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tree.go
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tree.go
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/*
Package pathmux implements a tree lookup for values associated to
paths.
This package is a fork of https://github.com/dimfeld/httptreemux.
*/
package pathmux
import (
"fmt"
"net/url"
"strings"
)
// Matcher objects, when using the LookupMatcher function, can be used for additional checks and to override the
// default result in case of path matches. The argument passed to the Match function is the original value
// passed to the Tree.Add function.
type Matcher interface {
// Match should return true and the object to be returned by the lookup, when the argument value fulfils the
// conditions defined by the custom logic in the matcher itself. If it returns false, it instructs the
// lookup to continue with backtracking from the current tree position.
Match(value interface{}) (bool, interface{})
}
type trueMatcher struct{}
func (m *trueMatcher) Match(value interface{}) (bool, interface{}) {
return true, value
}
var tm *trueMatcher
func init() {
tm = &trueMatcher{}
}
type node struct {
path string
priority int
// The list of static children to check.
staticIndices []byte
staticChild []*node
// If none of the above match, check the wildcard children
wildcardChild *node
// If none of the above match, then we use the catch-all, if applicable.
catchAllChild *node
isCatchAll bool
leafValue interface{}
}
// Tree structure to store values associated to paths.
type Tree node
func (n *node) sortStaticChild(i int) {
for i > 0 && n.staticChild[i].priority > n.staticChild[i-1].priority {
n.staticChild[i], n.staticChild[i-1] = n.staticChild[i-1], n.staticChild[i]
n.staticIndices[i], n.staticIndices[i-1] = n.staticIndices[i-1], n.staticIndices[i]
i -= 1
}
}
func (n *node) addPath(path string) (*node, error) {
leaf := len(path) == 0
if leaf {
return n, nil
}
c := path[0]
nextSlash := strings.Index(path, "/")
var thisToken string
var tokenEnd int
if c == '/' {
thisToken = "/"
tokenEnd = 1
} else if nextSlash == -1 {
thisToken = path
tokenEnd = len(path)
} else {
thisToken = path[0:nextSlash]
tokenEnd = nextSlash
}
remainingPath := path[tokenEnd:]
if c == '*' {
// Token starts with a *, so it's a catch-all
thisToken = thisToken[1:]
if n.catchAllChild == nil {
n.catchAllChild = &node{path: thisToken, isCatchAll: true}
}
if path[1:] != n.catchAllChild.path {
return nil, fmt.Errorf(
"catch-all name in %s doesn't match %s",
path, n.catchAllChild.path)
}
if nextSlash != -1 {
return nil, fmt.Errorf("/ after catch-all found in %s", path)
}
return n.catchAllChild, nil
} else if c == ':' {
// Token starts with a :
if n.wildcardChild == nil {
n.wildcardChild = &node{path: "wildcard"}
}
return n.wildcardChild.addPath(remainingPath)
} else {
if strings.ContainsAny(thisToken, ":*") {
return nil, fmt.Errorf("* or : in middle of path component %s", path)
}
// Do we have an existing node that starts with the same byte?
for i, index := range n.staticIndices {
if c == index {
// Yes. Split it based on the common prefix of the existing
// node and the new one.
child, prefixSplit := n.splitCommonPrefix(i, thisToken)
child.priority++
n.sortStaticChild(i)
return child.addPath(path[prefixSplit:])
}
}
// No existing node starting with this byte, so create it.
child := &node{path: thisToken}
if n.staticIndices == nil {
n.staticIndices = []byte{c}
n.staticChild = []*node{child}
} else {
n.staticIndices = append(n.staticIndices, c)
n.staticChild = append(n.staticChild, child)
}
return child.addPath(remainingPath)
}
}
func (n *node) splitCommonPrefix(existingNodeIndex int, path string) (*node, int) {
childNode := n.staticChild[existingNodeIndex]
if strings.HasPrefix(path, childNode.path) {
// No split needs to be done. Rather, the new path shares the entire
// prefix with the existing node, so the new node is just a child of
// the existing one. Or the new path is the same as the existing path,
// which means that we just move on to the next token. Either way,
// this return accomplishes that
return childNode, len(childNode.path)
}
// Find the length of the common prefix of the child node and the new path.
i := commonPrefixLen(childNode.path, path)
commonPrefix := path[0:i]
childNode.path = childNode.path[i:]
// Create a new intermediary node in the place of the existing node, with
// the existing node as a child.
newNode := &node{
path: commonPrefix,
priority: childNode.priority,
// Index is the first byte of the non-common part of the path.
staticIndices: []byte{childNode.path[0]},
staticChild: []*node{childNode},
}
n.staticChild[existingNodeIndex] = newNode
return newNode, i
}
func commonPrefixLen(x, y string) int {
n := 0
for n < len(x) && n < len(y) && x[n] == y[n] {
n++
}
return n
}
func (n *node) search(path string, m Matcher) (found *node, params []string, value interface{}) {
pathLen := len(path)
if pathLen == 0 {
if n.leafValue == nil {
return nil, nil, nil
}
var match bool
match, value = m.Match(n.leafValue)
if !match {
return nil, nil, nil
}
return n, nil, value
}
// First see if this matches a static token.
firstChar := path[0]
for i, staticIndex := range n.staticIndices {
if staticIndex == firstChar {
child := n.staticChild[i]
childPathLen := len(child.path)
if pathLen >= childPathLen && child.path == path[:childPathLen] {
nextPath := path[childPathLen:]
found, params, value = child.search(nextPath, m)
}
break
}
}
if found != nil {
return
}
if n.wildcardChild != nil {
// Didn't find a static token, so check for a wildcard.
nextSlash := 0
for nextSlash < pathLen && path[nextSlash] != '/' {
nextSlash++
}
thisToken := path[0:nextSlash]
nextToken := path[nextSlash:]
if len(thisToken) > 0 { // Don't match on empty tokens.
found, params, value = n.wildcardChild.search(nextToken, m)
if found != nil {
unescaped, err := url.QueryUnescape(thisToken)
if err != nil {
unescaped = thisToken
}
if params == nil {
params = []string{unescaped}
} else {
params = append(params, unescaped)
}
return
}
}
}
catchAllChild := n.catchAllChild
if catchAllChild != nil {
// Hit the catchall, so just assign the whole remaining path.
unescaped, err := url.QueryUnescape(path)
if err != nil {
unescaped = path
}
var match bool
match, value = m.Match(catchAllChild.leafValue)
if !match {
return nil, nil, nil
}
return catchAllChild, []string{unescaped}, value
}
return nil, nil, nil
}
// Add a value to the tree associated with a path. Paths may contain
// wildcards. Wildcards can be of two types:
//
// - simple wildcard: e.g. /some/:wildcard/path, where a wildcard is
// matched to a single name in the path.
//
// - free wildcard: e.g. /some/path/*wildcard, where a wildcard at the
// end of a path matches anything.
func (t *Tree) Add(path string, value interface{}) error {
n, err := (*node)(t).addPath(path[1:])
if err != nil {
return err
}
n.leafValue = value
return nil
}
// Lookup tries to find a value in the tree associated to a path. If the found path definition contains
// wildcards, the values of the wildcards are returned in the second argument.
func (t *Tree) Lookup(path string) (interface{}, []string) {
node, params, _ := t.LookupMatcher(path, tm)
return node, params
}
// LookupMatcher tries to find value in the tree associated to a path. If the found path definition contains
// wildcards, the values of the wildcards are returned in the second argument. When a value is found,
// the matcher is called to check if the value meets the conditions implemented by the custom matcher. If it
// returns true, then the lookup is done and the additional return value from the matcher is returned as the
// lookup result. If it returns false, the lookup continues with backtracking from the current tree position.
func (t *Tree) LookupMatcher(path string, m Matcher) (interface{}, []string, interface{}) {
if path == "" {
path = "/"
}
node, params, value := (*node)(t).search(path[1:], m)
if node == nil {
return nil, nil, nil
}
return node.leafValue, params, value
}