x/net/http2: client should allow 'trailers' Transfer-Encoding header

[rolandshoemaker]

1. What version of Go are you using (go version)?
   go1.6
2. What operating system and processor architecture are you using (go env)?
   Ubuntu 15.10 amd64
3. What did you do?

package main

import (
    "log"
    "net/http"
)

func main() {
    // Enables HTTP/2 in the DefaultClient on Go 1.6.0
    if tr, ok := http.DefaultTransport.(*http.Transport); ok {
        tr.ExpectContinueTimeout = 0
    }
    req, err := http.NewRequest("GET", "https://www.google.com", nil)
    if err != nil {
        log.Fatal(err)
    }
    req.Header.Set("Transfer-Encoding", "trailers")
    _, err = http.DefaultClient.Do(req)
    if err != nil {
        log.Fatal(err)
    }
}

1. What did you expect to see?
   No error
2. What did you see instead?
   http2: invalid Transfer-Encoding request header.

checkConnHeaders fails on any Transfer-Encoding header values other than chunked, but encodeHeaders ignores any Transfer-Encoding headers anyway. This is contrary to the spec which says

The only exception to this is the TE header field, which MAY be present in an HTTP/2 request; when it is, it MUST NOT contain any value other than "trailers".

[bradfitz]

TE and Transfer-Encoding are different headers:

http://tools.ietf.org/html/rfc7230#section-4.3 (TE)
http://tools.ietf.org/html/rfc7230#section-3.3.1 (Transfer-Encoding)

[rolandshoemaker]

Confusing names are confusing, my bad!

[bradfitz]

No prob. Thanks for fixing the other one.

[rolandshoemaker]

Now that I look checkConnHeaders should probably be checking TE == ("trailers" || "")?

[bradfitz]

Yeah, looks like it.