Bencoded dictionary keys are in lexicographical order

Author: marksamman

README.md

@@ -30,11 +30,6 @@ func main() {
 }
 ```
 
-If a specific order is desired for dictionary keys when generating a bencode string, specify the keys in desired order in the dictionary key "\_\_keys". For dictionaries generated from bencode.Decode, "\_\_keys" is already set to the order the keys were read from the file. Example:
-```go
-dict["__keys"] = []string{"int key", "string key"}
-```
-
 ### Decode
 bencode.Decode takes an io.Reader as argument and returns (map[string]interface{}, error). Example:
 ```go

decoder.go

@@ -107,7 +107,6 @@ func (decoder *decoder) readString() (string, error) {
 
 func (decoder *decoder) readDictionary() (map[string]interface{}, error) {
 	dict := make(map[string]interface{})
-	keys := []string{}
 	for {
 		key, err := decoder.readString()
 		if err != nil {
@@ -145,15 +144,12 @@ func (decoder *decoder) readDictionary() (map[string]interface{}, error) {
 			return nil, err
 		}
 
-		keys = append(keys, key)
 		if nextByte == 'e' {
 			break
 		} else if err := decoder.UnreadByte(); err != nil {
 			return nil, err
 		}
 	}
-
-	dict["__keys"] = keys
 	return dict, nil
 }
 

encoder.go

@@ -25,6 +25,7 @@ package bencode
 import (
 	"bytes"
 	"strconv"
+	"sort"
 )
 
 type encoder struct {
@@ -87,17 +88,19 @@ func (encoder *encoder) writeList(list []interface{}) {
 }
 
 func (encoder *encoder) writeDictionary(dict map[string]interface{}) {
+	// Sort in lexicographical order
+	list := make(sort.StringSlice, len(dict))
+	i := 0
+	for key, _ := range dict {
+		list[i] = key
+		i++
+	}
+	list.Sort()
+
 	encoder.WriteByte('d')
-	if keys, ok := dict["__keys"]; ok {
-		for _, v := range keys.([]string) {
-			encoder.writeString(v)              // Key
-			encoder.writeInterfaceType(dict[v]) // Value
-		}
-	} else {
-		for k, v := range dict {
-			encoder.writeString(k)        // Key
-			encoder.writeInterfaceType(v) // Value
-		}
+	for _, key := range list {
+		encoder.writeString(key)              // Key
+		encoder.writeInterfaceType(dict[key]) // Value
 	}
 	encoder.WriteByte('e')
 }

encoder_test.go

@@ -30,7 +30,6 @@ import (
 
 func TestEncodeSinglefileTorrentBencode(t *testing.T) {
 	dict := make(map[string]interface{})
-	dict["__keys"] = []string{"announce", "comment", "creation date", "httpseeds", "info"}
 	dict["announce"] = "http://bttracker.debian.org:6969/announce"
 	dict["comment"] = "\"Debian CD from cdimage.debian.org\""
 	dict["creation date"] = 1391870037
@@ -40,7 +39,6 @@ func TestEncodeSinglefileTorrentBencode(t *testing.T) {
 	}
 
 	infoDict := make(map[string]interface{})
-	infoDict["__keys"] = []string{"length", "name", "piece length", "pieces"}
 	infoDict["length"] = 232783872
 	infoDict["name"] = "debian-7.4.0-amd64-netinst.iso"
 	infoDict["piece length"] = 262144