proposal: net/http/httptest: add support for 1XX responses

[dunglas]

There is currently no way to test 1XX responses with the httptest package.

Support for 1XX responses has been added to the built-in HTTP server and reverse proxy in Go 1.19 (#42597, #53164).

I propose to add support for inspecting 1XX responses with the test package by integrating the httptrace package with it (as we've done for the reverse proxy).

Regarding the API, I suggest implementing the same API as when using the non-test client:

func Test1xx(t *testing.T) {
	trace := &httptrace.ClientTrace{
		Got100Continue: func() {
			// do something
		},
		Got1xxResponse: func(code int, header textproto.MIMEHeader) error {
			// do something

			return nil
		},
	}

	r, _ := http.NewRequest("GET", "http://example.com", nil)
	rw := httptest.NewRecorder()
	rw.ClientTrace = trace
	func(rw http.ResponseWriter, _ *http.Request) {
		rw.Header().Add("Link", "</image.png>; rel=preload; as=image")
		rw.WriteHeader(http.StatusEarlyHints)

		// ...
	}(rw, r)

       // ...
}

Proposal implementation: #56151

[ianlancetaylor]

Could you outline the new API in this issue, so that we don't have to work it out from the CL? Thanks.

CC @neild @bradfitz

[dunglas]

@ianlancetaylor description updated

[dunglas]

Updated API proposal following https://go-review.googlesource.com/c/go/+/442215/1#message-b8b8e699ed0237031dbfec5e34b8adf1bf8a31d8:

// InformationalResponse is an HTTP response sent with a [1xx status code].
//
// [1xx status code]: https://httpwg.org/specs/rfc9110.html#status.1xx
type InformationalResponse struct {
	// Code is the 1xx HTTP response code of this informational response.
	Code int

	// Header contains the headers of this informational response.
	Header http.Header
}

type ResponseRecorder struct {
	// Informational HTTP responses (1xx status code) sent before the main response.
	InformationalResponses []InformationalResponse

	// ...
}

[gopherbot]

Change https://go.dev/cl/442215 mentions this issue: net/http/httptest: add support for 1XX responses