Rework implementation to use exiftool as the facit

.github/workflows/test.yml

@@ -1,40 +1,44 @@
 on:
   push:
-    branches: [ main ]
+    branches: [main]
   pull_request:
 name: Test
 jobs:
   test:
     strategy:
       matrix:
-        go-version: [1.21.x,1.22.x]
+        go-version: [1.21.x, 1.22.x]
         platform: [ubuntu-latest, macos-latest, windows-latest]
     runs-on: ${{ matrix.platform }}
     steps:
-    - name: Install Go
-      uses: actions/setup-go@v4
-      with:
-        go-version: ${{ matrix.go-version }}
-    - name: Install staticcheck
-      run: go install honnef.co/go/tools/cmd/staticcheck@latest
-      shell: bash
-    - name: Install golint
-      run: go install golang.org/x/lint/golint@latest
-      shell: bash
-    - name: Update PATH
-      run: echo "$(go env GOPATH)/bin" >> $GITHUB_PATH
-      shell: bash
-    - name: Checkout code
-      uses: actions/checkout@v3
-    - name: Fmt
-      if: matrix.platform != 'windows-latest' # :(
-      run: "diff <(gofmt -d .) <(printf '')"
-      shell: bash
-    - name: Vet
-      run: go vet ./...
-    - name: Staticcheck
-      run: staticcheck ./...
-    - name: Lint
-      run: golint ./...
-    - name: Test
-      run: go test -race ./...
+      - name: Install Go
+        uses: actions/setup-go@v4
+        with:
+          go-version: ${{ matrix.go-version }}
+      - name: Install staticcheck
+        run: go install honnef.co/go/tools/cmd/staticcheck@latest
+        shell: bash
+      - name: Install golint
+        run: go install golang.org/x/lint/golint@latest
+        shell: bash
+      - name: Update PATH
+        run: echo "$(go env GOPATH)/bin" >> $GITHUB_PATH
+        shell: bash
+      - name: Checkout code
+        uses: actions/checkout@v3
+      - name: Fmt
+        if: matrix.platform != 'windows-latest' # :(
+        run: "diff <(gofmt -d .) <(printf '')"
+        shell: bash
+      - name: Vet
+        run: go vet ./...
+      - name: Staticcheck
+        run: staticcheck ./...
+      - name: Lint
+        run: golint ./...
+      - name: Test
+        run: go test -race ./... -coverpkg=./... -coverprofile=coverage.txt -covermode=atomic
+      - name: Upload coverage reports to Codecov
+        uses: codecov/[email protected]
+        with:
+          token: ${{ secrets.CODECOV_TOKEN }}

.gitignore

@@ -13,3 +13,5 @@
 
 # Dependency directories (remove the comment below to include it)
 # vendor/
+
+.DS_Store

README.md

@@ -1,8 +1,58 @@
 [![Tests on Linux, MacOS and Windows](https://github.com/bep/imagemeta/workflows/Test/badge.svg)](https://github.com/bep/imagemeta/actions?query=workflow:Test)
 [![Go Report Card](https://goreportcard.com/badge/github.com/bep/imagemeta)](https://goreportcard.com/report/github.com/bep/imagemeta)
+[![codecov](https://codecov.io/gh/bep/imagemeta/branch/master/graph/badge.svg)](https://codecov.io/gh/bep/imagemeta)
 [![GoDoc](https://godoc.org/github.com/bep/imagemeta?status.svg)](https://godoc.org/github.com/bep/imagemeta)
 
-# Work in progress
+## This is about READING image metadata
 
-This is not ready, yet, but the goal is to use this as the library to read image metadata in Hugo. The existing Go libraries I have found is not maintained anymore and too complex to build on top of. The goal of this library is to be relatively small and simple, but I may prove myself wrong.
+Writing is not supported, and never will.
 
+I welcome PRs with fixes, but please raise an issue first if you want to add new features.
+
+## Performance
+
+Extracting `EXIF` performs well, ref. the benhcmark below. Note that you can get a significant boost if you only need a subset of the fields (e.g. only the `Orientation`). The last line is with the library that [Hugo](https://github.com/gohugoio/hugo) used before it was replaced with this.
+
+```bash
+BenchmarkDecodeExif/bep/imagemeta/exif/jpg/alltags-10              69238             17702 ns/op            4418 B/op        167 allocs/op
+BenchmarkDecodeExif/bep/imagemeta/exif/jpg/orientation-10         302263              3831 ns/op             650 B/op         19 allocs/op
+BenchmarkDecodeExif/rwcarlsen/goexif/exif/jpg/alltags-10           25791             47415 ns/op          175548 B/op        812 allocs/op
+```
+
+Looking at some more extensive tests, testing different image formats and tag sources, we see that the current XMP implementation leaves a lot to be desired (you can provide your own XMP handler if you want). 
+
+```bash
+BenchmarkDecode/bep/imagemeta/png/exif-10                  23444             50991 ns/op            4425 B/op        168 allocs/op
+BenchmarkDecode/bep/imagemeta/webp/all-10                   2980            399424 ns/op          177917 B/op       2436 allocs/op
+BenchmarkDecode/bep/imagemeta/webp/xmp-10                   3135            371387 ns/op          139866 B/op       2265 allocs/op
+BenchmarkDecode/bep/imagemeta/webp/exif-10                 37627             32057 ns/op           38187 B/op        177 allocs/op
+BenchmarkDecode/bep/imagemeta/jpg/exif-10                  68041             17813 ns/op            4420 B/op        167 allocs/op
+BenchmarkDecode/bep/imagemeta/jpg/iptc-10                 152806              7684 ns/op            1011 B/op         66 allocs/op
+BenchmarkDecode/bep/imagemeta/jpg/xmp-10                    3222            371182 ns/op          139860 B/op       2264 allocs/op
+BenchmarkDecode/bep/imagemeta/jpg/all-10                    2940            394144 ns/op          145267 B/op       2489 allocs/op
+```
+
+## When in doubt, Exiftools is right
+
+The output of this library is tested against `exiftool -n -json`. This means, for example, that:
+
+*  We use f-numbers and not APEX for aperture values.
+*  We use seconds and not APEX for shutter speed values.
+*  EXIF field definitions are fetched from this table:  https://exiftool.org/TagNames/EXIF.html
+*  IPTC field definitions are fetched from this table:  https://exiftool.org/TagNames/IPTC.html
+*  The XMP handling is currently very simple, you can supply your own XMP handler (see the `HandleXMP` option) if you need more.
+
+## Development
+
+Many of the tests depends on generated golden files. To update these, run:
+
+```bash
+ go generate ./gen
+```
+
+Note that you need a working `exiftool` and updated binary in your `PATH` for this to work. This was tested OK with:
+
+```
+exiftool -ver
+12.76
+```

codecov.yml

@@ -0,0 +1,10 @@
+coverage:
+  status:
+    project:
+      default:
+        target: auto
+        threshold: 0.5%
+    patch: off
+
+comment:
+  require_changes: true

gen/main.go

@@ -0,0 +1,53 @@
+//go:generate go run main.go
+package main
+
+import (
+	"bytes"
+	"log"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+)
+
+func main() {
+	outDir := "testdata_exiftool"
+	os.RemoveAll(outDir)
+	if err := os.MkdirAll(outDir, 0o755); err != nil {
+		log.Fatal(err)
+	}
+	base := "../testdata"
+
+	if err := filepath.Walk(base, func(path string, info os.FileInfo, err error) error {
+		if err != nil {
+			return err
+		}
+		if info.IsDir() || strings.HasPrefix(info.Name(), ".") {
+			return nil
+		}
+
+		basePath := strings.TrimPrefix(path, base)
+
+		var buf bytes.Buffer
+		cmd := exec.Command("exiftool", path, "-json", "-n", "-g", "-e")
+		cmd.Stdout = &buf
+		cmd.Stderr = os.Stderr
+
+		if err := cmd.Run(); err != nil {
+			return err
+		}
+
+		outFilename := filepath.Join(outDir, basePath+".json")
+		if err := os.MkdirAll(filepath.Dir(outFilename), 0o755); err != nil {
+			return err
+		}
+
+		if err := os.WriteFile(outFilename, buf.Bytes(), 0o644); err != nil {
+			return err
+		}
+
+		return nil
+	}); err != nil {
+		log.Fatal(err)
+	}
+}