tree.go

package enlight

import (
	"strings"
)

// tree.go is based upon https://github.com/julienschmidt/httprouter/blob/master/tree.go
// nearly all code comes from there.

type nodeType uint8

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

// node is a path
type node struct {
	path      string
	children  []*node
	handle    HandleFunc
	maxParams uint16
	indices   string
	wildChild bool
	nType     nodeType
	priority  uint32
	once      bool // node gets destroyed on call
}

func countParams(path string) uint16 {
	var n uint
	for i := range []byte(path) {
		switch path[i] {
		case ':', '*':
			n++
		}
	}
	return uint16(n)
}

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
}

// 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) (wilcard 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
}

// 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
}

func (n *node) dropRoute(path string) {
	var handle HandleFunc
	var p Params
	parent := n
walk:
	for {
		prefix := n.path
		if len(path) > len(prefix) {
			if path[:len(prefix)] == prefix {
				path = path[len(prefix):]
				if !n.wildChild {
					idxc := path[0]
					for i, c := range []byte(n.indices) {
						if c == idxc {
							parent = n
							n = n.children[i]
							continue walk
						}
					}
					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++
					}
					// We need to go deeper!
					if end < len(path) {
						if len(n.children) > 0 {
							path = path[end:]
							parent = n
							n = n.children[0]
							continue walk
						}
						return
					}

					if handle = n.handle; 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]
					}

					return
				case catchAll:
					if p == nil {
						// lazy allocation
						p = make(Params, 0, n.maxParams)
					}
					p = append(p, Param{
						Key:   n.path[2:],
						Value: path,
					})

					handle = n.handle
					return
				default:
					panic("invalid node type")
				}
			}

		} else if path == prefix {
			var idxcPos int
			children := []*node{}
			for key, value := range parent.children {
				if value.path != prefix {
					children = append(children, value)
				} else {
					idxcPos = key
				}
			}
			// remove key from indices...
			parent.indices = parent.indices[0:idxcPos] + parent.indices[idxcPos+1:]
			// replace children by new children
			parent.children = children
			return
		}
	}
}

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

	// Empty tree
	if len(n.path) == 0 && len(n.indices) == 0 {
		n.insertChild(path, fullPath, handle, once)
		n.nType = root
		return
	}
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 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,
				nType:     static,
				indices:   n.indices,
				children:  n.children,
				handle:    n.handle,
				priority:  n.priority - 1,
				once:      once,
			}

			// 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}
			// []byte for proper unicode char conversion, see #65
			n.indices = string([]byte{n.path[i]})
			n.path = path[:i]
			n.handle = nil
			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)] &&
					// 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
				} else {
					// Wildcard conflict
					pathSeg := path
					if n.nType != catchAll {
						pathSeg = strings.SplitN(pathSeg, "/", 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 +
						"'")
				}
			}

			idxc := path[0]

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

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

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

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

func (n *node) insertChild(path, fullPath string, handle HandleFunc, once bool) {
	for {
		// Find prefix until first wildcard
		wildcard, i, valid := findWildcard(path)
		if i < 0 { // No wilcard 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,
				once:  once,
			}
			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,
				}
				n.children = []*node{child}
				n = child
				continue
			}

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

		}

		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 + "'")
		}

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

		n.path = path[:i]

		// First node: catchAll node with empty path
		child := &node{
			wildChild: true,
			nType:     catchAll,
			once:      once,
		}
		n.children = []*node{child}
		n.indices = string('/')
		n = child
		n.priority++

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

		return
	}

	// If no wildcard was found, simply insert the path and handle
	n.path = path
	n.handle = handle
}

// 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 HandleFunc, p Params, tsr bool) {

walk: // Outer loop for walking the tree
	for {
		prefix := n.path
		if len(path) > len(prefix) {
			if path[:len(prefix)] == prefix {
				path = path[len(prefix):]

				// 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 {
					idxc := path[0]
					for i, c := range []byte(n.indices) {
						if c == idxc {
							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(Params, 0, n.maxParams)
					}
					p = append(p, Param{
						Key:   n.path[1:],
						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 = n.handle; 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:
					if p == nil {
						// lazy allocation
						p = make(Params, 0, n.maxParams)
					}
					p = append(p, Param{
						Key:   n.path[2:],
						Value: path,
					})

					handle = n.handle
					return
				default:
					panic("invalid node type")
				}
			}
		} else if path == prefix {

			// We should have reached the node containing the handle.
			// Check if this node has a handle registered.
			if handle = n.handle; handle != nil {
				return
			}

			// If there is no handle for this route, but this route has a
			// wildcard child, there must be a handle for this path with an
			// additional trailing slash
			if path == "/" && n.wildChild && n.nType != root {
				tsr = true
				return
			}

			// No handle found. Check if a handle for this path + a
			// trailing slash exists for trailing slash recommendation
			for i, c := range []byte(n.indices) {
				if c == '/' {
					n = n.children[i]
					tsr = (len(n.path) == 1 && 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(prefix) == len(path)+1 && prefix[len(path)] == '/' &&
				path == prefix[:len(prefix)-1] && n.handle != nil)
		return
	}
}