speed up dictionary key unmarshalling

Author: IncSW

README.md

@@ -25,29 +25,31 @@ data, err := bencode.Unmarshal(value)
 
 ## Performance
 
-### Go 1.13.1, Debian 9.1, i7-7700
+### Go 1.16, Debian 9.1, i7-7700
 
 ### Marshal
 
-| Library            |    Time    | Bytes Allocated | Objects Allocated |
-| :----------------- | :--------: | :-------------: | :---------------: |
-| IncSW/go-bencode   | 485 ns/op  |     16 B/op     |    2 allocs/op    |
-| marksamman/bencode | 897 ns/op  |    400 B/op     |    8 allocs/op    |
-| chihaya/bencode    | 1846 ns/op |    1010 B/op    |   53 allocs/op    |
-| nabilanam/bencode  | 2027 ns/op |    1216 B/op    |   44 allocs/op    |
-| jackpal/bencode-go | 4968 ns/op |    2128 B/op    |   57 allocs/op    |
-| zeebo/bencode      | 5147 ns/op |    1488 B/op    |   45 allocs/op    |
+| Library             |    Time     | Bytes Allocated | Objects Allocated |
+| :------------------ | :---------: | :-------------: | :---------------: |
+| IncSW/go-bencode    | 795.9 ns/op |    176 B/op     |    6 allocs/op    |
+| marksamman/bencode  | 820.3 ns/op |    384 B/op     |    8 allocs/op    |
+| cristalhq/bencode   | 994.2 ns/op |    928 B/op     |    4 allocs/op    |
+| aleksatr/go-bencode | 1061 ns/op  |    736 B/op     |    9 allocs/op    |
+| nabilanam/bencode   | 2103 ns/op  |    1192 B/op    |   44 allocs/op    |
+| jackpal/bencode-go  | 4676 ns/op  |    2016 B/op    |   45 allocs/op    |
+| zeebo/bencode       | 4889 ns/op  |    1376 B/op    |   33 allocs/op    |
 
 ### Unmarshal
 
-| Library            |    Time    | Bytes Allocated | Objects Allocated |
-| :----------------- | :--------: | :-------------: | :---------------: |
-| nabilanam/bencode  | 1341 ns/op |    1264 B/op    |   39 allocs/op    |
-| IncSW/go-bencode   | 1435 ns/op |    1248 B/op    |   25 allocs/op    |
-| jackpal/bencode-go | 2652 ns/op |    1712 B/op    |   59 allocs/op    |
-| marksamman/bencode | 2877 ns/op |    5920 B/op    |   66 allocs/op    |
-| chihaya/bencode    | 2896 ns/op |    5904 B/op    |   61 allocs/op    |
-| zeebo/bencode      | 6595 ns/op |    6576 B/op    |   99 allocs/op    |
+| Library             |    Time    | Bytes Allocated | Objects Allocated |
+| :------------------ | :--------: | :-------------: | :---------------: |
+| IncSW/go-bencode    | 1149 ns/op |    960 B/op     |   18 allocs/op    |
+| cristalhq/bencode   | 1160 ns/op |    960 B/op     |   18 allocs/op    |
+| nabilanam/bencode   | 1379 ns/op |    1240 B/op    |   39 allocs/op    |
+| aleksatr/go-bencode | 2270 ns/op |    1816 B/op    |   51 allocs/op    |
+| jackpal/bencode-go  | 2577 ns/op |    1688 B/op    |   59 allocs/op    |
+| marksamman/bencode  | 2725 ns/op |    5768 B/op    |   54 allocs/op    |
+| zeebo/bencode       | 5988 ns/op |    6392 B/op    |   92 allocs/op    |
 
 ## License
 

unmarshaler.go

@@ -64,38 +64,41 @@ func (u *unmarshaler) unmarshal() (interface{}, error) {
 				u.cursor += 1
 				return dictionary, nil
 			}
-			value, err := u.unmarshal()
+			key, err := u.unmarshalString()
 			if err != nil {
-				return nil, err
-			}
-			key, ok := value.([]byte)
-			if !ok {
 				return nil, errors.New("bencode: non-string dictionary key")
 			}
-			value, err = u.unmarshal()
+			value, err := u.unmarshal()
 			if err != nil {
 				return nil, err
 			}
 			dictionary[b2s(key)] = value
 		}
 
 	default:
-		index := bytes.IndexByte(u.data[u.cursor:], ':')
-		if index == -1 {
-			return nil, errors.New("bencode: invalid string field")
-		}
-		index += u.cursor
-		stringLength, err := strconv.ParseInt(b2s(u.data[u.cursor:index]), 10, 64)
-		if err != nil {
-			return nil, err
-		}
-		index += 1
-		endIndex := index + int(stringLength)
-		if endIndex > u.length {
-			return nil, errors.New("bencode: not a valid bencoded string")
-		}
-		value := u.data[index:endIndex]
-		u.cursor = endIndex
-		return value, nil
+		return u.unmarshalString()
+	}
+}
+
+func (u *unmarshaler) unmarshalString() ([]byte, error) {
+	if u.data[u.cursor] < '0' || u.data[u.cursor] > '9' {
+		return nil, errors.New("bencode: invalid string field")
+	}
+	index := bytes.IndexByte(u.data[u.cursor:], ':')
+	if index == -1 {
+		return nil, errors.New("bencode: invalid string field")
+	}
+	index += u.cursor
+	stringLength, err := strconv.ParseInt(b2s(u.data[u.cursor:index]), 10, 64)
+	if err != nil {
+		return nil, err
+	}
+	index += 1
+	endIndex := index + int(stringLength)
+	if endIndex > u.length {
+		return nil, errors.New("bencode: not a valid bencoded string")
 	}
+	value := u.data[index:endIndex]
+	u.cursor = endIndex
+	return value, nil
 }

unmarshaler_test.go

@@ -7,7 +7,7 @@ import (
 )
 
 var (
-	unmarshalTestData      = []byte("d4:infod6:lengthi170917888e12:piece lengthi262144e4:name30:debian-8.8.0-arm64-netinst.isoe8:announce38:udp://tracker.publicbt.com:80/announce13:announce-listll38:udp://tracker.publicbt.com:80/announceel44:udp://tracker.openbittorrent.com:80/announceee7:comment33:Debian CD from cdimage.debian.orge")
+	unmarshalTestData      = []byte("d8:announce38:udp://tracker.publicbt.com:80/announce13:announce-listll38:udp://tracker.publicbt.com:80/announceel44:udp://tracker.openbittorrent.com:80/announceee7:comment33:Debian CD from cdimage.debian.org4:infod6:lengthi170917888e4:name30:debian-8.8.0-arm64-netinst.iso12:piece lengthi262144eee")
 	unmarshalWrongTestData = []byte("d4:infod6:lengthi170917888e12:piece lengthi262144e4:name30:debian-8.8.0-arm64-netinst.isoe8:announce38:udp://tracker.publicbt.com:80/announce13:announce-listll38:udp://tracker.publicbt.com:80/announceel44:udp://tracker.openbittorrent.com:80/announceee7:comment35:Debian CD from cdimage.debian.orge")
 )