Save PNG compressed, WebP at effort 4 and AVIF at effort 1 (closes #232)

Each output format now has its own govips export with its settings
named, in place of govips' generic Export, which sent libvips a zero for
some settings it was not given: PNG had no compression and WebP effort
0. PNG now gets libvips' default compression, 6, and WebP its default
effort, 4. GIF and JPEG output is unchanged.

AVIF was at libvips' default effort, 4, which takes minutes for an
8192x8192 image with one libvips thread, far past the default
downstream_timeout. Effort 1, the lowest govips can set, takes about 51
seconds for an image of random pixels, the worst case, and WebP at 4
about 43. A 16-bit source gets 8 bits per sample, not libvips' 12, which
take over four times as long.

Model: opus-5-5

Dockerfile

@@ -17,13 +17,14 @@ COPY . .
 RUN golangci-lint run --config .golangci.yml ./...
 
 # Test phase. script/test builds it alone.
-# golang:1.25.4-alpine, 2026-02-25
+# golang:1.25.4-alpine3.22, 2026-02-25; the runtime stage uses Alpine 3.22 too
-FROM golang:1.25.4-alpine@sha256:d3f0cf7723f3429e3f9ed846243970b20a2de7bae6a5b66fc5914e228d831bbb AS test
+FROM golang:1.25.4-alpine3.22@sha256:d3f0cf7723f3429e3f9ed846243970b20a2de7bae6a5b66fc5914e228d831bbb AS test
 
 WORKDIR /src
 
-# script/bootstrap --cgo installs the build dependencies (a C compiler
+# script/bootstrap --cgo installs the build dependencies (a C compiler,
-# and the libvips and libheif headers) and downloads the Go modules.
+# the libvips and libheif headers, and libvips' JPEG XL support, which
+# the tests need) and downloads the Go modules.
 COPY script/ ./script/
 COPY go.mod go.sum ./
 RUN script/bootstrap --cgo
@@ -39,8 +40,8 @@ RUN go test -count=1 -timeout 90s -race -cover ./... || \
 # Build stage. Nothing is wanted from the two phases above: these copies
 # make BuildKit build them first, so this stage runs only when lint and
 # test passed.
-# golang:1.25.4-alpine, 2026-02-25
+# golang:1.25.4-alpine3.22, 2026-02-25; the runtime stage uses Alpine 3.22 too
-FROM golang:1.25.4-alpine@sha256:d3f0cf7723f3429e3f9ed846243970b20a2de7bae6a5b66fc5914e228d831bbb AS builder
+FROM golang:1.25.4-alpine3.22@sha256:d3f0cf7723f3429e3f9ed846243970b20a2de7bae6a5b66fc5914e228d831bbb AS builder
 
 COPY --from=lint /src/go.sum /dev/null
 COPY --from=test /src/go.sum /dev/null
@@ -76,13 +77,17 @@ RUN version="${VERSION:-$(git describe --tags --always)}"; \
         -o /pixad ./cmd/pixad
 
 # Runtime stage, and the last one: a plain `docker build .` builds this
-# stage and what it depends on, and nothing else.
+# stage and what it depends on, and nothing else. It must use the Alpine
-# alpine:3.21, 2026-02-25
+# release the golang image above is based on, so that pixad runs against
-FROM alpine:3.21@sha256:c3f8e73fdb79deaebaa2037150150191b9dcbfba68b4a46d70103204c53f4709
+# the libvips and musl it was built with.
+# alpine:3.22, 2026-10-08
+FROM alpine:3.22@sha256:5291449c3df73caf6ed85e649dec1b9e818b39a5d8c871e97afc13e9cd5e8fa8
 
-# Install runtime dependencies only
+# Install runtime dependencies only. vips-jxl is libvips' JPEG XL
+# support, without which pixad does not start.
 RUN apk add --no-cache \
     vips \
+    vips-jxl \
     libheif \
     ca-certificates \
     tzdata \

README.md

@@ -88,8 +88,11 @@ or with 1 when images were still being processed after those 5 seconds or
 another part of pixa failed to stop. A request not finished by then is cut off.
 `docker stop` waits 10 seconds before it kills the container.
 
-Outside Docker, pixa needs libvips (the image has 8.15) and libheif to run, as
+Outside Docker, pixa needs libvips (the image has 8.16) and libheif to run, as
-it uses libvips through CGO; building it also needs their development files,
+it uses libvips through CGO. pixad does not start unless libvips has its JPEG XL
+support, which on Alpine is the `vips-jxl` package and which the nix and brew
+packages of libvips include, as do the apt ones from Debian 12 and Ubuntu 24.04
+on. Building pixa also needs the development files of libvips and libheif,
 `pkg-config` and a C compiler. `script/bootstrap --cgo` installs all of these,
 as the `Dockerfile` does where it compiles pixa. Plain `script/bootstrap`, which
 `script/setup` and `script/cibuild` run, installs git, make and Go, and Node,
@@ -172,20 +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
@@ -228,10 +232,11 @@ proxy in front of pixa must pass that header on unchanged. A form body over 1
 MiB is refused with 413. The image routes answer the errors listed for them with
 JSON holding `error`, `status` and `timestamp`.
 
-An image URL has this form:
+An image URL has one of these forms, the second with no format:
 
 ```
 /v1/image/<host>/<path>/<size>.<format>?sig=<signature>&exp=<expiration>&q=<quality>&fit=<fit>
+/v1/image/<host>/<path>/<size>?sig=<signature>&exp=<expiration>&q=<quality>&fit=<fit>
 ```
 
 Images are only fetched from origins using TLS with valid certificates, unless
@@ -242,7 +247,9 @@ A request whose query string cannot be decoded, or gives any parameter more than
 once, is refused with 400.
 
 - `<format>`: one of `orig` (or `original`), `jpeg` (or `jpg`), `png`, `webp`,
-  `avif`, `gif`, or `auto` (below)
+  `avif`, `jxl` (JPEG XL), `gif`, or `auto` (below). A URL with no format (the
+  second form, with no dot after the size) is served as JPEG XL, the default, as
+  with `jxl`
 - `<size>`: `orig` or `<width>x<height>` (e.g. `800x600`)
 - `sig` and `exp`: the signature and its expiry, needed unless the host is
   allowlisted (see Signature Specification)
@@ -250,23 +257,29 @@ once, is refused with 400.
   both optional (values under Signature Specification). Both are part of what is
   cached, so each value of either is a separate cached image.
 
+The source image may be JPEG, PNG, GIF, WebP, AVIF, JPEG XL or SVG. The
+upstream's `Content-Type` must name its format, and the image's first bytes must
+match it.
+
 With the format `auto`, pixa chooses the format for each request from its
 `Accept` header, in this order:
 
-1. AVIF, when the header names `image/avif`;
+1. JPEG XL, when the header names `image/jxl`;
-2. WebP, when it names `image/webp`;
+2. AVIF, when it names `image/avif`;
-3. JPEG, when the first of `image/jpeg`, `image/*` and `*/*` that it names
+3. WebP, when it names `image/webp`;
+4. JPEG, when the first of `image/jpeg`, `image/*` and `*/*` that it names
    allows it, or when there is no `Accept` header or it is empty.
 
 An entry with `q=0` refuses its format; other `q` values do not change the
-order. AVIF and WebP must be named, as clients that cannot show them also send
+order. JPEG XL, AVIF and WebP must be named, as clients that cannot show them
-`image/*` and `*/*`. pixa never sends a format the client refused: when the
+also send `image/*` and `*/*`. pixa never sends a format the client refused:
-header allows none of the three, the answer is 406, and a header that does not
+when the header allows none of the four, the answer is 406, and a header that
-parse, or has a `q` that is not a number from 0 to 1, is refused with 400. The
+does not parse, or has a `q` that is not a number from 0 to 1, is refused
-signature, or the token of an encrypted URL, covers `auto` itself, so one URL
+with 400. The signature, or the token of an encrypted URL, covers `auto` itself,
-serves every client. Each format chosen is cached as a separate image, and every
+so one URL serves every client. Each format chosen is cached as a separate
-answer that depends on `Accept` (the image, a 304, and the 400 and 406 above)
+image, and every answer that depends on `Accept` (the image, a 304, and the 400
-carries `Vary: Accept`, so a shared cache keeps the formats apart too.
+and 406 above) carries `Vary: Accept`, so a shared cache keeps the formats apart
+too.
 
 An image is served with `Cache-Control: public, max-age=<seconds>, immutable`.
 When the URL has an expiry (an `exp`, or the TTL of an encrypted URL), `max-age`
@@ -312,13 +325,15 @@ nor change what it asks for.
    lasts 30 days, or until `/logout`.
 2. On the generator page, give the source image's URL, the width and height, the
    format, quality and fit, and how long the URL lasts, then submit the form
-   (`POST /generate`). Width and height both empty or `0` keep the original
+   (`POST /generate`). The format is JPEG XL unless another is chosen; a form
-   size; if only one of them is empty or `0`, that side is scaled to keep the
+   sent with an empty format, or none, also makes a JPEG XL URL. Width and
-   image's proportions.
+   height both empty or `0` keep the original size; if only one of them is empty
+   or `0`, that side is scaled to keep the image's proportions.
 3. The page shows the URL, `https://<host>/v1/e/<token>/img.<format>`, and when
    it expires. `<host>` is the host the page was opened on, and the URL starts
    with `http` instead while `debug` is on. The name after the token is ignored
-   and only gives the URL a file extension, `jpg` for `orig` and `auto`.
+   and only gives the URL a file extension, `jpg` for `orig` and `auto`, and
+   `jxl` for a form with no format.
 
 The token holds the source's host, path and query and the size, format, quality,
 fit and expiry, encrypted with a key derived from `signing_key`. The source
@@ -347,6 +362,10 @@ turned off.
 - An image with an ICC profile is converted to sRGB first, since clients show an
   image with no profile as sRGB. Colours outside sRGB, such as the most
   saturated ones in a Display P3 photo, are clipped.
+- The one exception is JPEG XL with libvips 8.16 and later: libvips then writes
+  an EXIF block of its own into the image, as govips cannot ask libvips to leave
+  it out. It holds the image's size and otherwise fixed values, such as an
+  orientation of 1 and a resolution of 72 dpi, and nothing from the source.
 
 ### Source Hosts
 
@@ -374,8 +393,9 @@ Where:
 - `width` — requested width in pixels, `0` for original
 - `height` — requested height in pixels, `0` for original
 - `format` — output format, one of those listed under Routes, with `original`
-  signed as `orig` and `jpg` as `jpeg`; `auto` is signed as `auto`, not as the
+  signed as `orig`, `jpg` as `jpeg`, and no format as `jxl`, so a URL with no
-  format chosen for the request
+  format has the signature of the same URL ending in `.jxl`; `auto` is signed as
+  `auto`, not as the format chosen for the request
 - `expiration` — the URL's `exp` query parameter, the Unix timestamp when the
   signature expires; a request whose `exp` is not a whole number, an empty
   `exp=` included, is refused with 400
@@ -583,8 +603,8 @@ provide:
 
 - `script/bootstrap` — install git, make, Go, Node, Yarn and prettier and
   download the Go modules (idempotent); with `--cgo`, the C compiler and the
-  libvips and libheif libraries that compiling pixa needs instead of Node, Yarn
+  libvips (with its JPEG XL support) and libheif libraries that compiling and
-  and prettier
+  testing pixa need instead of Node, Yarn and prettier
 - `script/setup` — make a fresh clone ready for development (bootstrap, then
   install-precommit)
 - `script/projectname` — output the project name ("pixa")

TODO.md

@@ -30,6 +30,51 @@ P2: security: per-IP rate limiting on the image routes
 
 # Completed Steps
 
+- 2026-10-08 every output format is saved with settings pixa sets on purpose
+  (closes #232): each format has its own govips export, as JPEG XL does, in
+  place of govips' generic `Export`, which sent libvips a zero for some settings
+  it was not given. PNG gets libvips' default compression, 6, where it had none,
+  and WebP libvips' default effort, 4, where it had 0. GIF was already at
+  libvips' default effort, 7, and JPEG output is unchanged. AVIF is saved at
+  effort 1, the lowest govips can set, where it had libvips' default, 4. With
+  one libvips thread, an 8192x8192 image of random pixels, the worst case, takes
+  about 51 seconds as AVIF at effort 1 and 43 as WebP at effort 4, against the
+  default `downstream_timeout` of 60 seconds. On an image of milder noise, which
+  AVIF at effort 1 saves in about 12 seconds, effort 4 takes minutes. AVIF is
+  also saved with 8 bits per sample from a 16-bit source, which libvips would
+  save with 12: a 16-bit 8192x8192 image of milder noise takes about 54 seconds
+  at effort 1 with 12 bits, nearly all of the default `downstream_timeout`, and
+  about 12 with 8.
+- 2026-10-08 JPEG XL is the default output (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 has the signature of the same URL
+  ending in `.jxl`. An encrypted URL whose token holds no format is served as
+  JPEG XL (`encurl.DefaultFormat`). The generator page selects JPEG XL until
+  another format is chosen, and a form with an empty format, or none, makes a
+  JPEG XL URL whose name ends in `.jxl`. The image processor no longer takes an
+  empty format as `orig`: both routes give every request a format, and it
+  refuses a request with none. `auto` still ends with JPEG.
+- 2026-10-08 JPEG XL as an input and output format (part of #222): a source
+  whose bytes start with either JPEG XL signature, the bare codestream's `FF 0A`
+  or the container's, is detected as `image/jxl`, which the upstream fetch
+  accepts; `orig` of such a source is JPEG XL. The format `jxl` works in plain
+  and encrypted URLs and on the generator page, served as `image/jxl` and cached
+  like the other formats. `auto` chooses JPEG XL first when `Accept` names
+  `image/jxl`. govips sends libvips a JPEG XL distance with every save, so
+  libvips ignores the quality: pixa turns `q` into a distance with libvips' own
+  formula, keeping 100 lossy, and removes the metadata from the image before
+  saving, as govips cannot have libvips strip it from JPEG XL. libvips 8.16 and
+  later still write an EXIF block of their own into JPEG XL, from the image's
+  size, orientation and resolution, and fixed values; the image is upright and
+  is given 72 dpi before the save, so the block holds nothing from the source.
+  An image with an ICC profile is converted to sRGB before the JPEG XL save too,
+  and a CMYK image with none is converted to sRGB, as libvips cannot save CMYK
+  as JPEG XL. libvips' default effort, 7, is kept. JPEG XL is not yet the
+  default output.
+- 2026-10-08 pixad runs on the Alpine release it is built on (closes #229): the
+  runtime stage of the `Dockerfile` uses `alpine:3.22`, the release of the
+  `golang:1.25.4-alpine3.22` image that the test phase and the build stage use,
+  so all three have libvips 8.16, where the runtime image had 8.15.
 - 2026-10-08 requests no longer wait behind eviction queries that read a whole
   table (closes #227): the new `cache_usage` table holds the total cache usage,
   kept up to date by triggers on `source_content` and `variant_content` in the
@@ -38,6 +83,14 @@ P2: security: per-IP rate limiting on the image routes
   and corrects the total when it differs, unless a row changed while it summed.
   Source rows get `last_accessed_at` when added, so choosing source images to
   evict reads that column's index instead of sorting the whole table.
+- 2026-10-08 libvips' JPEG XL support is installed and required (part of #222):
+  `script/bootstrap --cgo` installs `vips-jxl` when its package manager is apk,
+  as Alpine's `vips` package lacks the support, and the runtime stage of the
+  `Dockerfile` installs it too. `imgcache.NewService` fails, naming the fix,
+  when `imageprocessor.CheckJPEGXLSupport` finds that libvips cannot load and
+  save JPEG XL, so pixad does not start without it. A test saves an image as
+  JPEG XL with govips and loads it back. JPEG XL is not yet a format pixa
+  serves.
 - 2026-10-08 SQLite writes no longer fail with "database is locked" under load
   (closes #223): `internal/database` opens the database with one connection, so
   pixa's own reads and writes run on it one at a time instead of competing for

internal/encurl/encurl.go

@@ -14,7 +14,7 @@ import (
 // Default values for optional fields.
 const (
 	DefaultQuality = 85
-	DefaultFormat  = imgcache.FormatOriginal
+	DefaultFormat  = imgcache.FormatJXL
 	DefaultFitMode = imgcache.FitCover
 
 	// HKDF salt for URL encryption key derivation
@@ -37,7 +37,7 @@ type Payload struct {
 	SourceQuery string               `cbor:"q,omitempty"`  // optional
 	Width       int                  `cbor:"w,omitempty"`  // 0 = original
 	Height      int                  `cbor:"ht,omitempty"` // 0 = original
-	Format      imgcache.ImageFormat `cbor:"f,omitempty"`  // default: orig
+	Format      imgcache.ImageFormat `cbor:"f,omitempty"`  // default: jxl
 	Quality     int                  `cbor:"ql,omitempty"` // default: 85
 	FitMode     imgcache.FitMode     `cbor:"fm,omitempty"` // default: cover
 	ExpiresAt   int64                `cbor:"e,omitempty"`  // 0 = never expires

internal/handlers/auth.go

@@ -369,10 +369,15 @@ func (s *Handlers) buildGeneratedURL(r *http.Request, token, format string) stri
 		scheme = "http"
 	}
 
-	// Determine file extension for the trailing filename
+	// Determine file extension for the trailing filename. A form with no
+	// format makes a token with none, which is served as encurl.DefaultFormat.
 	ext := format
-	if ext == "" || ext == "orig" || ext == "auto" {
+
-		ext = "jpg" // Default extension
+	switch format {
+	case "":
+		ext = string(encurl.DefaultFormat)
+	case "orig", "auto":
+		ext = "jpg"
 	}
 
 	return scheme + "://" + r.Host + "/v1/e/" + url.PathEscape(token) + "/img." + ext

internal/handlers/format_auto.go

@@ -14,8 +14,8 @@ import (
 // Errors for an Accept header that an auto URL cannot be served for.
 var (
 	errInvalidAccept = errors.New("invalid Accept header")
-	errNotAcceptable = errors.New(
+	errNotAcceptable = errors.New("not acceptable: auto serves " +
-		"not acceptable: auto serves image/avif, image/webp or image/jpeg")
+		"image/jxl, image/avif, image/webp or image/jpeg")
 )
 
 // chooseAutoFormat replaces the format auto in req with the format
@@ -51,11 +51,11 @@ func (s *Handlers) chooseAutoFormat(
 }
 
 // formatForAccept returns the format an auto URL is served in for the Accept
-// header accept: AVIF when it names image/avif, else WebP when it names
+// header accept: JPEG XL when it names image/jxl, else AVIF when it names
-// image/webp, else JPEG when its most specific entry of image/jpeg, image/*
+// image/avif, else WebP when it names image/webp, else JPEG when its most
-// and */* allows it, or when it names nothing. A q of 0 refuses a format.
+// specific entry of image/jpeg, image/* and */* allows it, or when it names
-// AVIF and WebP must be named, as clients that cannot show them send image/*
+// nothing. A q of 0 refuses a format. JPEG XL, AVIF and WebP must be named, as
-// and */* too.
+// clients that cannot show them send image/* and */* too.
 func formatForAccept(accept string) (imgcache.ImageFormat, error) {
 	qualities, err := parseAccept(accept)
 	if err != nil {
@@ -66,6 +66,10 @@ func formatForAccept(accept string) (imgcache.ImageFormat, error) {
 		return imgcache.FormatJPEG, nil
 	}
 
+	if qualities["image/jxl"] > 0 {
+		return imgcache.FormatJXL, nil
+	}
+
 	if qualities["image/avif"] > 0 {
 		return imgcache.FormatAVIF, nil
 	}

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/handlers/jpegxl_default_internal_test.go

@@ -0,0 +1,162 @@
+package handlers
+
+import (
+	"fmt"
+	"log/slog"
+	"maps"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/davidbyttow/govips/v2/vips"
+
+	"sneak.berlin/go/pixa/internal/encurl"
+	"sneak.berlin/go/pixa/internal/imgcache"
+	"sneak.berlin/go/pixa/internal/signature"
+)
+
+// requireJPEGXL requires that rec answers 200 with a JPEG XL image.
+func requireJPEGXL(t *testing.T, rec *httptest.ResponseRecorder) {
+	t.Helper()
+
+	if rec.Code != http.StatusOK {
+		t.Fatalf("status = %d, want %d; body %q",
+			rec.Code, http.StatusOK, rec.Body.String())
+	}
+
+	if got := rec.Header().Get("Content-Type"); got != jxlType {
+		t.Errorf("Content-Type = %q, want %s", got, jxlType)
+	}
+
+	if got := vips.DetermineImageType(rec.Body.Bytes()); got != vips.ImageTypeJXL {
+		t.Errorf("body is %s, want jxl", vips.ImageTypes[got])
+	}
+}
+
+// TestImageWithoutFormat_ServesJPEGXL verifies that a /v1/image/ URL whose
+// last segment is a size with no format, 50x50 or orig, answers JPEG XL.
+func TestImageWithoutFormat_ServesJPEGXL(t *testing.T) {
+	t.Parallel()
+
+	route := newImageRoute(t, newPhotoFetcher(t, allowlistedHost))
+
+	for _, size := range []string{"50x50", "orig"} {
+		target := "/v1/image/" + allowlistedHost + photoPath + "/" + size
+		requireJPEGXL(t, sendGet(t, route, target))
+	}
+}
+
+// TestImageWithoutFormat_SignedAsJXL verifies that a /v1/image/ URL with no
+// format is signed as jxl: the signature made for the URL ending in .jxl is
+// accepted for the same URL without .jxl.
+func TestImageWithoutFormat_SignedAsJXL(t *testing.T) {
+	t.Parallel()
+
+	route := newImageRoute(t, newPhotoFetcher(t, signedHost))
+	expires := time.Now().Add(time.Hour)
+
+	sig := signature.New(testSigningKey).Sign(&signature.Request{
+		SourceHost: signedHost,
+		SourcePath: photoPath,
+		Width:      50,
+		Height:     50,
+		Format:     string(imgcache.FormatJXL),
+		Quality:    encurl.DefaultQuality,
+		FitMode:    string(imgcache.FitCover),
+		Expires:    expires,
+	})
+	query := fmt.Sprintf("?sig=%s&exp=%d", sig, expires.Unix())
+
+	for _, size := range []string{"50x50.jxl", "50x50"} {
+		target := "/v1/image/" + signedHost + photoPath + "/" + size + query
+		requireJPEGXL(t, sendGet(t, route, target))
+	}
+}
+
+// TestImageEncWithoutFormat_ServesJPEGXL verifies that an encrypted URL whose
+// token holds no format answers JPEG XL.
+func TestImageEncWithoutFormat_ServesJPEGXL(t *testing.T) {
+	t.Parallel()
+
+	h, srv := newSignedHostServer(t, slog.New(slog.DiscardHandler))
+
+	token, err := h.encGen.Generate(&encurl.Payload{
+		SourceHost: signedHost,
+		SourcePath: photoPath,
+		Width:      50,
+		Height:     50,
+	})
+	if err != nil {
+		t.Fatalf("Generate() error = %v", err)
+	}
+
+	requireJPEGXL(t, getEncToken(srv, token))
+}
+
+// TestGeneratorPage_SelectsJPEGXL verifies that the generator page's format
+// choice is JPEG XL until another is chosen.
+func TestGeneratorPage_SelectsJPEGXL(t *testing.T) {
+	t.Parallel()
+
+	h, srv := newCSRFTestRouter(t)
+
+	req := httptest.NewRequestWithContext(t.Context(), http.MethodGet, "/", nil)
+	req.AddCookie(newSessionCookie(t, h))
+
+	rec := httptest.NewRecorder()
+	srv.ServeHTTP(rec, req)
+
+	if !strings.Contains(rec.Body.String(), `<option value="jxl" selected>`) {
+		t.Errorf("generator page does not select JPEG XL: %s", rec.Body.String())
+	}
+}
+
+// TestGeneratePost_NoFormat_MakesJPEGXLURL verifies that the generator form
+// sent with an empty format field, or with none, makes a URL whose name ends
+// in .jxl and which answers JPEG XL.
+func TestGeneratePost_NoFormat_MakesJPEGXLURL(t *testing.T) {
+	t.Parallel()
+
+	photo := url.Values{
+		sourceURLField: {"https://" + signedHost + photoPath},
+		widthField:     {"50"},
+		heightField:    {"50"},
+	}
+
+	emptyFormat := maps.Clone(photo)
+	emptyFormat.Set(formatField, "")
+
+	for name, form := range map[string]url.Values{
+		"empty format field": emptyFormat,
+		"no format field":    photo,
+	} {
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+
+			_, imageSrv := newSignedHostServer(t, slog.New(slog.DiscardHandler))
+
+			rec := generatePost(t, form)
+
+			match := generatedURLPattern.FindStringSubmatch(rec.Body.String())
+			if match == nil {
+				t.Fatalf("generator page shows no URL: %d %s",
+					rec.Code, rec.Body.String())
+			}
+
+			t.Logf("generated URL path: %s", match[1])
+
+			if !strings.HasSuffix(match[1], "/img.jxl") {
+				t.Errorf("generated URL %s does not end in /img.jxl", match[1])
+			}
+
+			imageRec := httptest.NewRecorder()
+			imageSrv.ServeHTTP(imageRec, httptest.NewRequestWithContext(
+				t.Context(), http.MethodGet, match[1], nil))
+
+			requireJPEGXL(t, imageRec)
+		})
+	}
+}

internal/handlers/jpegxl_internal_test.go

@@ -0,0 +1,73 @@
+package handlers
+
+import (
+	"log/slog"
+	"net/http"
+	"testing"
+
+	"github.com/davidbyttow/govips/v2/vips"
+
+	"sneak.berlin/go/pixa/internal/imgcache"
+)
+
+// jxlType is the content type of JPEG XL.
+const jxlType = "image/jxl"
+
+// TestFormatForAccept_JPEGXL verifies that the format auto chooses JPEG XL
+// when Accept names image/jxl, ahead of AVIF whatever their q, and AVIF when
+// Accept refuses JPEG XL with q=0.
+func TestFormatForAccept_JPEGXL(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name   string
+		accept string
+		want   imgcache.ImageFormat
+	}{
+		{"JPEG XL-capable browser",
+			"image/jxl,image/avif,image/webp,image/*,*/*;q=0.8", imgcache.FormatJXL},
+		{"JPEG XL only", jxlType, imgcache.FormatJXL},
+		{"JPEG XL with a lower q than AVIF", "image/avif,image/jxl;q=0.5",
+			imgcache.FormatJXL},
+		{"q=0 on JPEG XL", "image/jxl;q=0,image/avif,*/*", imgcache.FormatAVIF},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			got, err := formatForAccept(tt.accept)
+			if got != tt.want || err != nil {
+				t.Errorf("formatForAccept(%q) = %q, %v, want %q",
+					tt.accept, got, err, tt.want)
+			}
+		})
+	}
+}
+
+// TestFormatAuto_JPEGXL requests an auto URL on each image route with an
+// Accept header that names image/jxl, and checks that the answer is a JPEG XL
+// image.
+func TestFormatAuto_JPEGXL(t *testing.T) {
+	t.Parallel()
+
+	h, srv := newSignedHostServer(t, slog.New(slog.DiscardHandler))
+	signedURL, encryptedURL := autoPhotoURLs(t, h)
+
+	for _, target := range []string{signedURL, encryptedURL} {
+		rec := requestImage(t, srv, http.MethodGet, target,
+			"image/jxl,image/avif,image/webp,*/*;q=0.8")
+		gotType := rec.Header().Get("Content-Type")
+
+		if rec.Code != http.StatusOK || gotType != jxlType {
+			t.Errorf("%s: %d %s, want 200 %s; body %s",
+				target, rec.Code, gotType, jxlType, rec.Body)
+
+			continue
+		}
+
+		if got := vips.DetermineImageType(rec.Body.Bytes()); got != vips.ImageTypeJXL {
+			t.Errorf("%s: body is %s, want jxl", target, vips.ImageTypes[got])
+		}
+	}
+}

internal/httpfetcher/httpfetcher.go

@@ -45,6 +45,7 @@ const (
 	contentTypeGIF         = "image/gif"
 	contentTypeWebP        = "image/webp"
 	contentTypeAVIF        = "image/avif"
+	contentTypeJXL         = "image/jxl"
 	contentTypeSVG         = "image/svg+xml"
 	contentTypeOctetStream = "application/octet-stream"
 )
@@ -156,6 +157,7 @@ func DefaultConfig() *Config {
 			contentTypeGIF,
 			contentTypeWebP,
 			contentTypeAVIF,
+			contentTypeJXL,
 			contentTypeSVG,
 		},
 		AllowHTTP:             false,

internal/httpfetcher/jpegxl_internal_test.go

@@ -0,0 +1,20 @@
+package httpfetcher
+
+import "testing"
+
+// TestJPEGXLContentType verifies that the fetcher accepts an upstream answer
+// of type image/jxl by default, and that the mock fetcher serves a .jxl file
+// as image/jxl.
+func TestJPEGXLContentType(t *testing.T) {
+	t.Parallel()
+
+	const jxlType = "image/jxl"
+
+	if !New(DefaultConfig()).isAllowedContentType(jxlType) {
+		t.Errorf("isAllowedContentType(%q) = false, want true", jxlType)
+	}
+
+	if got := detectContentTypeFromPath("images/photo.jxl"); got != jxlType {
+		t.Errorf("detectContentTypeFromPath(photo.jxl) = %q, want %q", got, jxlType)
+	}
+}

internal/httpfetcher/mock.go

@@ -109,6 +109,8 @@ func detectContentTypeFromPath(path string) string {
 		return contentTypeWebP
 	case strings.HasSuffix(path, ".avif"):
 		return contentTypeAVIF
+	case strings.HasSuffix(path, ".jxl"):
+		return contentTypeJXL
 	case strings.HasSuffix(path, ".svg"):
 		return contentTypeSVG
 	default:

internal/imageprocessor/empty_format_internal_test.go

@@ -0,0 +1,21 @@
+package imageprocessor
+
+import (
+	"bytes"
+	"errors"
+	"testing"
+)
+
+// TestImageProcessor_EmptyFormatRefused verifies that a request with no format
+// is refused, as both image routes give every request a format before it is
+// processed.
+func TestImageProcessor_EmptyFormatRefused(t *testing.T) {
+	t.Parallel()
+
+	_, err := New(Params{}).Process(
+		t.Context(), bytes.NewReader(createTestJPEG(t, 20, 20)), &Request{},
+	)
+	if !errors.Is(err, ErrUnsupportedOutputFormat) {
+		t.Errorf("Process() error = %v, want %v", err, ErrUnsupportedOutputFormat)
+	}
+}

internal/imageprocessor/encoder_settings_internal_test.go

@@ -0,0 +1,145 @@
+package imageprocessor
+
+import (
+	"bytes"
+	"image"
+	"image/color"
+	"image/png"
+	"testing"
+
+	"github.com/davidbyttow/govips/v2/vips"
+)
+
+// processedSize runs input through Process and returns the output's size in
+// bytes.
+func processedSize(t *testing.T, input []byte, req *Request) int64 {
+	t.Helper()
+
+	result, err := New(Params{}).Process(t.Context(), bytes.NewReader(input), req)
+	if err != nil {
+		t.Fatalf("Process() error = %v", err)
+	}
+
+	_ = result.Content.Close()
+
+	return result.ContentLength
+}
+
+// encodePNG encodes img as PNG with Go's encoder.
+func encodePNG(t *testing.T, img image.Image) []byte {
+	t.Helper()
+
+	var buf bytes.Buffer
+
+	err := png.Encode(&buf, img)
+	if err != nil {
+		t.Fatalf("failed to encode test PNG: %v", err)
+	}
+
+	return buf.Bytes()
+}
+
+// decode decodes input with vips, as Process does.
+func decode(t *testing.T, input []byte) *vips.ImageRef {
+	t.Helper()
+
+	img, err := vips.NewImageFromBuffer(input)
+	if err != nil {
+		t.Fatalf("failed to decode input: %v", err)
+	}
+
+	t.Cleanup(img.Close)
+
+	return img
+}
+
+// TestImageProcessor_PNGIsCompressed verifies that a PNG output is
+// compressed: a flat 200x150 image, 90,000 bytes of raw pixels, comes out at
+// a small fraction of that.
+func TestImageProcessor_PNGIsCompressed(t *testing.T) {
+	t.Parallel()
+
+	const width, height = 200, 150
+
+	flat := image.NewRGBA(image.Rect(0, 0, width, height))
+	for y := range height {
+		for x := range width {
+			flat.Set(x, y, color.RGBA{R: 40, G: 120, B: 200, A: 255})
+		}
+	}
+
+	size := processedSize(t, encodePNG(t, flat), &Request{Format: FormatPNG})
+
+	const rawBytes = width * height * 3
+	if size > rawBytes/10 {
+		t.Errorf("PNG output is %d bytes, want under a tenth of its %d raw",
+			size, rawBytes)
+	}
+}
+
+// TestImageProcessor_WebPAtDefaultEffort verifies that WebP is saved at
+// libvips' default effort, 4: the output is the size of the same image saved
+// at that effort.
+func TestImageProcessor_WebPAtDefaultEffort(t *testing.T) {
+	t.Parallel()
+
+	input := createTestJPEG(t, 200, 150)
+
+	size := processedSize(t, input, &Request{Format: FormatWebP, Quality: 85})
+
+	want, _, err := decode(t, input).ExportWebp(&vips.WebpExportParams{
+		StripMetadata:   true,
+		Quality:         85,
+		ReductionEffort: 4,
+	})
+	if err != nil {
+		t.Fatalf("ExportWebp() error = %v", err)
+	}
+
+	if size != int64(len(want)) {
+		t.Errorf("WebP output is %d bytes, want %d, the size at effort 4",
+			size, len(want))
+	}
+}
+
+// TestImageProcessor_AVIFAtEffort1 verifies that AVIF is saved at effort 1
+// with 8 bits per sample: the output is the size of the same image saved
+// with those settings. The source is 16-bit, which libvips saves with 12
+// bits when it is not given a bit depth, and 640x480: on a small image,
+// such as 64x48, efforts 1 and 2 give the same output.
+func TestImageProcessor_AVIFAtEffort1(t *testing.T) {
+	t.Parallel()
+
+	const width, height = 640, 480
+
+	source := image.NewRGBA64(image.Rect(0, 0, width, height))
+	for y := range height {
+		for x := range width {
+			source.Set(x, y, color.RGBA64{
+				R: uint16((x * 65535 / width) & 0xffff),
+				G: uint16((y * 65535 / height) & 0xffff),
+				B: 32768,
+				A: 65535,
+			})
+		}
+	}
+
+	input := encodePNG(t, source)
+
+	size := processedSize(t, input, &Request{Format: FormatAVIF, Quality: 85})
+
+	want, _, err := decode(t, input).ExportAvif(&vips.AvifExportParams{
+		StripMetadata: true,
+		Quality:       85,
+		Effort:        1,
+		Bitdepth:      8,
+	})
+	if err != nil {
+		t.Fatalf("ExportAvif() error = %v", err)
+	}
+
+	if size != int64(len(want)) {
+		t.Errorf("AVIF output is %d bytes, want %d, the size at effort 1 "+
+			"and 8 bits", size, len(want))
+	}
+}

internal/imageprocessor/imageprocessor.go

@@ -37,6 +37,24 @@ func initVips() {
 	})
 }
 
+// errNoJPEGXL is returned by CheckJPEGXLSupport.
+var errNoJPEGXL = errors.New("libvips lacks JPEG XL support: install " +
+	"vips-jxl on Alpine, or use a libvips built with libjxl")
+
+// CheckJPEGXLSupport returns an error, naming the fix, when libvips
+// cannot load and save JPEG XL.
+func CheckJPEGXLSupport() error {
+	initVips()
+
+	// govips counts a format as supported when libvips has its loader;
+	// libvips builds the JPEG XL loader and saver together.
+	if !vips.IsTypeSupported(vips.ImageTypeJXL) {
+		return errNoJPEGXL
+	}
+
+	return nil
+}
+
 // Format represents supported output image formats.
 type Format string
 
@@ -47,6 +65,7 @@ const (
 	FormatPNG      Format = "png"
 	FormatWebP     Format = "webp"
 	FormatAVIF     Format = "avif"
+	FormatJXL      Format = "jxl"
 	FormatGIF      Format = "gif"
 )
 
@@ -237,9 +256,9 @@ func (p *ImageProcessor) Process(
 		}
 	}
 
-	// Determine output format
+	// orig is the source's own format; encode refuses an empty format
 	outputFormat := req.Format
-	if outputFormat == FormatOriginal || outputFormat == "" {
+	if outputFormat == FormatOriginal {
 		outputFormat = p.formatFromString(inputFormat)
 	}
 
@@ -287,6 +306,7 @@ const (
 	mimeGIF  = "image/gif"
 	mimeWebP = "image/webp"
 	mimeAVIF = "image/avif"
+	mimeJXL  = "image/jxl"
 )
 
 // SupportedInputFormats returns MIME types this processor can read.
@@ -297,6 +317,7 @@ func (p *ImageProcessor) SupportedInputFormats() []string {
 		mimeGIF,
 		mimeWebP,
 		mimeAVIF,
+		mimeJXL,
 	}
 }
 
@@ -308,6 +329,7 @@ func (p *ImageProcessor) SupportedOutputFormats() []Format {
 		FormatGIF,
 		FormatWebP,
 		FormatAVIF,
+		FormatJXL,
 	}
 }
 
@@ -324,6 +346,8 @@ func FormatToMIME(format Format) string {
 		return mimeGIF
 	case FormatAVIF:
 		return mimeAVIF
+	case FormatJXL:
+		return mimeJXL
 	case FormatOriginal:
 		return "application/octet-stream"
 	default:
@@ -393,9 +417,11 @@ func (p *ImageProcessor) detectFormat(img *vips.ImageRef) string {
 		return "webp"
 	case vips.ImageTypeAVIF, vips.ImageTypeHEIF:
 		return string(FormatAVIF)
+	case vips.ImageTypeJXL:
+		return string(FormatJXL)
 	case vips.ImageTypeUnknown, vips.ImageTypeMagick, vips.ImageTypePDF,
 		vips.ImageTypeSVG, vips.ImageTypeTIFF, vips.ImageTypeBMP,
-		vips.ImageTypeJP2K, vips.ImageTypeJXL:
+		vips.ImageTypeJP2K:
 		return "unknown"
 	default:
 		return "unknown"
@@ -467,44 +493,6 @@ func (p *ImageProcessor) encode(
 		quality = defaultQuality
 	}
 
-	var params vips.ExportParams
-
-	switch format {
-	case FormatJPEG:
-		params = vips.ExportParams{
-			Format:  vips.ImageTypeJPEG,
-			Quality: quality,
-		}
-
-	case FormatPNG:
-		params = vips.ExportParams{
-			Format: vips.ImageTypePNG,
-		}
-
-	case FormatGIF:
-		params = vips.ExportParams{
-			Format: vips.ImageTypeGIF,
-		}
-
-	case FormatWebP:
-		params = vips.ExportParams{
-			Format:  vips.ImageTypeWEBP,
-			Quality: quality,
-		}
-
-	case FormatAVIF:
-		params = vips.ExportParams{
-			Format:  vips.ImageTypeAVIF,
-			Quality: quality,
-		}
-
-	case FormatOriginal:
-		return nil, fmt.Errorf("%w: %s", ErrUnsupportedOutputFormat, format)
-
-	default:
-		return nil, fmt.Errorf("%w: %s", ErrUnsupportedOutputFormat, format)
-	}
-
 	// Stripping drops the ICC profile as well, and clients show an image
 	// with no profile as sRGB, so convert to sRGB first. "srgb" names
 	// libvips' built-in profile; govips' own sRGB path variable is set on
@@ -516,11 +504,166 @@ func (p *ImageProcessor) encode(
 		}
 	}
 
-	// Drop EXIF, XMP, IPTC and the ICC profile. govips ignores this for
+	switch format {
-	// GIF, which carries none of them.
+	case FormatJPEG:
-	params.StripMetadata = true
+		return exportJPEG(img, quality)
 
-	output, _, err := img.Export(&params)
+	case FormatPNG:
+		return exportPNG(img)
+
+	case FormatGIF:
+		return exportGIF(img)
+
+	case FormatWebP:
+		return exportWebP(img, quality)
+
+	case FormatAVIF:
+		return exportAVIF(img, quality)
+
+	case FormatJXL:
+		return exportJXL(img, quality)
+
+	case FormatOriginal:
+		return nil, fmt.Errorf("%w: %s", ErrUnsupportedOutputFormat, format)
+
+	default:
+		return nil, fmt.Errorf("%w: %s", ErrUnsupportedOutputFormat, format)
+	}
+}
+
+// govips sends libvips Go's zero value for some settings an export leaves
+// out, such as no compression at all for PNG, so each export below sets
+// every setting whose zero value is not what pixa wants. Stripping metadata
+// drops EXIF, XMP, IPTC and the ICC profile.
+
+// exportJPEG encodes img as JPEG at quality, without metadata. The settings
+// it leaves out are at libvips' defaults.
+func exportJPEG(img *vips.ImageRef, quality int) ([]byte, error) {
+	output, _, err := img.ExportJpeg(&vips.JpegExportParams{
+		StripMetadata: true,
+		Quality:       quality,
+	})
+
+	return output, err
+}
+
+// pngCompression is libvips' default PNG compression, from 0 (none) to 9.
+const pngCompression = 6
+
+// exportPNG encodes img as PNG at libvips' default compression and row
+// filter, without metadata.
+func exportPNG(img *vips.ImageRef) ([]byte, error) {
+	output, _, err := img.ExportPng(&vips.PngExportParams{
+		StripMetadata: true,
+		Compression:   pngCompression,
+		Filter:        vips.PngFilterNone,
+	})
+
+	return output, err
+}
+
+// gifEffort is libvips' default GIF effort, from 1 to 10.
+const gifEffort = 7
+
+// exportGIF encodes img as GIF at libvips' default effort. govips cannot
+// have libvips strip metadata from GIF, which carries none.
+func exportGIF(img *vips.ImageRef) ([]byte, error) {
+	output, _, err := img.ExportGIF(&vips.GifExportParams{Effort: gifEffort})
+
+	return output, err
+}
+
+// webpEffort is libvips' default WebP effort, from 0 (fastest) to 6.
+const webpEffort = 4
+
+// exportWebP encodes img as lossy WebP at quality and libvips' default
+// effort, without metadata.
+func exportWebP(img *vips.ImageRef, quality int) ([]byte, error) {
+	output, _, err := img.ExportWebp(&vips.WebpExportParams{
+		StripMetadata:   true,
+		Quality:         quality,
+		ReductionEffort: webpEffort,
+	})
+
+	return output, err
+}
+
+// avifEffort is the AVIF effort, from 0 (fastest) to 9; 1 is the lowest
+// govips can set. With one thread, as pixad runs libvips, 1 takes about 51
+// seconds to save an 8192x8192 image of random pixels, the worst case,
+// against the default downstream_timeout of 60 seconds. On an image of
+// milder noise, which 1 saves in about 12 seconds, 2 takes nearly a minute
+// and libvips' default, 4, takes minutes.
+const avifEffort = 1
+
+// avifBitdepth is the AVIF bit depth, 8 bits per sample for every image.
+// libvips would save a 16-bit image with 12, but at avifEffort that takes
+// about 54 seconds for a 16-bit 8192x8192 image of milder noise, nearly all
+// of the default downstream_timeout, and about 12 seconds with 8.
+const avifBitdepth = 8
+
+// exportAVIF encodes img as lossy AVIF at quality, avifEffort and
+// avifBitdepth, without metadata.
+func exportAVIF(img *vips.ImageRef, quality int) ([]byte, error) {
+	output, _, err := img.ExportAvif(&vips.AvifExportParams{
+		StripMetadata: true,
+		Quality:       quality,
+		Effort:        avifEffort,
+		Bitdepth:      avifBitdepth,
+	})
+
+	return output, err
+}
+
+// jxlResolution is the resolution every JPEG XL image is saved with, in
+// pixels per millimetre as libvips counts it: 72 dpi, what libvips gives a
+// JPEG that names none.
+const jxlResolution = 72 / 25.4
+
+// exportJXL encodes img as JPEG XL at quality, with libvips' default effort
+// and without metadata. govips sends libvips a distance, the JPEG XL
+// encoder's own measure of quality, along with the quality, and libvips then
+// uses the distance alone, so the quality is also given as a distance.
+func exportJXL(img *vips.ImageRef, quality int) ([]byte, error) {
+	// libvips converts a CMYK image to sRGB before it saves WebP, AVIF or
+	// PNG, but cannot save one as JPEG XL. encode has already converted
+	// any image with an ICC profile to sRGB, so this is CMYK with none.
+	if img.Interpretation() == vips.InterpretationCMYK {
+		err := img.ToColorSpace(vips.InterpretationSRGB)
+		if err != nil {
+			return nil, fmt.Errorf("failed to convert CMYK to sRGB: %w", err)
+		}
+	}
+
+	// govips cannot make libvips strip metadata from JPEG XL, so it is
+	// removed from the image itself. RemoveMetadata removes EXIF, XMP and
+	// IPTC but keeps the ICC profile.
+	err := img.RemoveMetadata()
+	if err != nil {
+		return nil, err
+	}
+
+	err = img.RemoveICCProfile()
+	if err != nil {
+		return nil, err
+	}
+
+	// libvips 8.16 and later still write an EXIF block of their own, from
+	// the image's size, orientation and resolution, and fixed values. The
+	// image is upright, so its orientation is 1, but its resolution is still
+	// the source's.
+	toSave, err := img.CopyChangingResolution(jxlResolution, jxlResolution)
+	if err != nil {
+		return nil, err
+	}
+
+	defer toSave.Close()
+
+	params := vips.NewJxlExportParams()
+	params.Quality = quality
+	params.Distance = jxlDistance(quality)
+
+	output, _, err := toSave.ExportJxl(params)
 	if err != nil {
 		return nil, err
 	}
@@ -528,6 +671,22 @@ func (p *ImageProcessor) encode(
 	return output, nil
 }
 
+// jxlDistance turns a quality from 1 to 100 into the JPEG XL encoder's
+// distance, with the formula libvips and libjxl use for their own quality
+// setting, except that 100 stays lossy (distance 0.1) where libjxl makes it
+// lossless.
+//
+//nolint:mnd // the constants of that formula
+func jxlDistance(quality int) float64 {
+	q := float64(quality)
+
+	if quality >= 30 {
+		return 0.1 + (100-q)*0.09
+	}
+
+	return 53.0/3000.0*q*q - 23.0/20.0*q + 25.0
+}
+
 // formatFromString converts a format string to Format.
 func (p *ImageProcessor) formatFromString(format string) Format {
 	switch format {
@@ -541,6 +700,8 @@ func (p *ImageProcessor) formatFromString(format string) Format {
 		return FormatWebP
 	case string(FormatAVIF):
 		return FormatAVIF
+	case string(FormatJXL):
+		return FormatJXL
 	default:
 		return FormatJPEG
 	}

internal/imageprocessor/jpegxl_internal_test.go

@@ -0,0 +1,52 @@
+package imageprocessor
+
+import (
+	"testing"
+
+	"github.com/davidbyttow/govips/v2/vips"
+)
+
+// TestCheckJPEGXLSupport fails when libvips lacks JPEG XL support, as on
+// Alpine without the vips-jxl package.
+func TestCheckJPEGXLSupport(t *testing.T) {
+	t.Parallel()
+
+	err := CheckJPEGXLSupport()
+	if err != nil {
+		t.Fatalf("CheckJPEGXLSupport() error = %v", err)
+	}
+}
+
+// TestLibvipsSavesAndLoadsJPEGXL saves an image as JPEG XL with govips and
+// loads it back. It fails when libvips lacks JPEG XL support, as on Alpine
+// without the vips-jxl package.
+func TestLibvipsSavesAndLoadsJPEGXL(t *testing.T) {
+	t.Parallel()
+
+	img, err := vips.NewImageFromBuffer(createTestJPEG(t, 64, 48))
+	if err != nil {
+		t.Fatalf("failed to load test JPEG: %v", err)
+	}
+
+	defer img.Close()
+
+	jxl, _, err := img.ExportJxl(vips.NewJxlExportParams())
+	if err != nil {
+		t.Fatalf("ExportJxl() error = %v", err)
+	}
+
+	loaded, err := vips.NewImageFromBuffer(jxl)
+	if err != nil {
+		t.Fatalf("failed to load the JPEG XL image: %v", err)
+	}
+
+	defer loaded.Close()
+
+	if loaded.Format() != vips.ImageTypeJXL {
+		t.Errorf("loaded format = %s, want jxl", vips.ImageTypes[loaded.Format()])
+	}
+
+	if loaded.Width() != 64 || loaded.Height() != 48 {
+		t.Errorf("loaded size = %dx%d, want 64x48", loaded.Width(), loaded.Height())
+	}
+}

internal/imageprocessor/jpegxl_output_internal_test.go

@@ -0,0 +1,244 @@
+package imageprocessor
+
+import (
+	"bytes"
+	"io"
+	"math"
+	"os"
+	"testing"
+
+	"github.com/davidbyttow/govips/v2/vips"
+)
+
+// TestImageProcessor_EncodeJPEGXL converts a JPEG to a smaller JPEG XL and
+// checks the content type, and the format and size the output loads as.
+func TestImageProcessor_EncodeJPEGXL(t *testing.T) {
+	t.Parallel()
+
+	req := &Request{Size: Size{Width: 100, Height: 75}, Format: FormatJXL}
+
+	result, err := New(Params{}).Process(
+		t.Context(), bytes.NewReader(createTestJPEG(t, 200, 150)), req,
+	)
+	if err != nil {
+		t.Fatalf("Process() error = %v", err)
+	}
+
+	defer func() { _ = result.Content.Close() }()
+
+	if result.ContentType != "image/jxl" {
+		t.Errorf("ContentType = %q, want image/jxl", result.ContentType)
+	}
+
+	data, err := io.ReadAll(result.Content)
+	if err != nil {
+		t.Fatalf("failed to read result: %v", err)
+	}
+
+	output, err := vips.NewImageFromBuffer(data)
+	if err != nil {
+		t.Fatalf("failed to load the output: %v", err)
+	}
+
+	defer output.Close()
+
+	if output.Format() != vips.ImageTypeJXL {
+		t.Errorf("output format = %s, want jxl", vips.ImageTypes[output.Format()])
+	}
+
+	if output.Width() != 100 || output.Height() != 75 {
+		t.Errorf("output size = %dx%d, want 100x75", output.Width(), output.Height())
+	}
+}
+
+// TestImageProcessor_JPEGXLQuality verifies that the quality reaches the JPEG
+// XL encoder: the same image comes out smaller at quality 30 than at 90.
+func TestImageProcessor_JPEGXLQuality(t *testing.T) {
+	t.Parallel()
+
+	input := createTestJPEG(t, 400, 300)
+	outputBytes := make(map[int]int64)
+
+	for _, quality := range []int{30, 90} {
+		result, err := New(Params{}).Process(t.Context(),
+			bytes.NewReader(input), &Request{Format: FormatJXL, Quality: quality})
+		if err != nil {
+			t.Fatalf("Process() at quality %d error = %v", quality, err)
+		}
+
+		_ = result.Content.Close()
+		outputBytes[quality] = result.ContentLength
+	}
+
+	if outputBytes[30] >= outputBytes[90] {
+		t.Errorf("%d bytes at quality 30, %d at 90, want fewer at 30",
+			outputBytes[30], outputBytes[90])
+	}
+}
+
+// TestImageProcessor_JPEGXLDropsSourceEXIF verifies that none of the source's
+// EXIF reaches a JPEG XL output. libvips 8.16 and later write an EXIF block of
+// their own into JPEG XL (orientation, resolution, size, colour space and
+// fixed defaults), and govips cannot ask them to leave it out, so the test
+// looks for the source's fields rather than for no EXIF at all.
+func TestImageProcessor_JPEGXLDropsSourceEXIF(t *testing.T) {
+	t.Parallel()
+
+	input, err := os.ReadFile("testdata/gps-exif.jpg")
+	if err != nil {
+		t.Fatalf("failed to read test JPEG: %v", err)
+	}
+
+	exif := processAndDecode(t, input, &Request{Format: FormatJXL}).GetExif()
+
+	for _, field := range []string{
+		"exif-ifd0-Make", "exif-ifd0-Model", "exif-ifd2-BodySerialNumber",
+		"exif-ifd2-DateTimeOriginal", "exif-ifd3-GPSLatitude",
+		"exif-ifd3-GPSLongitude",
+	} {
+		if value, found := exif[field]; found {
+			t.Errorf("output has %s: %s", field, value)
+		}
+	}
+}
+
+// TestImageProcessor_JPEGXLDropsSourceResolution verifies that the source's
+// resolution does not reach the EXIF block libvips 8.16 and later write into
+// JPEG XL. A JPEG XL image holds its resolution in that block alone, so the
+// resolution the output loads with is the block's.
+func TestImageProcessor_JPEGXLDropsSourceResolution(t *testing.T) {
+	t.Parallel()
+
+	// dpi-300.jpg is a flat 8x8 grey image with a resolution of 300 dpi.
+	input, err := os.ReadFile("testdata/dpi-300.jpg")
+	if err != nil {
+		t.Fatalf("failed to read test JPEG: %v", err)
+	}
+
+	output := processAndDecode(t, input, &Request{Format: FormatJXL})
+
+	// libvips gives the resolution in pixels per millimetre.
+	xDPI := math.Round(output.ResX() * 25.4)
+	yDPI := math.Round(output.ResY() * 25.4)
+
+	if xDPI == 300 || yDPI == 300 {
+		t.Errorf("output resolution = %vx%v dpi, the source's", xDPI, yDPI)
+	}
+}
+
+// TestImageProcessor_JPEGXLAppliesEXIFOrientation verifies that a JPEG XL
+// output is turned upright, as TestImageProcessor_AppliesEXIFOrientation does
+// for PNG.
+func TestImageProcessor_JPEGXLAppliesEXIFOrientation(t *testing.T) {
+	t.Parallel()
+
+	// orientation-6.jpg is stored 16x8, red on the left and blue on the
+	// right, with EXIF orientation 6 (turn 90 degrees clockwise to view).
+	// Upright it is 8x16, red on top and blue below.
+	input, err := os.ReadFile("testdata/orientation-6.jpg")
+	if err != nil {
+		t.Fatalf("failed to read test JPEG: %v", err)
+	}
+
+	output := processAndDecode(t, input, &Request{Format: FormatJXL})
+
+	if output.Width() != 8 || output.Height() != 16 {
+		t.Fatalf("output is %dx%d, want 8x16", output.Width(), output.Height())
+	}
+
+	top, err := output.GetPoint(4, 0)
+	if err != nil {
+		t.Fatalf("GetPoint() error = %v", err)
+	}
+
+	bottom, err := output.GetPoint(4, 15)
+	if err != nil {
+		t.Fatalf("GetPoint() error = %v", err)
+	}
+
+	if top[0] <= top[2] || bottom[2] <= bottom[0] {
+		t.Errorf("top pixel = %v, bottom pixel = %v, want red above blue",
+			top, bottom)
+	}
+}
+
+// TestImageProcessor_JPEGXLConvertsWideGamutToSRGB verifies that a JPEG XL
+// output is converted to sRGB, as TestImageProcessor_ConvertsWideGamutToSRGB
+// does for PNG. It does not check for an ICC profile, as libvips reports one
+// for every JPEG XL image it loads.
+func TestImageProcessor_JPEGXLConvertsWideGamutToSRGB(t *testing.T) {
+	t.Parallel()
+
+	// display-p3.jpg is a flat 8x8 image with the Display P3 profile
+	// embedded, filled with Display P3 (234, 51, 35), which is sRGB red.
+	input, err := os.ReadFile("testdata/display-p3.jpg")
+	if err != nil {
+		t.Fatalf("failed to read test JPEG: %v", err)
+	}
+
+	output := processAndDecode(t, input, &Request{Format: FormatJXL})
+
+	pixel, err := output.GetPoint(4, 4)
+	if err != nil {
+		t.Fatalf("GetPoint() error = %v", err)
+	}
+
+	want := []float64{255, 0, 0}
+	for i := range want {
+		if math.Abs(pixel[i]-want[i]) > 5 {
+			t.Fatalf("pixel = %v, want within 5 of %v", pixel, want)
+		}
+	}
+}
+
+// TestImageProcessor_JPEGXLFromCMYK verifies that a CMYK JPEG with no ICC
+// profile can be served as JPEG XL, in sRGB.
+func TestImageProcessor_JPEGXLFromCMYK(t *testing.T) {
+	t.Parallel()
+
+	// cmyk.jpg is a flat 8x8 CMYK image with no ICC profile, filled with
+	// full cyan and no magenta, yellow or black.
+	input, err := os.ReadFile("testdata/cmyk.jpg")
+	if err != nil {
+		t.Fatalf("failed to read test JPEG: %v", err)
+	}
+
+	output := processAndDecode(t, input, &Request{Format: FormatJXL})
+
+	if output.Bands() != 3 {
+		t.Fatalf("output has %d bands, want 3", output.Bands())
+	}
+
+	pixel, err := output.GetPoint(4, 4)
+	if err != nil {
+		t.Fatalf("GetPoint() error = %v", err)
+	}
+
+	// Cyan in sRGB: little red, much green and blue.
+	if pixel[0] > 50 || pixel[1] < 100 || pixel[2] < 200 {
+		t.Errorf("pixel = %v, want cyan", pixel)
+	}
+}
+
+// TestJXLDistance verifies the JPEG XL distance for a few qualities: 90 is
+// distance 1, the encoder's own default, and 100 stays lossy.
+func TestJXLDistance(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		quality int
+		want    float64
+	}{
+		{quality: 100, want: 0.1},
+		{quality: 90, want: 1},
+		{quality: 30, want: 6.4},
+		{quality: 20, want: 9.0667},
+	}
+
+	for _, tt := range tests {
+		got := jxlDistance(tt.quality)
+		if math.Abs(got-tt.want) > 0.0001 {
+			t.Errorf("jxlDistance(%d) = %v, want %v", tt.quality, got, tt.want)
+		}
+	}
+}

internal/imgcache/cache.go

@@ -96,6 +96,17 @@ type Cache struct {
 	// deterministically pause inside that window to exercise
 	// concurrent stores against it; production code leaves it nil.
 	evictSourceBlobTestHook func(ContentHash)
+
+	// reconciliationPageSize is the most rows one read of a content table
+	// returns in the reconciliation pass and in Stats. newCache sets it to
+	// defaultReconciliationPageSize; tests set it smaller.
+	reconciliationPageSize int
+
+	// reconciliationReadTestHook, when set, is called after each of those
+	// reads with the number of rows the read covered, so tests can check
+	// that no read covers more than one page; production code leaves it
+	// nil.
+	reconciliationReadTestHook func(rows int)
 }
 
 // NewCache creates a new cache instance.
@@ -127,6 +138,8 @@ func newCache(
 		evictionDone:     make(chan struct{}),
 		metaCache:        metaCache,
 		contentLocks:     newContentLock(),
+
+		reconciliationPageSize: defaultReconciliationPageSize,
 	}
 
 	if c.disabled {

internal/imgcache/cache_usage_internal_test.go

@@ -2,7 +2,7 @@ package imgcache
 
 import (
 	"bytes"
-	"fmt"
+	"strconv"
 	"strings"
 	"testing"
 )
@@ -148,64 +148,43 @@ func TestUsageTotalNotCorrectedFromAnOlderSum(t *testing.T) {
 	}
 }
 
-// TestReconciliationReadsAPageAtATime adds one row more than a page to
+// TestReconciliationReadsAPageAtATime stores five source images and five
-// each content table, none of them with a file. Each reconciliation read
+// variants, sets the page size to two rows and runs a reconciliation
-// must return one page at most, so a request's query waits for one page
+// pass. No read the pass makes of a content table, to check its rows or
-// at most, and the pass must still reach every row: it sums all of them
+// to sum them, may cover more than two rows, so a request's query waits
-// and drops all of them.
+// for one page at most. Between them the reads must still cover every
+// row of both tables twice, once to check it and once to sum it, and the
+// sum must put a wrong total right.
 func TestReconciliationReadsAPageAtATime(t *testing.T) {
 	t.Parallel()
 
 	cache, _ := newEvictionTestCache(t, 1<<30)
 	ctx := t.Context()
 
-	const rowsPerTable = reconciliationPageSize + 1
+	const pageSize = 2
 
-	for i := range rowsPerTable {
+	cache.reconciliationPageSize = pageSize
-		_, err := cache.db.ExecContext(ctx, `
-			INSERT INTO variant_content (cache_key, size_bytes, content_type)
-			VALUES (?, 1, ?)
-		`, fmt.Sprintf("%012x", i), testContentTypeWebP)
-		if err != nil {
-			t.Fatalf("failed to insert variant row %d: %v", i, err)
-		}
 
-		_, err = cache.db.ExecContext(ctx, `
+	// Sources of 100 bytes and variants of 10, five of each.
-			INSERT INTO source_content (content_hash, content_type, size_bytes)
+	for i := range 5 {
-			VALUES (?, ?, 1)
+		content := []byte(strconv.Itoa(i))
-		`, fmt.Sprintf("%064x", i), testContentTypeJPEG)
+
-		if err != nil {
+		storeEvictionTestSource(t, cache, "pages.example.com",
-			t.Fatalf("failed to insert source row %d: %v", i, err)
+			"/"+strconv.Itoa(i)+".jpg", bytes.Repeat(content, 100))
-		}
+		storeEvictionTestVariant(t, cache, VariantKey("aabbccdd000"+strconv.Itoa(i)),
+			bytes.Repeat(content, 10))
 	}
 
-	keys, err := cache.variantKeysAfter(ctx, "")
+	_, err := cache.db.ExecContext(ctx,
+		`UPDATE cache_usage SET total_size_bytes = 1 WHERE id = 1`)
 	if err != nil {
-		t.Fatalf("variantKeysAfter failed: %v", err)
+		t.Fatalf("failed to set a wrong total: %v", err)
 	}
 
-	if len(keys) != reconciliationPageSize {
+	var rowsPerRead []int
-		t.Errorf("one read returned %d variant keys, want %d",
-			len(keys), reconciliationPageSize)
-	}
 
-	hashes, err := cache.sourceContentHashesAfter(ctx, "")
+	cache.reconciliationReadTestHook = func(rows int) {
-	if err != nil {
+		rowsPerRead = append(rowsPerRead, rows)
-		t.Fatalf("sourceContentHashesAfter failed: %v", err)
-	}
-
-	if len(hashes) != reconciliationPageSize {
-		t.Errorf("one read returned %d source hashes, want %d",
-			len(hashes), reconciliationPageSize)
-	}
-
-	sum, err := cache.sumContentSizeBytes(ctx)
-	if err != nil {
-		t.Fatalf("sumContentSizeBytes failed: %v", err)
-	}
-
-	if sum != 2*rowsPerTable {
-		t.Errorf("sumContentSizeBytes() = %d, want %d", sum, 2*rowsPerTable)
 	}
 
 	err = cache.reconcileAccounting(ctx)
@@ -213,12 +192,31 @@ func TestReconciliationReadsAPageAtATime(t *testing.T) {
 		t.Fatalf("reconcileAccounting failed: %v", err)
 	}
 
-	if n := countRows(t, cache, `SELECT COUNT(*) FROM variant_content`); n != 0 {
+	t.Logf("rows covered by each read, in order: %v", rowsPerRead)
-		t.Errorf("%d variant rows without a file are left, want 0", n)
+
+	coveredRows := 0
+
+	for _, rows := range rowsPerRead {
+		if rows > pageSize {
+			t.Errorf("a read covered %d rows, want at most %d", rows, pageSize)
+		}
+
+		coveredRows += rows
 	}
 
-	if n := countRows(t, cache, `SELECT COUNT(*) FROM source_content`); n != 0 {
+	// Ten rows, each read once to check it and once to sum it.
-		t.Errorf("%d source rows without a file are left, want 0", n)
+	if coveredRows != 20 {
+		t.Errorf("the reads covered %d rows in all, want 20", coveredRows)
+	}
+
+	usage, err := cache.UsageBytes(ctx)
+	if err != nil {
+		t.Fatalf("UsageBytes failed: %v", err)
+	}
+
+	if usage != 550 {
+		t.Errorf("UsageBytes() after reconciliation = %d, want 550 (5*100 + 5*10)",
+			usage)
 	}
 }
 

internal/imgcache/cachesize.go

@@ -72,7 +72,7 @@ func (c *Cache) computeDefaultMaxBytes(
 	}
 
 	// Both terms are at most math.MaxInt64, so the sum cannot overflow.
-	//nolint:gosec // G115: UsageBytes sums file sizes, never negative
+	//nolint:gosec // G115: UsageBytes returns the total cache usage, never negative
 	spaceBytes := min(freeBytes, math.MaxInt64) + uint64(usedBytes)
 
 	computed := spaceBytes / freeSpaceFractionDenominator * freeSpaceFractionNumerator

internal/imgcache/eviction.go

@@ -21,10 +21,11 @@ const DefaultEvictionInterval = 5 * time.Minute
 // and source blobs) one eviction pass fetches from the database.
 const evictionBatchSize = 100
 
-// reconciliationPageSize is the most rows one read of the reconciliation
+// defaultReconciliationPageSize is the most rows one read of the
-// pass returns. Each read is a query of its own, so a request waits for
+// reconciliation pass returns, unless a test sets
-// one page at most, however large the cache is.
+// Cache.reconciliationPageSize smaller. Each read is a query of its own,
-const reconciliationPageSize = 1000
+// so a request waits for one page at most, however large the cache is.
+const defaultReconciliationPageSize = 1000
 
 // staleTempFileAge is how old an orphaned temp file (left behind by a
 // crashed write) must be before reconciliation removes it. Fresh temp
@@ -676,6 +677,10 @@ func (c *Cache) reconcileVariantRows(ctx context.Context) error {
 			return err
 		}
 
+		if c.reconciliationReadTestHook != nil {
+			c.reconciliationReadTestHook(len(keys))
+		}
+
 		if len(keys) == 0 {
 			return nil
 		}
@@ -702,7 +707,7 @@ func (c *Cache) reconcileVariantRows(ctx context.Context) error {
 	}
 }
 
-// variantKeysAfter returns, in order, up to reconciliationPageSize
+// variantKeysAfter returns, in order, up to c.reconciliationPageSize
 // tracked variant cache keys that sort after the given one.
 func (c *Cache) variantKeysAfter(
 	ctx context.Context, after VariantKey,
@@ -710,7 +715,7 @@ func (c *Cache) variantKeysAfter(
 	return queryStringColumn[VariantKey](ctx, c.db, `
 		SELECT cache_key FROM variant_content
 		WHERE cache_key > ? ORDER BY cache_key LIMIT ?
-	`, "variant keys", "variant key", string(after), reconciliationPageSize)
+	`, "variant keys", "variant key", string(after), c.reconciliationPageSize)
 }
 
 // queryStringColumn runs a single-column query with args and returns the
@@ -823,6 +828,10 @@ func (c *Cache) reconcileSourceRows(ctx context.Context) error {
 			return err
 		}
 
+		if c.reconciliationReadTestHook != nil {
+			c.reconciliationReadTestHook(len(hashes))
+		}
+
 		if len(hashes) == 0 {
 			return nil
 		}
@@ -851,7 +860,7 @@ func (c *Cache) reconcileSourceRows(ctx context.Context) error {
 }
 
 // sourceContentHashesAfter returns, in order, up to
-// reconciliationPageSize tracked source content hashes that sort after
+// c.reconciliationPageSize tracked source content hashes that sort after
 // the given one.
 func (c *Cache) sourceContentHashesAfter(
 	ctx context.Context, after ContentHash,
@@ -859,20 +868,24 @@ func (c *Cache) sourceContentHashesAfter(
 	return queryStringColumn[ContentHash](ctx, c.db, `
 		SELECT content_hash FROM source_content
 		WHERE content_hash > ? ORDER BY content_hash LIMIT ?
-	`, "source content hashes", "content hash", string(after), reconciliationPageSize)
+	`, "source content hashes", "content hash", string(after),
+		c.reconciliationPageSize)
 }
 
 // Each of these queries sums size_bytes over the next page of rows of
 // one content table, the rows that sort after a key, and returns the
-// page's last key with the sum. Past the last row the key is NULL.
+// page's last key, the sum and the number of rows in the page. Past the
+// last row the page has no rows and the key is NULL.
 const (
 	sourceSizePageQuery = `
-		SELECT MAX(content_hash), COALESCE(SUM(size_bytes), 0) FROM (
+		SELECT MAX(content_hash), COALESCE(SUM(size_bytes), 0), COUNT(*)
+		FROM (
 			SELECT content_hash, size_bytes FROM source_content
 			WHERE content_hash > ? ORDER BY content_hash LIMIT ?
 		)`
 	variantSizePageQuery = `
-		SELECT MAX(cache_key), COALESCE(SUM(size_bytes), 0) FROM (
+		SELECT MAX(cache_key), COALESCE(SUM(size_bytes), 0), COUNT(*)
+		FROM (
 			SELECT cache_key, size_bytes FROM variant_content
 			WHERE cache_key > ? ORDER BY cache_key LIMIT ?
 		)`
@@ -908,13 +921,19 @@ func (c *Cache) sumSizeBytesInPages(
 
 		var pageBytes int64
 
-		err := c.db.QueryRowContext(ctx, pageQuery, after, reconciliationPageSize).
+		var pageRows int
-			Scan(&lastKey, &pageBytes)
+
+		err := c.db.QueryRowContext(ctx, pageQuery, after, c.reconciliationPageSize).
+			Scan(&lastKey, &pageBytes, &pageRows)
 		if err != nil {
 			return 0, fmt.Errorf("failed to sum cache content sizes: %w", err)
 		}
 
-		if !lastKey.Valid {
+		if c.reconciliationReadTestHook != nil {
+			c.reconciliationReadTestHook(pageRows)
+		}
+
+		if pageRows == 0 {
 			return total, nil
 		}
 

internal/imgcache/imgcache.go

@@ -21,11 +21,12 @@ const (
 	FormatPNG      ImageFormat = "png"
 	FormatWebP     ImageFormat = "webp"
 	FormatAVIF     ImageFormat = "avif"
+	FormatJXL      ImageFormat = "jxl"
 	FormatGIF      ImageFormat = "gif"
 
-	// FormatAuto stands for AVIF, WebP or JPEG, chosen for each request
+	// FormatAuto stands for JPEG XL, AVIF, WebP or JPEG, chosen for each
-	// from its Accept header once the URL's signature or token has been
+	// request from its Accept header once the URL's signature or token has
-	// checked; it is never processed or cached as itself.
+	// been checked; it is never processed or cached as itself.
 	FormatAuto ImageFormat = "auto"
 )
 

internal/imgcache/service.go

@@ -100,6 +100,13 @@ func NewService(cfg *ServiceConfig) (*Service, error) {
 		allowHTTP = cfg.FetcherConfig.AllowHTTP
 	}
 
+	// JPEG XL is the default output format, so pixad does not start
+	// without it.
+	err := imageprocessor.CheckJPEGXLSupport()
+	if err != nil {
+		return nil, err
+	}
+
 	maxResponseSize := fetcherCfg.MaxResponseSize
 	processor := imageprocessor.New(imageprocessor.Params{
 		MaxInputBytes:           maxResponseSize,

internal/imgcache/urlparser.go

@@ -38,8 +38,10 @@ func ValidateDimension(name string, value int) error {
 	return nil
 }
 
-// sizeFormatRegex matches patterns like "800x600.webp", "0x0.jpeg", "orig.png"
+// sizeFormatRegex matches patterns like "800x600.webp", "0x0.jpeg", "orig.png",
-var sizeFormatRegex = regexp.MustCompile(`^(\d+)x(\d+)\.(\w+)$|^(orig)\.(\w+)$`)
+// and a size with no format, such as "800x600" or "orig"
+var sizeFormatRegex = regexp.MustCompile(
+	`^(\d+)x(\d+)(?:\.(\w+))?$|^(orig)(?:\.(\w+))?$`)
 
 // ParsedURL contains the parsed components of an image proxy URL.
 type ParsedURL struct {
@@ -56,12 +58,13 @@ type ParsedURL struct {
 }
 
 // ParseImagePath parses the path captured by chi's wildcard:
-// <host>/<path>/<size>.<format>
+// <host>/<path>/<size>.<format>, or <host>/<path>/<size> for JPEG XL
 // This is the primary entry point when using chi routing.
 // Examples:
 //   - cdn.example.com/photos/cat.jpg/800x600.webp
 //   - cdn.example.com/photos/cat.jpg/0x0.jpeg
 //   - cdn.example.com/photos/cat.jpg/orig.png
+//   - cdn.example.com/photos/cat.jpg/800x600
 func ParseImagePath(path string) (*ParsedURL, error) {
 	// Strip leading slash if present (chi may include it)
 	path = strings.TrimPrefix(path, "/")
@@ -72,7 +75,8 @@ func ParseImagePath(path string) (*ParsedURL, error) {
 	return parseImageComponents(path)
 }
 
-// ParseImageURL parses a full URL path like /v1/image/<host>/<path>/<size>.<format>
+// ParseImageURL parses a full URL path like /v1/image/<host>/<path>/<size>.<format>,
+// or /v1/image/<host>/<path>/<size> for JPEG XL
 // Use ParseImagePath instead when working with chi's wildcard capture.
 func ParseImageURL(urlPath string) (*ParsedURL, error) {
 	// Remove the /v1/image/ prefix
@@ -89,7 +93,8 @@ func ParseImageURL(urlPath string) (*ParsedURL, error) {
 	return parseImageComponents(remainder)
 }
 
-// parseImageComponents parses <host>/<path>/<size>.<format> structure.
+// parseImageComponents parses <host>/<path>/<size>.<format>, or
+// <host>/<path>/<size> for JPEG XL.
 func parseImageComponents(remainder string) (*ParsedURL, error) {
 	// Check for path traversal before any other processing
 	err := checkPathTraversal(remainder)
@@ -97,7 +102,7 @@ func parseImageComponents(remainder string) (*ParsedURL, error) {
 		return nil, err
 	}
 
-	// Find the last path segment which contains size.format
+	// Find the last path segment, which holds "size" or "size.format"
 	lastSlash := strings.LastIndex(remainder, "/")
 	if lastSlash == -1 {
 		return nil, ErrMissingSize
@@ -212,7 +217,7 @@ func checkPathTraversal(path string) error {
 	return nil
 }
 
-// parseSizeFormat parses strings like "800x600.webp" or "orig.png"
+// parseSizeFormat parses strings like "800x600.webp", "orig.png" or "800x600"
 func parseSizeFormat(s string) (Size, ImageFormat, error) {
 	matches := sizeFormatRegex.FindStringSubmatch(s)
 	if matches == nil {
@@ -225,11 +230,11 @@ func parseSizeFormat(s string) (Size, ImageFormat, error) {
 	)
 
 	if matches[4] == "orig" {
-		// "orig.format" pattern
+		// "orig" or "orig.format" pattern
 		size = Size{Width: 0, Height: 0}
 		formatStr = matches[5]
 	} else {
-		// "WxH.format" pattern
+		// "WxH" or "WxH.format" pattern
 		width, err := strconv.Atoi(matches[1])
 		if err != nil {
 			return Size{}, "", ErrInvalidSize
@@ -254,6 +259,11 @@ func parseSizeFormat(s string) (Size, ImageFormat, error) {
 		return Size{}, "", err
 	}
 
+	// A URL that names no format is served, and signed, as JPEG XL
+	if formatStr == "" {
+		return size, FormatJXL, nil
+	}
+
 	format, err := parseFormat(formatStr)
 	if err != nil {
 		return Size{}, "", err
@@ -275,6 +285,8 @@ func parseFormat(s string) (ImageFormat, error) {
 		return FormatWebP, nil
 	case "avif":
 		return FormatAVIF, nil
+	case "jxl":
+		return FormatJXL, nil
 	case "gif":
 		return FormatGIF, nil
 	case "auto":

internal/magic/jpegxl_internal_test.go

@@ -0,0 +1,58 @@
+package magic
+
+import "testing"
+
+// testMIMEJXL is the MIME type of JPEG XL.
+const testMIMEJXL = "image/jxl"
+
+// TestDetectFormatJPEGXL verifies that both JPEG XL signatures, that of a
+// bare codestream and that of the container, are detected as image/jxl.
+func TestDetectFormatJPEGXL(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name string
+		data []byte
+	}{
+		{"codestream", pad(0xFF, 0x0A)},
+		{"container", pad(
+			0x00, 0x00, 0x00, 0x0C, 0x4A, 0x58, 0x4C, 0x20, 0x0D, 0x0A, 0x87, 0x0A,
+		)},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			got, err := DetectFormat(tt.data)
+			if err != nil || got != MIMETypeJXL {
+				t.Errorf("DetectFormat() = %q, %v, want %q", got, err, testMIMEJXL)
+			}
+
+			err = ValidateMagicBytes(tt.data, testMIMEJXL)
+			if err != nil {
+				t.Errorf("ValidateMagicBytes(%q) error = %v", testMIMEJXL, err)
+			}
+		})
+	}
+}
+
+// TestJPEGXLMIMEType verifies that image/jxl is a supported input type and
+// maps to and from the format jxl.
+func TestJPEGXLMIMEType(t *testing.T) {
+	t.Parallel()
+
+	if !IsSupportedMIMEType(testMIMEJXL) {
+		t.Errorf("IsSupportedMIMEType(%q) = false", testMIMEJXL)
+	}
+
+	format, ok := MIMEToImageFormat(testMIMEJXL)
+	if format != FormatJXL || !ok {
+		t.Errorf("MIMEToImageFormat(%q) = %q, %v, want %q, true",
+			testMIMEJXL, format, ok, FormatJXL)
+	}
+
+	if got := ImageFormatToMIME(FormatJXL); got != testMIMEJXL {
+		t.Errorf("ImageFormatToMIME(%q) = %q, want %q", FormatJXL, got, testMIMEJXL)
+	}
+}

internal/magic/magic.go

@@ -26,6 +26,7 @@ const (
 	MIMETypeWebP = MIMEType("image/webp")
 	MIMETypeGIF  = MIMEType("image/gif")
 	MIMETypeAVIF = MIMEType("image/avif")
+	MIMETypeJXL  = MIMEType("image/jxl")
 	MIMETypeSVG  = MIMEType("image/svg+xml")
 )
 
@@ -40,6 +41,7 @@ const (
 	FormatPNG      ImageFormat = "png"
 	FormatWebP     ImageFormat = "webp"
 	FormatAVIF     ImageFormat = "avif"
+	FormatJXL      ImageFormat = "jxl"
 	FormatGIF      ImageFormat = "gif"
 )
 
@@ -62,6 +64,11 @@ var (
 	// AVIF uses the ftyp box with brand "avif" or "avis"
 	// Format: size(4 bytes) + "ftyp" + brand(4 bytes)
 	magicFtyp = []byte{0x66, 0x74, 0x79, 0x70} // "ftyp"
+	// JPEG XL is a bare codestream or a codestream in a container
+	magicJXLCodestream = []byte{0xFF, 0x0A}
+	magicJXLContainer  = []byte{
+		0x00, 0x00, 0x00, 0x0C, 0x4A, 0x58, 0x4C, 0x20, 0x0D, 0x0A, 0x87, 0x0A,
+	}
 )
 
 // WebP identifier appears at offset 8 after RIFF header.
@@ -115,6 +122,12 @@ func DetectFormat(data []byte) (MIMEType, error) {
 		}
 	}
 
+	// Check JPEG XL (FF0A, or the 12-byte container signature)
+	if bytes.HasPrefix(data, magicJXLCodestream) ||
+		bytes.HasPrefix(data, magicJXLContainer) {
+		return MIMETypeJXL, nil
+	}
+
 	// Check SVG - look for XML declaration or SVG tag
 	if detectSVG(data) {
 		return MIMETypeSVG, nil
@@ -181,7 +194,8 @@ func normalizeMIMEType(mimeType string) string {
 func IsSupportedMIMEType(mimeType string) bool {
 	normalized := normalizeMIMEType(mimeType)
 	switch MIMEType(normalized) {
-	case MIMETypeJPEG, MIMETypePNG, MIMETypeWebP, MIMETypeGIF, MIMETypeAVIF, MIMETypeSVG:
+	case MIMETypeJPEG, MIMETypePNG, MIMETypeWebP, MIMETypeGIF, MIMETypeAVIF,
+		MIMETypeJXL, MIMETypeSVG:
 		return true
 	default:
 		return false
@@ -226,6 +240,8 @@ func MIMEToImageFormat(mimeType string) (ImageFormat, bool) {
 		return FormatGIF, true
 	case MIMETypeAVIF:
 		return FormatAVIF, true
+	case MIMETypeJXL:
+		return FormatJXL, true
 	case MIMETypeSVG:
 		// SVG has no corresponding output format.
 		return "", false
@@ -247,6 +263,8 @@ func ImageFormatToMIME(format ImageFormat) string {
 		return string(MIMETypeGIF)
 	case FormatAVIF:
 		return string(MIMETypeAVIF)
+	case FormatJXL:
+		return string(MIMETypeJXL)
 	case FormatOriginal:
 		// Original format passes content through unchanged.
 		return mimeOctetStream

internal/server/jpegxl_internal_test.go

@@ -0,0 +1,72 @@
+package server
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"testing"
+
+	"github.com/davidbyttow/govips/v2/vips"
+)
+
+// TestImageProxyFlowJPEGXL requests the JPEG XL testdata/red.jxl, 64x48 and
+// made with libvips, through pixa's router, upstream fetcher, image processor
+// and disk cache: resized as PNG, resized as JPEG XL, and at its own size and
+// format, which is JPEG XL. The second request for each URL is a cache hit.
+func TestImageProxyFlowJPEGXL(t *testing.T) {
+	t.Parallel()
+
+	source, err := os.ReadFile("testdata/red.jxl")
+	if err != nil {
+		t.Fatalf("reading the test image: %v", err)
+	}
+
+	upstream := httptest.NewServer(http.HandlerFunc(
+		func(w http.ResponseWriter, _ *http.Request) {
+			w.Header().Set("Content-Type", "image/jxl")
+			_, _ = w.Write(source)
+		}))
+	t.Cleanup(upstream.Close)
+
+	s, _, _ := startImageProxy(t, upstream)
+
+	tests := []struct {
+		sizeFormat    string // the <size>.<format> part of the image URL
+		contentType   string
+		imageType     vips.ImageType
+		width, height int
+	}{
+		{"32x24.png", "image/png", vips.ImageTypePNG, 32, 24},
+		{"32x24.jxl", "image/jxl", vips.ImageTypeJXL, 32, 24},
+		{"orig.orig", "image/jxl", vips.ImageTypeJXL, 64, 48},
+	}
+
+	for _, tt := range tests {
+		target := "/v1/image/" + upstreamHost + "/red.jxl/" + tt.sizeFormat
+
+		for _, wantCache := range []string{"MISS", "HIT"} {
+			rec := getImage(t, s, target)
+			gotType := rec.Header().Get("Content-Type")
+			gotCache := rec.Header().Get("X-Pixa-Cache")
+
+			if gotType != tt.contentType || gotCache != wantCache {
+				t.Errorf("%s: %s, X-Pixa-Cache %s, want %s, %s",
+					target, gotType, gotCache, tt.contentType, wantCache)
+			}
+
+			img, err := vips.NewImageFromBuffer(rec.Body.Bytes())
+			if err != nil {
+				t.Fatalf("%s: loading the image: %v", target, err)
+			}
+
+			if img.Format() != tt.imageType ||
+				img.Width() != tt.width || img.Height() != tt.height {
+				t.Errorf("%s: %s %dx%d, want %s %dx%d", target,
+					vips.ImageTypes[img.Format()], img.Width(), img.Height(),
+					vips.ImageTypes[tt.imageType], tt.width, tt.height)
+			}
+
+			img.Close()
+		}
+	}
+}

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())
 

internal/templates/generator.html

@@ -95,11 +95,12 @@
                     </label>
                     <select id="format" name="format">
                         <option value="orig" {{if eq .FormFormat "orig"}}selected{{end}}>Original</option>
-                        <option value="auto" {{if eq .FormFormat "auto"}}selected{{end}}>Auto (AVIF, WebP or JPEG)</option>
+                        <option value="auto" {{if eq .FormFormat "auto"}}selected{{end}}>Auto (JPEG XL, AVIF, WebP or JPEG)</option>
                         <option value="jpeg" {{if eq .FormFormat "jpeg"}}selected{{end}}>JPEG</option>
                         <option value="png" {{if eq .FormFormat "png"}}selected{{end}}>PNG</option>
                         <option value="webp" {{if eq .FormFormat "webp"}}selected{{end}}>WebP</option>
                         <option value="avif" {{if eq .FormFormat "avif"}}selected{{end}}>AVIF</option>
+                        <option value="jxl" {{if or (eq .FormFormat "jxl") (eq .FormFormat "")}}selected{{end}}>JPEG XL</option>
                         <option value="gif" {{if eq .FormFormat "gif"}}selected{{end}}>GIF</option>
                     </select>
                 </div>

script/bootstrap

@@ -14,11 +14,12 @@
 #                            script/fmt-check: all the host needs, as
 #                            the checks compile pixa in Docker
 #   script/bootstrap --cgo   git, make, Go, and a C compiler and the
-#                            CGO image libraries (pkg-config, vips,
+#                            CGO image libraries (pkg-config, vips
-#                            libheif) for the govips bindings instead
+#                            with its JPEG XL support, libheif) for
-#                            of Node: to compile pixa, in the
+#                            the govips bindings instead of Node: to
-#                            Dockerfile's test phase and build stage,
+#                            compile pixa, in the Dockerfile's test
-#                            which format nothing
+#                            phase and build stage, which format
+#                            nothing
 set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
@@ -150,6 +151,16 @@ ensure_cgo_deps() {
     if ! pkg-config --exists vips; then
         pkg_install vips libvips-dev vips vips-dev
     fi
+    # libvips' JPEG XL loader and saver are in the nix and brew vips
+    # packages, and in apt's from Debian 12 and Ubuntu 24.04 on, but in
+    # the package vips-jxl on Alpine. detect_pkgmgr is called only where
+    # apk exists, as on apt it updates the package lists.
+    if ! missing apk; then
+        detect_pkgmgr
+    fi
+    if [ "$PKGMGR" = "apk" ] && ! apk info -e vips-jxl >/dev/null; then
+        apk add --no-cache vips-jxl
+    fi
     if ! pkg-config --exists libheif; then
         pkg_install libheif libheif-dev libheif libheif-dev
     fi