When will envoy return "100-continue" to the client and write it into access log? #14008
Description
In our production environment, we recently noticed there are some access log record showing envoy return RESPONSE_CODE:100 to the client. But from client side, we got confirmed they never send any Expect: 100-continue header. Also I have tried if I added the -H "Expect: 100-continue" in the curl command with -v, I can see the response including a HTTP 100 response code followed by a HTTP 200 response code (as below curl output). And in the access log, this request is recorded as RESPONSE_CODE:200. Then it is confusing what triggered envoy return and record status code 100?
... ...
> POST /v1/foo/bar HTTP/1.1
> Host: foo.bar.net
> User-Agent: curl/7.58.0
> Accept: */*
> Expect: 100-continue
> Authorization: Bearer <tooooo long>
> Content-Type: application/json
> Content-Length: 332
>
* TLSv1.3 (IN), TLS Unknown, Certificate Status (22):
* TLSv1.3 (IN), TLS handshake, Newsession Ticket (4):
* TLSv1.3 (IN), TLS handshake, Newsession Ticket (4):
* TLSv1.3 (IN), TLS Unknown, Unknown (23):
< HTTP/1.1 100 Continue
* TLSv1.3 (OUT), TLS Unknown, Unknown (23):
* We are completely uploaded and fine
* TLSv1.3 (IN), TLS Unknown, Unknown (23):
< HTTP/1.1 200 OK
< server: foo-bar-server
< date: Thu, 12 Nov 2020 01:01:54 GMT
< content-type: application/json
... ...
Thanks!