chipmunk/vendor/github.com/googleapis/gax-go/path_template_parser.go
2017-01-24 18:27:39 -08:00

228 lines
6.6 KiB
Go

// Copyright 2016, Google Inc.
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
// * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
package gax
import (
"fmt"
"io"
"strings"
)
// This parser follows the syntax of path templates, from
// https://github.com/googleapis/googleapis/blob/master/google/api/http.proto.
// The differences are that there is no custom verb, we allow the initial slash
// to be absent, and that we are not strict as
// https://tools.ietf.org/html/rfc6570 about the characters in identifiers and
// literals.
type pathTemplateParser struct {
r *strings.Reader
runeCount int // the number of the current rune in the original string
nextVar int // the number to use for the next unnamed variable
seenName map[string]bool // names we've seen already
seenPathWildcard bool // have we seen "**" already?
}
func parsePathTemplate(template string) (pt *PathTemplate, err error) {
p := &pathTemplateParser{
r: strings.NewReader(template),
seenName: map[string]bool{},
}
// Handle panics with strings like errors.
// See pathTemplateParser.error, below.
defer func() {
if x := recover(); x != nil {
errmsg, ok := x.(errString)
if !ok {
panic(x)
}
pt = nil
err = ParseError{p.runeCount, template, string(errmsg)}
}
}()
segs := p.template()
// If there is a path wildcard, set its length. We can't do this
// until we know how many segments we've got all together.
for i, seg := range segs {
if _, ok := seg.matcher.(pathWildcardMatcher); ok {
segs[i].matcher = pathWildcardMatcher(len(segs) - i - 1)
break
}
}
return &PathTemplate{segments: segs}, nil
}
// Used to indicate errors "thrown" by this parser. We don't use string because
// many parts of the standard library panic with strings.
type errString string
// Terminates parsing immediately with an error.
func (p *pathTemplateParser) error(msg string) {
panic(errString(msg))
}
// Template = [ "/" ] Segments
func (p *pathTemplateParser) template() []segment {
var segs []segment
if p.consume('/') {
// Initial '/' needs an initial empty matcher.
segs = append(segs, segment{matcher: labelMatcher("")})
}
return append(segs, p.segments("")...)
}
// Segments = Segment { "/" Segment }
func (p *pathTemplateParser) segments(name string) []segment {
var segs []segment
for {
subsegs := p.segment(name)
segs = append(segs, subsegs...)
if !p.consume('/') {
break
}
}
return segs
}
// Segment = "*" | "**" | LITERAL | Variable
func (p *pathTemplateParser) segment(name string) []segment {
if p.consume('*') {
if name == "" {
name = fmt.Sprintf("$%d", p.nextVar)
p.nextVar++
}
if p.consume('*') {
if p.seenPathWildcard {
p.error("multiple '**' disallowed")
}
p.seenPathWildcard = true
// We'll change 0 to the right number at the end.
return []segment{{name: name, matcher: pathWildcardMatcher(0)}}
}
return []segment{{name: name, matcher: wildcardMatcher(0)}}
}
if p.consume('{') {
if name != "" {
p.error("recursive named bindings are not allowed")
}
return p.variable()
}
return []segment{{name: name, matcher: labelMatcher(p.literal())}}
}
// Variable = "{" FieldPath [ "=" Segments ] "}"
// "{" is already consumed.
func (p *pathTemplateParser) variable() []segment {
// Simplification: treat FieldPath as LITERAL, instead of IDENT { '.' IDENT }
name := p.literal()
if p.seenName[name] {
p.error(name + " appears multiple times")
}
p.seenName[name] = true
var segs []segment
if p.consume('=') {
segs = p.segments(name)
} else {
// "{var}" is equivalent to "{var=*}"
segs = []segment{{name: name, matcher: wildcardMatcher(0)}}
}
if !p.consume('}') {
p.error("expected '}'")
}
return segs
}
// A literal is any sequence of characters other than a few special ones.
// The list of stop characters is not quite the same as in the template RFC.
func (p *pathTemplateParser) literal() string {
lit := p.consumeUntil("/*}{=")
if lit == "" {
p.error("empty literal")
}
return lit
}
// Read runes until EOF or one of the runes in stopRunes is encountered.
// If the latter, unread the stop rune. Return the accumulated runes as a string.
func (p *pathTemplateParser) consumeUntil(stopRunes string) string {
var runes []rune
for {
r, ok := p.readRune()
if !ok {
break
}
if strings.IndexRune(stopRunes, r) >= 0 {
p.unreadRune()
break
}
runes = append(runes, r)
}
return string(runes)
}
// If the next rune is r, consume it and return true.
// Otherwise, leave the input unchanged and return false.
func (p *pathTemplateParser) consume(r rune) bool {
rr, ok := p.readRune()
if !ok {
return false
}
if r == rr {
return true
}
p.unreadRune()
return false
}
// Read the next rune from the input. Return it.
// The second return value is false at EOF.
func (p *pathTemplateParser) readRune() (rune, bool) {
r, _, err := p.r.ReadRune()
if err == io.EOF {
return r, false
}
if err != nil {
p.error(err.Error())
}
p.runeCount++
return r, true
}
// Put the last rune that was read back on the input.
func (p *pathTemplateParser) unreadRune() {
if err := p.r.UnreadRune(); err != nil {
p.error(err.Error())
}
p.runeCount--
}