file_server: Use HTTPS port when a qualifying domain is specified

Also little comment cleanups

modules/caddyhttp/fileserver/command.go

@@ -18,12 +18,14 @@ import (
 	"encoding/json"
 	"flag"
 	"log"
+	"strconv"
 
 	"github.com/caddyserver/caddy/v2"
 	"github.com/caddyserver/caddy/v2/caddyconfig"
 	"github.com/caddyserver/caddy/v2/caddyconfig/httpcaddyfile"
 	caddycmd "github.com/caddyserver/caddy/v2/cmd"
 	"github.com/caddyserver/caddy/v2/modules/caddyhttp"
+	"github.com/mholt/certmagic"
 )
 
 func init() {
@@ -36,12 +38,13 @@ func init() {
 A simple but production-ready file server. Useful for quick deployments,
 demos, and development.
 
-If a qualifying hostname is specified with --domain, the server will use
-HTTPS if domain validation succeeds. Ensure A/AAAA records are properly
-configured before using this option.
-
 The listener's socket address can be customized with the --listen flag.
 
+If a qualifying hostname is specified with --domain, the default listener
+address will be changed to the HTTPS port and the server will use HTTPS
+if domain validation succeeds. Ensure A/AAAA records are properly
+configured before using this option.
+
 If --browse is enabled, requests for folders without an index file will
 respond with a file listing.`,
 		Flags: func() *flag.FlagSet {
@@ -83,7 +86,11 @@ func cmdFileServer(fs caddycmd.Flags) (int, error) {
 		Routes: caddyhttp.RouteList{route},
 	}
 	if listen == "" {
-		listen = ":" + httpcaddyfile.DefaultPort
+		if certmagic.HostQualifies(domain) {
+			listen = ":" + strconv.Itoa(certmagic.HTTPSPort)
+		} else {
+			listen = ":" + httpcaddyfile.DefaultPort
+		}
 	}
 	server.Listen = []string{listen}
 

modules/caddyhttp/fileserver/staticfiles.go

@@ -150,9 +150,6 @@ func (fsrv *FileServer) ServeHTTP(w http.ResponseWriter, r *http.Request, next c
 		return fsrv.notFound(w, r, next)
 	}
 
-	// TODO: maybe there should be a way to serve the next handler
-	// instead of returning 404 if a file is not found?
-
 	// TODO: content negotiation (brotli sidecar files, etc...)
 
 	// one last check to ensure the file isn't hidden (we might
@@ -193,7 +190,7 @@ func (fsrv *FileServer) ServeHTTP(w http.ResponseWriter, r *http.Request, next c
 		if mtyp == "" {
 			// do not allow Go to sniff the content-type; see
 			// https://www.youtube.com/watch?v=8t8JYpt0egE
-			// TODO: Consider writing a default mime type of application/octet-stream - this is secure but violates spec
+			// TODO: If we want a Content-Type, consider writing a default of application/octet-stream - this is secure but violates spec
 			w.Header()["Content-Type"] = nil
 		} else {
 			w.Header().Set("Content-Type", mtyp)