Add binary patch types and binary marker parsing

The binary marker is the text that appears where a text fragment
normally would and indicates that the file is binary. It's not quite a
header, because content is optional in a binary patch. If the patch does
include binary fragments, they have their own format, with a header.

Author: bluekeyes

gitdiff/gitdiff.go

@@ -26,6 +26,15 @@ type File struct {
 	// TextFragments contains the fragments describing changes to a text file. It
 	// may be empty if the file is empty or if only the mode changes.
 	TextFragments []*TextFragment
+
+	// IsBinary is true if the file is a binary file. If the patch includes
+	// binary data, BinaryFragment will be non-nil and describe the changes to
+	// the data. If the patch is reversible, ReverseBinaryFragment will also be
+	// non-nil and describe the changes needed to restore the original file
+	// after applying the changes in BinaryFragment.
+	IsBinary              bool
+	BinaryFragment        *BinaryFragment
+	ReverseBinaryFragment *BinaryFragment
 }
 
 // TextFragment describes changed lines starting at a specific line in a text file.
@@ -86,3 +95,18 @@ func (op LineOp) String() string {
 	return "?"
 }
 
+// BinaryFragment describes changes to a binary file.
+type BinaryFragment struct {
+	Method BinaryPatchMethod
+	Data   []byte
+}
+
+// BinaryPatchMethod is the method used to create and apply the binary patch.
+type BinaryPatchMethod int
+
+const (
+	// BinaryPatchDelta indicates the data uses Git's packfile encoding
+	BinaryPatchDelta BinaryPatchMethod = iota
+	// BinaryPatchLiteral indicates the data is the exact file content
+	BinaryPatchLiteral
+)

gitdiff/parser.go

@@ -33,7 +33,7 @@ func Parse(r io.Reader) ([]*File, string, error) {
 
 		for _, fn := range []func(*File) (int, error){
 			p.ParseTextFragments,
-			p.ParseBinaryFragment,
+			p.ParseBinaryFragments,
 		} {
 			n, err := fn(file)
 			if err != nil {
@@ -316,8 +316,34 @@ func (p *parser) ParseTextChunk(frag *TextFragment) error {
 	return nil
 }
 
-func (p *parser) ParseBinaryFragment(f *File) (n int, err error) {
-	panic("TODO(bkeyes): unimplemented")
+func (p *parser) ParseBinaryFragments(f *File) (n int, err error) {
+	isBinary, hasData, err := p.ParseBinaryMarker()
+	if err != nil || !isBinary {
+		return 0, err
+	}
+
+	f.IsBinary = true
+	if hasData {
+		panic("TODO(bkeyes): unimplemented")
+	}
+
+	return 0, nil
+}
+
+func (p *parser) ParseBinaryMarker() (isBinary bool, hasData bool, err error) {
+	switch p.Line(0) {
+	case "GIT binary patch\n":
+		hasData = true
+	case "Binary files differ\n":
+	case "Files differ\n":
+	default:
+		return false, false, nil
+	}
+
+	if err = p.Next(); err != nil && err != io.EOF {
+		return true, hasData, err
+	}
+	return true, hasData, nil
 }
 
 func parseRange(s string) (start int64, end int64, err error) {