package patch

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

6 files changed, 1065 insertions, 0 deletions

diff --git a/src/pkg/patch/Makefile b/src/pkg/patch/Makefile
new file mode 100644
index 000000000..c32a56ed8
--- /dev/null
+++ b/src/pkg/patch/Makefile
@@ -0,0 +1,14 @@
+# 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.
+
+include $(GOROOT)/src/Make.$(GOARCH)
+
+TARG=patch
+GOFILES=\
+	apply.go\
+	git.go\
+	patch.go\
+	textdiff.go\
+
+include $(GOROOT)/src/Make.pkg
diff --git a/src/pkg/patch/apply.go b/src/pkg/patch/apply.go
new file mode 100644
index 000000000..154133028
--- /dev/null
+++ b/src/pkg/patch/apply.go
@@ -0,0 +1,54 @@
+// 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 "os"
+
+// An Op is a single operation to execute to apply a patch.
+type Op struct {
+	Verb	Verb;	// action
+	Src	string;	// source file
+	Dst	string;	// destination file
+	Mode	int;	// mode for destination (if non-zero)
+	Data	[]byte;	// data for destination (if non-nil)
+}
+
+// Apply applies the patch set to the files named in the patch set,
+// constructing an in-memory copy of the new file state.
+// It is the client's job to write the changes to the file system
+// if desired.
+//
+// The function readFile should return the contents of the named file.
+// Typically this function will be io.ReadFile.
+//
+func (set *Set) Apply(readFile func(string) ([]byte, os.Error)) ([]Op, os.Error) {
+	op := make([]Op, len(set.File));
+
+	for i, f := range set.File {
+		o := &op[i];
+		o.Verb = f.Verb;
+		o.Src = f.Src;
+		o.Dst = f.Dst;
+		o.Mode = f.NewMode;
+		if f.Diff != NoDiff || o.Verb != Edit {
+			// Clients assume o.Data == nil means no data diff.
+			// Start with a non-nil data.
+			var old []byte = make([]byte, 0);	// not nil
+			var err os.Error;
+			if f.Src != "" {
+				old, err = readFile(f.Src);
+				if err != nil {
+					return nil, &os.PathError{string(f.Verb), f.Src, err};
+				}
+			}
+			o.Data, err = f.Diff.Apply(old);
+			if err != nil {
+				return nil, &os.PathError{string(f.Verb), f.Src, err};
+			}
+		}
+	}
+
+	return op, nil;
+}
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");
+}
diff --git a/src/pkg/patch/patch.go b/src/pkg/patch/patch.go
new file mode 100644
index 000000000..c0fdadb84
--- /dev/null
+++ b/src/pkg/patch/patch.go
@@ -0,0 +1,323 @@
+// 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 implements parsing and execution of the textual and
+// binary patch descriptions used by version control tools such as
+// CVS, GIT, Mercurial, and Subversion.
+package patch
+
+import (
+	"bytes";
+	"os";
+	"path";
+	"strings";
+)
+
+// A Set represents a set of patches to be applied as a single atomic unit.
+// Patch sets are often preceded by a descriptive header.
+type Set struct {
+	Header	string;	// free-form text
+	File	[]*File;
+}
+
+// A File represents a collection of changes to be made to a single file.
+type File struct {
+	Verb			Verb;
+	Src			string;	// source for Verb == Copy, Verb == Rename
+	Dst			string;
+	OldMode, NewMode	int;	// 0 indicates not used
+	Diff;				// changes to data; == NoDiff if operation does not edit file
+}
+
+// A Verb is an action performed on a file.
+type Verb string
+
+const (
+	Add	Verb	= "add";
+	Copy	Verb	= "copy";
+	Delete	Verb	= "delete";
+	Edit	Verb	= "edit";
+	Rename	Verb	= "rename";
+)
+
+// A Diff is any object that describes changes to transform
+// an old byte stream to a new one.
+type Diff interface {
+	// Apply applies the changes listed in the diff
+	// to the string s, returning the new version of the string.
+	// Note that the string s need not be a text string.
+	Apply(old []byte) (new []byte, err os.Error);
+}
+
+// NoDiff is a no-op Diff implementation: it passes the
+// old data through unchanged.
+var NoDiff Diff = noDiffType(0)
+
+type noDiffType int
+
+func (noDiffType) Apply(old []byte) ([]byte, os.Error) {
+	return old, nil;
+}
+
+// A SyntaxError represents a syntax error encountered while parsing a patch.
+type SyntaxError string
+
+func (e SyntaxError) String() string {
+	return string(e);
+}
+
+var newline = []byte{'\n'}
+
+// Parse patches the patch text to create a patch Set.
+// The patch text typically comprises a textual header and a sequence
+// of file patches, as would be generated by CVS, Subversion,
+// Mercurial, or GIT.
+func Parse(text []byte) (*Set, os.Error) {
+	// Split text into files.
+	// CVS and Subversion begin new files with
+	//	Index: file name.
+	//	==================
+	//	diff -u blah blah
+	//
+	// Mercurial and GIT use
+	//	diff [--git] a/file/path b/file/path.
+	//
+	// First look for Index: lines.  If none, fall back on diff lines.
+	text, files := sections(text, "Index: ");
+	if len(files) == 0 {
+		text, files = sections(text, "diff ");
+	}
+
+	set := &Set{string(text), make([]*File, len(files))};
+
+	// Parse file header and then
+	// parse files into patch chunks.
+	// Each chunk begins with @@.
+	for i, raw := range files {
+		p := new(File);
+		set.File[i] = p;
+
+		// First line of hdr is the Index: that
+		// begins the section.  After that is the file name.
+		s, raw, _ := getLine(raw, 1);
+		if hasPrefix(s, "Index: ") {
+			p.Dst = string(bytes.TrimSpace(s[7:len(s)]));
+			goto HaveName;
+		} else if hasPrefix(s, "diff ") {
+			str := string(bytes.TrimSpace(s));
+			i := strings.LastIndex(str, " b/");
+			if i >= 0 {
+				p.Dst = str[i+3 : len(str)];
+				goto HaveName;
+			}
+		}
+		return nil, SyntaxError("unexpected patch header line: " + string(s));
+	HaveName:
+		p.Dst = path.Clean(p.Dst);
+		if strings.HasPrefix(p.Dst, "../") || strings.HasPrefix(p.Dst, "/") {
+			return nil, SyntaxError("invalid path: " + p.Dst);
+		}
+
+		// Parse header lines giving file information:
+		//	new file mode %o	- file created
+		//	deleted file mode %o	- file deleted
+		//	old file mode %o	- file mode changed
+		//	new file mode %o	- file mode changed
+		//	rename from %s	- file renamed from other file
+		//	rename to %s
+		//	copy from %s		- file copied from other file
+		//	copy to %s
+		p.Verb = Edit;
+		for len(raw) > 0 {
+			oldraw := raw;
+			var l []byte;
+			l, raw, _ = getLine(raw, 1);
+			l = bytes.TrimSpace(l);
+			if m, s, ok := atoi(l, "new file mode ", 8); ok && len(s) == 0 {
+				p.NewMode = m;
+				p.Verb = Add;
+				continue;
+			}
+			if m, s, ok := atoi(l, "deleted file mode ", 8); ok && len(s) == 0 {
+				p.OldMode = m;
+				p.Verb = Delete;
+				p.Src = p.Dst;
+				p.Dst = "";
+				continue;
+			}
+			if m, s, ok := atoi(l, "old file mode ", 8); ok && len(s) == 0 {
+				// usually implies p.Verb = "rename" or "copy"
+				// but we'll get that from the rename or copy line.
+				p.OldMode = m;
+				continue;
+			}
+			if m, s, ok := atoi(l, "old mode ", 8); ok && len(s) == 0 {
+				p.OldMode = m;
+				continue;
+			}
+			if m, s, ok := atoi(l, "new mode ", 8); ok && len(s) == 0 {
+				p.NewMode = m;
+				continue;
+			}
+			if s, ok := skip(l, "rename from "); ok && len(s) > 0 {
+				p.Src = string(s);
+				p.Verb = Rename;
+				continue;
+			}
+			if s, ok := skip(l, "rename to "); ok && len(s) > 0 {
+				p.Verb = Rename;
+				continue;
+			}
+			if s, ok := skip(l, "copy from "); ok && len(s) > 0 {
+				p.Src = string(s);
+				p.Verb = Copy;
+				continue;
+			}
+			if s, ok := skip(l, "copy to "); ok && len(s) > 0 {
+				p.Verb = Copy;
+				continue;
+			}
+			if s, ok := skip(l, "Binary file "); ok && len(s) > 0 {
+				// Hg prints
+				//	Binary file foo has changed
+				// when deleting a binary file.
+				continue;
+			}
+			if s, ok := skip(l, "RCS file: "); ok && len(s) > 0 {
+				// CVS prints
+				//	RCS file: /cvs/plan9/bin/yesterday,v
+				//	retrieving revision 1.1
+				// for each file.
+				continue;
+			}
+			if s, ok := skip(l, "retrieving revision "); ok && len(s) > 0 {
+				// CVS prints
+				//	RCS file: /cvs/plan9/bin/yesterday,v
+				//	retrieving revision 1.1
+				// for each file.
+				continue;
+			}
+			if hasPrefix(l, "===") || hasPrefix(l, "---") || hasPrefix(l, "+++") || hasPrefix(l, "diff ") {
+				continue;
+			}
+			if hasPrefix(l, "@@ -") {
+				diff, err := ParseTextDiff(oldraw);
+				if err != nil {
+					return nil, err;
+				}
+				p.Diff = diff;
+				break;
+			}
+			if hasPrefix(l, "index ") || hasPrefix(l, "GIT binary patch") {
+				diff, err := ParseGITBinary(oldraw);
+				if err != nil {
+					return nil, err;
+				}
+				p.Diff = diff;
+				break;
+			}
+			return nil, SyntaxError("unexpected patch header line: " + string(l));
+		}
+		if p.Diff == nil {
+			p.Diff = NoDiff;
+		}
+		if p.Verb == Edit {
+			p.Src = p.Dst;
+		}
+	}
+
+	return set, nil;
+}
+
+// getLine returns the first n lines of data and the remainder.
+// If data has no newline, getLine returns data, nil, false
+func getLine(data []byte, n int) (first []byte, rest []byte, ok bool) {
+	rest = data;
+	ok = true;
+	for ; n > 0; n-- {
+		nl := bytes.Index(rest, newline);
+		if nl < 0 {
+			rest = nil;
+			ok = false;
+			break;
+		}
+		rest = rest[nl+1 : len(rest)];
+	}
+	first = data[0 : len(data)-len(rest)];
+	return;
+}
+
+// sections returns a collection of file sections,
+// each of which begins with a line satisfying prefix.
+// text before the first instance of such a line is
+// returned separately.
+func sections(text []byte, prefix string) ([]byte, [][]byte) {
+	n := 0;
+	for b := text; ; {
+		if hasPrefix(b, prefix) {
+			n++;
+		}
+		nl := bytes.Index(b, newline);
+		if nl < 0 {
+			break;
+		}
+		b = b[nl+1 : len(b)];
+	}
+
+	sect := make([][]byte, n+1);
+	n = 0;
+	for b := text; ; {
+		if hasPrefix(b, prefix) {
+			sect[n] = text[0 : len(text)-len(b)];
+			n++;
+			text = b;
+		}
+		nl := bytes.Index(b, newline);
+		if nl < 0 {
+			sect[n] = text;
+			break;
+		}
+		b = b[nl+1 : len(b)];
+	}
+	return sect[0], sect[1:len(sect)];
+}
+
+// if s begins with the prefix t, skip returns
+// s with that prefix removed and ok == true.
+func skip(s []byte, t string) (ss []byte, ok bool) {
+	if len(s) < len(t) || string(s[0:len(t)]) != t {
+		return nil, false;
+	}
+	return s[len(t):len(s)], true;
+}
+
+// if s begins with the prefix t and then is a sequence
+// of digits in the given base, atoi returns the number
+// represented by the digits and s with the
+// prefix and the digits removed.
+func atoi(s []byte, t string, base int) (n int, ss []byte, ok bool) {
+	if s, ok = skip(s, t); !ok {
+		return;
+	}
+	var i int;
+	for i = 0; i < len(s) && '0' <= s[i] && s[i] <= byte('0'+base-1); i++ {
+		n = n*base + int(s[i]-'0');
+	}
+	if i == 0 {
+		return;
+	}
+	return n, s[i:len(s)], true;
+}
+
+// hasPrefix returns true if s begins with t.
+func hasPrefix(s []byte, t string) bool {
+	_, ok := skip(s, t);
+	return ok;
+}
+
+// splitLines returns the result of splitting s into lines.
+// The \n on each line is preserved.
+func splitLines(s []byte) [][]byte {
+	return bytes.SplitAfter(s, newline, 0);
+}
diff --git a/src/pkg/patch/patch_test.go b/src/pkg/patch/patch_test.go
new file mode 100644
index 000000000..d1d4f9302
--- /dev/null
+++ b/src/pkg/patch/patch_test.go
@@ -0,0 +1,382 @@
+// 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
+
+// TODO(rsc): test Apply
+
+import (
+	"strings";
+	"testing";
+)
+
+type Test struct {
+	in	string;
+	out	string;
+	diff	string;
+}
+
+func TestFileApply(t *testing.T) {
+	for i, test := range tests {
+		set, err := Parse(strings.Bytes(test.diff));
+		if err != nil {
+			t.Errorf("#%d: Parse: %s", i, err);
+			continue;
+		}
+		if len(set.File) != 1 {
+			t.Errorf("#%d: Parse returned %d patches, want 1", i, len(set.File));
+			continue;
+		}
+		new, err := set.File[0].Apply(strings.Bytes(test.in));
+		if err != nil {
+			t.Errorf("#%d: Apply: %s", i, err);
+			continue;
+		}
+		if s := string(new); s != test.out {
+			t.Errorf("#%d:\n--- have\n%s--- want\n%s", i, s, test.out);
+		}
+	}
+}
+
+var tests = []Test{
+	Test{
+		"hello, world\n",
+		"goodbye, world\n",
+		"Index: a\n"
+		"--- a/a\n"
+		"+++ b/b\n"
+		"@@ -1 +1 @@\n"
+		"-hello, world\n"
+		"+goodbye, world\n",
+	},
+	Test{
+		"hello, world\n",
+		"goodbye, world\n",
+		"diff a/a b/b\n"
+		"--- a/a\n"
+		"+++ b/b\n"
+		"@@ -1,1 +1,1 @@\n"
+		"-hello, world\n"
+		"+goodbye, world\n",
+	},
+	Test{
+		"hello, world",
+		"goodbye, world\n",
+		"diff --git a/a b/b\n"
+		"--- a/a\n"
+		"+++ b/b\n"
+		"@@ -1 +1 @@\n"
+		"-hello, world\n"
+		"\\ No newline at end of file\n"
+		"+goodbye, world\n",
+	},
+	Test{
+		"hello, world\n",
+		"goodbye, world",
+		"Index: a\n"
+		"--- a/a\n"
+		"+++ b/b\n"
+		"@@ -1 +1 @@\n"
+		"-hello, world\n"
+		"+goodbye, world\n"
+		"\\ No newline at end of file\n",
+	},
+	Test{
+		"hello, world",
+		"goodbye, world",
+		"Index: a\n"
+		"--- a/a\n"
+		"+++ b/b\n"
+		"@@ -1 +1 @@\n"
+		"-hello, world\n"
+		"\\ No newline at end of file\n"
+		"+goodbye, world\n"
+		"\\ No newline at end of file\n",
+	},
+	Test{
+		"a\nb\nc\nd\ne\nf\ng\nh\ni\nj\nk\nl\nm\nn\n",
+		"a\nB\nC\nD\ne\nf\ng\nj\nk\nl\nm\nN\n",
+		"Index: a\n"
+		"--- a/a\n"
+		"+++ b/b\n"
+		"@@ -1,14 +1,12 @@\n"
+		" a\n"
+		"-b\n"
+		"-c\n"
+		"-d\n"
+		"+B\n"
+		"+C\n"
+		"+D\n"
+		" e\n"
+		" f\n"
+		" g\n"
+		"-h\n"
+		"-i\n"
+		" j\n"
+		" k\n"
+		" l\n"
+		" m\n"
+		"-n\n"
+		"+N\n",
+	},
+	Test{
+		"a\nb\nc\nd\ne\nf\ng\nh\ni\nj\nk\nl\nm\nn\no\np\nq\nr\ns\nt\nu\nv\nw\nx\ny\nz\n",
+		"a\nb\nc\ng\nh\ni\nj\nk\nl\nm\nN\nO\np\nq\nr\ns\nt\nu\nv\nw\nd\ne\nf\nx\n",
+		"Index: a\n"
+		"--- a/a\n"
+		"+++ b/b\n"
+		"@@ -1,9 +1,6 @@\n"
+		" a\n"
+		" b\n"
+		" c\n"
+		"-d\n"
+		"-e\n"
+		"-f\n"
+		" g\n"
+		" h\n"
+		" i\n"
+		"@@ -11,8 +8,8 @@ j\n"
+		" k\n"
+		" l\n"
+		" m\n"
+		"-n\n"
+		"-o\n"
+		"+N\n"
+		"+O\n"
+		" p\n"
+		" q\n"
+		" r\n"
+		"\n"
+		"@@ -21,6 +18,7 @@ t\n"
+		" u\n"
+		" v\n"
+		" w\n"
+		"+d\n"
+		"+e\n"
+		"+f\n"
+		" x\n"
+		"-y\n"
+		"-z\n",
+	},
+	Test{
+		"a\nb\nc\ng\nh\ni\nj\nk\nl\nm\nN\nO\np\nq\nr\ns\nt\nu\nv\nw\nd\ne\nf\nx\n",
+		"a\nb\nc\nd\ne\nf\ng\nh\ni\nj\nk\nl\nm\nn\no\np\nq\nr\ns\nt\nu\nv\nw\nx\ny\nz\n",
+		"Index: a\n"
+		"--- a/b\n"
+		"+++ b/a\n"
+		"@@ -1,6 +1,9 @@\n"
+		" a\n"
+		" b\n"
+		" c\n"
+		"+d\n"
+		"+e\n"
+		"+f\n"
+		" g\n"
+		" h\n"
+		" i\n"
+		"@@ -8,8 +11,8 @@ j\n"
+		" k\n"
+		" l\n"
+		" m\n"
+		"-N\n"
+		"-O\n"
+		"+n\n"
+		"+o\n"
+		" p\n"
+		" q\n"
+		" r\n"
+		"@@ -18,7 +21,6 @@ t\n"
+		" u\n"
+		" v\n"
+		" w\n"
+		"-d\n"
+		"-e\n"
+		"-f\n"
+		" x\n"
+		"+y\n"
+		"+z\n",
+	},
+	Test{
+		"a\nb\nc\nd\ne\nf\ng\nh\ni\nj\nk\nl\nm\nn\no\np\nq\nr\ns\nt\nu\nv\nw\nx\ny\nz\n",
+		"",
+		"Index: a\n"
+		"deleted file mode 100644\n"
+		"--- a/a\n"
+		"+++ /dev/null\n"
+		"@@ -1,26 +0,0 @@\n"
+		"-a\n"
+		"-b\n"
+		"-c\n"
+		"-d\n"
+		"-e\n"
+		"-f\n"
+		"-g\n"
+		"-h\n"
+		"-i\n"
+		"-j\n"
+		"-k\n"
+		"-l\n"
+		"-m\n"
+		"-n\n"
+		"-o\n"
+		"-p\n"
+		"-q\n"
+		"-r\n"
+		"-s\n"
+		"-t\n"
+		"-u\n"
+		"-v\n"
+		"-w\n"
+		"-x\n"
+		"-y\n"
+		"-z\n",
+	},
+	Test{
+		"",
+		"a\nb\nc\nd\ne\nf\ng\nh\ni\nj\nk\nl\nm\nn\no\np\nq\nr\ns\nt\nu\nv\nw\nx\ny\nz\n",
+		"Index: a\n"
+		"new file mode 100644\n"
+		"--- /dev/null\n"
+		"+++ b/a\n"
+		"@@ -0,0 +1,26 @@\n"
+		"+a\n"
+		"+b\n"
+		"+c\n"
+		"+d\n"
+		"+e\n"
+		"+f\n"
+		"+g\n"
+		"+h\n"
+		"+i\n"
+		"+j\n"
+		"+k\n"
+		"+l\n"
+		"+m\n"
+		"+n\n"
+		"+o\n"
+		"+p\n"
+		"+q\n"
+		"+r\n"
+		"+s\n"
+		"+t\n"
+		"+u\n"
+		"+v\n"
+		"+w\n"
+		"+x\n"
+		"+y\n"
+		"+z\n",
+	},
+	Test{
+		"\xc2\xd8\xf9\x63\x8c\xf7\xc6\x9b\xb0\x3c\x39\xfa\x08\x8e\x42\x8f"
+		"\x1c\x7c\xaf\x54\x22\x87\xc3\xc5\x68\x9b\xe1\xbd\xbc\xc3\xe0\xda"
+		"\xcc\xe3\x96\xda\xc2\xaf\xbb\x75\x79\x64\x86\x60\x8a\x43\x9e\x07"
+		"\x9c\xaa\x92\x88\xd4\x30\xb9\x8b\x95\x04\x60\x71\xc7\xbb\x2d\x93"
+		"\x66\x73\x01\x24\xf3\x63\xbf\xe6\x1d\x38\x15\x56\x98\xc4\x1f\x85"
+		"\xc3\x60\x39\x3a\x0d\x57\x53\x0c\x29\x3f\xbb\x44\x7e\x56\x56\x9d"
+		"\x87\xcf\xf6\x88\xe8\x98\x05\x85\xf8\xfe\x44\x21\xfa\x33\xc9\xa4"
+		"\x22\xbe\x89\x05\x8b\x82\x76\xc9\x7c\xaf\x48\x28\xc4\x86\x15\x89"
+		"\xb9\x98\xfa\x41\xfc\x3d\x8d\x80\x29\x33\x17\x45\xa5\x7f\x67\x79"
+		"\x7f\x92\x3b\x2e\x4c\xc1\xd2\x1b\x9e\xcf\xed\x53\x56\xb2\x49\x58"
+		"\xd8\xe9\x9f\x98\xa3\xfe\x78\xe1\xe8\x74\x71\x04\x1a\x87\xd9\x68"
+		"\x18\x68\xd0\xae\x7b\xa4\x25\xe3\x06\x03\x7e\x8b\xd3\x50\x1f\xb1"
+		"\x67\x08\xe3\x93\xf4\x4f\xa1\xfb\x31\xcf\x99\x5a\x43\x9f\x4b\xc4"
+		"\xaa\x68\x1a\xf9\x8e\x97\x02\x80\x17\xf1\x25\x21\xdf\x94\xbf\x41"
+		"\x08\x59\x3d\xea\x36\x23\x03\xb5\x62\x4d\xb6\x8f\x9e\xdf\x1f\x03"
+		"\x7d\x70\xe0\x6f\x46\x08\x96\x79\x72\xb7\xae\x41\x2b\xbd\x2a\x95",
+
+		"\x8e\x5f\xf8\x79\x36\x8d\xbe\x68\xc4\x2c\x78\x8a\x46\x28\x40\x3e"
+		"\xcf\x3b\xb9\x14\xaf\xfa\x04\x9e\x4b\xa2\x52\x51\x51\xf0\xad\xd3"
+		"\x03\x1c\x03\x79\x5f\x53\xc7\x1a\xd5\x28\xe2\xd9\x19\x37\xa4\xfa"
+		"\xdd\xff\xac\xb5\xa9\x42\x4e\x17\xeb\xb4\x0d\x20\x67\x08\x43\x21"
+		"\x7d\x12\x27\xfa\x96\x7a\x85\xf8\x04\x5f\xf4\xfe\xda\x9f\x66\xf2"
+		"\xba\x04\x39\x00\xab\x3f\x23\x20\x84\x53\xb4\x88\xb6\xee\xa2\x9e"
+		"\xc1\xca\xd4\x09\x2a\x27\x89\x2f\xcb\xba\xa6\x41\xb6\xe9\xc5\x08"
+		"\xff\xf5\x95\x35\xab\xbb\x5c\x62\x96\xe7\x7c\x8f\xf2\x40\x12\xc9"
+		"\x2d\xfe\xff\x75\x4f\x70\x47\xc9\xcd\x15\x0a\x1c\x23\xe7\x0f\x15"
+		"\x95\x75\x30\x8f\x6e\x9f\x7e\xa5\x9d\xd1\x65\x1c\x4d\x4e\xf4\x32"
+		"\x49\x9b\xa1\x30\x44\x62\x6f\xe2\xe6\x69\x09\xf8\x7c\x7c\xbe\x07"
+		"\xa9\xb6\x14\x7a\x6b\x85\xe4\xbf\x48\xbe\x5b\x3b\x70\xb3\x79\x3b"
+		"\xc4\x35\x9d\x86\xf1\xfe\x2b\x6f\x80\x74\x50\xf3\x96\x59\x53\x1a"
+		"\x75\x46\x9d\x57\x72\xb3\xb1\x26\xf5\x81\xcd\x96\x08\xbc\x2b\x10"
+		"\xdc\x80\xbd\xd0\xdf\x03\x6d\x8d\xec\x30\x2b\x4c\xdb\x4d\x3b\xef"
+		"\x7d\x3a\x39\xc8\x5a\xc4\xcc\x24\x37\xde\xe2\x95\x2b\x04\x97\xb0",
+
+		// From git diff --binary
+		"Index: a\n"
+		"index cb34d9b1743b7c410fa750be8a58eb355987110b..0a01764bc1b2fd29da317f72208f462ad342400f 100644\n"
+		"GIT binary patch\n"
+		"literal 256\n"
+		"zcmV+b0ssDvU-)@8jlO8aEO?4WC_p~XJGm6E`UIX!qEb;&@U7DW90Pe@Q^y+BDB{@}\n"
+		"zH>CRA|E#sCLQWU!v<)C<2ty%#5-0kWdWHA|U-bUkpJwv91UUe!KO-Q7Q?!V-?xLQ-\n"
+		"z%G3!eCy6i1x~4(4>BR{D^_4ZNyIf+H=X{UyKoZF<{{MAPa7W3_6$%_9=MNQ?buf=^\n"
+		"zpMIsC(PbP>PV_QKo1rj7VsGN+X$kmze7*;%wiJ46h2+0TzFRwRvw1tjHJyg>{wr^Q\n"
+		"zbWrn_SyLKyMx9r3v#}=ifz6f(yekmgfW6S)18t4$Fe^;kO*`*>IyuN%#LOf&-r|)j\n"
+		"G1edVN^?m&S\n"
+		"\n"
+		"literal 256\n"
+		"zcmV+b0ssEO*!g3O_r{yBJURLZjzW(de6Lg@hr`8ao8i5@!{FM?<CfaOue)`5WQJgh\n"
+		"zL!Jkms*;G*Fu9AB1YmK;yDgJua{(mtW54DdI2Bfy#2<yjU^zMsS5pirKf6SJR#u&d\n"
+		"z&-RGum<5IS{zM`AGs&bPzKI2kf_BM#uSh7wh82mqnEFBdJ&k}VGZ#gre`k4rk~=O;\n"
+		"z!O|O^&+SuIvPoFj>7SUR{&?Z&ba4b4huLTtXwa^Eq$T491AdFsP#>{p2;-CVPoeuU\n"
+		"z&zV|7pG(B5Xd3yBmjZwn@g*VOl)pg;Sv~4DBLlT!O}3Ao-yZ{gaNuu72$p$rx2{1e\n"
+		"Gy(*Pb;D3Ms\n"
+		"\n",
+	},
+	Test{
+		"\xc2\xd8\xf9\x63\x8c\xf7\xc6\x9b\xb0\x3c\x39\xfa\x08\x8e\x42\x8f"
+		"\x1c\x7c\xaf\x54\x22\x87\xc3\xc5\x68\x9b\xe1\xbd\xbc\xc3\xe0\xda"
+		"\xcc\xe3\x96\xda\xc2\xaf\xbb\x75\x79\x64\x86\x60\x8a\x43\x9e\x07"
+		"\x9c\xaa\x92\x88\xd4\x30\xb9\x8b\x95\x04\x60\x71\xc7\xbb\x2d\x93"
+		"\x66\x73\x01\x24\xf3\x63\xbf\xe6\x1d\x38\x15\x56\x98\xc4\x1f\x85"
+		"\xc3\x60\x39\x3a\x0d\x57\x53\x0c\x29\x3f\xbb\x44\x7e\x56\x56\x9d"
+		"\x87\xcf\xf6\x88\xe8\x98\x05\x85\xf8\xfe\x44\x21\xfa\x33\xc9\xa4"
+		"\x22\xbe\x89\x05\x8b\x82\x76\xc9\x7c\xaf\x48\x28\xc4\x86\x15\x89"
+		"\xb9\x98\xfa\x41\xfc\x3d\x8d\x80\x29\x33\x17\x45\xa5\x7f\x67\x79"
+		"\x7f\x92\x3b\x2e\x4c\xc1\xd2\x1b\x9e\xcf\xed\x53\x56\xb2\x49\x58"
+		"\xd8\xe9\x9f\x98\xa3\xfe\x78\xe1\xe8\x74\x71\x04\x1a\x87\xd9\x68"
+		"\x18\x68\xd0\xae\x7b\xa4\x25\xe3\x06\x03\x7e\x8b\xd3\x50\x1f\xb1"
+		"\x67\x08\xe3\x93\xf4\x4f\xa1\xfb\x31\xcf\x99\x5a\x43\x9f\x4b\xc4"
+		"\xaa\x68\x1a\xf9\x8e\x97\x02\x80\x17\xf1\x25\x21\xdf\x94\xbf\x41"
+		"\x08\x59\x3d\xea\x36\x23\x03\xb5\x62\x4d\xb6\x8f\x9e\xdf\x1f\x03"
+		"\x7d\x70\xe0\x6f\x46\x08\x96\x79\x72\xb7\xae\x41\x2b\xbd\x2a\x95",
+
+		"\x8e\x5f\xf8\x79\x36\x8d\xbe\x68\xc4\x2c\x78\x8a\x46\x28\x40\x3e"
+		"\xcf\x3b\xb9\x14\xaf\xfa\x04\x9e\x4b\xa2\x52\x51\x51\xf0\xad\xd3"
+		"\x03\x1c\x03\x79\x5f\x53\xc7\x1a\xd5\x28\xe2\xd9\x19\x37\xa4\xfa"
+		"\xdd\xff\xac\xb5\xa9\x42\x4e\x17\xeb\xb4\x0d\x20\x67\x08\x43\x21"
+		"\x7d\x12\x27\xfa\x96\x7a\x85\xf8\x04\x5f\xf4\xfe\xda\x9f\x66\xf2"
+		"\xba\x04\x39\x00\xab\x3f\x23\x20\x84\x53\xb4\x88\xb6\xee\xa2\x9e"
+		"\xc1\xca\xd4\x09\x2a\x27\x89\x2f\xcb\xba\xa6\x41\xb6\xe9\xc5\x08"
+		"\xff\xf5\x95\x35\xab\xbb\x5c\x62\x96\xe7\x7c\x8f\xf2\x40\x12\xc9"
+		"\x2d\xfe\xff\x75\x4f\x70\x47\xc9\xcd\x15\x0a\x1c\x23\xe7\x0f\x15"
+		"\x95\x75\x30\x8f\x6e\x9f\x7e\xa5\x9d\xd1\x65\x1c\x4d\x4e\xf4\x32"
+		"\x49\x9b\xa1\x30\x44\x62\x6f\xe2\xe6\x69\x09\xf8\x7c\x7c\xbe\x07"
+		"\xa9\xb6\x14\x7a\x6b\x85\xe4\xbf\x48\xbe\x5b\x3b\x70\xb3\x79\x3b"
+		"\xc4\x35\x9d\x86\xf1\xfe\x2b\x6f\x80\x74\x50\xf3\x96\x59\x53\x1a"
+		"\x75\x46\x9d\x57\x72\xb3\xb1\x26\xf5\x81\xcd\x96\x08\xbc\x2b\x10"
+		"\xdc\x80\xbd\xd0\xdf\x03\x6d\x8d\xec\x30\x2b\x4c\xdb\x4d\x3b\xef"
+		"\x7d\x3a\x39\xc8\x5a\xc4\xcc\x24\x37\xde\xe2\x95\x2b\x04\x97\xb0",
+
+		// From hg diff --git
+		"Index: a\n"
+		"index cb34d9b1743b7c410fa750be8a58eb355987110b..0a01764bc1b2fd29da317f72208f462ad342400f\n"
+		"GIT binary patch\n"
+		"literal 256\n"
+		"zc$@(M0ssDvU-)@8jlO8aEO?4WC_p~XJGm6E`UIX!qEb;&@U7DW90Pe@Q^y+BDB{@}\n"
+		"zH>CRA|E#sCLQWU!v<)C<2ty%#5-0kWdWHA|U-bUkpJwv91UUe!KO-Q7Q?!V-?xLQ-\n"
+		"z%G3!eCy6i1x~4(4>BR{D^_4ZNyIf+H=X{UyKoZF<{{MAPa7W3_6$%_9=MNQ?buf=^\n"
+		"zpMIsC(PbP>PV_QKo1rj7VsGN+X$kmze7*;%wiJ46h2+0TzFRwRvw1tjHJyg>{wr^Q\n"
+		"zbWrn_SyLKyMx9r3v#}=ifz6f(yekmgfW6S)18t4$Fe^;kO*`*>IyuN%#LOf&-r|)j\n"
+		"G1edVN^?m&S\n"
+		"\n",
+	},
+	Test{
+		"",
+		"",
+		"Index: hello\n"
+		"===================================================================\n"
+		"old mode 100644\n"
+		"new mode 100755\n",
+	},
+}
diff --git a/src/pkg/patch/textdiff.go b/src/pkg/patch/textdiff.go
new file mode 100644
index 000000000..db8527682
--- /dev/null
+++ b/src/pkg/patch/textdiff.go
@@ -0,0 +1,171 @@
+package patch
+
+import (
+	"bytes";
+	"os";
+)
+
+type TextDiff []TextChunk
+
+// A TextChunk specifies an edit to a section of a file:
+// the text beginning at Line, which should be exactly Old,
+// is to be replaced with New.
+type TextChunk struct {
+	Line	int;
+	Old	[]byte;
+	New	[]byte;
+}
+
+func ParseTextDiff(raw []byte) (TextDiff, os.Error) {
+	// Copy raw so it is safe to keep references to slices.
+	_, chunks := sections(raw, "@@ -");
+	delta := 0;
+	diff := make(TextDiff, len(chunks));
+	for i, raw := range chunks {
+		c := &diff[i];
+
+		// Parse start line: @@ -oldLine,oldCount +newLine,newCount @@ junk
+		chunk := splitLines(raw);
+		chunkHeader := chunk[0];
+		var ok bool;
+		var oldLine, oldCount, newLine, newCount int;
+		s := chunkHeader;
+		if oldLine, s, ok = atoi(s, "@@ -", 10); !ok {
+		ErrChunkHdr:
+			return nil, SyntaxError("unexpected chunk header line: " + string(chunkHeader));
+		}
+		if len(s) == 0 || s[0] != ',' {
+			oldCount = 1;
+		} else if oldCount, s, ok = atoi(s, ",", 10); !ok {
+			goto ErrChunkHdr;
+		}
+		if newLine, s, ok = atoi(s, " +", 10); !ok {
+			goto ErrChunkHdr;
+		}
+		if len(s) == 0 || s[0] != ',' {
+			newCount = 1;
+		} else if newCount, s, ok = atoi(s, ",", 10); !ok {
+			goto ErrChunkHdr;
+		}
+		if !hasPrefix(s, " @@") {
+			goto ErrChunkHdr;
+		}
+
+		// Special case: for created or deleted files, the empty half
+		// is given as starting at line 0.  Translate to line 1.
+		if oldCount == 0 && oldLine == 0 {
+			oldLine = 1;
+		}
+		if newCount == 0 && newLine == 0 {
+			newLine = 1;
+		}
+
+		// Count lines in text
+		var dropOldNL, dropNewNL bool;
+		var nold, nnew int;
+		var lastch byte;
+		chunk = chunk[1:len(chunk)];
+		for _, l := range chunk {
+			if nold == oldCount && nnew == newCount && (len(l) == 0 || l[0] != '\\') {
+				if len(bytes.TrimSpace(l)) != 0 {
+					return nil, SyntaxError("too many chunk lines");
+				}
+				continue;
+			}
+			if len(l) == 0 {
+				return nil, SyntaxError("empty chunk line");
+			}
+			switch l[0] {
+			case '+':
+				nnew++;
+			case '-':
+				nold++;
+			case ' ':
+				nnew++;
+				nold++;
+			case '\\':
+				if _, ok := skip(l, "\\ No newline at end of file"); ok {
+					switch lastch {
+					case '-':
+						dropOldNL = true;
+					case '+':
+						dropNewNL = true;
+					case ' ':
+						dropOldNL = true;
+						dropNewNL = true;
+					default:
+						return nil, SyntaxError("message `\\ No newline at end of file' out of context");
+					}
+					break;
+				}
+				fallthrough;
+			default:
+				return nil, SyntaxError("unexpected chunk line: " + string(l));
+			}
+			lastch = l[0];
+		}
+
+		// Does it match the header?
+		if nold != oldCount || nnew != newCount {
+			return nil, SyntaxError("chunk header does not match line count: " + string(chunkHeader));
+		}
+		if oldLine+delta != newLine {
+			return nil, SyntaxError("chunk delta is out of sync with previous chunks");
+		}
+		delta += nnew-nold;
+		c.Line = oldLine;
+
+		var old, new bytes.Buffer;
+		nold = 0;
+		nnew = 0;
+		for _, l := range chunk {
+			if nold == oldCount && nnew == newCount {
+				break;
+			}
+			ch, l := l[0], l[1:len(l)];
+			if ch == '\\' {
+				continue;
+			}
+			if ch != '+' {
+				old.Write(l);
+				nold++;
+			}
+			if ch != '-' {
+				new.Write(l);
+				nnew++;
+			}
+		}
+		c.Old = old.Bytes();
+		c.New = new.Bytes();
+		if dropOldNL {
+			c.Old = c.Old[0 : len(c.Old)-1];
+		}
+		if dropNewNL {
+			c.New = c.New[0 : len(c.New)-1];
+		}
+	}
+	return diff, nil;
+}
+
+var ErrPatchFailure = os.NewError("patch did not apply cleanly")
+
+// Apply applies the changes listed in the diff
+// to the data, returning the new version.
+func (d TextDiff) Apply(data []byte) ([]byte, os.Error) {
+	var buf bytes.Buffer;
+	line := 1;
+	for _, c := range d {
+		var ok bool;
+		var prefix []byte;
+		prefix, data, ok = getLine(data, c.Line - line);
+		if !ok || !bytes.HasPrefix(data, c.Old) {
+			return nil, ErrPatchFailure;
+		}
+		buf.Write(prefix);
+		data = data[len(c.Old):len(data)];
+		buf.Write(c.New);
+		line = c.Line + bytes.Count(c.Old, newline);
+	}
+	buf.Write(data);
+	return buf.Bytes(), nil;
+}