Serve JPEG XL when a request names no format (closes #222)

A /v1/image/ URL whose last segment is a size with no format, such as
800x600 or orig, is served as JPEG XL and signed as jxl, so it shares
the signature of the same URL ending in .jxl. An encrypted URL whose
token holds no format is served as JPEG XL, as encurl.DefaultFormat is
now jxl. The generator page selects JPEG XL by default, and a form
with an empty format, or none, makes a URL whose name ends in .jxl.

The image processor no longer takes an empty format as orig: both
routes give every request a format, so it refuses a request with none
instead of keeping a second default. auto still ends with JPEG.

Model: opus-5-5

README.md

@@ -175,20 +175,21 @@ path under `/v1/` answers 200, in maintenance mode too.
   with the page naming a field that is not valid; 500 when the URL cannot be
   made.
 - `GET /logout` — end the login session. Needs: nothing. Answers: 303 to `/`.
-- `GET` or `HEAD` `/v1/image/<host>/<path>/<size>.<format>` — an image, fetched,
+- `GET` or `HEAD` `/v1/image/<host>/<path>/<size>.<format>`, or
-  resized and converted (below). Needs: a signature, unless the host is
+  `/v1/image/<host>/<path>/<size>` with no format — an image, fetched, resized
-  allowlisted (see Source Hosts). Answers: 200; 304 when `If-None-Match` matches
+  and converted (below). Needs: a signature, unless the host is allowlisted (see
-  the image's `ETag`; 400 for a URL or parameter that is not valid, or for the
+  Source Hosts). Answers: 200; 304 when `If-None-Match` matches the image's
-  format `auto` an `Accept` header that is not valid; 406 for the format `auto`
+  `ETag`; 400 for a URL or parameter that is not valid, or for the format `auto`
-  when `Accept` allows none of the formats it chooses from; 401 for a missing or
+  an `Accept` header that is not valid; 406 for the format `auto` when `Accept`
-  wrong signature, a missing `exp` or an `exp` in the past; 403 when the
+  allows none of the formats it chooses from; 401 for a missing or wrong
-  request's `Referer` names a host in `referer_blocklist`, checked before the
+  signature, a missing `exp` or an `exp` in the past; 403 when the request's
-  signature, the cache and the upstream fetch; 403 when the upstream host, or a
+  `Referer` names a host in `referer_blocklist`, checked before the signature,
-  host it redirects to, is `localhost`, ends in `.localhost` or `.local`, or has
+  the cache and the upstream fetch; 403 when the upstream host, or a host it
-  an address in a blocked network (see `blocked_networks`); 502 when the
+  redirects to, is `localhost`, ends in `.localhost` or `.local`, or has an
-  upstream answered with an error status, and for 5 minutes after that for the
+  address in a blocked network (see `blocked_networks`); 502 when the upstream
-  same source URL; 503 when pixa is busy or in maintenance mode; 500 for any
+  answered with an error status, and for 5 minutes after that for the same
-  other failure.
+  source URL; 503 when pixa is busy or in maintenance mode; 500 for any other
+  failure.
 - `GET` or `HEAD` `/v1/e/<token>/<name>` — an image through an encrypted URL
   (see Encrypted URLs). Needs: nothing but the URL. Answers: 200; 304 when
   `If-None-Match` matches the image's `ETag`; 400 for a token that does not

internal/handlers/image.go

@@ -18,7 +18,8 @@ import (
 )
 
 // HandleImage handles the main image proxy route:
-// /v1/image/<host>/<path>/<width>x<height>.<format>
+// /v1/image/<host>/<path>/<width>x<height>.<format>, or with no format
+// /v1/image/<host>/<path>/<width>x<height>
 func (s *Handlers) HandleImage() http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
 		if s.refuseBlockedReferer(w, r) {

internal/imgcache/service.go

@@ -100,8 +100,8 @@ func NewService(cfg *ServiceConfig) (*Service, error) {
 		allowHTTP = cfg.FetcherConfig.AllowHTTP
 	}
 
-	// JPEG XL is to become the default output format, so pixad does not
+	// JPEG XL is the default output format, so pixad does not start
-	// start without it.
+	// without it.
 	err := imageprocessor.CheckJPEGXLSupport()
 	if err != nil {
 		return nil, err

internal/server/routes.go

@@ -89,7 +89,8 @@ func (s *Server) SetupRoutes() {
 			r.Use(s.refuseDuringMaintenance)
 
 			// Main image proxy route
-			// /v1/image/<host>/<path>/<width>x<height>.<format>
+			// /v1/image/<host>/<path>/<width>x<height>.<format>, or with no
+			// format /v1/image/<host>/<path>/<width>x<height>
 			r.Get("/image/*", s.h.HandleImage())
 			r.Head("/image/*", s.h.HandleImage())