rtsp over http over a proxy

Question

I am trying to fetch an RTSP stream over HTTP using a proxy. The behavior of the Real client seems to be a bit hectic: it tries all the possible ports, methods and protocols at once. The only thing that should work is HTTP GET over port 80. Such a request is indeed issued, and is received on the server. Here's how the request looks when it is sent by the proxy to the server:

GET /SmpDsBhgRl83c52ef2-d0f4-41ac-bada-93e5350f67d1?1="1" HTTP/1.0\r\n
Connection: Keep-Alive\r\n
Host: 10.194.5.162:80\r\n
Pragma: no-cache\r\n
User-Agent: RealPlayer G2\r\n
Expires: Mon, 18 May 1974 00:00:00 GMT\r\n
Accept: application/x-rtsp-tunnelled, */*\r\n
ClientID: WinNT_5.1_6.0.14.806_RealPlayer_R41UKD_en-GB_686\r\n
X-Actual-URL: rtsp://10.194.5.162:554/01.mp3\r\n
\r\n

Here's the server's response:

HTTP/1.0 200 OK\r\n
Server: RMServer 1.0\r\n
Expires: Mon, 18 May 1974 00:00:00 GMT\r\n
Pragma: no-cache\r\n
x-server-ipaddress: 10.194.5.162\r\n
Content-type: audio/x-pn-realaudio\r\n
\r\n

At this point 4 more bytes arrive from the server (their values are 48 02 02 00) - and that's it, nothing more. Does the server expect anything from the client at this point, and if so - what? Does this mode of operation work at all?

Some more info on this problem: apparently, the intended mechanism of working with RTSP over HTTP built into RealPlayer is as follows:

1. Try to connect to the following ports: 80, 8080, 554, 7070. (Try also to download the file directly, just for the heck of it, by issuing GET http://hostname:port/mediafilename on port 80)
2. For each of the above ports, create 2 connections.
3. Send a GET request to one of the connections to the url http://hostname:port/SmpDsBhgRl<guid>?1="1", where <guid> is, yes, a freshly created GUID. Add a header to this request called X-Actual-URL containing the original RTSP URL.
4. Send a POST request on the other connection, to the URL http://hostname:port/SmpDsBhgRl with the GUID above as part of the body of the request. Send a Content-Length header of 32767 bytes, to prevent the proxy from closing the connection prematurely.
5. Start issuing commands to the server through the POST request, and get the corresponding RTSP stream as part of the GET response.

The strange stuff (if the above isn't strange enough) is that, for example, it works with Squid, but not if you use either of the ports 3128 or 8080! Somehow, the client uses the port it connects to to decide on the order of the requests or on when a request should be canceled, but anyway, as hard to believe as it is, it works with proxy port 9090, 3129, 8081, but not with 3128 or 8080.

Update #2: Here's the source of the RealPlayer with the explanation of the above behavior. Still no solution though.

Update #3: OK, in the light of the above, the magic value of 48 02 02 00 is clear: 48 == 'h' is for HTTP_RESPONSE, the next 02 is the length of the following data, the next 02 is called POST_NOT_RECEIVED (meaning that the POST request did not reach the server within a second from the corresponding GET request).

Update #4: This behavior (i.e. POST requests with huge Content-Length) is also characteristic of an ActiveX used by WebEx (and, possibly, many other web apps that need an open channel to the server).

Answer 1

1. See whether issuing the same request but bypassing the proxy (e.g., replay the request you posted above using Netcat) results in more than four bytes streamed in the response body.
2. See what TCP packets the proxy is receiving, for example, by eavesdropping on the TCP traffic on the machine that's running the proxy, say, using Wireshark.

Answer 2

First, you might want to read this:

http://developer.apple.com/quicktime/icefloe/dispatch028.html

Second, the HTTP requests (both GET and POST) need to be formatted so that they get proxied properly. I've seen proxies that insist on caching too much of the POST request, preventing it from reaching the server. Those proxies are buggy, but there's nothing you can do about that, and I was not able to work around that issue. Mostly I've seen this with anti-virus software that attempts to do transparent proxying of POST requests coming from the browser to scan them for private information like social security numbers. You might be running into the same problem.

Are you using McAfee's anti virus by any chance?

Also, it appears that Real invented its own way of doing the same thing, but the basic design is very similar - GET for the downstream link, POST for the upstream, with some magic cookie (in this case, the GUID) to tie the two together on the server. Either way, the POST should get to the server, and in your case it seems like it doesn't.

By the way, since the problem seems to be with the POST request not going through the proxy, how about posting that request, in addition to the GET?