Golang篇-Gin学习笔记

Gin简介

Gin是用Go（Golang）编写的HTTP Web框架。它具有类似于Martini的API，但性能比Martini快40倍。

快速开始

环境要求

go

安装使用

1. 下载安装

$ go get -u github.com/gin-gonic/gin

2. 简单案例

package main

import (
  "net/http"
  "github.com/gin-gonic/gin"
)

func main() {
  r := gin.Default()
  r.GET("/ping", func(c *gin.Context) {
    c.JSON(http.StatusOK, gin.H{
      "message": "pong",
    })
  })
  r.Run() // listen and serve on 0.0.0.0:8080 (for windows "localhost:8080")
}

3. 启动服务器

go run main.go

4. 访问

   curl localhost:8080/ping

中 间 件

gin相关中间件其实相当于在我们处理器处理我们的业务请求之前会预先调用我们的中间件进行处理（链式调用），如通过配置跨域，鉴权的功能都可以实现

使用案例

func main() {
	router := gin.Default()
    //安装注册的先后顺序
	router.Use(func(context *gin.Context) {
		fmt.Println("鉴权中间件")
	})
	router.Use(func(context *gin.Context) {
		fmt.Println("黑白名单中间件")
	})
}

其Gin在进行链式调用的代码如下

func (c *Context) Next() {
	c.index++
	for c.index < int8(len(c.handlers)) {
		c.handlers[c.index](c)//调用处理器
		c.index++
	}
}

通过这种添加中间件的方式，我们可以在业务代码之前做一些增强来满足我们的业务需求

源码分析

路由实现

1. 创建根路由

Router := gin.Default()

func Default() *Engine {
	debugPrintWARNINGDefault()
	engine := New()
	engine.Use(Logger(), Recovery())
	return engine
}

2. 创建函数

func New() *Engine {
	debugPrintWARNINGNew()
	engine := &Engine{
		RouterGroup: RouterGroup{//根路由
			Handlers: nil,
			basePath: "/",
			root:     true,
		},
		FuncMap:                template.FuncMap{},
		RedirectTrailingSlash:  true,
		RedirectFixedPath:      false,
		HandleMethodNotAllowed: false,
		ForwardedByClientIP:    true,
		RemoteIPHeaders:        []string{"X-Forwarded-For", "X-Real-IP"},
		TrustedPlatform:        defaultPlatform,
		UseRawPath:             false,
		RemoveExtraSlash:       false,
		UnescapePathValues:     true,
		MaxMultipartMemory:     defaultMultipartMemory,
		trees:                  make(methodTrees, 0, 9),//这个其实就是我们的路由tree
		delims:                 render.Delims{Left: "{{", Right: "}}"},
		secureJSONPrefix:       "while(1);",
		trustedProxies:         []string{"0.0.0.0/0", "::/0"},
		trustedCIDRs:           defaultTrustedCIDRs,
	}
	engine.RouterGroup.engine = engine
	engine.pool.New = func() any {
		return engine.allocateContext()
	}
	return engine
}

3. 路由节点设计

gin的路由是通过切片存储node组成一个tree的方式来进行设计的，在每个node中有对应的路由处理器HandlersChain

type node struct {
	path      string //路由路径
	indices   string//
	wildChild bool
	nType     nodeType//root根路由(非子节点)/statis/...
	priority  uint32
    //子路由
	children  []*node // child nodes, at most 1 :param style node at the end of the array
	handlers  HandlersChain //该路由对应的处理器
	fullPath  string//全路径
}

4.添加路由

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)

	// Update maxParams
	if paramsCount := countParams(path); paramsCount > engine.maxParams {
		engine.maxParams = paramsCount
	}

	if sectionsCount := countSections(path); sectionsCount > engine.maxSections {
		engine.maxSections = sectionsCount
	}
}

5.处理请求入口

func (engine *Engine) ServeHTTP(w http.ResponseWriter, req *http.Request) {
	c := engine.pool.Get().(*Context)
	c.writermem.reset(w)
	c.Request = req
	c.reset()
	//主线：获取路由处理器进行调用
	engine.handleHTTPRequest(c)
	//把context放入并发安全的临时对象池中
	engine.pool.Put(c)
}

func (engine *Engine) handleHTTPRequest(c *Context) {
	httpMethod := c.Request.Method//请求方法
	rPath := c.Request.URL.Path//路径
	unescape := false
	if engine.UseRawPath && len(c.Request.URL.RawPath) > 0 {
		rPath = c.Request.URL.RawPath
		unescape = engine.UnescapePathValues
	}

	if engine.RemoveExtraSlash {
		rPath = cleanPath(rPath)
	}

	// Find root of the tree for the given HTTP method
	t := engine.trees//获取全局tree通过遍历的方式查找对应的路由处理器
	for i, tl := 0, len(t); i < tl; i++ {
		if t[i].method != httpMethod {//方法不匹配直接结束当前循环
			continue
		}
		root := t[i].root
        // 主线找到路由Tree中匹配的节点
		// Find route in tree
		value := root.getValue(rPath, c.params, c.skippedNodes, unescape)
		if value.params != nil {
			c.Params = *value.params
		}
		if value.handlers != nil {//如果对应的节点的处理器不为空则进行赋值给Context
			c.handlers = value.handlers
			c.fullPath = value.fullPath
			c.Next()//调用处理器链
			c.writermem.WriteHeaderNow()
			return
		}
		if httpMethod != http.MethodConnect && rPath != "/" {
			if value.tsr && engine.RedirectTrailingSlash {
				redirectTrailingSlash(c)
				return
			}
			if engine.RedirectFixedPath && redirectFixedPath(c, root, engine.RedirectFixedPath) {
				return
			}
		}
		break
	}

	if engine.HandleMethodNotAllowed {
		for _, tree := range engine.trees {
			if tree.method == httpMethod {
				continue
			}
			if value := tree.root.getValue(rPath, nil, c.skippedNodes, unescape); value.handlers != nil {
				c.handlers = engine.allNoMethod
				serveError(c, http.StatusMethodNotAllowed, default405Body)
				return
			}
		}
	}
	c.handlers = engine.allNoRoute
	serveError(c, http.StatusNotFound, default404Body)
}

查找路由树节点的方法

github.com/gin-gonic/gin@v1.8.2/tree.go

// 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, params *Params, skippedNodes *[]skippedNode, unescape bool) (value nodeValue) {
	var globalParamsCount int16
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):]

				// Try all the non-wildcard children first by matching the indices
				idxc := path[0]
				for i, c := range []byte(n.indices) {
					if c == idxc {
						//  strings.HasPrefix(n.children[len(n.children)-1].path, ":") == n.wildChild
						if n.wildChild {
							index := len(*skippedNodes)
							*skippedNodes = (*skippedNodes)[:index+1]
							(*skippedNodes)[index] = skippedNode{
								path: prefix + path,
								node: &node{
									path:      n.path,
									wildChild: n.wildChild,
									nType:     n.nType,
									priority:  n.priority,
									children:  n.children,
									handlers:  n.handlers,
									fullPath:  n.fullPath,
								},
								paramsCount: globalParamsCount,
							}
						}

						n = n.children[i]
						continue walk
					}
				}

				if !n.wildChild {
					// If the path at the end of the loop is not equal to '/' and the current node has no child nodes
					// the current node needs to roll back to last vaild skippedNode
					if path != "/" {
						for l := len(*skippedNodes); l > 0; {
							skippedNode := (*skippedNodes)[l-1]
							*skippedNodes = (*skippedNodes)[:l-1]
							if strings.HasSuffix(skippedNode.path, path) {
								path = skippedNode.path
								n = skippedNode.node
								if value.params != nil {
									*value.params = (*value.params)[:skippedNode.paramsCount]
								}
								globalParamsCount = skippedNode.paramsCount
								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, which is always at the end of the array
				n = n.children[len(n.children)-1]
				globalParamsCount++

				switch n.nType {
				case param:
					// fix truncate the parameter
					// tree_test.go  line: 204

					// Find param end (either '/' or path end)
					end := 0
					for end < len(path) && path[end] != '/' {
						end++
					}

					// Save param value
					if params != nil && cap(*params) > 0 {
						if value.params == nil {
							value.params = params
						}
						// Expand slice within preallocated capacity
						i := len(*value.params)
						*value.params = (*value.params)[:i+1]
						val := path[:end]
						if unescape {
							if v, err := url.QueryUnescape(val); err == nil {
								val = v
							}
						}
						(*value.params)[i] = Param{
							Key:   n.path[1:],
							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) || (n.path == "" && n.indices == "/")
					}
					return

				case catchAll:
					// Save param value
					if params != nil {
						if value.params == nil {
							value.params = params
						}
						// Expand slice within preallocated capacity
						i := len(*value.params)
						*value.params = (*value.params)[:i+1]
						val := path
						if unescape {
							if v, err := url.QueryUnescape(path); err == nil {
								val = v
							}
						}
						(*value.params)[i] = Param{
							Key:   n.path[2:],
							Value: val,
						}
					}

					value.handlers = n.handlers
					value.fullPath = n.fullPath
					return

				default:
					panic("invalid node type")
				}
			}
		}

		if path == prefix {
			// If the current path does not equal '/' and the node does not have a registered handle and the most recently matched node has a child node
			// the current node needs to roll back to last vaild skippedNode
			if n.handlers == nil && path != "/" {
				for l := len(*skippedNodes); l > 0; {
					skippedNode := (*skippedNodes)[l-1]
					*skippedNodes = (*skippedNodes)[:l-1]
					if strings.HasSuffix(skippedNode.path, path) {
						path = skippedNode.path
						n = skippedNode.node
						if value.params != nil {
							*value.params = (*value.params)[:skippedNode.paramsCount]
						}
						globalParamsCount = skippedNode.paramsCount
						continue walk
					}
				}
				//	n = latestNode.children[len(latestNode.children)-1]
			}
			// 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 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 {
				value.tsr = true
				return
			}

			if path == "/" && n.nType == static {
				value.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]
					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(prefix) == len(path)+1 && prefix[len(path)] == '/' &&
				path == prefix[:len(prefix)-1] && n.handlers != nil)

		// roll back to last valid skippedNode
		if !value.tsr && path != "/" {
			for l := len(*skippedNodes); l > 0; {
				skippedNode := (*skippedNodes)[l-1]
				*skippedNodes = (*skippedNodes)[:l-1]
				if strings.HasSuffix(skippedNode.path, path) {
					path = skippedNode.path
					n = skippedNode.node
					if value.params != nil {
						*value.params = (*value.params)[:skippedNode.paramsCount]
					}
					globalParamsCount = skippedNode.paramsCount
					continue walk
				}
			}
		}

		return
	}
}

6.分析总结

Gin的路由设计总体还是非常简洁的，这也是他高效的原因，我们通过创建engine的时候会初始化缺省的根路由，其总体的路由是以tree的结构进行存储，在查找时优先通过请求方法和路径获取我们对应的tree节点，得到节点来进行调用节点的处理器

相关资料

官网文档 ：https://github.com/gin-gonic/gin
参考博文 ：https://geektutu.com/post/quick-go-gin.html