在golang中实现一个简单的web服务很简单，代码以下:golang
package main
import ( "net/http" "fmt" ) func main() { http.HandleFunc("/", hello) http.ListenAndServe(":9090", nil) } func hello(w http.ResponseWriter, r *http.Request) { fmt.Fprintf(w, "hello world") }
首先咱们是经过ListenAndServe来监听本地端口的，以后ListenAndServe将收到的新建一个Response连同收到的Request
做为参数调用ServeMux结构体的ServeHTTP(省略了中间过程).ServeHTTP将Request做为参数调用
Handler函数，Handler的返回值为一个Handler类型的接口，ServeHTTP会调用接口实现的ServeHTTP处理Response.web
若是Request.URL.Path中有不合法的内容，则调用cleanPath清理，随后将Request.Host以及清理后的
内容传入handler函数,随后返回一个RedirectHandler以及handler所返回的路径。若是Request.URL.Path合法，那么
直接调用handler，返回值与handler返回值相同。express
handler中经过判断ServeMux.hosts来决定是否实现pattern = r.Host + r.URL.Path.以后将pattern做为参数调用match,并将
match的返回值返回.json
match的判别方式比较”有趣”,它虽然没实现为树形结构(只是用了映射),可是搜索的方法就是树形，由于URL路径就是个树形.它按照树的根节点
与子节点的关系进行判断，譬如路径”/home/select/usercourse”,match在匹配的时候会首先匹配到”/”(假如咱们注册了),其次是”/home”，
以后逐层匹配下来，假如咱们没注册过”/home/select/usercourse”,可是注册了”/home/select/”,那么match就会匹配到这一层.而后返回
“/home/select/”的Handler以及url(pattern).match函数的匹配规则实如今pathMatchapp
type ServeMux struct {
mu sync.RWMutex
m map[string]muxEntry
hosts bool // whether any patterns contain hostnames
}
type muxEntry struct {
explicit bool
h Handler
pattern string
}
DefaultServeMux变量就是直接调用这个函数，那么这个函数只make了一个变量m,也就是为map分配了空间，在golang的语法中，结构体里未申明的变量也是存在的(即分配了内存)ide
这个函数是ServeMux用来匹配路劲的主要函数，因此看一下策略仍是很重要的，函数中pattern是咱们注册的路劲，path是用户请求的路径svg
func pathMatch(pattern, path string) bool {
if len(pattern) == 0 {
// should not happen
return false
}
n := len(pattern)
if pattern[n-1] != '/' {
return pattern == path
}
return len(path) >= n && path[0:n] == pattern
}
若是咱们挂在的路径不是以/结尾的，那么就直接判断两个参数是否相同，若是是以/结尾的，只要path的路径包含pattern那么久被断定是匹配，也就是说，如若我注册了/home/select/，那么/home/select/hello也会被定位到/home/select/上面，挂在的HanderFunc上面，这样作至关于为路径设置了一个index，不符合规则的URL都会被Redirct到这个index上。
* ServeMux.Handler()
注释写的很清楚，这个函数就是处理URL，而后调用*ServeMux.handler().首先调用cleanPath清理请求URL中的不合法内容。若是存在不合法内容，
则将清理过的URL交由*ServeMux.handler()处理并得到匹配到的pattern,而后修改url.Path的内容并调用RedirectHandler.
若是内容合法，则直接调用*ServeMux.handler()并返回结果函数
ServeMux.handler()
调用ServeMux.match()(封装了pathMatch函数)来得到匹配到的Handler以及对应pattern,若是ServeMux.hosts==true,那么
传入的参数为host + path,若是找不到的话，调用NotFoundHandler函数，并将其结果返回.ui
ServeMux.Handle()
Handle函数是用来注册路径与处理过程的.若是该路径已经存在了一个用户注册的Handler则会panic(意思就是说不支持覆盖).判别了合法参数之后就将
pattern做为key,新建一个muxEntry类型变量做为value加入到map中。this
if pattern[0] != ‘/’ {
mux.hosts = true
}
这是这个函数中比较有意思的一个部分，经过这里咱们能够看到若是注册路径的时候并非以’/’开头的，那么ServeMux就会开启hosts，而后会在
请求到达的时候将URL.Host和URL.Path链接在一块儿放入match中寻找,具体信息请看这里
接下来是关于路径的处理，也就是关于”/home”与”/home/”的区别.咱们先来看看做者怎么说
// Helpful behavior: // If pattern is /tree/, insert an implicit permanent redirect for /tree. // It can be overridden by an explicit registration.
若是路径的末尾是以’/’结尾而且该路径去掉末尾的’/’之后并无被注册.那么将会去掉’/’而且为其绑定一个Redirect到如今的路径.
我本身写起来都以为绕，举个例子就清楚了.
我注册了一个路径”/home/”,可是没有注册”/home”,那么若是用户访问了”/home”会发生什么呢？是的，会被Redirect到”/home/”.
须要注意的是，这里的muxEntry中的explicit没有填，也就是说是false,那么便是能够覆盖的.
在http.ListenAndServe中的第二个参数传递处理hander能够自定义,这样就能够本身实现一个路由，在处理函数中必须实现ServeHTTP函数，这个函数在handler中直接执行。例子以下：
package routes
import (
"encoding/json"
"encoding/xml"
"io/ioutil"
"net/http"
"net/url"
"path/filepath"
"regexp"
"strconv"
"strings"
)
const (
CONNECT = "CONNECT"
DELETE = "DELETE"
GET = "GET"
HEAD = "HEAD"
OPTIONS = "OPTIONS"
PATCH = "PATCH"
POST = "POST"
PUT = "PUT"
TRACE = "TRACE"
)
//commonly used mime-types
const (
applicationJson = "application/json"
applicationXml = "application/xml"
textXml = "text/xml"
)
type route struct {
method string
regex *regexp.Regexp
params map[int]string
handler http.HandlerFunc
}
type RouteMux struct {
routes []*route
filters []http.HandlerFunc
}
func New() *RouteMux {
return &RouteMux{}
}
// Get adds a new Route for GET requests.
func (m *RouteMux) Get(pattern string, handler http.HandlerFunc) {
m.AddRoute(GET, pattern, handler)
}
// Put adds a new Route for PUT requests.
func (m *RouteMux) Put(pattern string, handler http.HandlerFunc) {
m.AddRoute(PUT, pattern, handler)
}
// Del adds a new Route for DELETE requests.
func (m *RouteMux) Del(pattern string, handler http.HandlerFunc) {
m.AddRoute(DELETE, pattern, handler)
}
// Patch adds a new Route for PATCH requests.
func (m *RouteMux) Patch(pattern string, handler http.HandlerFunc) {
m.AddRoute(PATCH, pattern, handler)
}
// Post adds a new Route for POST requests.
func (m *RouteMux) Post(pattern string, handler http.HandlerFunc) {
m.AddRoute(POST, pattern, handler)
}
// Adds a new Route for Static http requests. Serves
// static files from the specified directory
func (m *RouteMux) Static(pattern string, dir string) {
//append a regex to the param to match everything
// that comes after the prefix
pattern = pattern + "(.+)"
m.AddRoute(GET, pattern, func(w http.ResponseWriter, r *http.Request) {
path := filepath.Clean(r.URL.Path)
path = filepath.Join(dir, path)
http.ServeFile(w, r, path)
})
}
// Adds a new Route to the Handler
func (m *RouteMux) AddRoute(method string, pattern string, handler http.HandlerFunc) {
//split the url into sections
parts := strings.Split(pattern, "/")
//find params that start with ":"
//replace with regular expressions
j := 0
params := make(map[int]string)
for i, part := range parts {
if strings.HasPrefix(part, ":") {
expr := "([^/]+)"
//a user may choose to override the defult expression
// similar to expressjs: ‘/user/:id([0-9]+)’
if index := strings.Index(part, "("); index != -1 {
expr = part[index:]
part = part[:index]
}
params[j] = part
parts[i] = expr
j++
}
}
//recreate the url pattern, with parameters replaced
//by regular expressions. then compile the regex
pattern = strings.Join(parts, "/")
regex, regexErr := regexp.Compile(pattern)
if regexErr != nil {
//TODO add error handling here to avoid panic
panic(regexErr)
return
}
//now create the Route
route := &route{}
route.method = method
route.regex = regex
route.handler = handler
route.params = params
//and finally append to the list of Routes
m.routes = append(m.routes, route)
}
// Filter adds the middleware filter.
func (m *RouteMux) Filter(filter http.HandlerFunc) {
m.filters = append(m.filters, filter)
}
// FilterParam adds the middleware filter iff the REST URL parameter exists.
func (m *RouteMux) FilterParam(param string, filter http.HandlerFunc) {
if !strings.HasPrefix(param,":") {
param = ":"+param
}
m.Filter(func(w http.ResponseWriter, r *http.Request) {
p := r.URL.Query().Get(param)
if len(p) > 0 { filter(w, r) }
})
}
// Required by http.Handler interface. This method is invoked by the
// http server and will handle all page routing
func (m *RouteMux) ServeHTTP(rw http.ResponseWriter, r *http.Request) {
requestPath := r.URL.Path
//wrap the response writer, in our custom interface
w := &responseWriter{writer: rw}
//find a matching Route
for _, route := range m.routes {
//if the methods don't match, skip this handler
//i.e if request.Method is 'PUT' Route.Method must be 'PUT'
if r.Method != route.method {
continue
}
//check if Route pattern matches url
if !route.regex.MatchString(requestPath) {
continue
}
//get submatches (params)
matches := route.regex.FindStringSubmatch(requestPath)
//double check that the Route matches the URL pattern.
if len(matches[0]) != len(requestPath) {
continue
}
if len(route.params) > 0 {
//add url parameters to the query param map
values := r.URL.Query()
for i, match := range matches[1:] {
values.Add(route.params[i], match)
}
//reassemble query params and add to RawQuery
r.URL.RawQuery = url.Values(values).Encode() + "&" + r.URL.RawQuery
//r.URL.RawQuery = url.Values(values).Encode()
}
//execute middleware filters
for _, filter := range m.filters {
filter(w, r)
if w.started {
return
}
}
//Invoke the request handler
route.handler(w, r)
break
}
//if no matches to url, throw a not found exception
if w.started == false {
http.NotFound(w, r)
}
}
// -----------------------------------------------------------------------------
// Simple wrapper around a ResponseWriter
// responseWriter is a wrapper for the http.ResponseWriter
// to track if response was written to. It also allows us
// to automatically set certain headers, such as Content-Type,
// Access-Control-Allow-Origin, etc.
type responseWriter struct {
writer http.ResponseWriter
started bool
status int
}
// Header returns the header map that will be sent by WriteHeader.
func (w *responseWriter) Header() http.Header {
return w.writer.Header()
}
// Write writes the data to the connection as part of an HTTP reply,
// and sets `started` to true
func (w *responseWriter) Write(p []byte) (int, error) {
w.started = true
return w.writer.Write(p)
}
// WriteHeader sends an HTTP response header with status code,
// and sets `started` to true
func (w *responseWriter) WriteHeader(code int) {
w.status = code
w.started = true
w.writer.WriteHeader(code)
}
// -----------------------------------------------------------------------------
// Below are helper functions to replace boilerplate
// code that serializes resources and writes to the
// http response.
// ServeJson replies to the request with a JSON
// representation of resource v.
func ServeJson(w http.ResponseWriter, v interface{}) {
content, err := json.MarshalIndent(v, "", " ")
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}
w.Header().Set("Content-Length", strconv.Itoa(len(content)))
w.Header().Set("Content-Type", applicationJson)
w.Write(content)
}
// ReadJson will parses the JSON-encoded data in the http
// Request object and stores the result in the value
// pointed to by v.
func ReadJson(r *http.Request, v interface{}) error {
body, err := ioutil.ReadAll(r.Body)
r.Body.Close()
if err != nil {
return err
}
return json.Unmarshal(body, v)
}
// ServeXml replies to the request with an XML
// representation of resource v.
func ServeXml(w http.ResponseWriter, v interface{}) {
content, err := xml.Marshal(v)
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}
w.Header().Set("Content-Length", strconv.Itoa(len(content)))
w.Header().Set("Content-Type", "text/xml; charset=utf-8")
w.Write(content)
}
// ReadXml will parses the XML-encoded data in the http
// Request object and stores the result in the value
// pointed to by v.
func ReadXml(r *http.Request, v interface{}) error {
body, err := ioutil.ReadAll(r.Body)
r.Body.Close()
if err != nil {
return err
}
return xml.Unmarshal(body, v)
}
// ServeFormatted replies to the request with
// a formatted representation of resource v, in the
// format requested by the client specified in the
// Accept header.
func ServeFormatted(w http.ResponseWriter, r *http.Request, v interface{}) {
accept := r.Header.Get("Accept")
switch accept {
case applicationJson:
ServeJson(w, v)
case applicationXml, textXml:
ServeXml(w, v)
default:
ServeJson(w, v)
}
return
}