It seems that I have figured out what the problem is.
Just add a --noproxy parameter on curl command can fix the problem.
~$ curl –noproxy “*” -i -X POST --data-urlencode ‘payload={“text”: “Hello, this is some text\nThis is more text. :t
ada:”}’ http://172.28.64.51:8065/hooks/wdohzcuksjrgurb614gdk79zoc
HTTP/1.1 200 OK
Access-Control-Allow-Origin:
Content-Type: text/plain
X-Request-Id: 3nbkz4j63ff7upnuhfm6w6ppbh
X-Version-Id: 4.8.0.4.8.0.d39da9993707366832c9a9108a647ef3.false
Date: Sat, 07 Apr 2018 15:20:56 GMT
Content-Length: 2
But still have no idea about the blocking behavior of Squid. Can I think of that CURL uses Squid to process proxy ? 