return more clearly topic error message

[darrkz]

topic error was catch in ErrInvalidArg
but it can show more clearly

[cla-assistant]

All committers have signed the CLA.

[darrkz]

@milindl please review , thanks...

issue link
#1160

[milindl]

Thanks a lot for following up with a PR!

I have suggested some changes. Once you are done, could you also run go fmt on the changed files? Let me know if you have any questions.

[milindl]

Suggested change

	if msg == nil || len(*msg.TopicPartition.Topic) == 0 {
	return newErrorFromString(ErrInvalidArg, "")
	if msg == nil {
	return newErrorFromString(ErrInvalidArg, "msg cannot be nil")

[milindl]

Suggested change

	}else if msg.TopicPartition.Topic == nil{
	return newErrorFromString(ErrUnknownTopic, "topic is null, please check")
	} else if msg.TopicPartition.Topic == nil || len(*msg.TopicPartition.Topic) == 0 {
	return newErrorFromString(ErrInvalidArg, "topic cannot be nil or empty")

[milindl]

We must keep in mind, 2 things,

1. msg.TopicPartition.Topic == nil must be made before len(*msg.TopicPartition.Topic) == 0 , else it causes a nil pointer dereference and will panic.
2. We can't change the type of the error, only the message of it (since the type is a part of the public API so people might be relying on that)

[milindl]

Looks pretty good, thanks! Just one more thing, we should run go fmt on the changed files

[darrkz]

@milindl please review again and it can be merged

[milindl]

Hi @darrkz , please run the go fmt command on the codebase to fix the format issues automatically. I can run the CI and merge it after that.