// Copyright 2013 Joshua Tacoma. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package uritemplates is a level 3 implementation of RFC 6570 (URI
// Template, http://tools.ietf.org/html/rfc6570).
// uritemplates does not support composite values (in Go: slices or maps)
// and so does not qualify as a level 4 implementation.
package uritemplates
import (
"bytes"
"errors"
"regexp"
"strconv"
"strings"
)
var (
unreserved = regexp.MustCompile("[^A-Za-z0-9\\-._~]")
reserved = regexp.MustCompile("[^A-Za-z0-9\\-._~:/?#[\\]@!$&'()*+,;=]")
validname = regexp.MustCompile("^([A-Za-z0-9_\\.]|%[0-9A-Fa-f][0-9A-Fa-f])+$")
hex = []byte("0123456789ABCDEF")
)
func pctEncode(src []byte) []byte {
dst := make([]byte, len(src)*3)
for i, b := range src {
buf := dst[i*3 : i*3+3]
buf[0] = 0x25
buf[1] = hex[b/16]
buf[2] = hex[b%16]
}
return dst
}
// pairWriter is a convenience struct which allows escaped and unescaped
// versions of the template to be written in parallel.
type pairWriter struct {
escaped, unescaped bytes.Buffer
}
// Write writes the provided string directly without any escaping.
func (w *pairWriter) Write(s string) {
w.escaped.WriteString(s)
w.unescaped.WriteString(s)
}
// Escape writes the provided string, escaping the string for the
// escaped output.
func (w *pairWriter) Escape(s string, allowReserved bool) {
w.unescaped.WriteString(s)
if allowReserved {
w.escaped.Write(reserved.ReplaceAllFunc([]byte(s), pctEncode))
} else {
w.escaped.Write(unreserved.ReplaceAllFunc([]byte(s), pctEncode))
}
}
// Escaped returns the escaped string.
func (w *pairWriter) Escaped() string {
return w.escaped.String()
}
// Unescaped returns the unescaped string.
func (w *pairWriter) Unescaped() string {
return w.unescaped.String()
}
// A uriTemplate is a parsed representation of a URI template.
type uriTemplate struct {
raw string
parts []templatePart
}
// parse parses a URI template string into a uriTemplate object.
func parse(rawTemplate string) (*uriTemplate, error) {
split := strings.Split(rawTemplate, "{")
parts := make([]templatePart, len(split)*2-1)
for i, s := range split {
if i == 0 {
if strings.Contains(s, "}") {
return nil, errors.New("unexpected }")
}
parts[i].raw = s
continue
}
subsplit := strings.Split(s, "}")
if len(subsplit) != 2 {
return nil, errors.New("malformed template")
}
expression := subsplit[0]
var err error
parts[i*2-1], err = parseExpression(expression)
if err != nil {
return nil, err
}
parts[i*2].raw = subsplit[1]
}
return &uriTemplate{
raw: rawTemplate,
parts: parts,
}, nil
}
type templatePart struct {
raw string
terms []templateTerm
first string
sep string
named bool
ifemp string
allowReserved bool
}
type templateTerm struct {
name string
explode bool
truncate int
}
func parseExpression(expression string) (result templatePart, err error) {
switch expression[0] {
case '+':
result.sep = ","
result.allowReserved = true
expression = expression[1:]
case '.':
result.first = "."
result.sep = "."
expression = expression[1:]
case '/':
result.first = "/"
result.sep = "/"
expression = expression[1:]
case ';':
result.first = ";"
result.sep = ";"
result.named = true
expression = expression[1:]
case '?':
result.first = "?"
result.sep = "&"
result.named = true
result.ifemp = "="
expression = expression[1:]
case '&':
result.first = "&"
result.sep = "&"
result.named = true
result.ifemp = "="
expression = expression[1:]
case '#':
result.first = "#"
result.sep = ","
result.allowReserved = true
expression = expression[1:]
default:
result.sep = ","
}
rawterms := strings.Split(expression, ",")
result.terms = make([]templateTerm, len(rawterms))
for i, raw := range rawterms {
result.terms[i], err = parseTerm(raw)
if err != nil {
break
}
}
return result, err
}
func parseTerm(term string) (result templateTerm, err error) {
// TODO(djd): Remove "*" suffix parsing once we check that no APIs have
// mistakenly used that attribute.
if strings.HasSuffix(term, "*") {
result.explode = true
term = term[:len(term)-1]
}
split := strings.Split(term, ":")
if len(split) == 1 {
result.name = term
} else if len(split) == 2 {
result.name = split[0]
var parsed int64
parsed, err = strconv.ParseInt(split[1], 10, 0)
result.truncate = int(parsed)
} else {
err = errors.New("multiple colons in same term")
}
if !validname.MatchString(result.name) {
err = errors.New("not a valid name: " + result.name)
}
if result.explode && result.truncate > 0 {
err = errors.New("both explode and prefix modifers on same term")
}
return result, err
}
// Expand expands a URI template with a set of values to produce the
// resultant URI. Two forms of the result are returned: one with all the
// elements escaped, and one with the elements unescaped.
func (t *uriTemplate) Expand(values map[string]string) (escaped, unescaped string) {
var w pairWriter
for _, p := range t.parts {
p.expand(&w, values)
}
return w.Escaped(), w.Unescaped()
}
func (tp *templatePart) expand(w *pairWriter, values map[string]string) {
if len(tp.raw) > 0 {
w.Write(tp.raw)
return
}
var first = true
for _, term := range tp.terms {
value, exists := values[term.name]
if !exists {
continue
}
if first {
w.Write(tp.first)
first = false
} else {
w.Write(tp.sep)
}
tp.expandString(w, term, value)
}
}
func (tp *templatePart) expandName(w *pairWriter, name string, empty bool) {
if tp.named {
w.Write(name)
if empty {
w.Write(tp.ifemp)
} else {
w.Write("=")
}
}
}
func (tp *templatePart) expandString(w *pairWriter, t templateTerm, s string) {
if len(s) > t.truncate && t.truncate > 0 {
s = s[:t.truncate]
}
tp.expandName(w, t.name, len(s) == 0)
w.Escape(s, tp.allowReserved)
}
