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net/http: setting Content-Type header to []string{""} in http handler causes two Content-Type headers to be emitted #5953

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josharian opened this issue Jul 25, 2013 · 9 comments
Closed

net/http: setting Content-Type header to []string{""} in http handler causes two Content-Type headers to be emitted #5953

josharian opened this issue Jul 25, 2013 · 9 comments
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Go1.2

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@josharian
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What steps will reproduce the problem?

Start up this server locally:

http://play.golang.org/p/GSGc0TFU0A

then:

curl -v localhost:6000


What is the expected output?

Only one Content-Type header in the raw response. (See below.)


What do you see instead?

After trimming a bit of noise:

$ curl -v localhost:6000
> GET / HTTP/1.1
> User-Agent: curl/7.24.0 (x86_64-apple-darwin12.0) libcurl/7.24.0 OpenSSL/0.9.8x
zlib/1.2.5
> Host: localhost:6000
> Accept: */*
> 
< HTTP/1.1 200 OK
< Content-Type: 
< Content-Type: text/plain; charset=utf-8
< Content-Length: 0
< Date: Thu, 25 Jul 2013 01:08:53 GMT


Which compiler are you using (5g, 6g, 8g, gccgo)?

6g


Which operating system are you using?

OS X


Which version are you using?  (run 'go version')

1.1.1


Please provide any additional information below.

The problematic line is:

  header["Content-Type"] = []string{""}

Any non-empty string here will not trigger the double headers. See
https://golang.org/issue/5950 for context about why I encountered
this.

A similar issue does not occur for the Date header, the Content-Length header, nor any
other header that I tried.
@rsc
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rsc commented Jul 30, 2013

Comment 1:

This happens because we're cutting corners testing for the presence of the header.

Labels changed: added priority-later, removed priority-triage.

Owner changed to @bradfitz.

Status changed to Accepted.

@rsc
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rsc commented Jul 30, 2013

Comment 2:

Labels changed: added go1.2.

@bradfitz
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Comment 3:

https://golang.org/cl/12117043

Status changed to Started.

@bradfitz
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bradfitz commented Aug 1, 2013

Comment 4:

This issue was closed by revision 252c107.

Status changed to Fixed.

@dsymonds
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Comment 5:

This issue was closed by revision 21e6b90.

@rsc rsc added this to the Go1.2 milestone Apr 14, 2015
@rsc rsc removed the go1.2 label Apr 14, 2015
@odeke-em
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odeke-em commented Dec 5, 2015

This issue seems to persist for http2 please see CL https://go-review.googlesource.com/17462 that uncovered it
OR

commit eec4d694e3ed2fcc91d72f82c9a2c37c7d17f5c2
Author: Emmanuel Odeke <emm.odeke@gmail.com>
Date:   Fri Dec 4 17:21:08 2015 -0700

    net/http: sniffTest for 5953 set in http2 mode

    Change-Id: I345b6ea7024a1c85c805b2d2e22f9f79aeca5816

diff --git a/src/net/http/sniff_test.go b/src/net/http/sniff_test.go
index 293a7f5..a372210 100644
--- a/src/net/http/sniff_test.go
+++ b/src/net/http/sniff_test.go
@@ -88,15 +88,18 @@ func testServerContentType(t *testing.T, h2 bool) {

 // Issue 5953: shouldn't sniff if the handler set a Content-Type header,
 // even if it's the empty string.
-func TestServerIssue5953(t *testing.T) {
+func TestServerIssue5953_h1(t *testing.T) { testServerIssue5953(t, false) }
+func TestServerIssue5953_h2(t *testing.T) { testServerIssue5953(t, true) }
+
+func testServerIssue5953(t *testing.T, h2 bool) {
    defer afterTest(t)
-   ts := httptest.NewServer(HandlerFunc(func(w ResponseWriter, r *Request) {
+   cst := newClientServerTest(t, h2, HandlerFunc(func(w ResponseWriter, r *Request) {
        w.Header()["Content-Type"] = []string{""}
        fmt.Fprintf(w, "<html><head></head><body>hi</body></html>")
    }))
-   defer ts.Close()
+   defer cst.close()

-   resp, err := Get(ts.URL)
+   resp, err := cst.c.Get(cst.ts.URL)
    if err != nil {
        t.Fatal(err)
    }
$ go test --cover
--- FAIL: TestServerIssue5953_h2 (0.00s)
    sniff_test.go:110: Content-Type = ["" "text/html; charset=utf-8"]; want [""]
FAIL
coverage: 77.4% of statements
exit status 1
FAIL    net/http    22.409s

@odeke-em
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odeke-em commented Dec 5, 2015

cc @bradfitz

@bradfitz
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bradfitz commented Dec 5, 2015

@odeke-em, please open a new bug and reference this one. Once bugs are closed, we no longer use them.

@odeke-em
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odeke-em commented Dec 5, 2015

Aye aye, thanks for that. I'll do that right now.

@odeke-em odeke-em mentioned this issue Dec 5, 2015
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@bradfitz @dsymonds @josharian @rsc @odeke-em @gopherbot