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

@@ -175,21 +175,20 @@ 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>`, or
+- `GET` or `HEAD` `/v1/image/<host>/<path>/<size>.<format>` — an image, fetched,
-  `/v1/image/<host>/<path>/<size>` with no format — an image, fetched, resized
+  resized and converted (below). Needs: a signature, unless the host is
-  and converted (below). Needs: a signature, unless the host is allowlisted (see
+  allowlisted (see Source Hosts). Answers: 200; 304 when `If-None-Match` matches
-  Source Hosts). Answers: 200; 304 when `If-None-Match` matches the image's
+  the image's `ETag`; 400 for a URL or parameter that is not valid, or for the
-  `ETag`; 400 for a URL or parameter that is not valid, or for the format `auto`
+  format `auto` an `Accept` header that is not valid; 406 for the format `auto`
-  an `Accept` header that is not valid; 406 for the format `auto` when `Accept`
+  when `Accept` allows none of the formats it chooses from; 401 for a missing or
-  allows none of the formats it chooses from; 401 for a missing or wrong
+  wrong signature, a missing `exp` or an `exp` in the past; 403 when the
-  signature, a missing `exp` or an `exp` in the past; 403 when the request's
+  request's `Referer` names a host in `referer_blocklist`, checked before the
-  `Referer` names a host in `referer_blocklist`, checked before the signature,
+  signature, the cache and the upstream fetch; 403 when the upstream host, or a
-  the cache and the upstream fetch; 403 when the upstream host, or a host it
+  host it redirects to, is `localhost`, ends in `.localhost` or `.local`, or has
-  redirects to, is `localhost`, ends in `.localhost` or `.local`, or has an
+  an address in a blocked network (see `blocked_networks`); 502 when the
-  address in a blocked network (see `blocked_networks`); 502 when the upstream
+  upstream answered with an error status, and for 5 minutes after that for the
-  answered with an error status, and for 5 minutes after that for the same
+  same source URL; 503 when pixa is busy or in maintenance mode; 500 for any
-  source URL; 503 when pixa is busy or in maintenance mode; 500 for any other
+  other failure.
-  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

@@ -18,8 +18,7 @@ import (
 )
 
 // HandleImage handles the main image proxy route:
-// /v1/image/<host>/<path>/<width>x<height>.<format>, or with no format
+// /v1/image/<host>/<path>/<width>x<height>.<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 the default output format, so pixad does not start
+	// JPEG XL is to become the default output format, so pixad does not
-	// without it.
+	// start without it.
 	err := imageprocessor.CheckJPEGXLSupport()
 	if err != nil {
 		return nil, err

internal/server/routes.go

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