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tsweb: JSONHandler using reflect (#437)
Updates #395 #437 Signed-off-by: Zijie Lu <zijie@tailscale.com>
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halulu
GitHub
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125
tsweb/jsonhandler.go
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125
tsweb/jsonhandler.go
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@ -0,0 +1,125 @@
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// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package tsweb
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import (
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"encoding/json"
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"net/http"
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"reflect"
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)
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type response struct {
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Status string `json:"status"`
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Error string `json:"error,omitempty"`
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Data interface{} `json:"data,omitempty"`
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}
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func responseSuccess(data interface{}) *response {
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return &response{
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Status: "success",
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Data: data,
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}
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}
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func responseError(e string) *response {
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return &response{
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Status: "error",
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Error: e,
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}
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}
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func writeResponse(w http.ResponseWriter, s int, resp *response) {
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b, _ := json.Marshal(resp)
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w.WriteHeader(s)
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w.Header().Set("Content-Type", "application/json")
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w.Write(b)
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}
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func checkFn(t reflect.Type) {
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h := reflect.TypeOf(http.HandlerFunc(nil))
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switch t.NumIn() {
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case 2, 3:
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if !t.In(0).AssignableTo(h.In(0)) {
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panic("first argument must be http.ResponseWriter")
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}
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if !t.In(1).AssignableTo(h.In(1)) {
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panic("second argument must be *http.Request")
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}
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default:
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panic("JSONHandler: number of input parameter should be 2 or 3")
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}
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switch t.NumOut() {
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case 1:
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if !t.Out(0).Implements(reflect.TypeOf((*error)(nil)).Elem()) {
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panic("return value must be error")
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}
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case 2:
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if !t.Out(1).Implements(reflect.TypeOf((*error)(nil)).Elem()) {
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panic("second return value must be error")
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}
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default:
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panic("JSONHandler: number of return values should be 1 or 2")
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}
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}
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// JSONHandler wraps an HTTP handler function with a version that automatically
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// unmarshals and marshals requests and responses respectively into fn's arguments
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// and results.
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//
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// The fn parameter is a function. It must take two or three input arguments.
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// The first two arguments must be http.ResponseWriter and *http.Request.
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// The optional third argument can be of any type representing the JSON input.
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// The function's results can be either (error) or (T, error), where T is the
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// JSON-marshalled result type.
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//
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// For example:
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// fn := func(w http.ResponseWriter, r *http.Request, in *Req) (*Res, error) { ... }
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func JSONHandler(fn interface{}) http.Handler {
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v := reflect.ValueOf(fn)
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t := v.Type()
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checkFn(t)
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return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
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wv := reflect.ValueOf(w)
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rv := reflect.ValueOf(r)
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var vs []reflect.Value
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switch t.NumIn() {
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case 2:
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vs = v.Call([]reflect.Value{wv, rv})
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case 3:
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dv := reflect.New(t.In(2))
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err := json.NewDecoder(r.Body).Decode(dv.Interface())
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if err != nil {
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writeResponse(w, http.StatusBadRequest, responseError("bad json"))
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return
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}
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vs = v.Call([]reflect.Value{wv, rv, dv.Elem()})
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default:
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panic("JSONHandler: number of input parameter should be 2 or 3")
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}
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switch len(vs) {
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case 1:
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// todo support other error types
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if vs[0].IsNil() {
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writeResponse(w, http.StatusOK, responseSuccess(nil))
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} else {
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err := vs[0].Interface().(error)
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writeResponse(w, http.StatusBadRequest, responseError(err.Error()))
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}
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case 2:
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if vs[1].IsNil() {
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writeResponse(w, http.StatusOK, responseSuccess(vs[0].Interface()))
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} else {
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err := vs[1].Interface().(error)
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writeResponse(w, http.StatusBadRequest, responseError(err.Error()))
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}
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default:
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panic("JSONHandler: number of return values should be 1 or 2")
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}
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})
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}
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175
tsweb/jsonhandler_test.go
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175
tsweb/jsonhandler_test.go
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@ -0,0 +1,175 @@
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// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package tsweb
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import (
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"encoding/json"
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"errors"
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"net/http"
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"net/http/httptest"
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"strings"
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"testing"
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)
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type Data struct {
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Name string
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Price int
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}
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type Response struct {
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Status string
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Error string
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Data *Data
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}
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func TestNewJSONHandler(t *testing.T) {
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checkStatus := func(w *httptest.ResponseRecorder, status string) *Response {
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d := &Response{
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Data: &Data{},
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}
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t.Logf("%s", w.Body.Bytes())
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err := json.Unmarshal(w.Body.Bytes(), d)
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if err != nil {
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t.Logf(err.Error())
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return nil
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}
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if d.Status == status {
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t.Logf("ok: %s", d.Status)
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} else {
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t.Fatalf("wrong status: %s %s", d.Status, status)
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}
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return d
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}
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// 2 1
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h21 := JSONHandler(func(w http.ResponseWriter, r *http.Request) error {
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return nil
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})
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t.Run("2 1 simple", func(t *testing.T) {
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w := httptest.NewRecorder()
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r := httptest.NewRequest("GET", "/", nil)
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h21.ServeHTTP(w, r)
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checkStatus(w, "success")
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})
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// 2 2
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h22 := JSONHandler(func(w http.ResponseWriter, r *http.Request) (*Data, error) {
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return &Data{Name: "tailscale"}, nil
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})
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t.Run("2 2 get data", func(t *testing.T) {
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w := httptest.NewRecorder()
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r := httptest.NewRequest("GET", "/", nil)
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h22.ServeHTTP(w, r)
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checkStatus(w, "success")
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})
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// 3 1
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h31 := JSONHandler(func(w http.ResponseWriter, r *http.Request, d *Data) error {
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if d.Name == "" {
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return errors.New("name is empty")
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}
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return nil
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})
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t.Run("3 1 post data", func(t *testing.T) {
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w := httptest.NewRecorder()
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r := httptest.NewRequest("POST", "/", strings.NewReader(`{"Name": "tailscale"}`))
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h31.ServeHTTP(w, r)
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checkStatus(w, "success")
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})
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t.Run("3 1 bad json", func(t *testing.T) {
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w := httptest.NewRecorder()
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r := httptest.NewRequest("POST", "/", strings.NewReader(`{`))
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h31.ServeHTTP(w, r)
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checkStatus(w, "error")
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})
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t.Run("3 1 post data error", func(t *testing.T) {
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w := httptest.NewRecorder()
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r := httptest.NewRequest("POST", "/", strings.NewReader(`{}`))
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h31.ServeHTTP(w, r)
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resp := checkStatus(w, "error")
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if resp.Error != "name is empty" {
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t.Fatalf("wrong error")
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}
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})
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// 3 2
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h32 := JSONHandler(func(w http.ResponseWriter, r *http.Request, d *Data) (*Data, error) {
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if d.Price == 0 {
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return nil, errors.New("price is empty")
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}
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return &Data{Price: d.Price * 2}, nil
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})
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t.Run("3 2 post data", func(t *testing.T) {
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w := httptest.NewRecorder()
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r := httptest.NewRequest("POST", "/", strings.NewReader(`{"Price": 10}`))
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h32.ServeHTTP(w, r)
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resp := checkStatus(w, "success")
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t.Log(resp.Data)
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if resp.Data.Price != 20 {
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t.Fatalf("wrong price: %d %d", resp.Data.Price, 10)
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}
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})
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t.Run("3 2 post data error", func(t *testing.T) {
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w := httptest.NewRecorder()
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r := httptest.NewRequest("POST", "/", strings.NewReader(`{}`))
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h32.ServeHTTP(w, r)
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resp := checkStatus(w, "error")
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if resp.Error != "price is empty" {
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t.Fatalf("wrong error")
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}
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})
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// fn check
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shouldPanic := func() {
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r := recover()
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if r == nil {
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t.Fatalf("should panic")
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}
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t.Log(r)
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}
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t.Run("2 0 panic", func(t *testing.T) {
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defer shouldPanic()
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JSONHandler(func(w http.ResponseWriter, r *http.Request) {})
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})
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t.Run("2 1 panic return value", func(t *testing.T) {
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defer shouldPanic()
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JSONHandler(func(w http.ResponseWriter, r *http.Request) string {
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return ""
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})
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})
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t.Run("2 1 panic arguments", func(t *testing.T) {
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defer shouldPanic()
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JSONHandler(func(r *http.Request, w http.ResponseWriter) error {
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return nil
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})
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})
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t.Run("3 1 panic arguments", func(t *testing.T) {
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defer shouldPanic()
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JSONHandler(func(name string, r *http.Request, w http.ResponseWriter) error {
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return nil
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})
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})
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t.Run("3 2 panic return value", func(t *testing.T) {
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defer shouldPanic()
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//lint:ignore ST1008 intentional
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JSONHandler(func(name string, r *http.Request, w http.ResponseWriter) (error, string) {
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return nil, "panic"
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})
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})
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}
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