gin/tree.go

// Copyright 2013 Julien Schmidt. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be found
// at https://github.com/julienschmidt/httprouter/blob/master/LICENSE

package gin

import (
	"bytes"
	"net/url"
	"strings"
	"unicode"
	"unicode/utf8"

	"github.com/gin-gonic/gin/internal/bytesconv"
)

var (
	strColon = []byte(":")
	strStar  = []byte("*")
)

// Param is a single URL parameter, consisting of a key and a value.
type Param struct {
	Key   string
	Value string
}

// Params is a Param-slice, as returned by the router.
// The slice is ordered, the first URL parameter is also the first slice value.
// It is therefore safe to read values by the index.
type Params []Param

// Get returns the value of the first Param which key matches the given name.
// If no matching Param is found, an empty string is returned.
func (ps Params) Get(name string) (string, bool) {
	for _, entry := range ps {
		if entry.Key == name {
			return entry.Value, true
		}
	}
	return "", false
}

// ByName returns the value of the first Param which key matches the given name.
// If no matching Param is found, an empty string is returned.
func (ps Params) ByName(name string) (va string) {
	va, _ = ps.Get(name)
	return
}

type methodTree struct {
	method string
	root   *node
}

type methodTrees []methodTree

func (trees methodTrees) get(method string) *node {
	for _, tree := range trees {
		if tree.method == method {
			return tree.root
		}
	}
	return nil
}

func min(a, b int) int {
	if a <= b {
		return a
	}
	return b
}

func longestCommonPrefix(a, b string) int {
	i := 0
	max := min(len(a), len(b))
	for i < max && a[i] == b[i] {
		i++
	}
	return i
}

func countParams(path string) uint16 {
	var n uint16
	s := bytesconv.StringToBytes(path)
	n += uint16(bytes.Count(s, strColon))
	n += uint16(bytes.Count(s, strStar))
	return n
}

type nodeType uint8

const (
	static nodeType = iota // default
	root
	param
	catchAll
)

type node struct {
	path      string
	indices   string
	wildChild bool
	nType     nodeType
	priority  uint32
	children  []*node
	handlers  HandlersChain
	fullPath  string
}

// Increments priority of the given child and reorders if necessary
func (n *node) incrementChildPrio(pos int) int {
	cs := n.children
	cs[pos].priority++
	prio := cs[pos].priority

	// Adjust position (move to front)
	newPos := pos
	for ; newPos > 0 && cs[newPos-1].priority < prio; newPos-- {
		// Swap node positions
		cs[newPos-1], cs[newPos] = cs[newPos], cs[newPos-1]

	}

	// Build new index char string
	if newPos != pos {
		n.indices = n.indices[:newPos] + // Unchanged prefix, might be empty
			n.indices[pos:pos+1] + // The index char we move
			n.indices[newPos:pos] + n.indices[pos+1:] // Rest without char at 'pos'
	}

	return newPos
}

// addRoute adds a node with the given handle to the path.
// Not concurrency-safe!
func (n *node) addRoute(path string, handlers HandlersChain) {
	fullPath := path
	n.priority++

	// Empty tree
	if len(n.path) == 0 && len(n.children) == 0 {
		n.insertChild(path, fullPath, handlers)
		n.nType = root
		return
	}

	parentFullPathIndex := 0

walk:
	for {
		// Find the longest common prefix.
		// This also implies that the common prefix contains no ':' or '*'
		// since the existing key can't contain those chars.
		i := longestCommonPrefix(path, n.path)

		// Split edge
		if i < len(n.path) {
			child := node{
				path:      n.path[i:],
				wildChild: n.wildChild,
				indices:   n.indices,
				children:  n.children,
				handlers:  n.handlers,
				priority:  n.priority - 1,
				fullPath:  n.fullPath,
			}

			n.children = []*node{&child}
			// []byte for proper unicode char conversion, see #65
			n.indices = bytesconv.BytesToString([]byte{n.path[i]})
			n.path = path[:i]
			n.handlers = nil
			n.wildChild = false
			n.fullPath = fullPath[:parentFullPathIndex+i]
		}

		// Make new node a child of this node
		if i < len(path) {
			path = path[i:]

			if n.wildChild {
				parentFullPathIndex += len(n.path)
				n = n.children[0]
				n.priority++

				// Check if the wildcard matches
				if len(path) >= len(n.path) && n.path == path[:len(n.path)] &&
					// Adding a child to a catchAll is not possible
					n.nType != catchAll &&
					// Check for longer wildcard, e.g. :name and :names
					(len(n.path) >= len(path) || path[len(n.path)] == '/') {
					continue walk
				}

				pathSeg := path
				if n.nType != catchAll {
					pathSeg = strings.SplitN(path, "/", 2)[0]
				}
				prefix := fullPath[:strings.Index(fullPath, pathSeg)] + n.path
				panic("'" + pathSeg +
					"' in new path '" + fullPath +
					"' conflicts with existing wildcard '" + n.path +
					"' in existing prefix '" + prefix +
					"'")
			}

			c := path[0]

			// slash after param
			if n.nType == param && c == '/' && len(n.children) == 1 {
				parentFullPathIndex += len(n.path)
				n = n.children[0]
				n.priority++
				continue walk
			}

			// Check if a child with the next path byte exists
			for i, max := 0, len(n.indices); i < max; i++ {
				if c == n.indices[i] {
					parentFullPathIndex += len(n.path)
					i = n.incrementChildPrio(i)
					n = n.children[i]
					continue walk
				}
			}

			// Otherwise insert it
			if c != ':' && c != '*' {
				// []byte for proper unicode char conversion, see #65
				n.indices += bytesconv.BytesToString([]byte{c})
				child := &node{
					fullPath: fullPath,
				}
				n.children = append(n.children, child)
				n.incrementChildPrio(len(n.indices) - 1)
				n = child
			}
			n.insertChild(path, fullPath, handlers)
			return
		}

		// Otherwise and handle to current node
		if n.handlers != nil {
			panic("handlers are already registered for path '" + fullPath + "'")
		}
		n.handlers = handlers
		n.fullPath = fullPath
		return
	}
}

// Search for a wildcard segment and check the name for invalid characters.
// Returns -1 as index, if no wildcard was found.
func findWildcard(path string) (wildcard string, i int, valid bool) {
	// Find start
	for start, c := range []byte(path) {
		// A wildcard starts with ':' (param) or '*' (catch-all)
		if c != ':' && c != '*' {
			continue
		}

		// Find end and check for invalid characters
		valid = true
		for end, c := range []byte(path[start+1:]) {
			switch c {
			case '/':
				return path[start : start+1+end], start, valid
			case ':', '*':
				valid = false
			}
		}
		return path[start:], start, valid
	}
	return "", -1, false
}

func (n *node) insertChild(path string, fullPath string, handlers HandlersChain) {
	for {
		// Find prefix until first wildcard
		wildcard, i, valid := findWildcard(path)
		if i < 0 { // No wildcard found
			break
		}

		// The wildcard name must not contain ':' and '*'
		if !valid {
			panic("only one wildcard per path segment is allowed, has: '" +
				wildcard + "' in path '" + fullPath + "'")
		}

		// check if the wildcard has a name
		if len(wildcard) < 2 {
			panic("wildcards must be named with a non-empty name in path '" + fullPath + "'")
		}

		// Check if this node has existing children which would be
		// unreachable if we insert the wildcard here
		if len(n.children) > 0 {
			panic("wildcard segment '" + wildcard +
				"' conflicts with existing children in path '" + fullPath + "'")
		}

		if wildcard[0] == ':' { // param
			if i > 0 {
				// Insert prefix before the current wildcard
				n.path = path[:i]
				path = path[i:]
			}

			n.wildChild = true
			child := &node{
				nType:    param,
				path:     wildcard,
				fullPath: fullPath,
			}
			n.children = []*node{child}
			n = child
			n.priority++

			// if the path doesn't end with the wildcard, then there
			// will be another non-wildcard subpath starting with '/'
			if len(wildcard) < len(path) {
				path = path[len(wildcard):]

				child := &node{
					priority: 1,
					fullPath: fullPath,
				}
				n.children = []*node{child}
				n = child
				continue
			}

			// Otherwise we're done. Insert the handle in the new leaf
			n.handlers = handlers
			return
		}

		// catchAll
		if i+len(wildcard) != len(path) {
			panic("catch-all routes are only allowed at the end of the path in path '" + fullPath + "'")
		}

		if len(n.path) > 0 && n.path[len(n.path)-1] == '/' {
			panic("catch-all conflicts with existing handle for the path segment root in path '" + fullPath + "'")
		}