packet: fix misusing of defer

[shizhx]

defer capture arguments at once, so modify arguments after defer line not works
Closes #728

[lance6716]

Thanks for fixing it!

Just for discussing, do you think we should also remove two buf = nil below? Because we know BytesBufferPut can skip putting it back to cache pool when it's too big.
But line 113 "exposing the buf.Bytes() to caller" must be used along with "not putting buf back to cache pool". Explicitly assigning buf to nil is better than implicitly doing it in BytesBufferPut.

For now I slightly prefer we remove the buf = nil in line 108 and its if-block. What do you think?

[shizhx]

If we remove the buf = nil line, we need to add a new API to achieve "copy buffer" feature, maybe utils.BytesBufferCopyAndPut or a better name, the new API implementation can decide between "actually copy buffer" and "return buffer".

But the new API only suitable for successful return, failed return we also have to call "BytesBufferPut".

So, I think removing the buf = nil line is difficult.

[lance6716]

I can't understand why we need to add a new API to remove buf = nil. Can you explain why current code plus deleting buf = nil is not proper?

[shizhx]

I can't understand why we need to add a new API to remove buf = nil. Can you explain why current code plus deleting buf = nil is not proper?

as your post above:

But line 113 "exposing the buf.Bytes() to caller" must be used along with "not putting buf back to cache pool". Explicitly assigning buf to nil is better than implicitly doing it in BytesBufferPut.

If we simply remove the buf = nil line, when the put or not condition changed in BytesBufferPut, current code maybe buggy.

So we need an explicit API to do it, maybe a BytesBufferCopyAndPut or IsBytesBufferActuallyPut.

[atercattus]

Hello.
What is wrong with defer here? :) buf is a *bytes.Buffer, and we do not modify it (expect buf = nil cases).

[shizhx]

@atercattus The following code buf = nil want utils.BytesBufferPut(nil) to prevent actually put buf. but defer utils.BytesBufferPut(buf) cannot achieve that, always non-nil argument passed to utils.BytesBufferPut.

[atercattus]

Oh, sorry, I'm blind :)
It's my fault, I missed it in #651.

And I agree what a better way is wrap defer to func here.