net/http: ResponseWriter doesn't overwrite content-type after WriteHeader is called. #17083
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odeke-em
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@GordonJiang this behavior is documented in https://golang.org/pkg/net/http/#ResponseWriter as the documentation for property Header(). Closing this issue unless someone else thinks we should do more. |
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Working as intended.
WriteHeader is supposed to write (all) the headers, so when it's called, it
will write the current Content-Type. Later update to the Header map won't
affect header that has already been written.
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Please answer these questions before submitting your issue. Thanks!
What version of Go are you using (
go version)?1.7
What operating system and processor architecture are you using (
go env)?ubuntu, amd64
What did you do?
in a http server handler,
first call w.WriteHeader(http.StatusOK)
then call w.Header().Set("Content-Type", "application/json")
then w.Write(somedata compressed by gzip)
What did you expect to see?
The Content-Type in response message captured by troubleshooting tool of chrome/firefox becomes application/x-gzip
What did you see instead?
The Content-Type should be application/json as I set.
On the other hand, if I change the order. call w.Header().Set("Content-Type", "application/json") ahead of the w.WriteHeader(http.StatusOK), the Content-Type keeps what it is. Seems setting status ahead of write content-type trigger the logic to DetectContentType automatically. It's overwrite whatever content-type I set later.
Because of that, gzip content can't be parsed in firefox. Of course, I worked around it by changing the code to set content-type first. But it apparently a trap since there is no doc saying you should always set content-type before set status by WriteHeader.
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