revproxy: simplify the rules for host matching

Remove the wildcard matches, since we do not issue wildcard certs.  We could do
so, but that way lies madness. Do it if we need to, but later.

Author: creachadair

revproxy/internal_test.go

@@ -45,7 +45,7 @@ import (
 // Cache-Control does not include "no-store", and does include "immutable".
 //
 // In addition, a successful response that is not immutable and specifies a
-// max-age will be cached temporarily in-memory, up to the maximum of 1h.
+// max-age will be cached temporarily in-memory.
 //
 // # Cache Format
 //
@@ -67,10 +67,7 @@ import (
 // the storage key of the cache object.
 type Server struct {
 	// Targets is the list of hosts for which the proxy should forward requests.
-	//
-	// Each target is either a hostname ("host.domain.com"), which matches
-	// hostnames exactly, or a pattern of the form "*.domain.com" which matches
-	// hostnames like "domain.com" and "something.domain.com".
+	// Host names should be fully-qualified ("host.example.com").
 	Targets []string
 
 	// Local is the path of a local cache directory where responses are cached.
@@ -149,8 +146,8 @@ func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	s.reqReceived.Add(1)
 
 	// Check whether this request is to a target we are permitted to proxy for.
-	if !hostMatchesTarget(r.URL.Host, s.Targets) {
-		s.logf("reject proxy request for non-target %q", r.URL)
+	if !hostMatchesTarget(r.Host, s.Targets) {
+		s.logf("reject proxy request for non-target %q", r.Host)
 		http.Error(w, http.StatusText(http.StatusBadGateway), http.StatusBadGateway)
 		return
 	}
@@ -273,16 +270,7 @@ func (s *Server) logf(msg string, args ...any) {
 }
 
 func hostMatchesTarget(host string, targets []string) bool {
-	return slices.ContainsFunc(targets, func(s string) bool {
-		if s == host {
-			return true
-		} else if tail, ok := strings.CutPrefix(s, "*"); ok {
-			if strings.HasSuffix(host, tail) || host == strings.TrimPrefix(tail, ".") {
-				return true
-			}
-		}
-		return false
-	})
+	return slices.Contains(targets, host)
 }
 
 // canCacheRequest reports whether r is a request whose response can be cached.