urlEncode() should only copy if necessary

source/vibe/textfilter/urlencode.d

@@ -20,12 +20,34 @@ import std.format;
 */
 string urlEncode(string str, string allowed_chars = null)
 @safe {
+	foreach(ubyte c; str) {
+		switch(c) {
+			case '-':
+			case '.':
+			case '0': .. case '9':
+			case 'A': .. case 'Z':
+			case '_':
+			case 'a': .. case 'z':
+			case '~':
+				break;
+			default:
+				goto needsEncoding;
+		}
+	}
+    return str;
+
+needsEncoding:
 	auto dst = appender!string();
 	dst.reserve(str.length);
 	filterURLEncode(dst, str, allowed_chars);
 	return dst.data;
 }
 
+unittest {
+    string s = "hello-world";
+    assert(s.urlEncode().ptr == s.ptr);
+}
+
 /** Returns the decoded version of a given URL encoded string.
 */
 string urlDecode(string str)
@@ -69,7 +91,7 @@ string formDecode(string str)
 
 /** Writes the URL encoded version of the given string to an output range.
 */
-void filterURLEncode(R)(ref R dst, string str, string allowed_chars = null, bool form_encoding = false) 
+void filterURLEncode(R)(ref R dst, string str, string allowed_chars = null, bool form_encoding = false)
 {
 	while( str.length > 0 ) {
 		switch(str[0]) {
@@ -96,7 +118,7 @@ void filterURLEncode(R)(ref R dst, string str, string allowed_chars = null, bool
 
 /** Writes the decoded version of the given URL encoded string to an output range.
 */
-void filterURLDecode(R)(ref R dst, string str, bool form_encoding = false) 
+void filterURLDecode(R)(ref R dst, string str, bool form_encoding = false)
 {
 	while( str.length > 0 ) {
 		switch(str[0]) {