Minimal in-place edit support

LICENSE

@@ -0,0 +1,19 @@
+Copyright (c) 2020 Neil Pankey <[email protected]>
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.

README.md

@@ -5,3 +5,90 @@
 Basic reading of [JPEG File Interchange Format (JFIF)][wiki-jfif] segments
 
 [wiki-jfif]: https://en.wikipedia.org/wiki/JPEG_File_Interchange_Format#File_format_structure
+
+## Install
+
+Use `go get` to install the module
+
+```
+go get neilpa.me/go-jfif
+```
+
+Or use it and rely on go modules to "do the right thing".
+
+## Usage
+
+Reading JFIF segments from an existing JPEG.
+
+```go
+package main
+
+import (
+	"fmt"
+	"log"
+	"os"
+
+	"neilpa.me/go-jfif"
+)
+
+func main() {
+	f, err := os.Open("path/to/file.jpg")
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// See also jfif.ScanSegments which doesn't read the segment payload.
+	// This is used to detect the segment "signatures" for some APPn segments.
+	segs, err := jfif.DecodeSegments(f)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	for _, s := range segs {
+		sig, _, _ := s.AppPayload()
+		sig = jfif.CleanSig(sig)
+		fmt.Printf("%d\t%s\t%s\n", s.Length, s.Marker, sig)
+	}
+}
+```
+
+Appending new segments to a JPEG. (Under the hood this edits a copy of the file before renaming the copy
+to finalize the updates).
+
+```go
+package main
+
+import (
+	"log"
+
+	"neilpa.me/go-jfif"
+)
+
+func main() {
+	err := jfif.Add("path/to/file.jpg", jfif.COM, []byte("adding a comment to this file"))
+	if err != nil {
+		log.Fatal(err)
+	}
+}
+```
+
+## Tools
+
+There are a few simple CLI tools include for manipulating JPEG/JFIF files that exercise functionality
+exposed by this module.
+
+### jfifcom
+
+Append free-form comment (`COM`) segments to an existing JPEG file.
+
+### jfifstat
+
+Prints segment markers, sizes, and optional `APPN` signatures from a JPEG until the image stream.
+
+### xmpdump
+
+Extracts and prints [XMP](https://www.adobe.com/products/xmp.html) data from `APP1` segments from JPEG file(s).
+
+## License
+
+[MIT](/LICENSE)

cmd/jfifcom/.gitignore

@@ -0,0 +1 @@
+jfifcom

cmd/jfifcom/main.go

@@ -0,0 +1,63 @@
+// jfifcom embeds a new comment segment with the data from stdin
+// before the start of stream (SOS) segment.
+package main
+
+import (
+	"flag"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"os"
+
+	"neilpa.me/go-jfif"
+)
+
+func main() {
+	os.Exit(realMain(os.Args[1:], os.Stdin))
+}
+
+func realMain(args []string, stdin io.Reader) int {
+	flag.Usage = printUsage
+	flag.CommandLine.Parse(args)
+
+	if flag.NArg() == 0 {
+		return usageError("no files specified")
+	}
+
+	buf, err := ioutil.ReadAll(stdin)
+	if err != nil {
+		return fatal(err.Error())
+	}
+
+	for _, arg := range flag.Args() {
+		//fmt.Println("embeddding", arg, "buf", buf)
+
+		err = jfif.Add(arg, jfif.COM, buf)
+		if err != nil {
+			return fatal(err.Error()) // todo: continue writing the other files?
+		}
+	}
+	return 0
+}
+
+func fatal(format string, args ...interface{}) int {
+	format = os.Args[0] + ": " + format + "\n"
+	fmt.Fprintf(os.Stderr, format, args...)
+	return 1
+}
+
+func usageError(msg string) int {
+	fmt.Fprintln(os.Stderr, msg)
+	printUsage()
+	return 2
+}
+
+func printUsage() {
+	fmt.Fprintf(os.Stderr, `Usage: %s jpeg [jpeg...] < ...
+
+  jfifcomment embeds a new comment segment with the data from stdin
+  before the start of stream (SOS) segment.
+`, os.Args[0])
+	flag.PrintDefaults()
+	fmt.Fprintln(os.Stderr)
+}

cmd/jfifcom/main_test.go

@@ -0,0 +1,71 @@
+package main
+
+import (
+	"bytes"
+	"io"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func TestMain(t *testing.T) {
+	root := filepath.Join("..", "..", "testdata")
+
+	tests := []struct {
+		in     string
+		golden string
+	}{
+		{
+			"min.jpg",
+			"min.jfifcom.jpg",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.golden, func(t *testing.T) {
+			temp, err := ioutil.TempFile(os.TempDir(), "jfifcom-test-main-"+tt.in)
+			if err != nil {
+				t.Fatal(err)
+			}
+			path := temp.Name()
+			defer os.Remove(path)
+			defer temp.Close()
+
+			src, err := os.Open(filepath.Join(root, tt.in))
+			if err != nil {
+				t.Fatal(err)
+			}
+			defer src.Close()
+
+			_, err = io.Copy(temp, src)
+			if err != nil {
+				t.Fatal(err)
+			}
+			temp.Close()
+			src.Close()
+
+			exit := realMain([]string{path}, strings.NewReader("hello"))
+			if exit != 0 {
+				t.Fatalf("invalid exit %d", exit)
+			}
+
+			compareFiles(t, path, filepath.Join(root, tt.golden))
+		})
+	}
+}
+
+func compareFiles(t *testing.T, path, golden string) {
+	want, err := ioutil.ReadFile(golden)
+	if err != nil {
+		t.Fatal(err)
+	}
+	got, err := ioutil.ReadFile(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(got, want) {
+		t.Errorf("bytes don't match\ngot:  % x\nwant: % x", got, want) // TODO Better diff
+	}
+}

go.mod

@@ -2,4 +2,4 @@ module neilpa.me/go-jfif
 
 go 1.14
 
-require neilpa.me/go-x v0.2.0
+require neilpa.me/go-x v0.2.1

go.sum

@@ -1,2 +1,2 @@
-neilpa.me/go-x v0.2.0 h1:GbLRDtAZ9MgVrwrIe3jWnHF2W40LCFA9Ng/aDbd9GVs=
-neilpa.me/go-x v0.2.0/go.mod h1:aIemU+pQYLLV3dygXotHKF7SantXe5HzZR6VIjzY/4g=
+neilpa.me/go-x v0.2.1 h1:9eb+b9Hj3iVIqw8F84Kq9GlAIjNsMH6V0A3AwkZuhA4=
+neilpa.me/go-x v0.2.1/go.mod h1:aIemU+pQYLLV3dygXotHKF7SantXe5HzZR6VIjzY/4g=