Handle diffs on windows

Running the standard diff tool on windows
produces output with CRLF line endings.
Stripping trailing CR in the line reader utility
prevents errors in diff parsing.

Author: crsdrw

diff/diff_test.go

@@ -375,6 +375,44 @@ func TestParseMultiFileDiffHeaders(t *testing.T) {
 				},
 			},
 		},
+		{
+			filename: "sample_multi_file_new_win.diff",
+			wantDiffs: []*FileDiff{
+				{
+					OrigName: "/dev/null",
+					OrigTime: nil,
+					NewName:  "b/_vendor/go/build/syslist_test.go",
+					NewTime:  nil,
+					Extended: []string{
+						"diff --git a/_vendor/go/build/syslist_test.go b/_vendor/go/build/syslist_test.go",
+						"new file mode 100644",
+						"index 0000000..3be2928",
+					},
+				},
+				{
+					OrigName: "/dev/null",
+					OrigTime: nil,
+					NewName:  "b/_vendor/go/build/testdata/empty/dummy",
+					NewTime:  nil,
+					Extended: []string{
+						"diff --git a/_vendor/go/build/testdata/empty/dummy b/_vendor/go/build/testdata/empty/dummy",
+						"new file mode 100644",
+						"index 0000000..e69de29",
+					},
+				},
+				{
+					OrigName: "/dev/null",
+					OrigTime: nil,
+					NewName:  "b/_vendor/go/build/testdata/multi/file.go",
+					NewTime:  nil,
+					Extended: []string{
+						"diff --git a/_vendor/go/build/testdata/multi/file.go b/_vendor/go/build/testdata/multi/file.go",
+						"new file mode 100644",
+						"index 0000000..ee946eb",
+					},
+				},
+			},
+		},
 	}
 	for _, test := range tests {
 		diffData, err := ioutil.ReadFile(filepath.Join("testdata", test.filename))

diff/reader_util.go

@@ -2,7 +2,6 @@ package diff
 
 import (
 	"bufio"
-	"bytes"
 	"io"
 )
 
@@ -25,6 +24,14 @@ func readLine(r *bufio.Reader) ([]byte, error) {
 	} else if err != nil {
 		return nil, err
 	}
-	line := bytes.TrimSuffix(line_, []byte{'\n'})
-	return line, nil
+	line := line_[0:len(line_)-1]
+	return dropCR(line), nil
+}
+
+// dropCR drops a terminal \r from the data.
+func dropCR(data []byte) []byte {
+	if len(data) > 0 && data[len(data)-1] == '\r' {
+		return data[0 : len(data)-1]
+	}
+	return data
 }

diff/reader_util_test.go

@@ -0,0 +1,68 @@
+package diff
+
+import (
+	"reflect"
+	"bufio"
+	"io"
+	"strings"
+	"testing"
+)
+
+func TestReadLine(t *testing.T) {
+	tests := []struct {
+		name   string
+		input  string
+		want []string
+	}{
+		{
+			name:   "empty",
+			input:  "",
+			want: []string{},
+		},
+		{
+			name:   "single_line",
+			input:  "@@ -0,0 +1,62 @@",
+			want: []string{"@@ -0,0 +1,62 @@"},
+		},
+		{
+			name:   "single_lf_terminated_line",
+			input:  "@@ -0,0 +1,62 @@\n",
+			want: []string{"@@ -0,0 +1,62 @@"},
+		},
+		{
+			name:   "single_crlf_terminated_line",
+			input:  "@@ -0,0 +1,62 @@\r\n",
+			want: []string{"@@ -0,0 +1,62 @@"},
+		},
+		{
+			name:   "multi_line",
+			input:  `diff --git a/test.go b/test.go
+new file mode 100644
+index 0000000..3be2928`,
+			want: []string{
+				"diff --git a/test.go b/test.go",
+				"new file mode 100644",
+				"index 0000000..3be2928",
+			},
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T){
+			in := bufio.NewReader(strings.NewReader(test.input))
+			out := []string{}
+			for {
+				l, err := readLine(in)
+				if err == io.EOF {
+					break
+				}
+				if err != nil {
+					t.Fatal(err)
+				}
+				out = append(out, string(l))
+			}
+			if(!reflect.DeepEqual(test.want, out)){
+				t.Errorf("read lines not equal: want %v, got %v", test.want, out)
+			}
+		})
+	}
+}

diff/testdata/sample_multi_file_new_win.diff

@@ -0,0 +1,27 @@
+diff --git a/_vendor/go/build/syslist_test.go b/_vendor/go/build/syslist_test.go
+new file mode 100644
+index 0000000..3be2928
+--- /dev/null
++++ b/_vendor/go/build/syslist_test.go
+@@ -0,0 +1,62 @@
++func TestGoodOSArch(t *testing.T) {
++	for _, test := range tests {
++		if Default.goodOSArchFile(test.name, make(map[string]bool)) != test.result {
++			t.Fatalf("goodOSArchFile(%q) != %v", test.name, test.result)
++		}
++	}
++}
+diff --git a/_vendor/go/build/testdata/empty/dummy b/_vendor/go/build/testdata/empty/dummy
+new file mode 100644
+index 0000000..e69de29
+diff --git a/_vendor/go/build/testdata/multi/file.go b/_vendor/go/build/testdata/multi/file.go
+new file mode 100644
+index 0000000..ee946eb
+--- /dev/null
++++ b/_vendor/go/build/testdata/multi/file.go
+@@ -0,0 +1,5 @@
++// Test data - not compiled.
++
++package main
++
++func main() {}