Fix improper memory reuse in NewFastHTTPHandler

[sigmundxia]

Hi Developers,

This pull request fixes the improper memory reuse in NewFastHTTPHandler reported in this issue.

If there are any further adjustments or improvements you'd like me to make, please don't hesitate to reach out :)

Best regards!

[newacorn]

fasthttp/fasthttpadaptor/request.go

Lines 58 to 62 in c305051

	case "Transfer-Encoding":
	r.TransferEncoding = append(r.TransferEncoding, sv)
	default:
	r.Header.Set(sk, sv)
	}

I think performing deep copying through a case branch would be more appropriate here, as the comment in Request.VisitAll mentions that key and value cannot be referenced after the function f finishes executing. Directly modifying VisitAll may affect its efficiency.

[sigmundxia]

Agree :) I have revised and made a new commit

[newacorn]

Following your initial approach, it would be better to perform a deep copy only for the cookie header. The other references likely don't have any issues.If a deep copy of the value is needed here, the key should also be copied. It seems that either solution could work; it's just a trade-off between performance and memory safety.From a personal perspective. what do you think? @erikdubbelboer

[sigmundxia]

That makes sense, I added a new commit to limit deep copy to the cookie case only. If there are further results on the tradeoff between performance and memory safety, I'll be happy to continue to make changes

[gaby]

Looks good to me

[erikdubbelboer]

Thanks!