Re: Empty transfer-encoding header causes 502 response

Matthew H <squid@xxxxxxxxxxxxx> · Wed, 26 Oct 2022 01:55:20 +0100

Hi all,

Thanks for the replies.
I have included the requested output from tcpdump below:

 tcpdump -A -s 0 -ni enp4s0 "host 159.203.14.9 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&
0xf0)>>2)) != 0)"
tcpdump: verbose output suppressed, use -v[v]... for full protocol decode
listening on enp4s0, link-type EN10MB (Ethernet), snapshot length 262144 bytes

01:40:17.310479 IP 10.0.160.10.43426 > 159.203.14.9.1996: Flags [P.], seq 2955630477:2955630939, ack 2382737005, win 502, options [nop,nop,TS val 3000375654 ecr 1932743995], length 462
E....:@.?.7.
..
...     .....+W....m....Y......
...fs3U;GET http://nintendo.com/ HTTP/1.1
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:106.0) Gecko/20100101 Firefox/106.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,*/*;q=0.8
Accept-Language: en-GB,en;q=0.5
Accept-Encoding: gzip, deflate
Upgrade-Insecure-Requests: 1
Host: nintendo.com
Via: 1.1 dce3749b9671 (squid/5.6)
X-Forwarded-For: 10.0.130.210
Cache-Control: max-age=259200
Connection: keep-alive

01:40:18.957475 IP 159.203.14.9.1996 > 10.0.160.10.43426: Flags [P.], seq 1:1466, ack 462, win 114, options [nop,nop,TS val 1932744407 ecr 3000375654], length 1465
E....@@.3......
..
.......m.+Y[...r]......
s3V....fHTTP/1.1 200 OK
x-powered-by: Express
content-type: text/html; charset=iso-8859-1
transfer-encoding:
date: Wed, 26 Oct 2022 00:40:20 GMT
connection: close

<!DOCTYPE html PUBLIC "-//IETF//DTD HTML 2.0//EN"><html><head>
<!-- this automatically loads the hallway after 20 seconds -->
<meta http-equiv="refresh" content="20; url="" href="http://nintendo.com//./hallway/index.html">http://nintendo.com//./hallway/index.html">
<title>Nintendo Power Source</title>

On Tue, Oct 25, 2022 at 2:08 PM Alex Rousskov <rousskov@xxxxxxxxxxxxxxxxxxxxxxx> wrote:
On 10/23/22 20:36, Matthew H wrote:

> Hi,

> 

> I'm using Squid to proxy HTTP requests to another proxy. I can see squid 

> sending the request to the parent and getting a response, but it sends 

> the client that initiated the request a 502 Bad Gateway response.

> 

> On closer inspection it appears the parent proxy is sending an 

> empty transfer-encoding header, and this is causing Squid to send a 502. 

Do you know whether the response body was using chunked (or any other 

non-identity) encoding? I have already added your case to the list of 

known rejected responses[1], but it would be good to update that with 

the information on the actual response encoding.

[1] https://github.com/squid-cache/squid/pull/702#issuecomment-762459132

If the very first bytes of the response are "<html" or similar, then no 

encoding was probably applied. If you see what can be interpreted as a 

small hex number followed by a new line, then chunked encoding was 

probably applied (at least). If you cannot tell, or are not sure, feel 

free to share the response packet in libpcap format, captured with 

wireshark or "tcpdump -s0".

Thank you,

Alex.

> 2022/10/24 00:23:59.106| ctx: enter level  0: 'http://nintendo.com/ 

> <http://nintendo.com/>'

> 2022/10/24 00:23:59.106| 11,3| http.cc(666) processReplyHeader: 

> processReplyHeader: key '19010000000000000C00000000000000'

> 2022/10/24 00:23:59.106| 11,2| http.cc(720) processReplyHeader: HTTP 

> Server conn294 local=172.25.0.3:57802 

> <http://172.25.0.3:57802/> remote=159.203.14.9:1996 

> <http://159.203.14.9:1996/> FIRSTUP_PARENT FD 26 flags=1

> 2022/10/24 00:23:59.106| 11,2| http.cc(721) processReplyHeader: HTTP 

> Server RESPONSE:

> ---------

> HTTP/1.1 200 OK

> x-powered-by: Express

> content-type: text/html; charset=iso-8859-1

> transfer-encoding:

> date: Mon, 24 Oct 2022 00:23:57 GMT

> connection: close

> 

> ----------

> 2022/10/24 00:23:59.106| 55,3| HttpHeader.cc(882) getList: empty list 

> header: Transfer-Encoding(Transfer-Encoding[63])

> 2022/10/24 00:23:59.106| 55,2| HttpHeader.cc(559) parse: WARNING: 

> unsupported Transfer-Encoding used by client:

> 2022/10/24 00:23:59.106| ctx: exit level  0

> 2022/10/24 00:23:59.106| 20,3| store.cc(1673) reset: 

> http://nintendo.com/ <http://nintendo.com/>

> 2022/10/24 00:23:59.107| 17,3| FwdState.cc(492) fail: ERR_INVALID_RESP 

> "Bad Gateway"

> http://nintendo.com/ <http://nintendo.com/>

> 2022/10/24 00:23:59.107| 17,3| FwdState.cc(533) unregister: 

> http://nintendo.com/ <http://nintendo.com/>

> 

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