Implement a few channel member endpoints for APIv4 (#5304)

* Implement GET /channels/{channel_id}/members

* Implement GET /channels/{channel_id}/members/{user_id} endpoint for APIv4

* Implement /users/{user_id}/teams/{team_id}/channels/members endpoint for APIv4

* Fix unit test

api4/channel.go

@@ -17,6 +17,10 @@ func InitChannel() {
 
 	BaseRoutes.Channels.Handle("", ApiSessionRequired(createChannel)).Methods("POST")
 	BaseRoutes.Channels.Handle("/direct", ApiSessionRequired(createDirectChannel)).Methods("POST")
+
+	BaseRoutes.ChannelMembers.Handle("", ApiSessionRequired(getChannelMembers)).Methods("GET")
+	BaseRoutes.ChannelMembersForUser.Handle("", ApiSessionRequired(getChannelMembersForUser)).Methods("GET")
+	BaseRoutes.ChannelMember.Handle("", ApiSessionRequired(getChannelMember)).Methods("GET")
 }
 
 func createChannel(c *Context, w http.ResponseWriter, r *http.Request) {
@@ -83,3 +87,65 @@ func createDirectChannel(c *Context, w http.ResponseWriter, r *http.Request) {
 		w.Write([]byte(sc.ToJson()))
 	}
 }
+
+func getChannelMembers(c *Context, w http.ResponseWriter, r *http.Request) {
+	c.RequireChannelId()
+	if c.Err != nil {
+		return
+	}
+
+	if !app.SessionHasPermissionToChannel(c.Session, c.Params.ChannelId, model.PERMISSION_READ_CHANNEL) {
+		c.SetPermissionError(model.PERMISSION_READ_CHANNEL)
+		return
+	}
+
+	if members, err := app.GetChannelMembersPage(c.Params.ChannelId, c.Params.Page, c.Params.PerPage); err != nil {
+		c.Err = err
+		return
+	} else {
+		w.Write([]byte(members.ToJson()))
+	}
+}
+
+func getChannelMember(c *Context, w http.ResponseWriter, r *http.Request) {
+	c.RequireChannelId().RequireUserId()
+	if c.Err != nil {
+		return
+	}
+
+	if !app.SessionHasPermissionToChannel(c.Session, c.Params.ChannelId, model.PERMISSION_READ_CHANNEL) {
+		c.SetPermissionError(model.PERMISSION_READ_CHANNEL)
+		return
+	}
+
+	if member, err := app.GetChannelMember(c.Params.ChannelId, c.Params.UserId); err != nil {
+		c.Err = err
+		return
+	} else {
+		w.Write([]byte(member.ToJson()))
+	}
+}
+
+func getChannelMembersForUser(c *Context, w http.ResponseWriter, r *http.Request) {
+	c.RequireUserId().RequireTeamId()
+	if c.Err != nil {
+		return
+	}
+
+	if !app.SessionHasPermissionToTeam(c.Session, c.Params.TeamId, model.PERMISSION_VIEW_TEAM) {
+		c.SetPermissionError(model.PERMISSION_VIEW_TEAM)
+		return
+	}
+
+	if c.Session.UserId != c.Params.UserId && !app.SessionHasPermissionToTeam(c.Session, c.Params.TeamId, model.PERMISSION_MANAGE_SYSTEM) {
+		c.SetPermissionError(model.PERMISSION_MANAGE_SYSTEM)
+		return
+	}
+
+	if members, err := app.GetChannelMembersForUser(c.Params.TeamId, c.Params.UserId); err != nil {
+		c.Err = err
+		return
+	} else {
+		w.Write([]byte(members.ToJson()))
+	}
+}