[PR] fix: normalize the case of hosts carried on a service [apisix]

["AlinsRan (via GitHub)" <gi...@apache.org>]

AlinsRan opened a new pull request, #13781:
URL: https://github.com/apache/apisix/pull/13781

   ### Description
   
   Hostnames are case-insensitive, and route matching runs against `$host`, which nginx always lowercases (`ngx_http_validate_host()`). `apisix/router.lua` normalizes this on the route object:
   
   ```lua
   if route.value.host then
       route.value.host = str_lower(route.value.host)
   elseif route.value.hosts then
       for i, v in ipairs(route.value.hosts) do
           route.value.hosts[i] = str_lower(v)
       end
   end
   ```
   
   `apisix/http/service.lua` has no equivalent, so `service.hosts` is stored verbatim. `radixtree_host_uri` — the default router — builds its host buckets itself, keyed on the raw reversed host string:
   
   ```lua
   -- apisix/http/router/radixtree_host_uri.lua
   for i, host in ipairs(hosts) do
       local host_rev = host:reverse()
   ```
   
   A service host containing an uppercase character therefore ends up in a bucket keyed on e.g. `moc.elpmaxe.esaCdexiM`, which the lowercase `$host` can never reach. The route falls through to `only_uri_router`, and if nothing host-agnostic matches, the request 404s — for every path and every casing of the request `Host`, so the host is silently unroutable.
   
   `radixtree_uri` is not affected, because it passes `hosts` to lua-resty-radixtree, which lowercases on both the config side and the request side.
   
   Reproduced on 3.16.0 in standalone mode, with `service.hosts: ["MixedCase.example.com"]` and a route with no `hosts` of its own:
   
   | request `Host` | `radixtree_host_uri` (default) | `radixtree_uri` | after this patch |
   | --- | --- | --- | --- |
   | `MixedCase.example.com` | 404 | 200 | 200 |
   | `mixedcase.example.com` | 404 | 200 | 200 |
   | `MIXEDCASE.EXAMPLE.COM` | 404 | 200 | 200 |
   
   This patch lowercases the hosts in the service `filter()`, mirroring what `router.lua` already does for routes.
   
   Found via apache/apisix-ingress-controller#2822: the controller carries the host constraint on the service object, so an ingress route with an uppercase hostname is unroutable.
   
   #### Which issue(s) this PR fixes:
   
   N/A
   
   ### Checklist
   
   - [x] I have explained the need for this PR and the problem it solves
   - [x] I have explained the changes or the new features added to this PR
   - [x] I have added tests corresponding to this change
   - [ ] I have updated the documentation to reflect this change
   - [x] I have verified that this change is backward compatible (If not, please discuss on the [APISIX mailing list](https://github.com/apache/apisix/tree/master#community) first)
   


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Re: [PR] fix: normalize the case of hosts carried on a service [apisix]

["AlinsRan (via GitHub)" <gi...@apache.org>]

AlinsRan merged PR #13781:
URL: https://github.com/apache/apisix/pull/13781


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