fix: handling of nil passed as an arg to a typed interface parameter …

[shaunco]

…for #160

[vmihailenco]

Please add a test.

[shaunco]

Turns out the code path that I fixed was only used for messages that are never serialized with msgpack (such as memqueue). In writing the new unit test, I'm having very strange issues on the Redis side where msgpack is used:

Exception has occurred: panic
reflect.Set: value of type map[string]interface {} is not assignable to type taskq_test.testInterface
Stack:
	 2  0x0000000000494f91 in reflect.Value.assignTo
	     at /usr/local/go/src/reflect/value.go:2797
	 3  0x00000000004917f2 in reflect.Value.Set
	     at /usr/local/go/src/reflect/value.go:1905
	 4  0x00000000006f744f in github.com/vmihailenco/msgpack/v5.(*Decoder).interfaceValue
	     at /usr/local/go/pkg/mod/github.com/vmihailenco/msgpack/v5@v5.3.5/decode_value.go:201
	 5  0x00000000006f709b in github.com/vmihailenco/msgpack/v5.decodeInterfaceValue
	     at /usr/local/go/pkg/mod/github.com/vmihailenco/msgpack/v5@v5.3.5/decode_value.go:182
	 6  0x00000000006e8702 in github.com/vmihailenco/msgpack/v5.(*Decoder).DecodeValue
	     at /usr/local/go/pkg/mod/github.com/vmihailenco/msgpack/v5@v5.3.5/decode.go:309
	 7  0x00000000007489df in github.com/vmihailenco/taskq/v3.(*reflectFunc).fnArgs
	     at /dev/taskq-working/handler.go:147
	 8  0x000000000074804f in github.com/vmihailenco/taskq/v3.(*reflectFunc).HandleMessage
	     at /dev/taskq-working/handler.go:73
	 9  0x000000000074c61a in github.com/vmihailenco/taskq/v3.(*Task).HandleMessage
	     at /dev/taskq-working/task.go:112
	10  0x000000000074ba2a in github.com/vmihailenco/taskq/v3.(*TaskMap).HandleMessage
	     at /dev/taskq-working/registry.go:71
	11  0x0000000000742b7f in github.com/vmihailenco/taskq/v3.(*Consumer).Process
	     at /dev/taskq-working/consumer.go:539
	12  0x000000000074250d in github.com/vmihailenco/taskq/v3.(*Consumer).worker
	     at /dev/taskq-working/consumer.go:480
	13  0x0000000000741098 in github.com/vmihailenco/taskq/v3.(*Consumer).addWorker.func1
	     at /dev/taskq-working/consumer.go:276

msgpack seems to encode/decode nil interfaces just fine, but when I pass in an actual object as an interface the decode seems to think the interface object is a map[string]interface{}.

I don't know msgpack well enough to have a solution yet, but am still digging.

[shaunco]

Ok, ignore the above... After reading vmihailenco/msgpack#261 , I see my understanding of msgpack was flawed.

Since the code path I patched is just for memqueue (where args are not msgpacked), I put the test in memqueue_test.go.