improve http request handling for internal services and multiple domains

per listener, you could enable the admin/account/webmail/webapi handlers. but
that would serve those services on their configured paths (/admin/, /,
/webmail/, /webapi/) on all domains mox would be webserving, including any
non-mail domains. so your www.example/admin/ would be serving the admin web
interface, with no way to disabled that.

with this change, the admin interface is only served on requests to (based on
Host header):
- ip addresses
- the listener host name (explicitly configured in the listener, with fallback
  to global hostname)
- "localhost" (for ssh tunnel/forwarding scenario's)

the account/webmail/webapi interfaces are served on the same domains as the
admin interface, and additionally:
- the client settings domains, as optionally configured in each Domain in
  domains.conf. typically "mail.<yourdomain>".

this means the internal services are no longer served on other domains
configured in the webserver, e.g. www.example.org/admin/ will not be handled
specially.

the order of evaluation of routes/services is also changed:
before this change, the internal handlers would always be evaluated first.
with this change, only the system handlers for
MTA-STS/autoconfig/ACME-validation will be evaluated first. then the webserver
handlers. and finally the internal services (admin/account/webmail/webapi).
this allows an admin to configure overrides for some of the domains (per
hostname-matching rules explained above) that would normally serve these
services.

webserver handlers can now be configured that pass the request to an internal
service: in addition to the existing static/redirect/forward config options,
there is now an "internal" config option, naming the service
(admin/account/webmail/webapi) for handling the request. this allows enabling
the internal services on custom domains.

for issue #160 by TragicLifeHu, thanks for reporting!

http/web_test.go

@@ -6,10 +6,8 @@ import (
 	"net/http/httptest"
 	"os"
 	"path/filepath"
-	"strings"
 	"testing"
 
-	"github.com/mjl-/mox/dns"
 	"github.com/mjl-/mox/mox-"
 )
 
@@ -19,20 +17,8 @@ func TestServeHTTP(t *testing.T) {
 	mox.ConfigDynamicPath = filepath.Join(filepath.Dir(mox.ConfigStaticPath), "domains.conf")
 	mox.MustLoadConfig(true, false)
 
-	srv := &serve{
-		PathHandlers: []pathHandler{
-			{
-				HostMatch: func(dom dns.Domain) bool {
-					return strings.HasPrefix(dom.ASCII, "mta-sts.")
-				},
-				Path: "/.well-known/mta-sts.txt",
-				Handler: http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-					w.Write([]byte("mta-sts!"))
-				}),
-			},
-		},
-		Webserver: true,
-	}
+	portSrvs := portServes(mox.Conf.Static.Listeners["local"])
+	srv := portSrvs[80]
 
 	test := func(method, target string, expCode int, expContent string, expHeaders map[string]string) {
 		t.Helper()
@@ -43,22 +29,22 @@ func TestServeHTTP(t *testing.T) {
 		srv.ServeHTTP(rw, req)
 		resp := rw.Result()
 		if resp.StatusCode != expCode {
-			t.Fatalf("got statuscode %d, expected %d", resp.StatusCode, expCode)
+			t.Errorf("got statuscode %d, expected %d", resp.StatusCode, expCode)
 		}
 		if expContent != "" {
 			s := rw.Body.String()
 			if s != expContent {
-				t.Fatalf("got response data %q, expected %q", s, expContent)
+				t.Errorf("got response data %q, expected %q", s, expContent)
 			}
 		}
 		for k, v := range expHeaders {
 			if xv := resp.Header.Get(k); xv != v {
-				t.Fatalf("got %q for header %q, expected %q", xv, k, v)
+				t.Errorf("got %q for header %q, expected %q", xv, k, v)
 			}
 		}
 	}
 
-	test("GET", "http://mta-sts.mox.example/.well-known/mta-sts.txt", http.StatusOK, "mta-sts!", nil)
+	test("GET", "http://mta-sts.mox.example/.well-known/mta-sts.txt", http.StatusOK, "version: STSv1\nmode: enforce\nmax_age: 86400\nmx: mox.example\n", nil)
 	test("GET", "http://mox.example/.well-known/mta-sts.txt", http.StatusNotFound, "", nil) // mta-sts endpoint not in this domain.
 	test("GET", "http://mta-sts.mox.example/static/", http.StatusNotFound, "", nil)         // static not served on this domain.
 	test("GET", "http://mta-sts.mox.example/other", http.StatusNotFound, "", nil)
@@ -66,4 +52,24 @@ func TestServeHTTP(t *testing.T) {
 	test("GET", "http://mox.example/static/index.html", http.StatusOK, "html\n", map[string]string{"X-Test": "mox"})
 	test("GET", "http://mox.example/static/dir/", http.StatusOK, "", map[string]string{"X-Test": "mox"}) // Dir listing.
 	test("GET", "http://mox.example/other", http.StatusNotFound, "", nil)
+
+	// Webmail on IP, localhost, mail host, clientsettingsdomain, not others.
+	test("GET", "http://127.0.0.1/webmail/", http.StatusOK, "", nil)
+	test("GET", "http://localhost/webmail/", http.StatusOK, "", nil)
+	test("GET", "http://mox.example/webmail/", http.StatusOK, "", nil)
+	test("GET", "http://mail.mox.example/webmail/", http.StatusOK, "", nil)
+	test("GET", "http://mail.other.example/webmail/", http.StatusNotFound, "", nil)
+	test("GET", "http://remotehost/webmail/", http.StatusNotFound, "", nil)
+
+	// admin on IP, localhost, mail host, not clientsettingsdomain.
+	test("GET", "http://127.0.0.1/admin/", http.StatusOK, "", nil)
+	test("GET", "http://localhost/admin/", http.StatusOK, "", nil)
+	test("GET", "http://mox.example/admin/", http.StatusPermanentRedirect, "", nil) // Override by WebHandler.
+	test("GET", "http://mail.mox.example/admin/", http.StatusNotFound, "", nil)
+
+	// account is off.
+	test("GET", "http://127.0.0.1/", http.StatusNotFound, "", nil)
+	test("GET", "http://localhost/", http.StatusNotFound, "", nil)
+	test("GET", "http://mox.example/", http.StatusNotFound, "", nil)
+	test("GET", "http://mail.mox.example/", http.StatusNotFound, "", nil)
 }