Implement GET /users/email/{email} endpoint for APIv4 (#5309)

* added get user by email endpoint for APIv4

* added get user by email endpoint unit test and driver

* removed the appended return of user ids on logout

* Added RequireEmail to validate user email. Also updated the get user by email endpoint and unit test

api4/user.go

@@ -27,6 +27,8 @@ func InitUser() {
 	BaseRoutes.Users.Handle("/login", ApiHandler(login)).Methods("POST")
 	BaseRoutes.Users.Handle("/logout", ApiHandler(logout)).Methods("POST")
 
+	BaseRoutes.UserByEmail.Handle("", ApiSessionRequired(getUserByEmail)).Methods("GET")
+
 }
 
 func createUser(c *Context, w http.ResponseWriter, r *http.Request) {
@@ -88,6 +90,34 @@ func getUser(c *Context, w http.ResponseWriter, r *http.Request) {
 	}
 }
 
+func getUserByEmail(c *Context, w http.ResponseWriter, r *http.Request) {
+	c.RequireEmail()
+	if c.Err != nil {
+		return
+	}
+
+	// No permission check required
+
+	var user *model.User
+	var err *model.AppError
+
+	if user, err = app.GetUserByEmail(c.Params.Email); err != nil {
+		c.Err = err
+		return
+	}
+
+	etag := user.Etag(utils.Cfg.PrivacySettings.ShowFullName, utils.Cfg.PrivacySettings.ShowEmailAddress)
+
+	if HandleEtag(etag, "Get User", w, r) {
+		return
+	} else {
+		app.SanitizeProfile(user, c.IsSystemAdmin())
+		w.Header().Set(model.HEADER_ETAG_SERVER, etag)
+		w.Write([]byte(user.ToJson()))
+		return
+	}
+}
+
 func getUsers(c *Context, w http.ResponseWriter, r *http.Request) {
 	inTeamId := r.URL.Query().Get("in_team")
 	inChannelId := r.URL.Query().Get("in_channel")
@@ -292,9 +322,7 @@ func logout(c *Context, w http.ResponseWriter, r *http.Request) {
 	data["user_id"] = c.Session.UserId
 
 	Logout(c, w, r)
-	if c.Err == nil {
-		w.Write([]byte(model.MapToJson(data)))
-	}
+
 }
 
 func Logout(c *Context, w http.ResponseWriter, r *http.Request) {