commit 1ddb83634a37329d3ac7ac51bd73cd546ca5564b
parent 358f79b8c0652ed11aa86f6cdb373dce582aa5f7
Author: Jack Mordaunt <jackmordaunt.dev@gmail.com>
Date: Fri, 18 Sep 2026 16:09:36 -0400
build: hold the package against iconutil on macOS
Nothing outside this package had ever read what it writes, and its reading of
Apple output was checked by hand once. Apple ships the tool on the macOS
runner, so both directions become tests: it builds a file this package reads,
and it takes apart a file this package built.
Diffstat:
2 files changed, 180 insertions(+), 0 deletions(-)
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
@@ -4,6 +4,7 @@ on:
push:
branches: [main]
pull_request:
+ workflow_dispatch:
schedule:
# Weekly, so new advisories surface without waiting for a commit.
- cron: "0 6 * * 1"
@@ -62,6 +63,19 @@ jobs:
name: fuzz-corpus
path: testdata/fuzz
+ oracle:
+ name: iconutil oracle
+ # Apple's own tool is the only authority on the format, and it ships with
+ # the macOS runner. The tests are darwin-only, so this is where they run.
+ runs-on: macos-latest
+ steps:
+ - uses: actions/checkout@v4
+ - uses: actions/setup-go@v5
+ with:
+ go-version-file: go.mod
+ cache-dependency-path: go.sum
+ - run: go test -count=1 -v -run 'TestIconutil' .
+
shell-extension:
name: shell extension
runs-on: windows-latest
diff --git a/oracle_test.go b/oracle_test.go
@@ -0,0 +1,166 @@
+//go:build darwin
+
+package icns
+
+import (
+ "bytes"
+ "image"
+ "image/color"
+ "image/png"
+ "os"
+ "os/exec"
+ "path/filepath"
+ "sort"
+ "testing"
+)
+
+// These tests hold the package against iconutil, the tool Apple ships, in
+// both directions: a file it wrote has to read back as the artwork that went
+// in, and a file this package wrote has to come apart under its hands.
+
+// iconutil runs the tool, failing the test with whatever it printed.
+func iconutil(t *testing.T, args ...string) {
+ t.Helper()
+ cmd := exec.Command("iconutil", args...)
+ out, err := cmd.CombinedOutput()
+ if err != nil {
+ t.Fatalf("iconutil %v: %v\n%s", args, err, out)
+ }
+}
+
+func writePNG(t *testing.T, path string, img image.Image) {
+ t.Helper()
+ f, err := os.Create(path)
+ if err != nil {
+ t.Fatal(err)
+ }
+ defer f.Close()
+ if err := png.Encode(f, img); err != nil {
+ t.Fatal(err)
+ }
+}
+
+func readPNG(t *testing.T, path string) image.Image {
+ t.Helper()
+ f, err := os.Open(path)
+ if err != nil {
+ t.Fatal(err)
+ }
+ defer f.Close()
+ img, err := png.Decode(f)
+ if err != nil {
+ t.Fatalf("decoding %s: %v", path, err)
+ }
+ return img
+}
+
+// oracleArtwork paints one flat colour per slot, so a colour identifies the
+// file it came from wherever it ends up.
+func oracleArtwork() (map[Slot]image.Image, map[Slot]color.NRGBA) {
+ var (
+ images = map[Slot]image.Image{}
+ want = map[Slot]color.NRGBA{}
+ )
+ for i, slot := range Slots() {
+ c := color.NRGBA{R: uint8(10 + i*20), G: uint8(200 - i*15), B: 0x40, A: 0xFF}
+ images[slot] = solid(int(slot.Pixels()), c)
+ want[slot] = c
+ }
+ return images, want
+}
+
+func listDir(t *testing.T, dir string) []string {
+ t.Helper()
+ entries, err := os.ReadDir(dir)
+ if err != nil {
+ t.Fatalf("reading %s: %v", dir, err)
+ }
+ var names []string
+ for _, e := range entries {
+ names = append(names, e.Name())
+ }
+ sort.Strings(names)
+ return names
+}
+
+// TestIconutilWrites checks that a file built by Apple's tool reads back as
+// the artwork that went into it, element by element.
+func TestIconutilWrites(t *testing.T) {
+ dir := t.TempDir()
+ set := filepath.Join(dir, "Oracle.iconset")
+ if err := os.MkdirAll(set, 0o755); err != nil {
+ t.Fatal(err)
+ }
+ images, want := oracleArtwork()
+ for slot, img := range images {
+ writePNG(t, filepath.Join(set, "icon_"+slot.String()+".png"), img)
+ }
+ out := filepath.Join(dir, "apple.icns")
+ iconutil(t, "-c", "icns", "-o", out, set)
+
+ data, err := os.ReadFile(out)
+ if err != nil {
+ t.Fatal(err)
+ }
+ d, err := NewDecoder(bytes.NewReader(data))
+ if err != nil {
+ t.Fatalf("decoding what iconutil wrote: %v", err)
+ }
+ icons := d.Icons()
+ t.Logf("iconutil wrote %d icons this package reads", len(icons))
+ if len(icons) == 0 {
+ t.Fatal("no icons were read back")
+ }
+ for _, icon := range icons {
+ slot, ok := slotOf[icon.ID]
+ if !ok {
+ t.Errorf("iconutil wrote %s, which this package does not place in a slot", icon.ID)
+ continue
+ }
+ img, err := icon.Decode()
+ if err != nil {
+ t.Errorf("%s: %v", icon.ID, err)
+ continue
+ }
+ if got := uint(img.Bounds().Dx()); got != slot.Pixels() {
+ t.Errorf("%s is %d pixels, want %d", icon.ID, got, slot.Pixels())
+ }
+ if got := centre(img); got != want[slot] {
+ t.Errorf("%s holds %v, want %v from slot %s", icon.ID, got, want[slot], slot)
+ }
+ }
+}
+
+// TestIconutilReads checks that Apple's tool takes a file this package wrote
+// apart into the artwork that went in, which covers the run-length encoded
+// elements and the table of contents.
+func TestIconutilReads(t *testing.T) {
+ dir := t.TempDir()
+ images, want := oracleArtwork()
+ buf := bytes.NewBuffer(nil)
+ if err := NewEncoder(buf).EncodeSlots(images); err != nil {
+ t.Fatal(err)
+ }
+ ours := filepath.Join(dir, "ours.icns")
+ if err := os.WriteFile(ours, buf.Bytes(), 0o644); err != nil {
+ t.Fatal(err)
+ }
+ set := filepath.Join(dir, "ours.iconset")
+ iconutil(t, "-c", "iconset", "-o", set, ours)
+
+ t.Logf("iconutil extracted %v", listDir(t, set))
+ for slot, c := range want {
+ path := filepath.Join(set, "icon_"+slot.String()+".png")
+ if _, err := os.Stat(path); err != nil {
+ t.Errorf("iconutil did not extract slot %s", slot)
+ continue
+ }
+ img := readPNG(t, path)
+ if got := uint(img.Bounds().Dx()); got != slot.Pixels() {
+ t.Errorf("slot %s came out %d pixels, want %d", slot, got, slot.Pixels())
+ }
+ if got := centre(img); got != c {
+ t.Errorf("slot %s came out %v, want %v", slot, got, c)
+ }
+ }
+}
