From fce1fe166122bfa7dce917ee4dde7be5866414c5 Mon Sep 17 00:00:00 2001
From: Matt Joiner <anacrolix@gmail.com>
Date: Sun, 5 Nov 2017 15:38:09 +1100
Subject: [PATCH] bencode: Implement unbuffered scanner used by NewDecoder
Minimizes unused reads into the input Reader stream
---
bencode/api.go | 2 +-
bencode/decode_test.go | 12 ++++++++++++
bencode/scanner.go | 41 +++++++++++++++++++++++++++++++++++++++++
3 files changed, 54 insertions(+), 1 deletion(-)
create mode 100644 bencode/scanner.go
diff --git a/bencode/api.go b/bencode/api.go
index b5f026c5..1b77f588 100644
--- a/bencode/api.go
+++ b/bencode/api.go
@@ -129,7 +129,7 @@ func Unmarshal(data []byte, v interface{}) error {
}
func NewDecoder(r io.Reader) *Decoder {
- return &Decoder{r: bufio.NewReader(r)}
+ return &Decoder{r: &scanner{r: r}}
}
func NewEncoder(w io.Writer) *Encoder {
diff --git a/bencode/decode_test.go b/bencode/decode_test.go
index 1db0c7e4..572740b8 100644
--- a/bencode/decode_test.go
+++ b/bencode/decode_test.go
@@ -72,16 +72,28 @@ func TestDecoderConsecutive(t *testing.T) {
func TestDecoderConsecutiveDicts(t *testing.T) {
bb := bytes.NewBufferString("d4:herp4:derped3:wat1:ke17:oh baby a triple!")
+
d := NewDecoder(bb)
+ assert.EqualValues(t, "d4:herp4:derped3:wat1:ke17:oh baby a triple!", bb.Bytes())
+ assert.EqualValues(t, 0, d.offset)
+
var m map[string]interface{}
+
require.NoError(t, d.Decode(&m))
assert.Len(t, m, 1)
assert.Equal(t, "derp", m["herp"])
+ assert.Equal(t, "d3:wat1:ke17:oh baby a triple!", bb.String())
+ assert.EqualValues(t, 14, d.offset)
+
require.NoError(t, d.Decode(&m))
assert.Equal(t, "k", m["wat"])
+ assert.Equal(t, "17:oh baby a triple!", bb.String())
+ assert.EqualValues(t, 24, d.offset)
+
var s string
require.NoError(t, d.Decode(&s))
assert.Equal(t, "oh baby a triple!", s)
+ assert.EqualValues(t, 44, d.offset)
}
func check_error(t *testing.T, err error) {
diff --git a/bencode/scanner.go b/bencode/scanner.go
new file mode 100644
index 00000000..eaf22dd4
--- /dev/null
+++ b/bencode/scanner.go
@@ -0,0 +1,41 @@
+package bencode
+
+import (
+ "errors"
+ "io"
+)
+
+// Implements io.ByteScanner over io.Reader, for use in Decoder, to ensure
+// that as little as the undecoded input Reader is consumed as possible.
+type scanner struct {
+ r io.Reader
+ b [1]byte // Buffer for ReadByte
+ unread bool // True if b has been unread, and so should be returned next
+}
+
+func (me *scanner) Read(b []byte) (int, error) {
+ return me.r.Read(b)
+}
+
+func (me *scanner) ReadByte() (byte, error) {
+ if me.unread {
+ me.unread = false
+ return me.b[0], nil
+ }
+ n, err := me.r.Read(me.b[:])
+ if err != nil {
+ return me.b[0], err
+ }
+ if n != 1 {
+ panic(n)
+ }
+ return me.b[0], err
+}
+
+func (me *scanner) UnreadByte() error {
+ if me.unread {
+ return errors.New("byte already unread")
+ }
+ me.unread = true
+ return nil
+}
--
2.51.0