为什么RoundTrip不应该修改请求？

Question

Why shouldn't RoundTrip modify the request ?

https://golang.org/src/net/http/client.go#L103

What happens if http.Request gets modified by a RoundTripper (http.Transport for instance)?

Answer 1

The awnser is stated in the interface comment https://golang.org/src/net/http/client.go#L89

A RoundTripper must be safe for concurrent use by multiple goroutines.

If a server gets a request, and starts multiple goroutines, it must be ensured that all requests work on the same input. If a RoundTripper changes the request, it can make already collected data useless (which may not even be noticed)