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pattern.go
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pattern.go
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package navaros
import (
"errors"
"github.com/grafana/regexp"
)
// Pattern is used to compare and match request paths to route patterns.
// Patterns are used by the router to determine which handlers to execute for
// a given request.
type Pattern struct {
str string
regExp *regexp.Regexp
}
// NewPattern creates a new pattern from a string. The string should be a
// valid route pattern. If the string is not a valid route pattern, an error
// is returned.
func NewPattern(patternStr string) (*Pattern, error) {
patternRegExp, err := regExpFromPattern(patternStr)
if err != nil {
return nil, err
}
pattern := &Pattern{
str: patternStr,
regExp: patternRegExp,
}
return pattern, nil
}
// Match compares a path to the pattern and returns a map of named parameters
// extracted from the path as per the pattern. If the path matches the pattern,
// the second return value will be true. If the path does not match the pattern,
// the second return value will be false.
func (p *Pattern) Match(path string) (RequestParams, bool) {
matches := p.regExp.FindStringSubmatch(path)
if len(matches) == 0 {
return nil, false
}
keys := p.regExp.SubexpNames()
params := make(RequestParams, len(keys))
for i := 1; i < len(keys); i += 1 {
if keys[i] != "" {
params[keys[i]] = matches[i]
}
}
return params, true
}
func (p *Pattern) MatchInto(path string, params *RequestParams) bool {
matchIndices := p.regExp.FindStringSubmatchIndex(path)
if len(matchIndices) == 0 {
return false
}
keys := p.regExp.SubexpNames()
if *params == nil {
*params = make(map[string]string, len(keys))
}
for key := range *params {
delete(*params, key)
}
for i := 1; i < len(keys); i += 1 {
if keys[i] != "" {
(*params)[keys[i]] = path[matchIndices[i*2]:matchIndices[i*2+1]]
}
}
return true
}
// String returns the string representation of the pattern.
func (p *Pattern) String() string {
return p.str
}
type chunkKind int
const (
unknown chunkKind = iota
static
dynamic
wildcard
)
type chunkModifier int
const (
single chunkModifier = iota
optional
oneOrMore
zeroOrMore
)
type chunk = struct {
kind chunkKind
modifier chunkModifier
key string
pattern string
}
// regExpFromPattern converts a route pattern string to a regular expression.
// This is the heart of Pattern and parses the pattern character by character.
func regExpFromPattern(patternStr string) (*regexp.Regexp, error) {
patternRunes := []rune(patternStr)
patternRunesLen := len(patternRunes)
var currentChunk *chunk
chunks := make([]chunk, 0)
for i := 0; i < patternRunesLen; i += 1 {
isLastRune := i+1 == patternRunesLen
isLastRuneInChunk := isLastRune || patternRunes[i+1] == '/'
currentRune := patternRunes[i]
if currentRune == '/' {
if currentChunk != nil {
chunks = append(chunks, *currentChunk)
}
currentChunk = &chunk{}
continue
}
if currentChunk == nil {
return nil, errors.New("pattern must start with a leading slash")
}
if currentChunk.kind == unknown {
switch currentRune {
case ':':
currentChunk.kind = dynamic
case '*':
currentChunk.kind = wildcard
case '(':
currentChunk.kind = wildcard
i -= 1
default:
currentChunk.kind = static
i -= 1
}
continue
}
if currentRune == '(' {
if currentChunk.kind == dynamic && currentChunk.key == "" {
return nil, errors.New("dynamic chunks must have a name")
}
if currentChunk.pattern != "" {
return nil, errors.New("pattern chunks cannot contain multiple subpatterns")
}
for j := i + 1; j < patternRunesLen; j += 1 {
if patternRunes[j] == ')' {
currentChunk.pattern = string(patternRunes[i+1 : j])
i = j
break
}
}
continue
}
if isLastRuneInChunk {
switch currentRune {
case '?':
currentChunk.modifier = optional
case '+':
currentChunk.modifier = oneOrMore
case '*':
currentChunk.modifier = zeroOrMore
}
if currentChunk.modifier != single {
continue
}
}
switch currentChunk.kind {
case dynamic:
currentChunk.key += string(currentRune)
case static:
currentChunk.pattern += string(currentRune)
case wildcard:
}
}
if currentChunk != nil {
chunks = append(chunks, *currentChunk)
}
regExpStr := "^"
for _, currentChunk := range chunks {
if currentChunk.pattern == "" {
currentChunk.pattern = "[^\\/]+"
}
if currentChunk.kind == static || currentChunk.kind == wildcard {
switch currentChunk.modifier {
case single:
regExpStr += "\\/" + currentChunk.pattern
case optional:
regExpStr += "(?:\\/" + currentChunk.pattern + ")?"
case oneOrMore:
regExpStr += "\\/" + currentChunk.pattern + "(?:\\/" + currentChunk.pattern + ")*"
case zeroOrMore:
regExpStr += "(?:\\/" + currentChunk.pattern + "(?:\\/" + currentChunk.pattern + ")*)?"
}
} else if currentChunk.kind == dynamic {
switch currentChunk.modifier {
case single:
regExpStr += "\\/(?P<" + currentChunk.key + ">" + currentChunk.pattern + ")"
case optional:
regExpStr += "(?:\\/(?P<" + currentChunk.key + ">" + currentChunk.pattern + "))?"
case oneOrMore:
regExpStr += "\\/(?P<" + currentChunk.key + ">(?:" + currentChunk.pattern + ")(?:\\/" + currentChunk.pattern + ")*)"
case zeroOrMore:
regExpStr += "(?:\\/(?P<" + currentChunk.key + ">" + currentChunk.pattern + "(?:\\/" + currentChunk.pattern + ")*))?"
}
}
}
regExpStr += "\\/?$"
regExp, err := regexp.Compile(regExpStr)
if err != nil {
return nil, err
}
return regExp, nil
}