tree.go

/*
Copyright (c) 2013 Julien Schmidt. 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.
    * The names of the contributors may not 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 JULIEN SCHMIDT 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 siesta

import (
	"strings"
	"unicode"
)

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

func countParams(path string) uint8 {
	var n uint
	for i := 0; i < len(path); i++ {
		if path[i] != ':' && path[i] != '*' {
			continue
		}
		n++
	}
	if n >= 255 {
		return 255
	}
	return uint8(n)
}

type nodeType uint8

const (
	static   nodeType = 0
	param    nodeType = 1
	catchAll nodeType = 2
)

type node struct {
	path      string
	wildChild bool
	nType     nodeType
	maxParams uint8
	indices   []byte
	children  []*node
	handle    ContextHandler
	usage     string
	priority  uint32
}

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

	// adjust position (move to front)
	for j := i - 1; j >= 0 && n.children[j].priority < prio; j-- {
		// swap node positions
		tmpN := n.children[j]
		n.children[j] = n.children[i]
		n.children[i] = tmpN
		tmpI := n.indices[j]
		n.indices[j] = n.indices[i]
		n.indices[i] = tmpI

		i--
	}
	return i
}

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

	// non-empty tree
	if len(n.path) > 0 || len(n.children) > 0 {
	WALK:
		for {
			// Update maxParams of the current node
			if numParams > n.maxParams {
				n.maxParams = numParams
			}

			// Find the longest common prefix.
			// This also implies that the commom prefix contains no ':' or '*'
			// since the existing key can't contain this chars.
			i := 0
			for max := min(len(path), len(n.path)); i < max && path[i] == n.path[i]; i++ {
			}

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

				// Update maxParams (max of all children)
				for i := range child.children {
					if child.children[i].maxParams > child.maxParams {
						child.maxParams = child.children[i].maxParams
					}
				}

				n.children = []*node{&child}
				n.indices = []byte{n.path[i]}
				n.path = path[:i]
				n.handle = nil
				n.usage = ""
				n.wildChild = false
			}

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

				if n.wildChild {
					n = n.children[0]
					n.priority++

					// Update maxParams of the child node
					if numParams > n.maxParams {
						n.maxParams = numParams
					}
					numParams--

					// Check if the wildcard matches
					if len(path) >= len(n.path) && n.path == path[:len(n.path)] {
						// check for longer wildcard, e.g. :name and :names
						if len(n.path) >= len(path) || path[len(n.path)] == '/' {
							continue WALK
						}
					}

					panic("conflict with wildcard route")
				}

				c := path[0]

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

				// Check if a child with the next path byte exists
				for i, index := range n.indices {
					if c == index {
						i = n.incrementChildPrio(i)
						n = n.children[i]
						continue WALK
					}
				}

				// Otherwise insert it
				if c != ':' && c != '*' {
					n.indices = append(n.indices, c)
					child := &node{
						maxParams: numParams,
					}
					n.children = append(n.children, child)
					n.incrementChildPrio(len(n.indices) - 1)
					n = child
				}
				n.insertChild(numParams, path, usage, handle)
				return

			} else if i == len(path) { // Make node a (in-path) leaf
				if n.handle != nil {
					panic("a Handle is already registered for this path")
				}
				n.handle = handle
				n.usage = usage
			}
			return
		}
	} else { // Empty tree
		n.insertChild(numParams, path, usage, handle)
	}
}

func (n *node) insertChild(numParams uint8, path string, usage string, handle ContextHandler) {
	var offset int // already handled bytes of the path

	// find prefix until first wildcard (beginning with ':'' or '*'')
	for i, max := 0, len(path); numParams > 0; i++ {
		c := path[i]
		if c != ':' && c != '*' {
			continue
		}

		// check if this Node existing children which would be
		// unreachable if we insert the wildcard here
		if len(n.children) > 0 {
			panic("wildcard route conflicts with existing children")
		}

		// find wildcard end (either '/' or path end)
		end := i + 1
		for end < max && path[end] != '/' {
			switch path[end] {
			// the wildcard name must not contain ':' and '*'
			case ':', '*':
				panic("only one wildcard per path segment is allowed")
			default:
				end++
			}
		}

		// check if the wildcard has a name
		if end-i < 2 {
			panic("wildcards must be named with a non-empty name")
		}

		if c == ':' { // param
			// split path at the beginning of the wildcard
			if i > 0 {
				n.path = path[offset:i]
				offset = i
			}

			child := &node{
				nType:     param,
				maxParams: numParams,
			}
			n.children = []*node{child}
			n.wildChild = true
			n = child
			n.priority++
			numParams--

			// if the path doesn't end with the wildcard, then there
			// will be another non-wildcard subpath starting with '/'
			if end < max {
				n.path = path[offset:end]
				offset = end

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

		} else { // catchAll
			if end != max || numParams > 1 {
				panic("catch-all routes are only allowed at the end of the path")
			}

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

			// currently fixed width 1 for '/'
			i--
			if path[i] != '/' {
				panic("no / before catch-all")
			}

			n.path = path[offset:i]

			// first node: catchAll node with empty path
			child := &node{
				wildChild: true,
				nType:     catchAll,
				maxParams: 1,
			}
			n.children = []*node{child}
			n.indices = []byte{path[i]}
			n = child
			n.priority++

			// second node: node holding the variable
			child = &node{
				path:      path[i:],
				nType:     catchAll,
				maxParams: 1,
				handle:    handle,
				usage:     usage,
				priority:  1,
			}
			n.children = []*node{child}

			return
		}
	}

	// insert remaining path part and handle to the leaf
	n.path = path[offset:]
	n.handle = handle
	n.usage = usage
}

// Returns the handle registered with the given path (key). The values of
// wildcards are saved to a map.
// If no handle can be found, a TSR (trailing slash redirect) recommendation is
// made if a handle exists with an extra (without the) trailing slash for the
// given path.
func (n *node) getValue(path string) (handle ContextHandler, usage string, p routeParams, tsr bool) {
walk: // Outer loop for walking the tree
	for {
		if len(path) > len(n.path) {
			if path[:len(n.path)] == n.path {
				path = path[len(n.path):]
				// If this node does not have a wildcard (param or catchAll)
				// child,  we can just look up the next child node and continue
				// to walk down the tree
				if !n.wildChild {
					c := path[0]
					for i, index := range n.indices {
						if c == index {
							n = n.children[i]
							continue walk
						}
					}

					// Nothing found.
					// We can recommend to redirect to the same URL without a
					// trailing slash if a leaf exists for that path.
					tsr = (path == "/" && n.handle != nil)
					return

				}

				// handle wildcard child
				n = n.children[0]
				switch n.nType {
				case param:
					// find param end (either '/' or path end)
					end := 0
					for end < len(path) && path[end] != '/' {
						end++
					}

					// save param value
					if p == nil {
						// lazy allocation
						p = make(routeParams, 0, n.maxParams)
					}
					i := len(p)
					p = p[:i+1] // expand slice within preallocated capacity
					p[i].Key = n.path[1:]
					p[i].Value = path[:end]

					// we need to go deeper!
					if end < len(path) {
						if len(n.children) > 0 {
							path = path[end:]
							n = n.children[0]
							continue walk
						}

						// ... but we can't
						tsr = (len(path) == end+1)
						return
					}

					if handle, usage = n.handle, n.usage; handle != nil {
						return
					} else if len(n.children) == 1 {
						// No handle found. Check if a handle for this path + a
						// trailing slash exists for TSR recommendation
						n = n.children[0]
						tsr = (n.path == "/" && n.handle != nil)
					}

					return

				case catchAll:
					// save param value
					if p == nil {
						// lazy allocation
						p = make(routeParams, 0, n.maxParams)
					}
					i := len(p)
					p = p[:i+1] // expand slice within preallocated capacity
					p[i].Key = n.path[2:]
					p[i].Value = path

					handle = n.handle
					usage = n.usage
					return

				default:
					panic("Invalid node type")
				}
			}
		} else if path == n.path {
			// We should have reached the node containing the handle.
			// Check if this node has a handle registered.
			if handle, usage = n.handle, n.usage; handle != nil {
				return
			}

			// No handle found. Check if a handle for this path + a
			// trailing slash exists for trailing slash recommendation
			for i, index := range n.indices {
				if index == '/' {
					n = n.children[i]
					tsr = (n.path == "/" && n.handle != nil) ||
						(n.nType == catchAll && n.children[0].handle != nil)
					return
				}
			}

			return
		}

		// Nothing found. We can recommend to redirect to the same URL with an
		// extra trailing slash if a leaf exists for that path
		tsr = (path == "/") ||
			(len(n.path) == len(path)+1 && n.path[len(path)] == '/' &&
				path == n.path[:len(n.path)-1] && n.handle != nil)
		return
	}
}

// Makes a case-insensitive lookup of the given path and tries to find a handler.
// It can optionally also fix trailing slashes.
// It returns the case-corrected path and a bool indicating wether the lookup
// was successful.
func (n *node) findCaseInsensitivePath(path string, fixTrailingSlash bool) (ciPath []byte, found bool) {
	ciPath = make([]byte, 0, len(path)+1) // preallocate enough memory

	// Outer loop for walking the tree
	for len(path) >= len(n.path) && strings.ToLower(path[:len(n.path)]) == strings.ToLower(n.path) {
		path = path[len(n.path):]
		ciPath = append(ciPath, n.path...)

		if len(path) > 0 {
			// If this node does not have a wildcard (param or catchAll) child,
			// we can just look up the next child node and continue to walk down
			// the tree
			if !n.wildChild {
				r := unicode.ToLower(rune(path[0]))
				for i, index := range n.indices {
					// must use recursive approach since both index and
					// ToLower(index) could exist. We must check both.
					if r == unicode.ToLower(rune(index)) {
						out, found := n.children[i].findCaseInsensitivePath(path, fixTrailingSlash)
						if found {
							return append(ciPath, out...), true
						}
					}
				}

				// Nothing found. We can recommend to redirect to the same URL
				// without a trailing slash if a leaf exists for that path
				found = (fixTrailingSlash && path == "/" && n.handle != nil)
				return
			}

			n = n.children[0]
			switch n.nType {
			case param:
				// find param end (either '/' or path end)
				k := 0
				for k < len(path) && path[k] != '/' {
					k++
				}

				// add param value to case insensitive path
				ciPath = append(ciPath, path[:k]...)

				// we need to go deeper!
				if k < len(path) {
					if len(n.children) > 0 {
						path = path[k:]
						n = n.children[0]
						continue
					}

					// ... but we can't
					if fixTrailingSlash && len(path) == k+1 {
						return ciPath, true
					}
					return
				}

				if n.handle != nil {
					return ciPath, true
				} else if fixTrailingSlash && len(n.children) == 1 {
					// No handle found. Check if a handle for this path + a
					// trailing slash exists
					n = n.children[0]
					if n.path == "/" && n.handle != nil {
						return append(ciPath, '/'), true
					}
				}
				return

			case catchAll:
				return append(ciPath, path...), true

			default:
				panic("Invalid node type")
			}
		} else {
			// We should have reached the node containing the handle.
			// Check if this node has a handle registered.
			if n.handle != nil {
				return ciPath, true
			}

			// No handle found.
			// Try to fix the path by adding a trailing slash
			if fixTrailingSlash {
				for i, index := range n.indices {
					if index == '/' {
						n = n.children[i]
						if (n.path == "/" && n.handle != nil) ||
							(n.nType == catchAll && n.children[0].handle != nil) {
							return append(ciPath, '/'), true
						}
						return
					}
				}
			}
			return
		}
	}

	// Nothing found.
	// Try to fix the path by adding / removing a trailing slash
	if fixTrailingSlash {
		if path == "/" {
			return ciPath, true
		}
		if len(path)+1 == len(n.path) && n.path[len(path)] == '/' &&
			strings.ToLower(path) == strings.ToLower(n.path[:len(path)]) &&
			n.handle != nil {
			return append(ciPath, n.path...), true
		}
	}
	return
}