package patch

R=r
http://go/go-review/1018043

1 files changed, 121 insertions, 0 deletions

diff --git a/src/pkg/patch/git.go b/src/pkg/patch/git.go
new file mode 100644
index 000000000..fd03f4a92
--- /dev/null
+++ b/src/pkg/patch/git.go
@@ -0,0 +1,121 @@
+// Copyright 2009 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package patch
+
+import (
+	"bytes";
+	"compress/zlib";
+	"crypto/sha1";
+	"encoding/git85";
+	"fmt";
+	"io";
+	"os";
+)
+
+func gitSHA1(data []byte) []byte {
+	if len(data) == 0 {
+		// special case: 0 length is all zeros sum
+		return make([]byte, 20);
+	}
+	h := sha1.New();
+	fmt.Fprintf(h, "blob %d\x00", len(data));
+	h.Write(data);
+	return h.Sum();
+}
+
+// BUG(rsc): The GIT binary delta format is not implemented, only GIT binary literals.
+
+// GITBinaryLiteral represents a GIT binary literal diff.
+type GITBinaryLiteral struct {
+	OldSHA1	[]byte;	// if non-empty, the SHA1 hash of the original
+	New	[]byte;	// the new contents
+}
+
+// Apply implements the Diff interface's Apply method.
+func (d *GITBinaryLiteral) Apply(old []byte) ([]byte, os.Error) {
+	if sum := gitSHA1(old); !bytes.HasPrefix(sum, d.OldSHA1) {
+		return nil, ErrPatchFailure;
+	}
+	return d.New, nil;
+}
+
+func unhex(c byte) uint8 {
+	switch {
+	case '0' <= c && c <= '9':
+		return c-'0';
+	case 'a' <= c && c <= 'f':
+		return c-'a'+10;
+	case 'A' <= c && c <= 'F':
+		return c-'A'+10;
+	}
+	return 255;
+}
+
+func getHex(s []byte) (data []byte, rest []byte) {
+	n := 0;
+	for n < len(s) && unhex(s[n]) != 255 {
+		n++;
+	}
+	n &^= 1;	// Only take an even number of hex digits.
+	data = make([]byte, n/2);
+	for i := range data {
+		data[i] = unhex(s[2*i])<<4 | unhex(s[2*i + 1]);
+	}
+	rest = s[n:len(s)];
+	return;
+}
+
+// ParseGITBinary parses raw as a GIT binary patch.
+func ParseGITBinary(raw []byte) (Diff, os.Error) {
+	var oldSHA1, newSHA1 []byte;
+	var sawBinary bool;
+
+	for {
+		var first []byte;
+		first, raw, _ = getLine(raw, 1);
+		first = bytes.TrimSpace(first);
+		if s, ok := skip(first, "index "); ok {
+			oldSHA1, s = getHex(s);
+			if s, ok = skip(s, ".."); !ok {
+				continue;
+			}
+			newSHA1, s = getHex(s);
+			continue;
+		}
+		if _, ok := skip(first, "GIT binary patch"); ok {
+			sawBinary = true;
+			continue;
+		}
+		if n, _, ok := atoi(first, "literal ", 10); ok && sawBinary {
+			data := make([]byte, n);
+			d := git85.NewDecoder(bytes.NewBuffer(raw));
+			z, err := zlib.NewInflater(d);
+			if err != nil {
+				return nil, err;
+			}
+			defer z.Close();
+			if _, err = io.ReadFull(z, data); err != nil {
+				if err == os.EOF {
+					err = io.ErrUnexpectedEOF;
+				}
+				return nil, err;
+			}
+			var buf [1]byte;
+			m, err := z.Read(&buf);
+			if m != 0 || err != os.EOF {
+				return nil, os.NewError("GIT binary literal longer than expected");
+			}
+
+			if sum := gitSHA1(data); !bytes.HasPrefix(sum, newSHA1) {
+				return nil, os.NewError("GIT binary literal SHA1 mismatch");
+			}
+			return &GITBinaryLiteral{oldSHA1, data}, nil;
+		}
+		if !sawBinary {
+			return nil, os.NewError("unexpected GIT patch header: " + string(first));
+		}
+	}
+	panic("unreachable");
+}