jfifcom: CLI to embed comment sections

This is a quick tool to exercise inserting new JFIF segments and that it
works as expected.

cmd/jfifcom/.gitignore

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+jfifcom

cmd/jfifcom/main.go

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+// 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.Append(arg, jfif.Patch{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

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+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
+	}
+}