简介
Gin 源码解读, 基于 v1.5.0 版本.
HttpRouter 实现
添加路由主要是由 addRoute 完成:
func (engine *Engine) addRoute(method, path string, handlers HandlersChain) {
assert1(path[0] == '/', "path must begin with '/'")
assert1(method != "", "HTTP method can not be empty")
assert1(len(handlers) > 0, "there must be at least one handler")
debugPrintRoute(method, path, handlers)
root := engine.trees.get(method)
if root == nil {
root = new(node)
root.fullPath = "/"
engine.trees = append(engine.trees, methodTree{method: method, root: root})
}
root.addRoute(path, handlers)
}
Gin 的路由是通过 httprouter 实现的, 来深入了解下它的源代码.
数据结构
github 的文档解释了实现原理, 具体可以参考 How does it work?.
HttpRouter 内部使用了 Radix 树, 是前缀树的紧凑版变种.
上图来自维基百科, 显示了 Radix 树的结构. 相比普通前缀树, Radix 树的边上能存储多个字符, 极大的压缩了树的深度.
看一下数据结构的定义:
// 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
type methodTree struct {
method string
root *node
}
type methodTrees []methodTree
Engine.trees 的类型就是 methodTrees, 初始化语句是 trees: make(methodTrees, 0, 9),.
func (trees methodTrees) get(method string) *node {
for _, tree := range trees {
if tree.method == method {
return tree.root
}
}
return nil
}
前面添加路由的代码中第一步是找到 root, 即 root := engine.trees.get(method), 结合 get 代码,
我们可以发现 methodTrees 实际上根据 HTTP 方法分类的, 每种方法都对应一颗树.
如果当前该类型的 HTTP 方法不存在, 就新建一棵树 methodTree:
root = new(node)
root.fullPath = "/"
engine.trees = append(engine.trees, methodTree{method: method, root: root})
再看一下树的节点是如何定义的:
type nodeType uint8
const (
static nodeType = iota // default
root
param
catchAll
)
type node struct {
path string
indices string
children []*node
handlers HandlersChain
priority uint32
nType nodeType
maxParams uint8
wildChild bool
fullPath string
}
添加路由
数据结构已经了解了, 看一下路由到底是如何添加的, 即 root.addRoute(path, handlers).
// 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++
numParams := countParams(path)
parentFullPathIndex := 0
// 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 common prefix contains no ':' or '*'
// since the existing key can't contain those chars.
i := 0
max := min(len(path), len(n.path))
for 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,
handlers: n.handlers,
priority: n.priority - 1,
fullPath: n.fullPath,
}
// 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.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++
// 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
}
}
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 := 0; i < len(n.indices); 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 += string([]byte{c})
child := &node{
maxParams: numParams,
fullPath: fullPath,
}
n.children = append(n.children, child)
n.incrementChildPrio(len(n.indices) - 1)
n = child
}
n.insertChild(numParams, path, fullPath, handlers)
return
} else if i == len(path) { // Make node a (in-path) leaf
if n.handlers != nil {
panic("handlers are already registered for path '" + fullPath + "'")
}
n.handlers = handlers
}
return
}
} else { // Empty tree
n.insertChild(numParams, path, fullPath, handlers)
n.nType = root
}
}
addRoute
代码有点长, 先根据 if 语句分为两种情况, 一种是初始化的时候(即树是空的), 另一种是树是非空的.
n.insertChild(numParams, path, fullPath, handlers)
n.nType = root
树是空的情况下, 即 n.path 是空字符串(初始值) 且 n.children 是空切片.
这个时候, 只是通过 insertChild 插入节点, 然后将节点的类型设置为 root.
insertChild 的代码也有点长, 等下再来看.
当树是非空的, 进入到了一个 for 循环中, 先跟着注释看一下 for 大体上是做什么的.
// 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 := 0
max := min(len(path), len(n.path))
for i < max && path[i] == n.path[i] {
i++
}
// Split edge
// Make new node a child of this node
前面两个步骤, 更新 maxParams 和计算最长前缀的长度, 非常简单, 直接看代码就行.
看一下节点是如何分裂的, 即第三步:
// 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,
}
// 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.handlers = nil
n.wildChild = false
n.fullPath = fullPath[:parentFullPathIndex+i]
}
当公共前缀的长度小于 n.path 时, 当前节点就会分裂出一个子节点.
比如, 当前节点 node.path = "/ping", 遇到 path = "/pong" 时就会分裂,
公共前缀的长度 i=2, 因此节点会分裂为 node.path = "/p" 和 node.path = "ing".
分裂出来的后一个节点会占据当前节点的大部分属性.
接着看第四步, 如何为当前节点添加一个子节点, 是 root.addRoute(path, handlers) 的核心代码.
这也是一个 if 判断, 让我们先看一下后半部分, 即可能出错时的情况:
else if i == len(path) { // Make node a (in-path) leaf
if n.handlers != nil {
panic("handlers are already registered for path '" + fullPath + "'")
}
n.handlers = handlers
}
如果 handlers 不为空, 就会发生错误, 这说明 handlers 只被允许注册一次.
看一下 if 的前半部分, 即 if i < len(path) 时的情况:
// 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++
// 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
}
}
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 := 0; i < len(n.indices); 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 += string([]byte{c})
child := &node{
maxParams: numParams,
fullPath: fullPath,
}
n.children = append(n.children, child)
n.incrementChildPrio(len(n.indices) - 1)
n = child
}
n.insertChild(numParams, path, fullPath, handlers)
return
}
这一部分也是有点长, 也需要一步步拆解来看.
首先根据 path = path[i:], 发现 path 已经去除了公共前缀部分了.
先看一下第一个判断, if n.wildChild, 即存在通配符子节点:
if n.wildChild {
parentFullPathIndex += len(n.path)
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
}
}
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 +
"'")
}
通配符的判断中, 一般都是触发通配符冲突错误的, 除非前面通配符部分一样, 后面有 /.
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
}
当节点是 : 通配符且 path 开头为 / 后, 进入到新一轮的循环中.
// Check if a child with the next path byte exists
for i := 0; i < len(n.indices); i++ {
if c == n.indices[i] {
parentFullPathIndex += len(n.path)
i = n.incrementChildPrio(i)
n = n.children[i]
continue walk
}
}
检查是否存在一个孩子节点, 如果有的话就直接跳到那个节点, 然后进入新一轮的循环中.
前面节点分裂的时候, 设置了 n.indices = string([]byte{n.path[i]}).
// Otherwise insert it
if c != ':' && c != '*' {
// []byte for proper unicode char conversion, see #65
n.indices += string([]byte{c})
child := &node{
maxParams: numParams,
fullPath: fullPath,
}
n.children = append(n.children, child)
n.incrementChildPrio(len(n.indices) - 1)
n = child
}
经过了前面的判断之后, 走到这里, 如果 c 不是 : 或 *, 就会插入一个节点, 并替换当前节点为这个节点.
n.insertChild(numParams, path, fullPath, handlers)
return
最后依旧是调用 insertChild. 然后终于可以使用 return 跳出循环, 结束整个方法了.
insertChild
上面在两个地方调用了 n.insertChild(numParams, path, fullPath, handlers), 看一下它的实现.
func (n *node) insertChild(numParams uint8, path string, fullPath string, handlers HandlersChain) {
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
}
// 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, 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
if end-i < 2 {
panic("wildcards must be named with a non-empty name in path '" + fullPath + "'")
}
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,
fullPath: fullPath,
}
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,
fullPath: fullPath,
}
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 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,
fullPath: fullPath,
}
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,
handlers: handlers,
priority: 1,
fullPath: fullPath,
}
n.children = []*node{child}
return
}
}
// insert remaining path part and handle to the leaf
n.path = path[offset:]
n.handlers = handlers
n.fullPath = fullPath
}
折叠一下代码, 主要是两部分, 一个 for 循环, 以及一些更新属性的语句.
// insert remaining path part and handle to the leaf
n.path = path[offset:]
n.handlers = handlers
n.fullPath = fullPath
主要看一下 for 循环:
// find prefix until first wildcard (beginning with ':' or '*')
for i, max := 0, len(path); numParams > 0; i++ {
c := path[i]
if c != ':' && c != '*' {
continue
}
这几行判断, 如同注释说明的那般, 直到遇到通配符字符 ':' or '*' 才开始真正处理.
注意判断条件是 numParams, 这个参数指明了有几个通配符参数.
// 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, has: '" +
path[i:] + "' in path '" + fullPath + "'")
default:
end++
}
}
这也是个判断, 用于验证通配符名字中不能出现多个 ':' and '*'.
// 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
if end-i < 2 {
panic("wildcards must be named with a non-empty name in path '" + fullPath + "'")
}
又是两个判断, 第一个用于验证当前 node 不能存储子节点, 否则通配符节点就冲突了. 第二个用于验证通配符节点的名字必须有长度, 至少要有一个字符.
最后是根据通配符的不同分别构造, 先看一下 c == ':' 时的代码:
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,
fullPath: fullPath,
}
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,
fullPath: fullPath,
}
n.children = []*node{child}
n = child
}
}
然后是 c == '*' 时的代码, 也就是 else 部分:
else { // catchAll
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,
fullPath: fullPath,
}
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,
handlers: handlers,
priority: 1,
fullPath: fullPath,
}
n.children = []*node{child}
return
}
catchAll 通配符有点特殊, 这个通配符后面是不允许出现其他通配符参数的, 所以前几行都在判断要求是否符合.
这个过程中会创建两个类型为 catchAll 的节点, 第一个节点指示存储通配符子节点, 即wildChild=true,
第二个节点会占有具体的内容.
添加路由的过程基本上就是这样, 接下来看一下如何读取数据.
获取数据
从树中获取数据, 主要发生在 func (engine *Engine) handleHTTPRequest(c *Context) 中.
看一下代码片段:
root := t[i].root
// Find route in tree
value := root.getValue(rPath, c.Params, unescape)
if value.handlers != nil {
c.handlers = value.handlers
c.Params = value.params
c.fullPath = value.fullPath
c.Next()
c.writermem.WriteHeaderNow()
return
}
主要是通过 getValue 方法获取数据的, 完整代码如下:
// getValue 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, po Params, unescape bool) (value nodeValue) {
value.params = po
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 := 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.
value.tsr = path == "/" && n.handlers != 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 cap(value.params) < int(n.maxParams) {
value.params = make(Params, 0, n.maxParams)
}
i := len(value.params)
value.params = value.params[:i+1] // expand slice within preallocated capacity
value.params[i].Key = n.path[1:]
val := path[:end]
if unescape {
var err error
if value.params[i].Value, err = url.QueryUnescape(val); err != nil {
value.params[i].Value = val // fallback, in case of error
}
} else {
value.params[i].Value = val
}
// 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
value.tsr = len(path) == end+1
return
}
if value.handlers = n.handlers; value.handlers != nil {
value.fullPath = n.fullPath
return
}
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]
value.tsr = n.path == "/" && n.handlers != nil
}
return
case catchAll:
// save param value
if cap(value.params) < int(n.maxParams) {
value.params = make(Params, 0, n.maxParams)
}
i := len(value.params)
value.params = value.params[:i+1] // expand slice within preallocated capacity
value.params[i].Key = n.path[2:]
if unescape {
var err error
if value.params[i].Value, err = url.QueryUnescape(path); err != nil {
value.params[i].Value = path // fallback, in case of error
}
} else {
value.params[i].Value = path
}
value.handlers = n.handlers
value.fullPath = n.fullPath
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 value.handlers = n.handlers; value.handlers != nil {
value.fullPath = n.fullPath
return
}
if path == "/" && n.wildChild && n.nType != root {
value.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]
value.tsr = (len(n.path) == 1 && n.handlers != nil) ||
(n.nType == catchAll && n.children[0].handlers != 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
value.tsr = (path == "/") ||
(len(n.path) == len(path)+1 && n.path[len(path)] == '/' &&
path == n.path[:len(n.path)-1] && n.handlers != nil)
return
}
}
代码有点长, 先读一下注释. 主要是根据路径和参数, 获取注册在上面的 handlers.
// nodeValue holds return values of (*Node).getValue method
type nodeValue struct {
handlers HandlersChain
params Params
tsr bool
fullPath string
}
// Param is a single URL parameter, consisting of a key and a value.
type Param struct {
Key string
Value string
}
里面用到的结构体如上. 方法的主体部分是一个 for 循环.
for 循环里面, 前半部分是一个判断, 先看一下后半部分.
// Nothing found. We can recommend to redirect to the same URL with an
// extra trailing slash if a leaf exists for that path
value.tsr = (path == "/") ||
(len(n.path) == len(path)+1 && n.path[len(path)] == '/' &&
path == n.path[:len(n.path)-1] && n.handlers != nil)
return
如果没有找到对应的匹配, 会设置一个叫做 tsr 的标识, 用于判断是否符合 TSR (trailing slash redirect), 即尾部斜杆重定向. 比如 /path 可以重定向到 /path/.
回到 if 判断上来, 先看第一个判断部分, 即 if len(path) > len(n.path).
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.
value.tsr = path == "/" && n.handlers != 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 cap(value.params) < int(n.maxParams) {
value.params = make(Params, 0, n.maxParams)
}
i := len(value.params)
value.params = value.params[:i+1] // expand slice within preallocated capacity
value.params[i].Key = n.path[1:]
val := path[:end]
if unescape {
var err error
if value.params[i].Value, err = url.QueryUnescape(val); err != nil {
value.params[i].Value = val // fallback, in case of error
}
} else {
value.params[i].Value = val
}
// 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
value.tsr = len(path) == end+1
return
}
if value.handlers = n.handlers; value.handlers != nil {
value.fullPath = n.fullPath
return
}
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]
value.tsr = n.path == "/" && n.handlers != nil
}
return
case catchAll:
// save param value
if cap(value.params) < int(n.maxParams) {
value.params = make(Params, 0, n.maxParams)
}
i := len(value.params)
value.params = value.params[:i+1] // expand slice within preallocated capacity
value.params[i].Key = n.path[2:]
if unescape {
var err error
if value.params[i].Value, err = url.QueryUnescape(path); err != nil {
value.params[i].Value = path // fallback, in case of error
}
} else {
value.params[i].Value = path
}
value.handlers = n.handlers
value.fullPath = n.fullPath
return
default:
panic("invalid node type")
}
}
}
这部分的判断里嵌套了一个 if 判断, 用于判断路径的前缀和当前节点的 path 相符, 如果不相等就直接跳过.
然后是根据 n.wildChild 判断, 即基于是否有通配符子节点.
如果没有通配符子节点, 会继续查找下一个子节点, 然后进行新一轮的 for 循环.
如果找不到子节点, 就直接返回了. 是否存在子节点是根据 n.indices 判断的,
n.indices 是个字符串, 保存了所有子节点路径的第一个字符.
比如, 当前注册了两个路径, /ping 和 /pong, 那么当前的节点就是 /p 公共前缀,
然后它的 n.indices="io".
如果存在通配符子节点, 就会根据 n.nType 的类型进行选择处理.
如果类型是 param, 即使用 : 命名的变量, 就会先保存那个变量的值.
如果长度还有剩余 if end < len(path) {, 就会进入到新一个 for 循环中;
否认就认为是结束了, 将 handlers 和 fullPath 复制一下就行了.
如果类型是 catchAll, 即使用 * 命令的任意匹配变量, 处理就比较简单了,
因为不用考虑后面还有路径的问题, * 会匹配所有剩余的 path 路径.
直接保存变量值, 然后将 handlers 和 fullPath 复制一下就行了.
如果类型不符合上述的两种类型, 就会触发 panic.
接着看另一个判断, 即 else if path == n.path.
else if path == n.path {
// We should have reached the node containing the handle.
// Check if this node has a handle registered.
if value.handlers = n.handlers; value.handlers != nil {
value.fullPath = n.fullPath
return
}
if path == "/" && n.wildChild && n.nType != root {
value.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]
value.tsr = (len(n.path) == 1 && n.handlers != nil) ||
(n.nType == catchAll && n.children[0].handlers != nil)
return
}
}
return
}
这部分的处理也是比较简单的, 和前面的逻辑类似, 主要是看路径上是否有 handler 注册.
如果没有 handler 注册, 就会检查 value.tsr 的值, 是否属于尾部斜杆重定向.
由此, 从树中获取数据的过程也已经看完了.
总结
优秀的代码还是要多读读的, 即有助于理解原理, 又能开阔自己的视野. 另外一点, 读代码的时候调试器真的是非常有用, 尤其是观察数据结构是怎么存储的.
