Solved: Sprunge.us & Squid TCP_MISS/417

The Problem

An attempt to use sprunge.us (the only paste-bin worth using) with curl from behind a Squid proxy returns an error.

The Symptoms

Here's the Squid error message in case you forgot:

ERROR

The requested URL could not be retrieved.

While trying to process the request:

POST / HTTP/1.1
User-Agent: curl/7.15.5 (i486-pc-linux-gnu) libcurl/7.15.5 OpenSSL/0.9.8c zlib/1.2.3 libidn/0.6.5
Host: sprunge.us
Accept: */*
Content-Length: 1117
Expect: 100-continue
Content-Type: multipart/form-data; boundary=----------------------------e77c50e200fb

The following error was encountered:

• Invalid Request

Some aspect of the HTTP Request is invalid. Possible problems:

• Missing or unknown request method
• Missing URL
• Missing HTTP Identifier (HTTP/1.0)
• Request is too large
• Content-Length missing for POST or PUT requests
• Illegal character in hostname; underscores are not allowed

Your cache administrator is: abc@123.local

Generated Sun, 25 Oct 2009 14:34:23 GMT by 123.local (squid)

And the entry in the Squid access logs:

1256481202.378      1 10.254.22.109 TCP_MISS/417 1623 POST http://sprunge.us/ - NONE/- text/html

The Fix

Force curl to use HTTP 1.0 instead of the default HTTP 1.1 by adding the "-0" option.

~# iptables -L -n | curl -0 -F 'sprunge=<-' http://sprunge.us

Wait, what?

From the HTTP/1.1 RFC 2616:

Because of the presence of older implementations, the protocol allows ambiguous situations in which a client may send "Expect: 100-continue" without receiving either a 417 (Expectation Failed) status or a 100 (Continue) status. Therefore, when a client sends this header field to an origin server (possibly via a proxy) from which it has never seen a 100 (Continue) status, the client SHOULD NOT wait for an indefinite period before sending the request body.

Basically, Squid is HTTP 1.0, and "Expect: 100-continue" in the header is HTTP 1.1, so Squid throws an error. If curl is instructed to use HTTP 1.0, Squid is happy and the request is processed successfully.

Word Count: 356

Tags: curl, http, proxy, squid, tcp/ip

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