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net/http: checks for nil Response or Response.Body in Client.send causing some internal Google tests to fail #38095

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andybons opened this issue Mar 26, 2020 · 4 comments

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@andybons
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@andybons andybons commented Mar 26, 2020

With https://golang.org/cl/221818, we do explicit checks to see if a Response from a RoundTripper is nil or has a nil Body, returning an error if so. This is causing some test code to fail. A contrived example:

type fakeTransport func(*http.Request) (*http.Response, error)

func (f fakeTransport) RoundTrip(req *http.Request) (*http.Response, error) {
  return f(req)
}

...

func TestFoo(t *testing.T) {
  transport := fakeTransport(func(req *http.Request) (*http.Response, error) {
    return &http.Response{StatusCode: http.StatusOK}, nil
  })
  client := &http.Client{Transport: transport}
  // use client, get panic
  ...
}

It’s documented that http.Client.Do will always return a non-nil Body if its error is nil.

Should we be enforcing a non-nil Body in these scenarios? My general feeling is yes, though creating a NopCloser body pulls in ioutil and likely another package like strings or bytes for their NewReader functions in these cases.

Thoughts, @bcmills?

@bcmills
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@bcmills bcmills commented Mar 26, 2020

Reading the package docs, perhaps we could relax this check.

https://golang.org/pkg/net/http/#Response says (emphasis mine):

  // The http Client and Transport guarantee that Body is always
  // non-nil, even on responses without a body or responses with
  // a zero-length body. It is the caller's responsibility to
  // close Body. The default HTTP client's Transport may not
  // reuse HTTP/1.x "keep-alive" TCP connections if the Body is
  // not read to completion and closed.
  

But https://golang.org/pkg/net/http/#RoundTripper says:

 // … Callers
 // should not mutate or reuse the request until the Response's
 // Body has been closed.

which to me implies a non-nil Body. But perhaps it could be construed to mean “until the Response's body has been closed if non-nil”.

@andybons
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@andybons andybons commented Mar 26, 2020

Whatever you think is best.

@ianlancetaylor
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@ianlancetaylor ianlancetaylor commented Mar 26, 2020

Also CC @bradfitz

@bcmills bcmills self-assigned this Mar 27, 2020
@gopherbot
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@gopherbot gopherbot commented Mar 27, 2020

Change https://golang.org/cl/225717 mentions this issue: net/http: treat a nil Body from a custom RoundTripper as an empty one

@gopherbot gopherbot closed this in 2d77d33 Mar 31, 2020
atc0005 added a commit to atc0005/go-teams-notify that referenced this issue Aug 27, 2020
CHANGES

Apply fix provided by @davecheney in order to properly
implement the RoundTripper interface's expected
behavior:

- return response and nil error OR
- return nil and a non-nil error to explain failures
  to obtain a response

I likely *over* explained this with doc comments, but I
am still very much in "learning" mode here.

REFERENCES

- GH-46
- 2ce144f
- 6db6217

- http://hassansin.github.io/Unit-Testing-http-client-in-Go

- golang/go#41071
- golang/go#38095
  - golang/go@2d77d33
  - golang/go@12d02e7
- https://godoc.org/net/http#RoundTripper
- https://godoc.org/net/http#Response
  - https://godoc.org/net/http#Response.Body
@golang golang locked and limited conversation to collaborators Mar 31, 2021
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