Http server doesn't support writing multiple headers with the same name

[hoisie]

conn.SetHeader(name,val) by default overrides any previous value under the
same name. 

This makes it very difficult to write multiple Set-Cookie headers, for
instance. 

Headers with the same name are quite common for http servers. Just query
google.com and you'll see an example (the two Set-Cookie headers). 


mhoisie@Kenna gotest $ telnet google.com 80
Trying 74.125.19.106...
Connected to google.com.
Escape character is '^]'.
GET / HTTP/1.1

HTTP/1.1 200 OK
Date: Sat, 02 Jan 2010 17:21:48 GMT
Expires: -1
Cache-Control: private, max-age=0
Content-Type: text/html; charset=ISO-8859-1
Set-Cookie:
PREF=ID=c87cc887bc1adb8c:TM=1262452908:LM=1262452908:S=UkIVKQcywQeWefwp;
expires=Mon, 02-Jan-2012 17:21:48 GMT; path=/; domain=.google.com
Set-Cookie:
NID=30=ulQicanZo3Kkybu2XhzSJSPxzgqWseouLX8fCcqxnFy6n7A90LE_nFx0PE2ihD5Z9_bCMZZqy8XG-bP_OenKaMtS9AqQY6_0bn_5Oc2LCtbj7Oik9cLqaTre-Hwprlpc;
expires=Sun, 04-Jul-2010 17:21:48 GMT; path=/; domain=.google.com; HttpOnly
Server: gws
X-XSS-Protection: 0
Transfer-Encoding: chunked

[rsc]

Comment 1:

There should be a way to get at the current header value.
Set means set, i.e. overwrite.  But if you could get at the current
header value you could set the new value to the old one + ", " + 
the one you want to add.
RFC 2616 says that sending multiple headers must be
semantically equivalent to one header with the multiple
values separated by commas.

Owner changed to r...@golang.org.

Status changed to Accepted.

[bradfitz]

Comment 2:

We could replace ResponseWriter's SetHeader(k,v) with a Header() http.Header so client
code ends up looking like:
func handler(rw http.ResponseWriter, ...) {
     rw.Header().Set("Content-Length", "13")
     rw.Header().Add("X-Foo", "foo")
     rw.Header().Add("X-Foo", "foo")
}
If we do this, though, I'd like to change other stuff in ResponseWriter at the same
time.  Comments in https://golang.org/issue/1317?c=2

[bradfitz]

Comment 3:

Patch:
http://golang.org/cl/4239076/

Owner changed to bradf...@golang.org.

[bradfitz]

Comment 4:

This issue was closed by revision 2c420ec.

Status changed to Fixed.