check key order in dictionaries

lib/bencode.js

@@ -78,9 +78,6 @@ function findchar(str, pos, c) {
 
 function copy(str, start, len) {
 	return str.slice(start, start+len);
-// 	var buf = new Buffer(len);
-// 	str.copy(buf, 0, start, start+len);
-// 	return buf;
 }
 
 // parse a bencoded string
@@ -120,9 +117,18 @@ function bparseList(str, pos) {
 	return [list, pos+1];
 }
 
+function compareBuffers(a, b) {
+	var i, l = Math.min(a.length, b.length);
+	for (i = 0; i < l; ++i) {
+		if (a[i] != b[i]) return (a[i] < b[i]) ? -1 : 1;
+	}
+	if (a.length === b.length) return 0;
+	return (a.length < b.length) ? -1 : 1;
+}
+
 // parse a bencoded dictionary
 function bparseDict(str, pos) {
-	var key, val, dict = {};
+	var key, val, dict = {}, oldkey = false, cmpkey;
 	while (pos < str.length && str.charAt(pos) !== "e") {
 		key = bparseString(str, pos);
 		if (null === key) throw new Error("unexpected null element");
@@ -132,6 +138,13 @@ function bparseDict(str, pos) {
 		val = bparse(str, pos);
 		if (null === val) throw new Error("unexpected null element");
 
+		if (oldkey !== false) {
+			cmpkey = compareBuffers(oldkey, key[0]);
+			if (0 === cmpkey) throw new Error("duplicate key in dictionary");
+			if (1 === cmpkey) throw new Error("wrong key order in dictionary");
+		}
+		oldkey = key[0];
+
 		dict[key[0]] = val[0];
 		pos = val[1];
 	}

lib/test.js

@@ -38,3 +38,6 @@ checkDecodeThrows("d3:key5:value", Error, "unexpected end of data");
 
 checkDecodeThrows("l", Error, "unexpected end of data");
 checkDecodeThrows("l7:element", Error, "unexpected end of data");
+
+checkDecodeThrows("d3:kez0:3:key0:e", Error, "wrong key order in dictionary");
+checkDecodeThrows("d3:key0:3:key0:e", Error, "duplicate key in dictionary");