    public Endpoint(EquivalentAddressGroup eag) {
      checkNotNull(eag, "eag");

      addrs = new String[eag.getAddresses().size()];
      int i = 0;
      for (SocketAddress address : eag.getAddresses()) {
        addrs[i] = address.toString();
      }
      Arrays.sort(addrs);

      hashCode = Arrays.hashCode(addrs);
    }

You can see that the code iterates over the addresses in the eag and adds the toString() of each to the string array. But it does not increment the index i so all addresses go to the first array element, the rest are null. This throws an NPE when Arrays.sort() is called.

I assume it should be a trivial fix like addrs[i++] = address.toString();

[thegridman]

I am able to work around this by changing my custom NameResolver.

Currently I do this

List<SocketAddress> list = // my list of server socket addresses

NameResolver.ResolutionResult result = NameResolver.ResolutionResult.newBuilder()
                                    .setAddresses(Collections.singletonList(new EquivalentAddressGroup(list, attrs)))
                                    .setAttributes(Attributes.EMPTY)
                                    .build();

// result is then passed to a NameResolver.Listener2
listener.onResult(result);

If, instead of creating a EquivalentAddressGroup with multiple addresses I create multiple EquivalentAddressGroup instances with a single address, then it works (as there is only one address passed to the broken code above).

List<SocketAddress> list = // my list of server socket addresses

List<EquivalentAddressGroup> groupList = list.stream()
        .map(addr -> new EquivalentAddressGroup(addr, attrs))
        .collect(Collectors.toList());

NameResolver.ResolutionResult result = NameResolver.ResolutionResult.newBuilder()
                                    .setAddresses(groupList)
                                    .setAttributes(Attributes.EMPTY)
                                    .build();

// result is then passed to a NameResolver.Listener2
listener.onResult(result);

I assume this work around is still valid, one EquivalentAddressGroup with multiple addresses or multiple EquivalentAddressGroup with one address will not cause me a problem somewhere else.