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REST（Representational State Transfer，表现层状态转化）是近几年使用较广泛的分布式结点间同步通信的实现方式。REST原则描述网络中client-server的一种交互形式，即用URL定位资源，用HTTP方法描述操作的交互形式。如果CS之间交互的网络接口满足REST风格，则称为RESTful API。以下是 理解RESTful架构 总结的REST原则：
为什么要设计RESTful的API，个人理解原因在于：用HTTP的操作统一数据操作接口，限制URL为资源，即每次请求对应某种资源的某种操作，这种 无状态的设计可以实现client-server的解耦分离，保证系统两端都有横向扩展能力。
go-restful
go-restful is a package for building REST-style Web Services using Google Go。go-restful定义了Container WebService和Route三个重要数据结构。
最简单的使用实例，向WebService注册路由，将WebService添加到Container中，由Container负责分发。
func main() {
ws := new(restful.WebService)
ws.Path("/users")
ws.Route(ws.GET("/").To(u.findAllUsers).
Doc("get all users").
Metadata(restfulspec.KeyOpenAPITags, tags).
Writes([]User{}).
Returns(200, "OK", []User{}))
container := restful.NewContainer().Add(ws)
http.ListenAndServe(":8080", container)
}
container
container是根据标准库http的路由器ServeMux写的，并且它通过ServeMux的路由表实现了Handler接口，可参考以前的这篇 HTTP协议与Go的实现 。
type Container struct {
webServicesLock sync.RWMutex
webServices []*WebService
ServeMux *http.ServeMux
isRegisteredOnRoot bool
containerFilters []FilterFunction
doNotRecover bool // default is true
recoverHandleFunc RecoverHandleFunction
serviceErrorHandleFunc ServiceErrorHandleFunction
router RouteSelector // default is a CurlyRouter
contentEncodingEnabled bool // default is false
}
func (c *Container)ServeHTTP(httpwriter http.ResponseWriter, httpRequest *http.Request) {
c.ServeMux.ServeHTTP(httpwriter, httpRequest)
}
往Container内添加WebService，内部维护的webServices不能有重复的RootPath，
func (c *Container)Add(service *WebService)*Container {
c.webServicesLock.Lock()
defer c.webServicesLock.Unlock()
if !c.isRegisteredOnRoot {
c.isRegisteredOnRoot = c.addHandler(service, c.ServeMux)
}
c.webServices = append(c.webServices, service)
return c
}
添加到container并注册到mux的是dispatch这个函数，它负责根据不同WebService的rootPath进行分发。
func (c *Container)addHandler(service *WebService, serveMux *http.ServeMux)bool {
pattern := fixedPrefixPath(service.RootPath())
serveMux.HandleFunc(pattern, c.dispatch)
}
webservice
每组webservice表示一个共享rootPath的服务，其中rootPath通过 ws.Path() 设置。
type WebService struct {
rootPath string
pathExpr *pathExpression
routes []Route
produces []string
consumes []string
pathParameters []*Parameter
filters []FilterFunction
documentation string
apiVersion string
typeNameHandleFunc TypeNameHandleFunction
dynamicRoutes bool
routesLock sync.RWMutex
}
通过Route注册的路由最终构成Route结构体，添加到WebService的routes中。
func (w *WebService)Route(builder *RouteBuilder)*WebService {
w.routesLock.Lock()
defer w.routesLock.Unlock()
builder.copyDefaults(w.produces, w.consumes)
w.routes = append(w.routes, builder.Build())
return w
}
route
通过RouteBuilder构造Route信息，Path结合了rootPath和subPath。Function是路由Handler，即处理函数，它通过 ws.Get(subPath).To(function) 的方式加入。Filters实现了个类似gRPC拦截器的东西，也类似go-chassis的chain。
type Route struct {
Method string
Produces []string
Consumes []string
Path string // webservice root path + described path
Function RouteFunction
Filters []FilterFunction
If []RouteSelectionConditionFunction
// cached values for dispatching
relativePath string
pathParts []string
pathExpr *pathExpression
// documentation
Doc string
Notes string
Operation string
ParameterDocs []*Parameter
ResponseErrors map[int]ResponseError
ReadSample, WriteSample interface{}
Metadata map[string]interface{}
Deprecated bool
}
dispatch
server侧的主要功能就是路由选择和分发。http包实现了一个 ServeMux ，go-restful在这个基础上封装了多个服务，如何在从container开始将路由分发给webservice，再由webservice分发给具体处理函数。这些都在 dispatch 中实现。
func (c *Container)dispatch(httpWriter http.ResponseWriter, httpRequest *http.Request) {
func() {
c.webServicesLock.RLock()
defer c.webServicesLock.RUnlock()
webService, route, err = c.router.SelectRoute(
c.webServices,
httpRequest)
}()
pathProcessor, routerProcessesPath := c.router.(PathProcessor)
pathParams := pathProcessor.ExtractParameters(route, webService, httpRequest.URL.Path)
wrappedRequest, wrappedResponse := route.wrapRequestResponse(writer,
httpRequest, pathParams)
if len(c.containerFilters)+len(webService.filters)+len(route.Filters) > 0 {
chain := FilterChain{Filters: allFilters, Target: func(req *Request, resp *Response) {
// handle request by route after passing all filters
route.Function(wrappedRequest, wrappedResponse)
}}
chain.ProcessFilter(wrappedRequest, wrappedResponse)
} else {
route.Function(wrappedRequest, wrappedResponse)
}
}
go-chassis
go-chassis实现的rest-server是在go-restful上的一层封装。Register时只要将注册的schema解析成routes，并注册到webService中，Start启动server时 container.Add(r.ws) ，同时将container作为handler交给 http.Server , 最后开始ListenAndServe即可。
type restfulServer struct {
microServiceName string
container *restful.Container
ws *restful.WebService
opts server.Options
mux sync.RWMutex
exit chan chan error
server *http.Server
}
根据Method不同，向WebService注册不同方法的handle，从schema读取的routes信息包含Method，Func以及PathPattern。
func (r *restfulServer)Register(schemainterface{}, options ...server.RegisterOption)(string, error) {
schemaType := reflect.TypeOf(schema)
schemaValue := reflect.ValueOf(schema)
var schemaName string
tokens := strings.Split(schemaType.String(), ".")
if len(tokens) >= 1 {
schemaName = tokens[len(tokens)-1]
}
routes, err := GetRoutes(schema)
for _, route := range routes {
lager.Logger.Infof("Add route path: [%s] Method: [%s] Func: [%s]. ",
route.Path, route.Method, route.ResourceFuncName)
method, exist := schemaType.MethodByName(route.ResourceFuncName)
...
handle := func(req *restful.Request, rep *restful.Response) {
c, err := handler.GetChain(common.Provider, r.opts.ChainName)
inv := invocation.Invocation{
MicroServiceName: config.SelfServiceName,
SourceMicroService: req.HeaderParameter(common.HeaderSourceName),
Args: req,
Protocol: common.ProtocolRest,
SchemaID: schemaName,
OperationID: method.Name,
}
bs := NewBaseServer(context.TODO())
bs.req = req
bs.resp = rep
c.Next(&inv, func(ir *invocation.InvocationResponse)error {
if ir.Err != nil {
return ir.Err
}
method.Func.Call([]reflect.Value{schemaValue, reflect.ValueOf(bs)})
if bs.resp.StatusCode() >= http.StatusBadRequest {
return ...
}
return nil
})
}
switch route.Method {
case http.MethodGet:
r.ws.Route(r.ws.GET(route.Path).To(handle).
Doc(route.ResourceFuncName).
Operation(route.ResourceFuncName))
...
}
}
return reflect.TypeOf(schema).String(), nil
}
实在是比较简单，就不写了。今天好困。
遗留问题
