// Copyright 2015 Google Inc. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package httputil
// Percent-encode the supplied string so that it matches the grammar laid out
// for the 'segment' category in RFC 3986.
func EncodePathSegment(s string) string {
// Scan the string once to count how many bytes must be escaped.
escapeCount := 0
for i := 0; i < len(s); i++ {
c := s[i]
if shouldEscapeForPathSegment(c) {
escapeCount++
}
}
// Fast path: is there anything to do?
if escapeCount == 0 {
return s
}
// Make a buffer that is large enough, then fill it in.
t := make([]byte, len(s)+2*escapeCount)
j := 0
for i := 0; i < len(s); i++ {
c := s[i]
// Escape if necessary.
if shouldEscapeForPathSegment(c) {
t[j] = '%'
t[j+1] = "0123456789ABCDEF"[c>>4]
t[j+2] = "0123456789ABCDEF"[c&15]
j += 3
} else {
t[j] = c
j++
}
}
return string(t)
}
func shouldEscapeForPathSegment(c byte) bool {
// According to the following sections of the RFC:
//
// http://tools.ietf.org/html/rfc3986#section-3.3
// http://tools.ietf.org/html/rfc3986#section-3.4
//
// The grammar for a segment is:
//
// segment = *pchar
// pchar = unreserved / pct-encoded / sub-delims / ":" / "@"
// unreserved = ALPHA / DIGIT / "-" / "." / "_" / "~"
// pct-encoded = "%" HEXDIG HEXDIG
// sub-delims = "!" / "$" / "&" / "'" / "(" / ")"
// / "*" / "+" / "," / ";" / "="
//
// So we need to escape everything that is not in unreserved, sub-delims, or
// ":" and "@".
// unreserved (alphanumeric)
if 'A' <= c && c <= 'Z' || 'a' <= c && c <= 'z' || '0' <= c && c <= '9' {
return false
}
switch c {
// unreserved (non-alphanumeric)
case '-', '.', '_', '~':
return false
// sub-delims
case '!', '$', '&', '\'', '(', ')', '*', '+', ',', ';', '=':
return false
// other pchars
case ':', '@':
return false
}
// Everything else must be escaped.
return true
}