RFC for CONNECT requests not honored

[izzy]

I got an HTTP proxy that was working until now, which will send the Transfer-Encoding and Content-Length headers for a CONNECT request before sending the blank line(start of tunneling):

< HTTP/1.1 200 CONNECT OK
< Transfer-Encoding: chunked

To either of which curl will respond with an error like this:

* Transfer-Encoding: in 200 response
* Connection #0 to host localhost left intact
curl: (56) Transfer-Encoding: in 200 response

In lib/http_proxy.c, the code responsible for that errror is even commented with the right RFC - quoting the first part of RFC 7231 section 4.3.6. Sadly, the part important for curl as a client is completely ignored:

A client MUST ignore any Content-Length or Transfer-Encoding
header fields received in a successful response to CONNECT.

The proxy still worked in 7.47.0, with the recent upgrades on my test systems to 7.52.1(Debian 9) and 7.53.1(Arch Linux) this didn't work anymore

[jay]

bisected to c50b878 which is:

CONNECT: reject TE or CL in 2xx responses

A server MUST NOT send any Transfer-Encoding or Content-Length header
fields in a 2xx (Successful) response to CONNECT. (RFC 7231 section
4.3.6)

Also fixes the three test cases that did this.

RFC 7231 4.3.6:

   A server MUST NOT send any Transfer-Encoding or Content-Length header
   fields in a 2xx (Successful) response to CONNECT.  A client MUST
   ignore any Content-Length or Transfer-Encoding header fields received
   in a successful response to CONNECT.

I think we should do what the RFC says here, clearly this is a buggy premise but still.

Here is a patch, if there is a +1 I'll write up a test case and land it.

diff --git a/lib/http_proxy.c b/lib/http_proxy.c
index 7fde11d..a673286 100644
--- a/lib/http_proxy.c
+++ b/lib/http_proxy.c
@@ -515,33 +515,34 @@ CURLcode Curl_proxyCONNECT(struct connectdata *conn,
         }
         else if(checkprefix("Content-Length:", line_start)) {
           if(k->httpcode/100 == 2) {
-            /* A server MUST NOT send any Transfer-Encoding or
-               Content-Length header fields in a 2xx (Successful)
-               response to CONNECT. (RFC 7231 section 4.3.6) */
-            failf(data, "Content-Length: in %03d response",
+            /* A client MUST ignore any Content-Length or Transfer-Encoding
+               header fields received in a successful response to CONNECT.
+               "Successful" described as: 2xx (Successful). RFC 7231 4.3.6 */
+            infof(data, "Ignoring Content-Length in CONNECT %03d response\n",
                   k->httpcode);
-            return CURLE_RECV_ERROR;
           }
-
-          cl = curlx_strtoofft(line_start +
-                               strlen("Content-Length:"), NULL, 10);
+          else {
+            cl = curlx_strtoofft(line_start +
+                                 strlen("Content-Length:"), NULL, 10);
+          }
         }
         else if(Curl_compareheader(line_start, "Connection:", "close"))
           closeConnection = TRUE;
-        else if(Curl_compareheader(line_start,
-                                   "Transfer-Encoding:",
-                                   "chunked")) {
+        else if(checkprefix("Transfer-Encoding:", line_start)) {
           if(k->httpcode/100 == 2) {
-            /* A server MUST NOT send any Transfer-Encoding or
-               Content-Length header fields in a 2xx (Successful)
-               response to CONNECT. (RFC 7231 section 4.3.6) */
-            failf(data, "Transfer-Encoding: in %03d response", k->httpcode);
-            return CURLE_RECV_ERROR;
+            /* A client MUST ignore any Content-Length or Transfer-Encoding
+               header fields received in a successful response to CONNECT.
+               "Successful" described as: 2xx (Successful). RFC 7231 4.3.6 */
+            infof(data, "Ignoring Transfer-Encoding in "
+                  "CONNECT %03d response\n", k->httpcode);
+          }
+          else if(Curl_compareheader(line_start,
+                                     "Transfer-Encoding:", "chunked")) {
+            infof(data, "CONNECT responded chunked\n");
+            chunked_encoding = TRUE;
+            /* init our chunky engine */
+            Curl_httpchunk_init(conn);
           }
-          infof(data, "CONNECT responded chunked\n");
-          chunked_encoding = TRUE;
-          /* init our chunky engine */
-          Curl_httpchunk_init(conn);
         }
         else if(Curl_compareheader(line_start, "Proxy-Connection:", "close"))
           closeConnection = TRUE;

[jay]

Landed in ec1d0ed, thanks guys.