Updates-Via header in OPTIONS

The Solid WebSocket API Specs say that Updates-Via header can be found in an OPTIONS request to the server.

I am not finding an Updates-Via header in OPTIONS for node solid server, though I do get one if I do an HTTP HEAD:

$ curl -k -i  -X OPTIONS https://localhost:8443/public/
HTTP/1.1 204 No Content
X-Powered-By: solid-server/5.1.2
Vary: Accept, Authorization, Origin, Access-Control-Request-Headers
Access-Control-Allow-Credentials: true
Access-Control-Allow-Methods: OPTIONS,HEAD,GET,PATCH,POST,PUT,DELETE
Access-Control-Max-Age: 1728000
Access-Control-Expose-Headers: Authorization, User, Location, Link, Vary, Last-Modified, ETag, Accept-Patch, Accept-Post, Updates-Via, Allow, WAC-Allow, Content-Length, WWW-Authenticate
Allow: COPY,GET,HEAD,POST,PATCH,PUT,DELETE
Link: <https://localhost:8443/public/.well-known/solid>; rel="service", <https://localhost:8443>; rel="http://openid.net/specs/connect/1.0/issuer", <.acl>; rel="acl", <.meta>; rel="describedBy", <http://www.w3.org/ns/ldp#Container>; rel="type", <http://www.w3.org/ns/ldp#BasicContainer>; rel="type"
Accept-Patch: application/sparql-update
Accept-Post: */*
ETag: W/"23-dYHCBqdZ5e1V1nWlG0I6iB9SOvk"
Date: Wed, 05 Jun 2019 20:57:22 GMT
Connection: keep-alive

vs

$ curl -k --head https://localhost:8443/public/
HTTP/1.1 200 OK
X-Powered-By: solid-server/5.1.2
Vary: Accept, Authorization, Origin
Access-Control-Allow-Credentials: true
Access-Control-Expose-Headers: Authorization, User, Location, Link, Vary, Last-Modified, ETag, Accept-Patch, Accept-Post, Updates-Via, Allow, WAC-Allow, Content-Length, WWW-Authenticate
Allow: OPTIONS, HEAD, GET, PATCH, POST, PUT, DELETE
Link: <.acl>; rel="acl", <.meta>; rel="describedBy", <http://www.w3.org/ns/ldp#Container>; rel="type", <http://www.w3.org/ns/ldp#BasicContainer>; rel="type"
MS-Author-Via: SPARQL
Updates-Via: wss://localhost:8443
Content-Type: application/octet-stream; charset=utf-8
Content-Length: 2
ETag: W/"2-nOO9QiTIwXgNtWtBJezz8kv3SLc"
Date: Wed, 05 Jun 2019 20:57:00 GMT
Connection: keep-alive

This is using v5.1.2

首先定位 OPTIONS 和 HEAD 回應的請求處理邏輯，並搜尋 Updates-Via header 的產生位置。使用 issue 中針對受影響伺服器版本的 curl 指令重現這項差異，然後驗證預期的 header 行為在兩種方法中是否一致。