examples: add http examples (#822)

* add http examples

examples/http/upload/main.go

@@ -0,0 +1,50 @@
+package main
+
+import (
+	"fmt"
+	"io"
+	"log"
+	"net/http"
+	"os"
+
+	"github.com/go-kratos/kratos/v2"
+	transhttp "github.com/go-kratos/kratos/v2/transport/http"
+	"github.com/gorilla/mux"
+)
+
+func uploadFile(w http.ResponseWriter, r *http.Request) {
+	fileName := r.FormValue("name")
+	file, handler, err := r.FormFile("file")
+	if err != nil {
+		w.WriteHeader(http.StatusInternalServerError)
+		return
+	}
+	defer file.Close()
+
+	f, err := os.OpenFile(handler.Filename, os.O_WRONLY|os.O_CREATE, 0666)
+	if err != nil {
+		w.WriteHeader(http.StatusInternalServerError)
+		return
+	}
+	defer f.Close()
+	_, _ = io.Copy(f, file)
+	fmt.Fprint(w, "File "+fileName+" Uploaded successfully")
+}
+
+func main() {
+	router := mux.NewRouter()
+	router.HandleFunc("/upload", uploadFile).Methods("POST")
+
+	httpSrv := transhttp.NewServer(transhttp.Address(":8000"))
+	httpSrv.HandlePrefix("/", router)
+
+	app := kratos.New(
+		kratos.Name("upload"),
+		kratos.Server(
+			httpSrv,
+		),
+	)
+	if err := app.Run(); err != nil {
+		log.Println(err)
+	}
+}