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