之前在Gin中已经说到, Gin比Martini的效率高好多耶, 究其原因是因为使用了httprouter这个路由框架, httprouter的git地址是: httprouter源码. 今天稍微看了下httprouter的 实现原理, 其实就是使用了一个radix tree(前缀树)来管理请求的URL, 下面具体看看httprouter原理.
###1. httprouter基本结构
httprouter中, 对于每种方法都有一颗tree来管理, 例如所有的GET方法对应的请求会有一颗tree管理, 所有的POST同样如此. OK, 那首先看一下 这个router结构体长啥样:
type Router struct {
// 这个radix tree是最重要的结构
// 按照method将所有的方法分开, 然后每个method下面都是一个radix tree
trees map[string]*node
// Enables automatic redirection if the current route can't be matched but a
// handler for the path with (without) the trailing slash exists.
// For example if /foo/ is requested but a route only exists for /foo, the
// client is redirected to /foo with http status code 301 for GET requests
// and 307 for all other request methods.
// 当/foo/没有匹配到的时候, 是否允许重定向到/foo路径
RedirectTrailingSlash bool
// If enabled, the router tries to fix the current request path, if no
// handle is registered for it.
// First superfluous path elements like ../ or // are removed.
// Afterwards the router does a case-insensitive lookup of the cleaned path.
// If a handle can be found for this route, the router makes a redirection
// to the corrected path with status code 301 for GET requests and 307 for
// all other request methods.
// For example /FOO and /..//Foo could be redirected to /foo.
// RedirectTrailingSlash is independent of this option.
// 是否允许修正路径
RedirectFixedPath bool
// If enabled, the router checks if another method is allowed for the
// current route, if the current request can not be routed.
// If this is the case, the request is answered with 'Method Not Allowed'
// and HTTP status code 405.
// If no other Method is allowed, the request is delegated to the NotFound
// handler.
// 如果当前无法匹配, 那么检查是否有其他方法能match当前的路由
HandleMethodNotAllowed bool
// If enabled, the router automatically replies to OPTIONS requests.
// Custom OPTIONS handlers take priority over automatic replies.
// 是否允许路由自动匹配options, 注意: 手动匹配的option优先级高于自动匹配
HandleOPTIONS bool
// Configurable http.Handler which is called when no matching route is
// found. If it is not set, http.NotFound is used.
// 当no match的时候, 执行这个handler. 如果没有配置,那么返回NoFound
NotFound http.Handler
// Configurable http.Handler which is called when a request
// cannot be routed and HandleMethodNotAllowed is true.
// If it is not set, http.Error with http.StatusMethodNotAllowed is used.
// The "Allow" header with allowed request methods is set before the handler
// is called.
// 当no natch并且HandleMethodNotAllowed=true的时候,这个函数被使用
MethodNotAllowed http.Handler
// Function to handle panics recovered from http handlers.
// It should be used to generate a error page and return the http error code
// 500 (Internal Server Error).
// The handler can be used to keep your server from crashing because of
// unrecovered panics.
// panic函数
PanicHandler func(http.ResponseWriter, *http.Request, interface{})
}
上面的结构中, trees map[string]*node代表的一个森林, 里面有一颗GET tree, POST tree…
对应到每棵tree上的结构, 其实就是前缀树结构, 从github上盗了一张图:
假设上图是一颗GET tree, 那么其实是注册了下面这些GET方法:
GET("/search/", func1)
GET("/support/", func2)
GET("/blog/:post/", func3)
GET("/about-us/", func4)
GET("/about-us/team/", func5)
GET("/contact/", func6)
注意看到, tree的组成是根据前缀来划分的, 例如search和support存在共同前缀s, 所以将s作为单独的parent节点. 但是注意这个s节点是没有handle的. 对应/about-us/和/about-us/team/, 前者是后者的parent, 但是前者也是有 handle的, 这一点还是有点区别的.
总体来说, 创建节点和查询都是按照tree的层层查找来进行处理的. 下面顺便解释一下tree node的结构:
type node struct {
// 保存这个节点上的URL路径
// 例如上图中的search和support, 共同的parent节点的path="s"
// 后面两个节点的path分别是"earch"和"upport"
path string
// 判断当前节点路径是不是参数节点, 例如上图的:post部分就是wildChild节点
wildChild bool
// 节点类型包括static, root, param, catchAll
// static: 静态节点, 例如上面分裂出来作为parent的s
// root: 如果插入的节点是第一个, 那么是root节点
// catchAll: 有*匹配的节点
// param: 除上面外的节点
nType nodeType
// 记录路径上最大参数个数
maxParams uint8
// 和children[]对应, 保存的是分裂的分支的第一个字符
// 例如search和support, 那么s节点的indices对应的"eu"
// 代表有两个分支, 分支的首字母分别是e和u
indices string
// 保存孩子节点
children []*node
// 当前节点的处理函数
handle Handle
// 优先级, 看起来没什么卵用的样子@_@
priority uint32
}
###2. 建树过程
建树过程主要涉及到两个函数: addRoute和insertChild, 下面主要看看这两个函数:
首先是addRoute函数:
// addRoute adds a node with the given handle to the path.
// Not concurrency-safe!
// 向tree中增加节点
func (n *node) addRoute(path string, handle Handle) {
fullPath := path
n.priority++
numParams := countParams(path)
// non-empty tree
// 如果之前这个Method tree中已经存在节点了
if len(n.path) > 0 || len(n.children) > 0 {
walk:
for {
// Update maxParams of the current node
// 更新当前node的最大参数个数
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.
// 找到最长公共前缀
i := 0
max := min(len(path), len(n.path))
// 匹配相同的字符
for i < max && path[i] == n.path[i] {
i++
}
// Split edge
// 说明前面有一段是匹配的, 例如之前为:/search,现在来了一个/support
// 那么会将/s拿出来作为parent节点, 将child节点变成earch和upport
if i < len(n.path) {
// 将原本路径的i后半部分作为前半部分的child节点
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)
// 更新最大参数个数
for i := range child.children {
if child.children[i].maxParams > child.maxParams {
child.maxParams = child.children[i].maxParams
}
}
// 当前节点的孩子节点变成刚刚分出来的这个后半部分节点
n.children = []*node{&child}
// []byte for proper unicode char conversion, see #65
n.indices = string([]byte{n.path[i]})
// 路径变成前i半部分path
n.path = path[:i]
n.handle = nil
n.wildChild = false
}
// Make new node a child of this node
// 同时, 将新来的这个节点插入新的parent节点中当做孩子节点
if i < len(path) {
// i的后半部分作为路径, 即上面例子support中的upport
path = path[i:]
// 如果n是参数节点(包含:或者*)
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
// 例如: /blog/:ppp 和 /blog/:ppppppp, 需要检查更长的通配符
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("path segment '" + path +
"' conflicts with existing wildcard '" + n.path +
"' in path '" + fullPath + "'")
}
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
// 检查路径是否已经存在, 例如search和support第一个字符相同
for i := 0; i < len(n.indices); i++ {
// 找到第一个匹配的字符
if c == n.indices[i] {
i = n.incrementChildPrio(i)
n = n.children[i]
continue walk
}
}
// Otherwise insert it
// new一个node
if c != ':' && c != '*' {
// []byte for proper unicode char conversion, see #65
// 记录第一个字符,并放在indices中
n.indices += string([]byte{c})
child := &node{
maxParams: numParams,
}
// 增加孩子节点
n.children = append(n.children, child)
n.incrementChildPrio(len(n.indices) - 1)
n = child
}
// 插入节点
n.insertChild(numParams, path, fullPath, handle)
return
// 说明是相同的路径,仅仅需要将handle替换就OK
// 如果是nil那么说明取消这个handle, 不是空不允许
} 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 { // Empty tree
// 如果是空树, 那么插入节点
n.insertChild(numParams, path, fullPath, handle)
// 节点的种类是root
n.nType = root
}
}
上面函数的目的是找到插入节点的位置, 需要主要如果存在common前缀, 那么需要将节点进行分裂, 然后再插入child节点. 再看一些insertChild函数:
// 插入节点函数
// @1: 参数个数
// @2: 输入路径
// @3: 完整路径
// @4: 路径关联函数
func (n *node) insertChild(numParams uint8, path, fullPath string, handle Handle) {
var offset int // already handled bytes of the path
// find prefix until first wildcard (beginning with ':'' or '*'')
// 找到前缀, 直到遇到第一个wildcard匹配的参数
for i, max := 0, len(path); numParams > 0; i++ {
c := path[i]
if c != ':' && c != '*' {
continue
}
// find wildcard end (either '/' or path end)
end := i + 1
// 下面判断:或者*之后不能再有*或者:, 这样是属于参数错误
// 除非到了下一个/XXX
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, has: '" +
path[i:] + "' in path '" + fullPath + "'")
default:
end++
}
}
// check if this Node existing children which would be
// unreachable if we insert the wildcard here
if len(n.children) > 0 {
panic("wildcard route '" + path[i:end] +
"' conflicts with existing children in path '" + fullPath + "'")
}
// check if the wildcard has a name
// 下面的判断说明只有:或者*,没有name,这也是不合法的
if end-i < 2 {
panic("wildcards must be named with a non-empty name in path '" + fullPath + "'")
}
// 如果是':',那么匹配一个参数
if c == ':' { // param
// split path at the beginning of the wildcard
// 节点path是参数前面那么一段, offset代表已经处理了多少path中的字符
if i > 0 {
n.path = path[offset:i]
offset = i
}
// 构造一个child
child := &node{
nType: param,
maxParams: numParams,
}
n.children = []*node{child}
n.wildChild = true
// 下次的循环就是这个新的child节点了
n = child
// 最长匹配, 所以下面节点的优先级++
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
// *匹配所有参数
if end != max || numParams > 1 {
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[offset:i]
// first node: catchAll node with empty path
child := &node{
wildChild: true,
nType: catchAll,
maxParams: 1,
}
n.children = []*node{child}
n.indices = string(path[i])
n = child
n.priority++
// second node: node holding the variable
child = &node{
path: path[i:],
nType: catchAll,
maxParams: 1,
handle: handle,
priority: 1,
}
n.children = []*node{child}
return
}
}
// insert remaining path part and handle to the leaf
n.path = path[offset:]
n.handle = handle
}
insertChild函数是根据path本身进行分割, 将’/’分开的部分分别作为节点保存, 形成一棵树结构. 注意参数匹配中的’:’和’*‘的区别, 前者是匹配一个字段, 后者是匹配后面所有的路径. 具体的细节, 请查看代码中的注释.
###3. 查找path过程
这个过程其实就是匹配每个child的path, walk知道path最后.
// 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 Handle, p Params, tsr bool) {
walk: // outer loop for walking the tree
for {
// 意思是如果还没有走到路径end
if len(path) > len(n.path) {
// 前面一段必须和当前节点的path一样才OK
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
// 如果不是参数节点, 那么根据分支walk到下一个节点就OK
if !n.wildChild {
c := path[0]
// 找到分支的第一个字符=>找到child
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
// 下面处理通配符参数节点
n = n.children[0]
switch n.nType {
// 如果是普通':'节点, 那么找到/或者path end, 获得参数
case param:
// find param end (either '/' or path end)
end := 0
for end < len(path) && path[end] != '/' {
end++
}
// 获取参数
// 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
// 获取key和value
p[i].Key = n.path[1:]
p[i].Value = path[:end]
// we need to go deeper!
// 如果参数还没处理完, 继续walk
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
}
// 否则获得handle返回就OK
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")
}
}
// 走到路径end
} else if path == n.path {
// We should have reached the node containing the handle.
// Check if this node has a handle registered.
// 判断这个路径节点是都存在handle, 如果存在, 那么就可以直接返回了.
if handle = n.handle; handle != nil {
return
}
// 下面判断是不是需要进入重定向
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
// 判断path+'/'是否存在handle
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
}
}