Disable Etag response header for GET /protocol-version

[jasonrudolph]

Motivation: atom/teletype#318 (comment)

TODO

• Add middleware to disable the ETag response header for GET /protocol-version
• Add test(s)

Demo

Before

$ curl -i http://localhost:3000/protocol-version
HTTP/1.1 200 OK
X-Powered-By: Express
Access-Control-Allow-Origin: *
Content-Type: application/json; charset=utf-8
Content-Length: 13
ETag: W/"d-MaS+LUY/qwRdJ3/Z0vJ+lNsXnE8"
Date: Tue, 13 Feb 2018 22:16:53 GMT
Connection: keep-alive

{"version":6}

After

$ curl -i http://localhost:3000/protocol-version
HTTP/1.1 200 OK
X-Powered-By: Express
Access-Control-Allow-Origin: *
Content-Type: application/json; charset=utf-8
Content-Length: 13
Date: Tue, 13 Feb 2018 22:16:59 GMT
Connection: keep-alive

{"version":6}

[jasonrudolph]

/fyi @as-cii: Here's a potential solution for removing the ETag response header from GET /protocol-version to help address the issue seen in atom/teletype#318 (comment)

[jasonrudolph]

@as-cii: I think this is ready for code review. Would you mind reviewing it when you have a moment? It's probably easiest to review the individual commits, where each commit message explains the specific change that's taking place.

I'm especially curious to hear your thoughts on the changes to TestServer and on the introduction of HTTPTestServer, but I certainly appreciated feedback on anything at all. 😄

[as-cii]

Looks good to me. After a quick search it seems like another option would be to add a Cache-Control: no-store header to the response (see expressjs/express#2472). For instance:

app.get('/protocol-version', function (req, res) {
  res.set('Cache-Control', 'no-store')
  res.send({version: 7})
})

If we make it less general by using the approach above we may even consider avoiding to write tests at all for this particular behavior as it's pretty declarative already. What do you think?

[jasonrudolph]

another option would be to add a Cache-Control: no-store header to the response

Nice find, @as-cii. #47 implements that approach. I tested it out in Teletype, and it seems to do the trick (i.e., it prevents the client from caching the response from /protocol-version).

[jasonrudolph]

Closing in favor of #47.