net/http: Transport.RoundTrip errors could be more informative

go version go1.5 linux/amd64

Ubuntu 14.04.3 LTS

I made an HTTP request to a server that accepts all TCP connections and then immediately closes them. I was expecting a meaningful error such as "connection closed before request could be sent" but http.RoundTrip returned EOF.

Here are client and server snippets that reproduce this. The client:

package main

import (
    "fmt"
    "net"
    "net/http"
)

func main() {
    dialer := &net.Dialer{}
    transport := &http.Transport{
        Dial: dialer.Dial,
    }

    request, _ := http.NewRequest("GET", "http://127.0.0.1:19870/", nil)
    _, err := transport.RoundTrip(request)
    fmt.Println(err)
}

Output is:

EOF

And the server:

package main

import "net"

func main() {
    ln, _ := net.Listen("tcp", ":19870")
    conn, _ := ln.Accept()
    conn.Close()
}

Here is a dump of the TCP exchange:

17:16:31.017342 IP localhost.52287 > localhost.19870: Flags [S], seq 3991906392, win 43690, options [mss 65495,sackOK,TS val 27880590 ecr 0,nop,wscale 7], length 0
E..<..@.@.w..........?M....X.........0.........
..l.........
17:16:31.017356 IP localhost.19870 > localhost.52287: Flags [S.], seq 530413255, ack 3991906393, win 43690, options [mss 65495,sackOK,TS val 27880590 ecr 27880590,nop,wscale 7], length 0
E..<..@.@.<.........M..?..v....Y.....0.........
..l...l.....
17:16:31.017367 IP localhost.52287 > localhost.19870: Flags [.], ack 1, win 342, options [nop,nop,TS val 27880590 ecr 27880590], length 0
E..4..@.@.w..........?M....Y..v....V.(.....
..l...l.
17:16:31.017514 IP localhost.19870 > localhost.52287: Flags [F.], seq 1, ack 1, win 342, options [nop,nop,TS val 27880591 ecr 27880590], length 0
E..4.F@.@."|........M..?..v....Y...V.(.....
..l...l.
17:16:31.019472 IP localhost.52287 > localhost.19870: Flags [F.], seq 1, ack 2, win 342, options [nop,nop,TS val 27880591 ecr 27880591], length 0
E..4..@.@.w..........?M....Y..v....V.(.....
..l...l.
17:16:31.019493 IP localhost.19870 > localhost.52287: Flags [.], ack 2, win 342, options [nop,nop,TS val 27880591 ecr 27880591], length 0
E..4.G@.@."{........M..?..v....Z...V.(.....
..l...l.