Responses with a status code of `204` are not made according to spec

[albertov]

Description of the bug

According to the RFC7230 (http://tools.ietf.org/html/rfc7230#section-3.3.1):

A server MUST NOT send a Transfer-Encoding header field in any response with a status code of 1xx (Informational) or 204 (No Content).

hoverfly seems to break this restriction when using https (at least) which may break clients (eg: snoyberg/http-client#408)

Steps to reproduce the issue

Add this pair to a simulation.json, hoverctl import it, set hoverfly in simulate mode (hoverctl mode simulate) and use the proxy with a client that gives no leeway (eg: http-client)

{
                                "request": {
                                        "path": [
                                                {
                                                        "matcher": "exact",
                                                        "value": "/auth/tokens/jack-test-2"
                                                }
                                        ],
                                        "method": [
                                                {
                                                        "matcher": "exact",
                                                        "value": "GET"
                                                }
                                        ],
                                        "destination": [
                                                {
                                                        "matcher": "exact",
                                                        "value": "example.com"
                                                }
                                        ],
                                        "scheme": [
                                                {
                                                        "matcher": "exact",
                                                        "value": "https"
                                                }
                                        ],
                                        "body": [
                                                {
                                                        "matcher": "exact",
                                                        "value": ""
                                                }
                                        ]
                                },
                                "response": {
                                        "status": 204,
                                        "encodedBody": false,
                                        "headers": {
                                                "Connection": [
                                                        "keep-alive"
                                                ],
                                                "Content-Type": [
                                                        "application/json;charset=utf-8"
                                                ],
                                                "Date": [
                                                        "Mon, 08 Jul 2019 15:04:19 GMT"
                                                ],
                                                "Hoverfly": [
                                                        "Was-Here"
                                                ],
                                                "Server": [
                                                        "nginx/1.15.8"
                                                ],
                                                "Strict-Transport-Security": [
                                                        "max-age=15724800; includeSubDomains"
                                                ]
                                        },
                                        "templated": false
                                }
                        }

Observed result

Hoverfly error messages seen (If none, say none)

none

If possible, add screenshots to help explain your problem

A decrypted dump of the response given by Hoverfly with request/response pair given above:

The response body (highlighted) is 0\r\n\r\n which appear to be the chunk header for 0-sized chunk (\0\r\n) and the empty terminated chunk itself (\r\n)

Expected result

The responses with 204 status code and 1xx shouldn't have the transfer-encoding: chunked header nor perform that encoding on the empty response body.

Additional relevant information

1. Hoverfly version: cd51f9d with a patch to dump the private key to be able to decode the traffic with wireshark:

diff --git a/vendor/github.com/SpectoLabs/goproxy/signer.go b/vendor/github.com/SpectoLabs/goproxy/signer.go
index f6d99fc7..69d9de21 100644
--- a/vendor/github.com/SpectoLabs/goproxy/signer.go
+++ b/vendor/github.com/SpectoLabs/goproxy/signer.go
@@ -11,6 +11,9 @@ import (
        "runtime"
        "sort"
        "time"
+        "os"
+        "fmt"
+        "encoding/pem"
 )
 
 func hashSorted(lst []string) []byte {
@@ -76,6 +79,13 @@ func signHost(ca tls.Certificate, hosts []string) (cert tls.Certificate, err err
        if certpriv, err = rsa.GenerateKey(&csprng, 1024); err != nil {
                return
        }
+        pemPrivateFile, err := os.Create(hosts[0]+".private_key.pem")
+        if err != nil {
+            fmt.Println(err)
+            os.Exit(1)
+        }
+        pem.Encode(pemPrivateFile, &pem.Block{Type: "RSA PRIVATE KEY", Bytes:x509.MarshalPKCS1PrivateKey(certpriv) })
+        pemPrivateFile.Close()
        var derBytes []byte
        if derBytes, err = x509.CreateCertificate(&csprng, &template, x509ca, &certpriv.PublicKey, ca.PrivateKey); err != nil {
                return

2. Anything that might help us to diagnose the problem

[tommysitu]

Thank you for the detailed diagnostic report provided. Hoverfly undoubtedly has gaps in meeting the RFC7230 spec. We will look into this one.

[tommysitu]

Fixed in v1.1.1