HTTP response sent but never closed and ending with "HTTP/1.1 400 Bad Request"

[RobM]

Hello,

I wrote a really simple server :

-----------------------------------------------------------------------------------------------------

package main

 

import (

  "fmt"

  "net/http"

)

 

func main() {

  http.HandleFunc("/", root)

  fmt.Println("listening on port: 7777")

err := http.ListenAndServe(":7777", nil)

if err != nil {

 panic(err)

}

}

 

func root(res http.ResponseWriter, req *http.Request) {

fmt.Fprintf(res, "Hello")

}

-----------------------------------------------------------------------------------------------------------------------------

When I do "curl localhost:7777/" I see "hello" printed in the response so all is ok. But when I play the same request using netcat:

------------------------------------------------------------------------------------------------------------------------------

$> nc localhost 7777

GET / HTTP/1.1                                      #writing the request manually

User-Agent: curl/7.24.0 (x86_64-apple-darwin12.0) libcurl/7.24.0 OpenSSL/0.9.8y zlib/1.2.5

Host: localhost:7777

Accept: */*

HTTP/1.1 200 OK                                     #response headers

Content-Type: text/plain; charset=utf-8

Content-Length: 5

Date: Sun, 13 Oct 2013 18:42:55 GMT

Hello                                                         #here the connection stays open just after "Hello", when I type return

HTTP/1.1 400 Bad Request                        # I see this and the connection really close

------------------------------------------------------------------------------------------------------------------------------

What's happening here ? There is obviously something wrong but I can't tell what.

[minux]

the problem is that you typed return here.

your root handler doesn't output a \n, so you typed a \n, however, the HTTP server is

treating that empty line you just typed as a new request line, and then it says bad request

as the request line is empty. 

[RobM]

Ok thanks got it but even if I change "Hello" to "Hello\n" the connection stays opened ... Shouldn't it be closed once the handler returns ?

[minux]

On Sun, Oct 13, 2013 at 3:03 PM, RobM <robin...@gmail.com> wrote:

Ok thanks got it but even if I change "Hello" to "Hello\n" the connection stays opened ... Shouldn't it be closed once the handler returns ?

by default, the net/http tries to wait some time before closing the connection (http 1.1 keepalive),

so the the client don't need to open a new connection for each resource and can reuse the current

connection.

you can get the behavior you want by sending this:

GET / HTTP/1.0

or this:

GET / HTTP/1.1

Host: localhost

Connection: close

[RobM]

Thank you for your answer. I thought this was the reason why I couldn't get HTTP trailer working but it seems that it's not. Here is what I do at the end of my handler

----------------------------------------------------

trailers := map[string]string {

    "x-my-trailer": "here it is",

}

m := make(http.Header)

for k, v := range(trailers) {

   m.Add(k, v)

}

req.Trailer = m

----------------------------------------------------

I should see the trailer using netcat (did it before in node.js) but I don't. Any idea where is my mistake ?

[Dave Cheney]

If you want the remote server to close the connection it's response you need to ask it to do so. Two ways to do this are, using HTTP/1.0 or sending a Connection: close header with HTTP/1.1. 

On 14 Oct 2013, at 6:03, RobM <robin...@gmail.com> wrote:

Ok thanks got it but even if I change "Hello" to "Hello\n" the connection stays opened ... Shouldn't it be closed once the handler returns ?

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[RobM]

Ok guys thanks for that I understand now. Any ideas about my HTTP trailer issue ?

[Dave Cheney]

> Ok guys thanks for that I understand now. Any ideas about my HTTP trailer
> issue ?

Can you please remind me what the trailer issue is ?

[Benjamin Measures]

> I couldn't get HTTP trailer working but it seems that it's not. Here is what I do at the end of my handler

Make sure you're checking for errs:
http://golang.org/pkg/net/http/#pkg-variables
> ErrUnexpectedTrailer = &ProtocolError{"trailer header without chunked transfer encoding"}

You cannot use trailers unless HTTP/1.1 and chunked encoding.

Apart from that suggestion, my magic ball came up with nothing (show your code).

[RobM]

Here is the code I use in a handler to send HTTP trailers when the request ends:

----------------------------------------------------

res.Header().Add("Trailer", "x-my-trailer")    #warning the client that trailer is expected

//doint stuff here

trailers := map[string]string {

    "x-my-trailer": "here it is",

}

m := make(http.Header)                             #creating a trailer (of type http.Header)

for k, v := range(trailers) {

   m.Add(k, v)

}

req.Trailer = m                                          #setting the trailer

----------------------------------------------------

As I said before, I should see trailer at the end of my request using netcat (after the 0 sized chunk). I'm using HTTP 1.1 as well as chunked encoding.

Any idea ? I read that HTTP trailers are not yet fully supported in Go

[Dave Cheney]

I'm pretty sure I remember Brad saying that trailers are not supported. Does your client signal it is willing to accept trailers with the TE header?

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[RobM]

Well, it's supposed to be "partially complete". From http://golang.org/src/pkg/net/http/request.go :

// Trailer maps trailer keys to values.  Like for Header, if the
// response has multiple trailer lines with the same key, they will be
// concatenated, delimited by commas.
// For server requests, Trailer is only populated after Body has been
// closed or fully consumed.
// Trailer support is only partially complete.
Trailer Header

Client side request is ok, doing the same request on a nodejs server I get the trailers I expect. Trailer usage may not be possible yet ...

[Benjamin Measures]

On Monday, 14 October 2013 19:07:42 UTC+1, Dave Cheney wrote:

I'm pretty sure I remember Brad saying that trailers are not supported.

Oh yes:

http://golang.org/src/pkg/net/http/server.go#L278

> // zero EOF chunk, trailer key/value pairs (currently

> // unsupported in Go's server), followed by a blank

> // line.

(Beside not trying to modify request.Trailer) The OP will need to modify/implement their own http.server, possibly using httputil.ServerConn . Considering client support though (they can be silently dropped), it's hard to see how it's worth the effort.

[Robin Monjo]

Ok thanks I won't use trailer then.

[Kyle Lemons]

ResponseWriter has no trailer support.  You're trying to set the trailer on the incoming request, but that has no effect on the response sent to the client.

To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/A49C36A6-5EDF-4830-85E1-430C1E463EDC%40cheney.net.

[RobM]

Hum yes you're right, I got confused !