http.URLEscape: escape all bytes required by RFC 2396

Fixes #125.

R=r
https://golang.org/cl/154143

src/pkg/http/url.go

@@ -52,14 +52,16 @@ func (e URLEscapeError) String() string {
 	return "invalid URL escape " + strconv.Quote(string(e))
 }
 
-// Return true if the specified character should be escaped when appearing in a
-// URL string.
-//
-// TODO: for now, this is a hack; it only flags a few common characters that have
-// special meaning in URLs.  That will get the job done in the common cases.
+// Return true if the specified character should be escaped when
+// appearing in a URL string, according to RFC 2396.
 func shouldEscape(c byte) bool {
+	if c <= ' ' || c >= 0x7F {
+		return true
+	}
 	switch c {
-	case ' ', '?', '&', '=', '#', '+', '%':
+	case '<', '>', '#', '%', '"',	// RFC 2396 delims
+		'{', '}', '|', '\\', '^', '[', ']', '`',	// RFC2396 unwise
+		'?', '&', '=', '+':	// RFC 2396 reserved in path
 		return true
 	}
 	return false;

src/pkg/http/url_test.go

@@ -335,8 +335,8 @@ var escapeTests = []URLEscapeTest{
 		nil,
 	},
 	URLEscapeTest{
-		" ?&=#+%!",
-		"+%3f%26%3d%23%2b%25!",
+		" ?&=#+%!<>#\"{}|\\^[]`☺\t",
+		"+%3f%26%3d%23%2b%25!%3c%3e%23%22%7b%7d%7c%5c%5e%5b%5d%60%e2%98%ba%09",
 		nil,
 	},
 }