fix(router) handle a matching edge-case with uris

[thibaultcha]

Summary

When a request URI is matching (as a prefix) the uris of several APIs, but
other properties (say, hosts) differ, there was a possibility of
running into an edge-case, and try to match APIs with values of another
API. Doing so would result in a miss, and not return any API.

Full changelog

• fix edge-case
• simpler de-normalization logic when possible.
• simpler matching logic with updated reducer returning all APIs
  for a category as well as a minimalistic plain subset.
• use ngx.re.find instead of ngx.re.match when searching for hosts
  wildcard matching when categorizing.
• update variable names for clarifications
• some more comments to detail the logic

Issues resolved

Fix #2334

[Tieske]

@bungle assigned you for rreview as you've been working on the router already

[thibaultcha]

@bungle Could you give this patch a try on your side and make sure it still fixes the issue you were experiencing in your integration tests? Thank you!

[bungle]

@Tieske and @thibaultcha, I can confirm that this corrects the errors exposed by the integration test suite for #2315.

[bungle]

One comment though, not particularly for this PR.

I do not think we need to have ngx.req.get_headers() anywhere in a router code. Only header we ever read is ngx.var.http_host, and we possibly call it on hot path. At the same time we could get rid of that ugly grab_headers variable. exec doesn't need to pass any headers to find_api.

Or move that grab thing to find:

local host
if headers then
    host = headers["host"] or headers["Host"]

elseif grab_headers then
    host = ngx.var.http_host

end

-- or just use ngx.var.host and check that it is not "kong"

Then we don't need that empty_t anymore either.

[bungle]

Also on find_api we have this (totally unrelated):

local host = headers["host"] or headers["Host"]
if host then
  -- strip port number if given
  local m, err = re_match(host, "([^:]+)", "ajo")
  if not m then
    log(ERR, "could not strip port from Host header: ", err)
  end

  if m[0] then
    host = m[0]
  end
end

Why not just:

if host then
  local s = find(host, ":", nil, true)
  if s then
    host = sub(host, 1, s -1)
  end
end

Or:

local host = ngx.var.host
if host == "kong" then
  host = nil
end

Will also JIT compile.

[thibaultcha]

@bungle

I do not think we need to have ngx.req.get_headers() anywhere in a router code.

Yes, planning on changing this in another contribution as well.

Why not just:

if host then
local s = find(host, ":", nil, true)
if s then
host = sub(host, 1, s -1)
end
end

Good point! We should definitely do that as well.