Implement GET `/users/username/{username}` endpoint for APIv4 (#5310)

* added get user by username endpoint

* added get user by username unit test and driver

* changed username length to 22 characters max

* changed Params to UserName to Username

* reorganized get user by username and get user by email formatting in model/client4

6 files changed, 117 insertions, 2 deletions

diff --git a/api4/api.go b/api4/api.go
index a9f92c573..6c2faa96b 100644
--- a/api4/api.go
+++ b/api4/api.go
@@ -90,7 +90,7 @@ func InitApi(full bool) {
 
 	BaseRoutes.Users = BaseRoutes.ApiRoot.PathPrefix("/users").Subrouter()
 	BaseRoutes.User = BaseRoutes.Users.PathPrefix("/{user_id:[A-Za-z0-9]+}").Subrouter()
-	BaseRoutes.UserByUsername = BaseRoutes.Users.PathPrefix("/username/{username:[A-Za-z0-9_-.]+}").Subrouter()
+	BaseRoutes.UserByUsername = BaseRoutes.Users.PathPrefix("/username/{username:[A-Za-z0-9\\_\\-\\.]+}").Subrouter()
 	BaseRoutes.UserByEmail = BaseRoutes.Users.PathPrefix("/email/{email}").Subrouter()
 
 	BaseRoutes.Teams = BaseRoutes.ApiRoot.PathPrefix("/teams").Subrouter()
diff --git a/api4/apitestlib.go b/api4/apitestlib.go
index 2eaed4fd0..25bfe6f75 100644
--- a/api4/apitestlib.go
+++ b/api4/apitestlib.go
@@ -247,7 +247,7 @@ func GenerateTestEmail() string {
 }
 
 func GenerateTestUsername() string {
-	return "fakeuser" + model.NewId()
+	return "fakeuser" + model.NewRandomString(13)
 }
 
 func GenerateTestTeamName() string {
diff --git a/api4/context.go b/api4/context.go
index 7ad6f30b4..6a22b4103 100644
--- a/api4/context.go
+++ b/api4/context.go
@@ -359,6 +359,22 @@ func (c *Context) RequireChannelId() *Context {
 	return c
 }
 
+func (c *Context) RequireUsername() *Context {
+	if c.Err != nil {
+		return c
+	}
+
+	if len(c.Params.Username) < 3 {
+		c.SetInvalidUrlParam("username")
+	} 
+
+	if len(c.Params.Username) > 22 {
+		c.SetInvalidUrlParam("username")
+	}
+
+	return c
+}
+
 func (c *Context) RequireEmail() *Context {
 	if c.Err != nil {
 		return c
@@ -371,3 +387,4 @@ func (c *Context) RequireEmail() *Context {
 
 	return c
 }
+
diff --git a/api4/params.go b/api4/params.go
index a043919fa..4de1da401 100644
--- a/api4/params.go
+++ b/api4/params.go
@@ -26,6 +26,7 @@ type ApiParams struct {
 	HookId    string
 	EmojiId   string
 	Email     string
+	Username  string
 	Page      int
 	PerPage   int
 }
@@ -71,6 +72,10 @@ func ApiParamsFromRequest(r *http.Request) *ApiParams {
 		params.Email = val
 	}
 
+	if val, ok := props["username"]; ok {
+		params.Username = val
+	}
+
 	if val, err := strconv.Atoi(r.URL.Query().Get("page")); err != nil {
 		params.Page = PAGE_DEFAULT
 	} else {
diff --git a/api4/user.go b/api4/user.go
index 348ccf46c..d8d071cd2 100644
--- a/api4/user.go
+++ b/api4/user.go
@@ -30,6 +30,7 @@ func InitUser() {
 	BaseRoutes.Users.Handle("/login", ApiHandler(login)).Methods("POST")
 	BaseRoutes.Users.Handle("/logout", ApiHandler(logout)).Methods("POST")
 
+	BaseRoutes.UserByUsername.Handle("", ApiSessionRequired(getUserByUsername)).Methods("GET")
 	BaseRoutes.UserByEmail.Handle("", ApiSessionRequired(getUserByEmail)).Methods("GET")
 
 }
@@ -93,6 +94,34 @@ func getUser(c *Context, w http.ResponseWriter, r *http.Request) {
 	}
 }
 
+func getUserByUsername(c *Context, w http.ResponseWriter, r *http.Request) {
+	c.RequireUsername()
+	if c.Err != nil {
+		return
+	}
+
+	// No permission check required
+
+	var user *model.User
+	var err *model.AppError
+
+	if user, err = app.GetUserByUsername(c.Params.Username); 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 getUserByEmail(c *Context, w http.ResponseWriter, r *http.Request) {
 	c.RequireEmail()
 	if c.Err != nil {
diff --git a/api4/user_test.go b/api4/user_test.go
index 37f251c6d..82c7f921d 100644
--- a/api4/user_test.go
+++ b/api4/user_test.go
@@ -133,6 +133,70 @@ func TestGetUser(t *testing.T) {
 	}
 }
 
+func TestGetUserByUsername(t *testing.T) {
+	th := Setup().InitBasic().InitSystemAdmin()
+	defer TearDown()
+	Client := th.Client
+
+	user := th.BasicUser
+
+	ruser, resp := Client.GetUserByUsername(user.Username, "")
+	CheckNoError(t, resp)
+	CheckUserSanitization(t, ruser)
+
+	if ruser.Email != user.Email {
+		t.Fatal("emails did not match")
+	}
+
+	ruser, resp = Client.GetUserByUsername(user.Username, resp.Etag)
+	CheckEtag(t, ruser, resp)
+
+	_, resp = Client.GetUserByUsername(GenerateTestUsername(), "")
+	CheckNotFoundStatus(t, resp)
+
+	_, resp = Client.GetUserByUsername(model.NewRandomString(25), "")
+	CheckBadRequestStatus(t, resp)
+
+	// Check against privacy config settings
+	emailPrivacy := utils.Cfg.PrivacySettings.ShowEmailAddress
+	namePrivacy := utils.Cfg.PrivacySettings.ShowFullName
+	defer func() {
+		utils.Cfg.PrivacySettings.ShowEmailAddress = emailPrivacy
+		utils.Cfg.PrivacySettings.ShowFullName = namePrivacy
+	}()
+	utils.Cfg.PrivacySettings.ShowEmailAddress = false
+	utils.Cfg.PrivacySettings.ShowFullName = false
+
+	ruser, resp = Client.GetUserByUsername(user.Username, "")
+	CheckNoError(t, resp)
+
+	if ruser.Email != "" {
+		t.Fatal("email should be blank")
+	}
+	if ruser.FirstName != "" {
+		t.Fatal("first name should be blank")
+	}
+	if ruser.LastName != "" {
+		t.Fatal("last name should be blank")
+	}
+
+	Client.Logout()
+	_, resp = Client.GetUserByUsername(user.Username, "")
+	CheckUnauthorizedStatus(t, resp)
+
+	// System admins should ignore privacy settings
+	ruser, resp = th.SystemAdminClient.GetUserByUsername(user.Username, resp.Etag)
+	if ruser.Email == "" {
+		t.Fatal("email should not be blank")
+	}
+	if ruser.FirstName == "" {
+		t.Fatal("first name should not be blank")
+	}
+	if ruser.LastName == "" {
+		t.Fatal("last name should not be blank")
+	}
+}
+
 func TestGetUserByEmail(t *testing.T) {
 	th := Setup().InitBasic().InitSystemAdmin()
 	defer TearDown()