Avoid buffering when reader supports ReadString

Author: bluekeyes

Diff for: gitdiff/parser.go

@@ -13,7 +13,8 @@ import (
 // the first file is returned as the second value. If an error occurs while
 // parsing, it returns all files parsed before the error.
 func Parse(r io.Reader) ([]*File, string, error) {
-	p := &parser{r: bufio.NewReader(r)}
+	p := newParser(r)
+
 	if err := p.Next(); err != nil {
 		if err == io.EOF {
 			return nil, "", nil
@@ -66,14 +67,25 @@ func Parse(r io.Reader) ([]*File, string, error) {
 //     - if returning an object, advance to the first line after the object
 // - any exported parsing methods must initialize the parser by calling Next()
 
+type stringReader interface {
+	ReadString(delim byte) (string, error)
+}
+
 type parser struct {
-	r *bufio.Reader
+	r stringReader
 
 	eof    bool
 	lineno int64
 	lines  [3]string
 }
 
+func newParser(r io.Reader) *parser {
+	if r, ok := r.(stringReader); ok {
+		return &parser{r: r}
+	}
+	return &parser{r: bufio.NewReader(r)}
+}
+
 // Next advances the parser by one line. It returns any error encountered while
 // reading the line, including io.EOF when the end of stream is reached.
 func (p *parser) Next() error {

Diff for: gitdiff/parser_test.go

@@ -1,13 +1,12 @@
 package gitdiff
 
 import (
-	"bufio"
+	"bytes"
 	"encoding/binary"
 	"encoding/json"
 	"io"
 	"os"
 	"reflect"
-	"strings"
 	"testing"
 )
 
@@ -490,7 +489,7 @@ Date:   Tue Apr 2 22:55:40 2019 -0700
 }
 
 func newTestParser(input string, init bool) *parser {
-	p := &parser{r: bufio.NewReader(strings.NewReader(input))}
+	p := newParser(bytes.NewBufferString(input))
 	if init {
 		_ = p.Next()
 	}