Httprouter源码学习

简介

官方——https://github.com/julienschmidt/httprouter

HttpRouter is a lightweight high performance HTTP request router (also
called multiplexer or just mux for short) for Go.

In contrast to the default mux of Go’s net/http package, this router
supports variables in the routing pattern and matches against the
request method. It also scales better.

The router is optimized for high performance and a small memory
footprint. It scales well even with very long paths and a large number
of routes. A compressing dynamic trie (radix tree) structure is used
for efficient matching.

简单描述，httprouter是一个golang实现的路由组件。httprouter使用一个前缀树来维护映射的父子关系，通过前缀树快速路由。同时其里面的HttpRouter结构体实现了golang的net.http.server的Handler接口，可以作为httpHandle发布。golang以性能出名的gin使用的也就是httprouter来做路由处理。

依赖

require github.com/julienschmidt/httprouter latest

使用Demo

package httpRouterDemo

import (
	"net/http"
	"github.com/julienschmidt/httprouter"
)

func Index(w http.ResponseWriter, r *http.Request, _ httprouter.Params) {
	w.Write([]byte("hello world"))
}

func main() {
	router := httprouter.New()
	router.GET("/", Index)
	http.ListenAndServe(":80", router)
}

源码分析

New方法实际就是生成一个HttpRouter对象
接下来看看注册Get映射的实现

func (r *Router) GET(path string, handle Handle) {
	r.Handle(http.MethodGet, path, handle)
}
func (r *Router) Handle(method, path string, handle Handle) {
	if len(path) < 1 || path[0] != '/' {
		panic("path must begin with '/' in path '" + path + "'")
	}

	if r.trees == nil {
		r.trees = make(map[string]*node)
	}

	root := r.trees[method]
	if root == nil {
		root = new(node)
		r.trees[method] = root

		r.globalAllowed = r.allowed("*", "")
	}

	root.addRoute(path, handle)
}
func (n *node) addRoute(path string, handle Handle) {
	fullPath := path
	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
			}

			//查询最长公共前缀
			i := 0
			max := min(len(path), len(n.path))
			for i < max && path[i] == n.path[i] {
				i++
			}

			// 出现部分前缀匹配，最极端情况/根路径
			//创建一个以匹配部分为映射路径的空节点顶替当前匹配节点n，当前匹配节点n作为其子节点
			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,
				}

				// 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
			}
			//到这里可以确认，n绝对可以成为注册映射的祖先节点
			//找到最匹配的祖先节点作为自己的父节点
			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
						var pathSeg string
						if n.nType == catchAll {
							pathSeg = path
						} else {
							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 {
					n = n.children[0]
					n.priority++
					continue walk
				}

				// Check if a child with the next path byte exists
				for i := 0; i < len(n.indices); i++ {
					if c == n.indices[i] {
						i = n.incrementChildPrio(i)
						n = n.children[i]
						continue walk
					}
				}
				//插入子节点
				// Otherwise insert it
				if c != ':' && c != '*' {
					// []byte for proper unicode char conversion, see #65
					n.indices += string([]byte{c})
					child := &node{
						maxParams: numParams,
					}
					n.children = append(n.children, child)
					n.incrementChildPrio(len(n.indices) - 1)
					n = child
				}
				n.insertChild(numParams, path, fullPath, handle)
				return

			} else if i == len(path) { // Make node a (in-path) leaf
				if n.handle != nil {
					panic("a handle is already registered for path '" + fullPath + "'")
				}
				n.handle = handle
			}
			return
		}
	} else { 
		//树是空的，直接作为root
		n.insertChild(numParams, path, fullPath, handle)
		n.nType = root
	}
}

然后查看其处理请求的方式，也就是对前缀树进行查询

func (r *Router) ServeHTTP(w http.ResponseWriter, req *http.Request) {
	if r.PanicHandler != nil {
		defer r.recv(w, req)
	}

	path := req.URL.Path

	if root := r.trees[req.Method]; root != nil {
		//查询前缀树
		if handle, ps, tsr := root.getValue(path); handle != nil {
			//handle请求
			handle(w, req, ps)
			return
		} else if req.Method != http.MethodConnect && path != "/" {
			code := 301 // Permanent redirect, request with GET method
			if req.Method != http.MethodGet {
				// Temporary redirect, request with same method
				// As of Go 1.3, Go does not support status code 308.
				code = 307
			}

			if tsr && r.RedirectTrailingSlash {
				if len(path) > 1 && path[len(path)-1] == '/' {
					req.URL.Path = path[:len(path)-1]
				} else {
					req.URL.Path = path + "/"
				}
				http.Redirect(w, req, req.URL.String(), code)
				return
			}

			// Try to fix the request path
			if r.RedirectFixedPath {
				fixedPath, found := root.findCaseInsensitivePath(
					CleanPath(path),
					r.RedirectTrailingSlash,
				)
				if found {
					req.URL.Path = string(fixedPath)
					http.Redirect(w, req, req.URL.String(), code)
					return
				}
			}
		}
	}

	if req.Method == http.MethodOptions && r.HandleOPTIONS {
		// Handle OPTIONS requests
		if allow := r.allowed(path, http.MethodOptions); allow != "" {
			w.Header().Set("Allow", allow)
			if r.GlobalOPTIONS != nil {
				r.GlobalOPTIONS.ServeHTTP(w, req)
			}
			return
		}
	} else if r.HandleMethodNotAllowed { // Handle 405
		if allow := r.allowed(path, req.Method); allow != "" {
			w.Header().Set("Allow", allow)
			if r.MethodNotAllowed != nil {
				r.MethodNotAllowed.ServeHTTP(w, req)
			} else {
				http.Error(w,
					http.StatusText(http.StatusMethodNotAllowed),
					http.StatusMethodNotAllowed,
				)
			}
			return
		}
	}

	// Handle 404
	if r.NotFound != nil {
		r.NotFound.ServeHTTP(w, req)
	} else {
		http.NotFound(w, req)
	}
}
func (n *node) getValue(path string) (handle Handle, p Params, tsr bool) {
walk: // outer loop for walking the tree
	for {
		//查询前缀树节点
		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 := 0; i < len(n.indices); i++ {
						if c == n.indices[i] {
							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)
					}
					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 = 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:
					// save param value
					if p == nil {
						// lazy allocation
						p = make(Params, 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
					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 = n.handle; handle != nil {
				return
			}

			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 := 0; i < len(n.indices); i++ {
				if n.indices[i] == '/' {
					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(n.path) == len(path)+1 && n.path[len(path)] == '/' &&
				path == n.path[:len(n.path)-1] && n.handle != nil)
		return
	}
}

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