I'm designing a router API and I'd like to be able to lookup a path by its function. Something like:
createUser := func(w http.ResponseWriter, r *http.Request) {
// create a user
}
createPost := func(w http.ResponseWriter, r *http.Request) {
// create a post
}
router.Post("/users", createUser)
router.Post("/posts", createPost)
fmt.Println(router.Lookup(createPost))
Here's a playground link: https://play.golang.org/p/ec6U0jJUbfx
This is surprisingly hard to do because you can't test for equality on a function or stick it as a key in a map. Is this even possible?
Are there any other workarounds I'm not thinking of? A reflect solution would be just fine.
You can create a server struct with a ServerHTTP method that handles all the request. When there is a request you can look up for an specific method by the path and function
Here is an example:
type Server struct {
routes []route
}
func (s *Server) handlerServer(db mydb.IDB, ctx context.Context) http.HandlerFunc {
return func(w http.ResponseWriter, r *http.Request) {
ctx := ServerContext{w, r, db, ctx}
for i := 0; i < len(s.routes); i++ {
currentRoute := s.routes[i]
if isValidMethod(currentRoute, r) {
err := currentRoute.h(&ctx)
if err != nil {
log.Fatal(err)
}
}
}
}
}
I hope this is helpful
Related
I am trying to customize request pipeline through middleware pattern, the code as follow:
func helloHandler(w http.ResponseWriter, r *http.Request) {
fmt.Println("Hello, middleware!")
}
func middleware1(next http.HandlerFunc) func(w http.ResponseWriter, r *http.Request) {
return func(w http.ResponseWriter, r *http.Request) {
fmt.Println("[START] middleware1")
ctx := r.Context()
ctx = context.WithValue(ctx, middleware1Key, middleware1Value)
r = r.WithContext(ctx)
next(w, r)
fmt.Println("[END] middleware1")
ctx = r.Context()
if val, ok := ctx.Value(middleware2Key).(string); ok {
fmt.Printf("Value from middleware2 %s \n", val)
}
}
}
func middleware2(next http.HandlerFunc) func(w http.ResponseWriter, r *http.Request) {
return func(w http.ResponseWriter, r *http.Request) {
fmt.Println("[START] middleware2")
ctx := r.Context()
if val, ok := ctx.Value(middleware1Key).(string); ok {
fmt.Printf("Value from middleware1 %s \n", val)
}
ctx = context.WithValue(ctx, middleware2Key, middleware2Value)
r = r.WithContext(ctx)
next(w, r)
fmt.Println("[END] middleware2")
}
}
func main() {
mux := http.NewServeMux()
middlewares := newMws(middleware1, middleware2)
mux.HandleFunc("/hello", middlewares.then(helloHandler))
if err := http.ListenAndServe(":8080", mux); err != nil {
panic(err)
}
}
and the output is :
[START] middleware1
[START] middleware2
Value from middleware1 middleware1Value
Hello, middleware!
[END] middleware2
[END] middleware1
According to the output, the value could pass from parent to the child , while, if the child add something to the context, it is invisible to the parent
How can I propagate value from child middleware to parent?
What you're doing is creating a new pointer to the modified http.Request via WithContext method. So if you're passing it to next middleware in the chain everything works as expected since you're passing this new pointer as an argument.
If you want to modify the request and make it visible for those who hold the pointer to it, you need to dereference the pointer and set the modified value.
So in your 'child' middleware instead of:
r = r.WithContext(ctx)
Just do the following:
*r = *r.WithContext(ctx)
Good exercise to understand pointers in Go but you SHOULD NOT do similar operations in your production code. The docs are clear about it. See https://pkg.go.dev/net/http#Handler.
Another possible solution (without messing with the request itself) is to pass a map inside a context and read/write from/to map instead. So in your first middleware:
ctx := r.Context()
m := make(map[string]string)
m[middleware1Key] = middleware1Value
ctx = context.WithValue(ctx, dummyStoreKey, m)
r = r.WithContext(ctx)
...
if val, ok := m[middleware2Key]; ok {
fmt.Printf("Value from middleware2 %s \n", val)
}
And in the second one:
ctx := r.Context()
if store, ok := ctx.Value(dummyStoreKey).(map[string]string); ok {
if val, ok := store[middleware1Key]; ok {
fmt.Printf("Value from middleware1 %s \n", val)
}
store[middleware2Key] = middleware2Value
}
You could add a AddStoreMiddleware as the first one in the pipeline and then use it in each successor if needed. Remember, maps in Go are not concurrently safe so in some subtle cases you should serialize access.
Let say I have a function that handles request body in general
func GetReqBody(r *http.Request) (interface {}, error){
var data interface{}
decorder := json.NewDecoder(r.Body)
decorder.DisallowUnknownFields()
err := decorder.Decode(&data)
return data, err
}
Then in the controller, I will have to do type assertion
func post(w http.ResponseWriter, r *http.Request) {
data, err := utils.GetReqBody(r)
//req.User is a struct
newUser, ok := data.(req.User)
// ...
}
Is it possible to encapsulate the type assertion login inside the GetReqBody function? To do that I will need to pass the struct into the function, yet as it is not a value I am unable to do so.
"Is it possible to encapsulate the type assertion login inside the GetReqBody function?" -- No, it's not possible, not in any useful way.
However you could simplify your code thus:
func GetReqBody(r *http.Request, data interface{}) error {
decorder := json.NewDecoder(r.Body)
decorder.DisallowUnknownFields()
return decorder.Decode(data)
}
func post(w http.ResponseWriter, r *http.Request) {
var newUser req.User
if err := utils.GetReqBody(r, &newUser); err != nil {
// handle err
}
// ...
}
I have a function need to be tested, which looks like this:
func parmHandler(w http.ResponseWriter, r *http.Request) {
...
data, err = backenddb_call(r *http.Request)
...
return
}
function backenddb_call(r *http.Request) (data []Data, err error){
parm := r.URL.Query().Get(parm)
//Get Data from DB for parm
...
return
}
In this HTTP handler case, I cannot modify the parmHandler arguments and add a helper interface argument to help with mocking. How can I mock backenddb_call to return different responses?
You could have a function which returns your handler, which you pass the backenddb_call as an argument to:
https://play.golang.org/p/aSMxeEgJL8U
func GetHandler(fn func (r *http.Request) ([]Data, error)) http.Handler {
return http.HandlerFunc(func (w http.ResponseWriter, r *http.Request) {
data, err := fn(r)
fmt.Println(data, err)
})
}
Then, when you create it:
http.HandleFunc("/test", GetHandler(backenddb_call))
and to test it you can just pass in a different call:
GetHandler(func (r *http.Request) ([]Data, error) {
fmt.Println("Mock")
return []Data{"This", "Is", "A", "Fake", "Response"}, nil
})
I would like to ask if we can create 'middleware' functions for Go http client? Example I want to add a log function, so every sent request will be logged, or add setAuthToken so the token will be added to each request's header.
You can use the Transport parameter in HTTP client to that effect, with a composition pattern, using the fact that:
http.Client.Transport defines the function that will handle all HTTP requests;
http.Client.Transport has interface type http.RoundTripper, and can thus be replaced with your own implementation;
For example:
package main
import (
"fmt"
"net/http"
)
// This type implements the http.RoundTripper interface
type LoggingRoundTripper struct {
Proxied http.RoundTripper
}
func (lrt LoggingRoundTripper) RoundTrip(req *http.Request) (res *http.Response, e error) {
// Do "before sending requests" actions here.
fmt.Printf("Sending request to %v\n", req.URL)
// Send the request, get the response (or the error)
res, e = lrt.Proxied.RoundTrip(req)
// Handle the result.
if (e != nil) {
fmt.Printf("Error: %v", e)
} else {
fmt.Printf("Received %v response\n", res.Status)
}
return
}
func main() {
httpClient := &http.Client{
Transport: LoggingRoundTripper{http.DefaultTransport},
}
httpClient.Get("https://example.com/")
}
Feel free to alter names as you wish, I did not think on them for very long.
I worked on a project that had similar requirement so I built a middleware pipeline library that allows setting multiple middleware to the http client. You can check it out here.
Using the library, you would solve this in the following way
type LoggingMiddleware struct{}
func (s LoggingMiddleware) Intercept(pipeline pipeline.Pipeline, req *http.Request) (*http.Response, error) {
body, _ := httputil.DumpRequest(req, true)
log.Println(fmt.Sprintf("%s", string(body)))
/*
If you want to perform an action based on the response, do the following
resp, err = pipeline.Next
// perform some action
return resp, err
*/
return pipeline.Next(req)
}
transport := pipeline.NewCustomTransport(&LoggingMiddleware{})
client := &http.Client{Transport: transport}
resp, err := client.Get("https://example.com")
if err != nil {
// handle err
}
fmt.Println(resp.Status)
I wrote a small tutorial/library to do just that https://github.com/HereMobilityDevelopers/mediary
Here is some basic usage example:
client := mediary.Init().AddInterceptors(dumpInterceptor).Build()
client.Get("https://golang.org")
func dumpInterceptor(req *http.Request, handler mediary.Handler) (*http.Response, error) {
if bytes, err := httputil.DumpRequestOut(req, true); err == nil {
fmt.Printf("%s", bytes)
//GET / HTTP/1.1
//Host: golang.org
//User-Agent: Go-http-client/1.1
//Accept-Encoding: gzip
}
return handler(req)
}
There is also an explanation here https://github.com/HereMobilityDevelopers/mediary/wiki/Reasoning
Good idea! Here is a simple implementation of HTTP service middleware in Go.
Usually a simple http service framework is to register a bunch of routes, and then call different logics to process them according to the routes.
But in fact, there may be some unified processing involving almost all routes, such as logs, permissions, and so on.
So it is a good idea to engage in intermediate preprocessing at this time.
Define a middleware unit:
package main
import (
"net/http"
)
// AdaptorHandle middleware func type
type AdaptorHandle func(w http.ResponseWriter, r *http.Request) (next bool, err error)
// MiddleWareAdaptor router middlewares mapped by url
type MiddleWareAdaptor struct {
URLs map[string][]AdaptorHandle
}
// MakeMiddleWareAdaptor make a middleware adaptor
func MakeMiddleWareAdaptor() *MiddleWareAdaptor {
mwa := &MiddleWareAdaptor{
URLs: make(map[string][]AdaptorHandle),
}
return mwa
}
// Regist regist a adaptor
func (mw *MiddleWareAdaptor) Regist(url string, Adaptor ...AdaptorHandle) {
for _, adp := range Adaptor {
mw.URLs[url] = append(mw.URLs[url], adp)
// mw.URLs[url] = adp
}
}
// Exec exec middleware adaptor funcs...
func (mw *MiddleWareAdaptor) Exec(url string, w http.ResponseWriter, r *http.Request) (bool, error) {
if adps, ok := mw.URLs[url]; ok {
for _, adp := range adps {
if next, err := adp(w, r); !next || (err != nil) {
return next, err
}
}
}
return true, nil
}
Then wrap the route processing function with a middleware entry:
func middlewareHandler(next http.Handler) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
// before call handler
start := time.Now()
do, _ := mwa.Exec(r.URL.Path, w, r) // exec middleware
// call next handler
if do {
log.Println("middleware done. next...")
next.ServeHTTP(w, r)
} else {
log.Println("middleware done.break...")
}
// after call handle
log.Printf("Comleted %s in %v", r.URL.Path, time.Since(start))
})
}
mux.Handle("/", middlewareHandler(&uPlusRouterHandler{}))
type uPlusRouterHandler struct {
}
func (rh *uPlusRouterHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
...
}
Finally, register the middleware you need:
mwa = MakeMiddleWareAdaptor() // init middleware
mwa.Regist("/", testMWAfunc, testMWAfunc2) // regist middleware
...
func testMWAfunc(w http.ResponseWriter, r *http.Request) (bool, error) {
log.Println("I am Alice Middleware...")
log.Printf("Started %s %s", r.Method, r.URL.Path)
return true, nil
}
func testMWAfunc2(w http.ResponseWriter, r *http.Request) (bool, error) {
log.Println("I am Ben Middleware...")
return false, nil // return false,break follow-up actions.
}
This can be achieved using closure functions. It's probably more clear with an example:
package main
import (
"fmt"
"net/http"
)
func main() {
http.HandleFunc("/hello", logged(hello))
http.ListenAndServe(":3000", nil)
}
func logged(f func(http.ResponseWriter, *http.Request)) func(http.ResponseWriter, *http.Request) {
return func(w http.ResponseWriter, r *http.Request) {
fmt.Println("logging something")
f(w, r)
fmt.Println("finished handling request")
}
}
func hello(w http.ResponseWriter, r *http.Request) {
fmt.Fprintln(w, "<h1>Hello!</h1>")
}
credit goes to: http://www.calhoun.io/5-useful-ways-to-use-closures-in-go/
I can't seem to work out how to use middleware and Http Router properly together.
My code is:
type appContext struct {
db *mgo.Database
}
func main(){
c := appContext{session.DB("db-name")}
commonHandlers := alice.New(context.ClearHandler, basicAuthHandler)
router := NewRouter()
router.Post("/", commonHandlers.ThenFunc(c.final))
http.ListenAndServe(":5000", router)
}
The final middleware is:
func (c *appContext) final(w http.ResponseWriter, r *http.Request) {
log.Println("Executing finalHandler")
w.Write([]byte("TESTING"))
}
but I want my basicAuthHandler to be part of the commonHandlers. It also needs the context so that I can query the db.
I have tried this:
func (c *appContext) basicAuthHandler(w http.ResponseWriter, r *http.Request) {
var app App
err := c.db.C("apps").Find(bson.M{"id":"abcde"}).One(&app)
if err != nil {
panic(err)
}
//do something with the app
}
but I get the error undefined: basicAuthHandler. I understand why I'm getting the error but I don't know how to avoid it. How can I provide the context to the basicAuthHandler and still use it in the commonHandlers list for Alice?
Your middleware needs to have the signature
func(http.Handler) http.Handler
This way your middleware is wrapping handlers, not just providing a final handler. You need to accept an http.Handler, do whatever processing needs to be done, and call ServeHTTP on the next handler in the chain. Your basicAuthHandler example could look like this:
func (c *appContext) basicAuthHandler(h http.Handler) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
var app App
err := c.db.C("apps").Find(bson.M{"id": "abcde"}).One(&app)
if err != nil {
panic(err)
}
h.ServeHTTP(w, r)
})
}
(though you don't want to panic in your app, and should provide a better error response)