我可以使用 Curl 将文件上传到我的 Apache Web 服务器：
echo "[$(date)] file contents." | curl -T - http://WEB-SERVER/upload/sample.put
但是，如果我在中间放置一个 Squid 代理服务器，那么我将无法：
echo "[$(date)] file contents." | curl -x http://SQUID-PROXY:3128 -T - http://WEB-SERVER/upload/sample.put
Curl 报告以下错误：
注意：此错误响应采用 HTML 格式，但为了便于阅读，我已删除标签。
ERROR: The requested URL could not be retrieved
ERROR
The requested URL could not be retrieved
While trying to retrieve the URL:
http://WEB-SERVER/upload/sample.put
The following error was encountered:
Unsupported Request Method and Protocol
Squid does not support all request methods for all access protocols.
For example, you can not POST a Gopher request.
Your cache administrator is root.
My squid.conf似乎没有任何 ACL/规则应该禁止基于src or dstIP 地址，或protocol，或 HTTPmethod... 我可以做HTTP POST在同一个客户端和 Web 服务器之间就好了，中间有相同的代理。
万一失败HTTP PUT案例中，为了查看实际发生的请求和响应流量，我放置了netcatCurl 和 Squid 之间的过程，这就是我所看到的：
Request:
PUT http://WEB-SERVER/upload/sample.put HTTP/1.1
User-Agent: curl/7.15.5 (i686-redhat-linux-gnu) libcurl/7.15.5 OpenSSL/0.9.8b zlib/1.2.3 libidn/0.6.5
Host: WEB-SERVER
Pragma: no-cache
Accept: */*
Proxy-Connection: Keep-Alive
Transfer-Encoding: chunked
Expect: 100-continue
回复：
HTTP/1.0 501 Not Implemented
Server: squid/2.6.STABLE21
Date: Sun, 13 May 2012 02:11:39 GMT
Content-Type: text/html
Content-Length: 1078
Expires: Sun, 13 May 2012 02:11:39 GMT
X-Squid-Error: ERR_UNSUP_REQ 0
X-Cache: MISS from SQUID-PROXY-FQDN
X-Cache-Lookup: NONE from SQUID-PROXY-FQDN:3128
Via: 1.0 SQUID-PROXY-FQDN:3128 (squid/2.6.STABLE21)
Proxy-Connection: close
<SNIPPED the HTML error response already shown earlier above>
注意：出于可读性原因，我对 IP 地址和服务器名称进行了匿名处理。
