Adding a check for existing vary header before overwriting with CORS …

[yasuba]

…vary header

fixes #2003

[jmcardon]

I think this function can be Response[G] => Response[G], saving you a fold down the line

If you look down below:

checkVaryHeader(withMethodBasedHeader)
          .fold(withMethodBasedHeader)(h => withMethodBasedHeader.putHeaders(h))

you could simplify this into:

def varyHeader(response: Response[G]): Response[G] =  {
  // Match avoids a fold higher order call, but you can just do this with fold if you don't want
  response.headers.get(CaseInsensitiveString("Vary")) match {
    case None => 
      response.putHeaders(Header("Vary", "Origin,Access-Control-Request-Method"))
     case _ => 
       response
  }
}

and then, down the line:

varyHeader(withMethodBasedHeader)
  .putHeaders(..

[rossabaker]

This looks good to me. I'll leave it open for a short while in case @yasuba wants to polish it a bit more, but I think the logic is correct.

[rossabaker]

This could be maybeHeader.getOrElse(Header(...)). But I like @jmcardon's idea.

[yasuba]

I'd like to polish the PR a bit - thanks for the comments

[rossabaker]

Microoptimization: this default header could be stored in a val and shared by all requests.

[jmcardon]

A microoptimization suggested by Ross himself?!

Are my repeated pedantic comments on microoptimizations finally making a dent?

[rossabaker]

👍

[jmcardon]

Thanks for the contribution @yasuba !