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uritemplates.go
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/
uritemplates.go
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// 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 4 implementation of RFC 6570 (URI
// Template, http://tools.ietf.org/html/rfc6570).
//
// To use uritemplates, parse a template string and expand it with a value
// map:
//
// template, _ := uritemplates.Parse("https://api.github.com/repos{/user,repo}")
// values := make(map[string]interface{})
// values["user"] = "jtacoma"
// values["repo"] = "uritemplates"
// expanded, _ := template.ExpandString(values)
// fmt.Printf(expanded)
//
package uritemplates
import (
"bytes"
"errors"
"fmt"
"reflect"
"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
}
func escape(s string, allowReserved bool) (escaped string) {
if allowReserved {
escaped = string(reserved.ReplaceAllFunc([]byte(s), pctEncode))
} else {
escaped = string(unreserved.ReplaceAllFunc([]byte(s), pctEncode))
}
return escaped
}
// 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) (template *UriTemplate, err error) {
template = new(UriTemplate)
template.raw = rawtemplate
split := strings.Split(rawtemplate, "{")
template.parts = make([]templatePart, len(split)*2-1)
for i, s := range split {
if i == 0 {
if strings.Contains(s, "}") {
err = errors.New("unexpected }")
break
}
template.parts[i].raw = s
} else {
subsplit := strings.Split(s, "}")
if len(subsplit) != 2 {
err = errors.New("malformed template")
break
}
expression := subsplit[0]
template.parts[i*2-1], err = parseExpression(expression)
if err != nil {
break
}
template.parts[i*2].raw = subsplit[1]
}
}
if err != nil {
template = nil
}
return template, err
}
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) {
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 a string.
func (self *UriTemplate) Expand(value interface{}) (string, error) {
values, ismap := value.(map[string]interface{})
if !ismap {
if m, ismap := struct2map(value); !ismap {
return "", errors.New("expected map[string]interface{}, struct, or pointer to struct.")
} else {
return self.Expand(m)
}
}
var buf bytes.Buffer
for _, p := range self.parts {
err := p.expand(&buf, values)
if err != nil {
return "", err
}
}
return buf.String(), nil
}
func (self *templatePart) expand(buf *bytes.Buffer, values map[string]interface{}) error {
if len(self.raw) > 0 {
buf.WriteString(self.raw)
return nil
}
var zeroLen = buf.Len()
buf.WriteString(self.first)
var firstLen = buf.Len()
for _, term := range self.terms {
value, exists := values[term.name]
if !exists {
continue
}
if buf.Len() != firstLen {
buf.WriteString(self.sep)
}
switch v := value.(type) {
case string:
self.expandString(buf, term, v)
case []interface{}:
self.expandArray(buf, term, v)
case map[string]interface{}:
if term.truncate > 0 {
return errors.New("cannot truncate a map expansion")
}
self.expandMap(buf, term, v)
default:
if m, ismap := struct2map(value); ismap {
if term.truncate > 0 {
return errors.New("cannot truncate a map expansion")
}
self.expandMap(buf, term, m)
} else {
str := fmt.Sprintf("%v", value)
self.expandString(buf, term, str)
}
}
}
if buf.Len() == firstLen {
original := buf.Bytes()[:zeroLen]
buf.Reset()
buf.Write(original)
}
return nil
}
func (self *templatePart) expandName(buf *bytes.Buffer, name string, empty bool) {
if self.named {
buf.WriteString(name)
if empty {
buf.WriteString(self.ifemp)
} else {
buf.WriteString("=")
}
}
}
func (self *templatePart) expandString(buf *bytes.Buffer, t templateTerm, s string) {
if len(s) > t.truncate && t.truncate > 0 {
s = s[:t.truncate]
}
self.expandName(buf, t.name, len(s) == 0)
buf.WriteString(escape(s, self.allowReserved))
}
func (self *templatePart) expandArray(buf *bytes.Buffer, t templateTerm, a []interface{}) {
if len(a) == 0 {
return
} else if !t.explode {
self.expandName(buf, t.name, false)
}
for i, value := range a {
if t.explode && i > 0 {
buf.WriteString(self.sep)
} else if i > 0 {
buf.WriteString(",")
}
var s string
switch v := value.(type) {
case string:
s = v
default:
s = fmt.Sprintf("%v", v)
}
if len(s) > t.truncate && t.truncate > 0 {
s = s[:t.truncate]
}
if self.named && t.explode {
self.expandName(buf, t.name, len(s) == 0)
}
buf.WriteString(escape(s, self.allowReserved))
}
}
func (self *templatePart) expandMap(buf *bytes.Buffer, t templateTerm, m map[string]interface{}) {
if len(m) == 0 {
return
}
if !t.explode {
self.expandName(buf, t.name, len(m) == 0)
}
var firstLen = buf.Len()
for k, value := range m {
if firstLen != buf.Len() {
if t.explode {
buf.WriteString(self.sep)
} else {
buf.WriteString(",")
}
}
var s string
switch v := value.(type) {
case string:
s = v
default:
s = fmt.Sprintf("%v", v)
}
if t.explode {
buf.WriteString(escape(k, self.allowReserved))
buf.WriteRune('=')
buf.WriteString(escape(s, self.allowReserved))
} else {
buf.WriteString(escape(k, self.allowReserved))
buf.WriteRune(',')
buf.WriteString(escape(s, self.allowReserved))
}
}
}
func struct2map(v interface{}) (map[string]interface{}, bool) {
value := reflect.ValueOf(v)
switch value.Type().Kind() {
case reflect.Ptr:
return struct2map(value.Elem().Interface())
case reflect.Struct:
m := make(map[string]interface{})
for i := 0; i < value.NumField(); i++ {
tag := value.Type().Field(i).Tag
var name string
if strings.Contains(string(tag), ":") {
name = tag.Get("uri")
} else {
name = strings.TrimSpace(string(tag))
}
if len(name) == 0 {
name = value.Type().Field(i).Name
}
m[name] = value.Field(i).Interface()
}
return m, true
}
return nil, false
}