format/diff: unified diff encoder and public API

- Added Patch interface
- Added a Unified Diff encoder from Patches
- Added Change method to generate Patches
- Added Changes method to generate Patches
- Added Tree method to generate Patches
- Added Commit method to generate Patches

2 files changed, 55 insertions, 0 deletions

diff --git a/utils/binary/read.go b/utils/binary/read.go
index 0bcf11a..c256ffe 100644
--- a/utils/binary/read.go
+++ b/utils/binary/read.go
@@ -3,6 +3,7 @@
 package binary
 
 import (
+	"bufio"
 	"encoding/binary"
 	"io"
 
@@ -122,3 +123,33 @@ func ReadHash(r io.Reader) (plumbing.Hash, error) {
 
 	return h, nil
 }
+
+const sniffLen = 8000
+
+// IsBinary detects if data is a binary value based on:
+// http://git.kernel.org/cgit/git/git.git/tree/xdiff-interface.c?id=HEAD#n198
+func IsBinary(r io.Reader) (bool, error) {
+	reader := bufio.NewReader(r)
+	c := 0
+	for {
+		if c == sniffLen {
+			break
+		}
+
+		b, err := reader.ReadByte()
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			return false, err
+		}
+
+		if b == byte(0) {
+			return true, nil
+		}
+
+		c++
+	}
+
+	return false, nil
+}
diff --git a/utils/binary/read_test.go b/utils/binary/read_test.go
index 59dbc30..5674653 100644
--- a/utils/binary/read_test.go
+++ b/utils/binary/read_test.go
@@ -85,3 +85,27 @@ func (s *BinarySuite) TestReadHash(c *C) {
 	c.Assert(err, IsNil)
 	c.Assert(hash.String(), Equals, expected.String())
 }
+
+func (s *BinarySuite) TestIsBinary(c *C) {
+	buf := bytes.NewBuffer(nil)
+	buf.Write(bytes.Repeat([]byte{'A'}, sniffLen))
+	buf.Write([]byte{0})
+	ok, err := IsBinary(buf)
+	c.Assert(err, IsNil)
+	c.Assert(ok, Equals, false)
+
+	buf.Reset()
+
+	buf.Write(bytes.Repeat([]byte{'A'}, sniffLen-1))
+	buf.Write([]byte{0})
+	ok, err = IsBinary(buf)
+	c.Assert(err, IsNil)
+	c.Assert(ok, Equals, true)
+
+	buf.Reset()
+
+	buf.Write(bytes.Repeat([]byte{'A'}, 10))
+	ok, err = IsBinary(buf)
+	c.Assert(err, IsNil)
+	c.Assert(ok, Equals, false)
+}