360 lines
8.3 KiB
Go
360 lines
8.3 KiB
Go
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// Copyright 2013 Joshua Tacoma. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package uritemplates is a level 4 implementation of RFC 6570 (URI
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// Template, http://tools.ietf.org/html/rfc6570).
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//
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// To use uritemplates, parse a template string and expand it with a value
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// map:
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//
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// template, _ := uritemplates.Parse("https://api.github.com/repos{/user,repo}")
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// values := make(map[string]interface{})
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// values["user"] = "jtacoma"
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// values["repo"] = "uritemplates"
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// expanded, _ := template.ExpandString(values)
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// fmt.Printf(expanded)
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//
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package uritemplates
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import (
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"bytes"
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"errors"
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"fmt"
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"reflect"
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"regexp"
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"strconv"
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"strings"
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)
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var (
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unreserved = regexp.MustCompile("[^A-Za-z0-9\\-._~]")
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reserved = regexp.MustCompile("[^A-Za-z0-9\\-._~:/?#[\\]@!$&'()*+,;=]")
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validname = regexp.MustCompile("^([A-Za-z0-9_\\.]|%[0-9A-Fa-f][0-9A-Fa-f])+$")
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hex = []byte("0123456789ABCDEF")
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)
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func pctEncode(src []byte) []byte {
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dst := make([]byte, len(src)*3)
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for i, b := range src {
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buf := dst[i*3 : i*3+3]
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buf[0] = 0x25
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buf[1] = hex[b/16]
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buf[2] = hex[b%16]
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}
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return dst
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}
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func escape(s string, allowReserved bool) (escaped string) {
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if allowReserved {
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escaped = string(reserved.ReplaceAllFunc([]byte(s), pctEncode))
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} else {
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escaped = string(unreserved.ReplaceAllFunc([]byte(s), pctEncode))
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}
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return escaped
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}
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// A UriTemplate is a parsed representation of a URI template.
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type UriTemplate struct {
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raw string
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parts []templatePart
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}
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// Parse parses a URI template string into a UriTemplate object.
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func Parse(rawtemplate string) (template *UriTemplate, err error) {
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template = new(UriTemplate)
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template.raw = rawtemplate
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split := strings.Split(rawtemplate, "{")
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template.parts = make([]templatePart, len(split)*2-1)
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for i, s := range split {
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if i == 0 {
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if strings.Contains(s, "}") {
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err = errors.New("unexpected }")
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break
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}
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template.parts[i].raw = s
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} else {
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subsplit := strings.Split(s, "}")
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if len(subsplit) != 2 {
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err = errors.New("malformed template")
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break
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}
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expression := subsplit[0]
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template.parts[i*2-1], err = parseExpression(expression)
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if err != nil {
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break
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}
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template.parts[i*2].raw = subsplit[1]
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}
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}
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if err != nil {
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template = nil
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}
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return template, err
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}
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type templatePart struct {
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raw string
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terms []templateTerm
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first string
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sep string
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named bool
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ifemp string
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allowReserved bool
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}
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type templateTerm struct {
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name string
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explode bool
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truncate int
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}
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func parseExpression(expression string) (result templatePart, err error) {
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switch expression[0] {
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case '+':
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result.sep = ","
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result.allowReserved = true
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expression = expression[1:]
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case '.':
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result.first = "."
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result.sep = "."
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expression = expression[1:]
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case '/':
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result.first = "/"
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result.sep = "/"
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expression = expression[1:]
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case ';':
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result.first = ";"
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result.sep = ";"
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result.named = true
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expression = expression[1:]
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case '?':
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result.first = "?"
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result.sep = "&"
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result.named = true
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result.ifemp = "="
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expression = expression[1:]
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case '&':
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result.first = "&"
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result.sep = "&"
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result.named = true
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result.ifemp = "="
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expression = expression[1:]
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case '#':
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result.first = "#"
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result.sep = ","
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result.allowReserved = true
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expression = expression[1:]
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default:
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result.sep = ","
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}
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rawterms := strings.Split(expression, ",")
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result.terms = make([]templateTerm, len(rawterms))
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for i, raw := range rawterms {
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result.terms[i], err = parseTerm(raw)
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if err != nil {
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break
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}
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}
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return result, err
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}
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func parseTerm(term string) (result templateTerm, err error) {
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if strings.HasSuffix(term, "*") {
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result.explode = true
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term = term[:len(term)-1]
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}
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split := strings.Split(term, ":")
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if len(split) == 1 {
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result.name = term
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} else if len(split) == 2 {
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result.name = split[0]
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var parsed int64
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parsed, err = strconv.ParseInt(split[1], 10, 0)
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result.truncate = int(parsed)
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} else {
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err = errors.New("multiple colons in same term")
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}
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if !validname.MatchString(result.name) {
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err = errors.New("not a valid name: " + result.name)
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}
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if result.explode && result.truncate > 0 {
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err = errors.New("both explode and prefix modifers on same term")
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}
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return result, err
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}
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// Expand expands a URI template with a set of values to produce a string.
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func (self *UriTemplate) Expand(value interface{}) (string, error) {
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values, ismap := value.(map[string]interface{})
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if !ismap {
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if m, ismap := struct2map(value); !ismap {
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return "", errors.New("expected map[string]interface{}, struct, or pointer to struct.")
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} else {
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return self.Expand(m)
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}
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}
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var buf bytes.Buffer
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for _, p := range self.parts {
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err := p.expand(&buf, values)
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if err != nil {
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return "", err
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}
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}
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return buf.String(), nil
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}
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func (self *templatePart) expand(buf *bytes.Buffer, values map[string]interface{}) error {
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if len(self.raw) > 0 {
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buf.WriteString(self.raw)
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return nil
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}
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var zeroLen = buf.Len()
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buf.WriteString(self.first)
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var firstLen = buf.Len()
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for _, term := range self.terms {
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value, exists := values[term.name]
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if !exists {
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continue
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}
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if buf.Len() != firstLen {
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buf.WriteString(self.sep)
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}
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switch v := value.(type) {
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case string:
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self.expandString(buf, term, v)
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case []interface{}:
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self.expandArray(buf, term, v)
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case map[string]interface{}:
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if term.truncate > 0 {
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return errors.New("cannot truncate a map expansion")
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}
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self.expandMap(buf, term, v)
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default:
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if m, ismap := struct2map(value); ismap {
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if term.truncate > 0 {
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return errors.New("cannot truncate a map expansion")
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}
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self.expandMap(buf, term, m)
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} else {
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str := fmt.Sprintf("%v", value)
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self.expandString(buf, term, str)
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}
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}
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}
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if buf.Len() == firstLen {
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original := buf.Bytes()[:zeroLen]
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buf.Reset()
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buf.Write(original)
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}
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return nil
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}
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func (self *templatePart) expandName(buf *bytes.Buffer, name string, empty bool) {
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if self.named {
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buf.WriteString(name)
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if empty {
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buf.WriteString(self.ifemp)
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} else {
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buf.WriteString("=")
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}
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}
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}
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func (self *templatePart) expandString(buf *bytes.Buffer, t templateTerm, s string) {
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if len(s) > t.truncate && t.truncate > 0 {
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s = s[:t.truncate]
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}
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self.expandName(buf, t.name, len(s) == 0)
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buf.WriteString(escape(s, self.allowReserved))
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}
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func (self *templatePart) expandArray(buf *bytes.Buffer, t templateTerm, a []interface{}) {
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if len(a) == 0 {
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return
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} else if !t.explode {
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self.expandName(buf, t.name, false)
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}
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for i, value := range a {
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if t.explode && i > 0 {
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buf.WriteString(self.sep)
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} else if i > 0 {
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buf.WriteString(",")
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}
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var s string
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switch v := value.(type) {
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case string:
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s = v
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default:
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s = fmt.Sprintf("%v", v)
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}
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if len(s) > t.truncate && t.truncate > 0 {
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s = s[:t.truncate]
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}
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if self.named && t.explode {
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self.expandName(buf, t.name, len(s) == 0)
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}
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buf.WriteString(escape(s, self.allowReserved))
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}
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}
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func (self *templatePart) expandMap(buf *bytes.Buffer, t templateTerm, m map[string]interface{}) {
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if len(m) == 0 {
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return
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}
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if !t.explode {
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self.expandName(buf, t.name, len(m) == 0)
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}
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var firstLen = buf.Len()
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for k, value := range m {
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if firstLen != buf.Len() {
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if t.explode {
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buf.WriteString(self.sep)
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} else {
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buf.WriteString(",")
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}
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}
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var s string
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switch v := value.(type) {
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case string:
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s = v
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default:
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s = fmt.Sprintf("%v", v)
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}
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if t.explode {
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buf.WriteString(escape(k, self.allowReserved))
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buf.WriteRune('=')
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buf.WriteString(escape(s, self.allowReserved))
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} else {
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buf.WriteString(escape(k, self.allowReserved))
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buf.WriteRune(',')
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buf.WriteString(escape(s, self.allowReserved))
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}
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}
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}
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func struct2map(v interface{}) (map[string]interface{}, bool) {
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value := reflect.ValueOf(v)
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switch value.Type().Kind() {
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case reflect.Ptr:
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return struct2map(value.Elem().Interface())
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case reflect.Struct:
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m := make(map[string]interface{})
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for i := 0; i < value.NumField(); i++ {
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tag := value.Type().Field(i).Tag
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var name string
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if strings.Contains(string(tag), ":") {
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name = tag.Get("uri")
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} else {
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name = strings.TrimSpace(string(tag))
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}
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if len(name) == 0 {
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name = value.Type().Field(i).Name
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}
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m[name] = value.Field(i).Interface()
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}
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return m, true
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}
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return nil, false
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}
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