MM-64531: [Shared Channels] Users on different remote servers should not communicate unless the remotes have established secure connection. (#30985)

api/v4/source/sharedchannels.yaml

@@ -226,3 +226,88 @@
           $ref: "#/components/responses/Unauthorized"
         "403":
           $ref: "#/components/responses/Forbidden"
+
+  "/api/v4/sharedchannels/{channel_id}/remotes":
+    get:
+      tags:
+        - shared channels
+      summary: Get remote clusters for a shared channel
+      description: |
+        Gets the remote clusters information for a shared channel.
+        
+        __Minimum server version__: 10.11
+        
+        ##### Permissions
+        Must be authenticated and have the `read_channel` permission for the channel.
+      operationId: GetSharedChannelRemotes
+      parameters:
+        - name: channel_id
+          in: path
+          description: Channel GUID
+          required: true
+          schema:
+            type: string
+      responses:
+        "200":
+          description: Remote clusters retrieval successful
+          content:
+            application/json:
+              schema:
+                type: array
+                items:
+                  $ref: "#/components/schemas/RemoteClusterInfo"
+        "400":
+          $ref: "#/components/responses/BadRequest"
+        "401":
+          $ref: "#/components/responses/Unauthorized"
+        "403":
+          $ref: "#/components/responses/Forbidden"
+        "404":
+          $ref: "#/components/responses/NotFound"
+
+  "/api/v4/sharedchannels/users/{user_id}/can_dm/{other_user_id}":
+    get:
+      tags:
+        - shared channels
+      summary: Check if user can DM another user in shared channels context
+      description: |
+        Checks if a user can send direct messages to another user, considering shared channel restrictions.
+        This is specifically for shared channels where DMs require direct connections between clusters.
+        
+        __Minimum server version__: 10.11
+        
+        ##### Permissions
+        Must be authenticated and have permission to view the user.
+      operationId: CanUserDirectMessage
+      parameters:
+        - name: user_id
+          in: path
+          description: User GUID
+          required: true
+          schema:
+            type: string
+        - name: other_user_id
+          in: path
+          description: Other user GUID
+          required: true
+          schema:
+            type: string
+      responses:
+        "200":
+          description: DM permission check successful
+          content:
+            application/json:
+              schema:
+                type: object
+                properties:
+                  can_dm:
+                    type: boolean
+                    description: Whether the user can send DMs to the other user
+        "400":
+          $ref: "#/components/responses/BadRequest"
+        "401":
+          $ref: "#/components/responses/Unauthorized"
+        "403":
+          $ref: "#/components/responses/Forbidden"
+        "404":
+          $ref: "#/components/responses/NotFound"

server/channels/api4/shared_channel.go

@@ -15,6 +15,7 @@ func (api *API) InitSharedChannels() {
 	api.BaseRoutes.SharedChannels.Handle("/{team_id:[A-Za-z0-9]+}", api.APISessionRequired(getSharedChannels)).Methods(http.MethodGet)
 	api.BaseRoutes.SharedChannels.Handle("/remote_info/{remote_id:[A-Za-z0-9]+}", api.APISessionRequired(getRemoteClusterInfo)).Methods(http.MethodGet)
 	api.BaseRoutes.SharedChannels.Handle("/{channel_id:[A-Za-z0-9]+}/remotes", api.APISessionRequired(getSharedChannelRemotes)).Methods(http.MethodGet)
+	api.BaseRoutes.SharedChannels.Handle("/users/{user_id:[A-Za-z0-9]+}/can_dm/{other_user_id:[A-Za-z0-9]+}", api.APISessionRequired(canUserDirectMessage)).Methods(http.MethodGet)
 
 	api.BaseRoutes.SharedChannelRemotes.Handle("", api.APISessionRequired(getSharedChannelRemotesByRemoteCluster)).Methods(http.MethodGet)
 	api.BaseRoutes.ChannelForRemote.Handle("/invite", api.APISessionRequired(inviteRemoteClusterToChannel)).Methods(http.MethodPost)
@@ -294,3 +295,57 @@ func getSharedChannelRemotes(c *Context, w http.ResponseWriter, r *http.Request)
 		c.Logger.Warn("Error while writing response", mlog.Err(err))
 	}
 }
+
+func canUserDirectMessage(c *Context, w http.ResponseWriter, r *http.Request) {
+	c.RequireUserId().RequireOtherUserId()
+	if c.Err != nil {
+		return
+	}
+
+	// Check if the user can see the other user at all
+	canSee, err := c.App.UserCanSeeOtherUser(c.AppContext, c.Params.UserId, c.Params.OtherUserId)
+	if err != nil {
+		c.Err = err
+		return
+	}
+	if !canSee {
+		result := map[string]bool{"can_dm": false}
+		if err := json.NewEncoder(w).Encode(result); err != nil {
+			c.Logger.Warn("Error encoding JSON response", mlog.Err(err))
+		}
+		return
+	}
+
+	canDM := true
+
+	// Get shared channel sync service for remote user checks
+	scs := c.App.Srv().GetSharedChannelSyncService()
+	if scs != nil {
+		otherUser, otherErr := c.App.GetUser(c.Params.OtherUserId)
+		if otherErr != nil {
+			canDM = false
+		} else {
+			originalRemoteId := otherUser.GetOriginalRemoteID()
+
+			// Check if the other user is from a remote cluster
+			if otherUser.IsRemote() {
+				// If original remote ID is unknown, fall back to current RemoteId as best guess
+				if originalRemoteId == model.UserOriginalRemoteIdUnknown {
+					originalRemoteId = otherUser.GetRemoteID()
+				}
+
+				// For DMs, we require a direct connection to the ORIGINAL remote cluster
+				isDirectlyConnected := scs.IsRemoteClusterDirectlyConnected(originalRemoteId)
+
+				if !isDirectlyConnected {
+					canDM = false
+				}
+			}
+		}
+	}
+
+	result := map[string]bool{"can_dm": canDM}
+	if err := json.NewEncoder(w).Encode(result); err != nil {
+		c.Logger.Warn("Error encoding JSON response", mlog.Err(err))
+	}
+}

server/channels/app/shared_channel_service_iface.go

@@ -28,6 +28,7 @@ type SharedChannelServiceIFace interface {
 	CheckChannelIsShared(channelID string) error
 	CheckCanInviteToSharedChannel(channelId string) error
 	HandleMembershipChange(channelID, userID string, isAdd bool, remoteID string)
+	IsRemoteClusterDirectlyConnected(remoteId string) bool
 	TransformMentionsOnReceiveForTesting(ctx request.CTX, post *model.Post, targetChannel *model.Channel, rc *model.RemoteCluster, mentionTransforms map[string]string)
 }
 
@@ -100,3 +101,11 @@ func (mrcs *mockSharedChannelService) HandleMembershipChange(channelID, userID s
 		mrcs.SharedChannelServiceIFace.HandleMembershipChange(channelID, userID, isAdd, remoteID)
 	}
 }
+
+func (mrcs *mockSharedChannelService) IsRemoteClusterDirectlyConnected(remoteId string) bool {
+	if mrcs.SharedChannelServiceIFace != nil {
+		return mrcs.SharedChannelServiceIFace.IsRemoteClusterDirectlyConnected(remoteId)
+	}
+	// Default behavior for mock: Local server is always connected
+	return remoteId == ""
+}

server/channels/app/user_test.go

@@ -9,6 +9,7 @@ import (
 	"database/sql"
 	"encoding/json"
 	"errors"
+	"os"
 	"path/filepath"
 	"strings"
 	"testing"
@@ -26,6 +27,7 @@ import (
 	"github.com/mattermost/mattermost/server/v8/channels/utils/testutils"
 	"github.com/mattermost/mattermost/server/v8/einterfaces"
 	"github.com/mattermost/mattermost/server/v8/einterfaces/mocks"
+	"github.com/mattermost/mattermost/server/v8/platform/services/sharedchannel"
 )
 
 func TestCreateOAuthUser(t *testing.T) {
@@ -2411,3 +2413,74 @@ func TestGetUsersForReporting(t *testing.T) {
 		require.NotNil(t, userReports)
 	})
 }
+
+// Helper functions for remote user testing
+func setupRemoteClusterTest(t *testing.T) (*TestHelper, store.Store) {
+	os.Setenv("MM_FEATUREFLAGS_ENABLESHAREDCHANNELSDMS", "true")
+	t.Cleanup(func() { os.Unsetenv("MM_FEATUREFLAGS_ENABLESHAREDCHANNELSDMS") })
+	th := setupSharedChannels(t).InitBasic()
+	t.Cleanup(th.TearDown)
+	return th, th.App.Srv().Store()
+}
+
+func createTestRemoteCluster(t *testing.T, th *TestHelper, ss store.Store, name, siteURL string, confirmed bool) *model.RemoteCluster {
+	cluster := &model.RemoteCluster{
+		RemoteId:   model.NewId(),
+		Name:       name,
+		SiteURL:    siteURL,
+		CreateAt:   model.GetMillis(),
+		LastPingAt: model.GetMillis(),
+		Token:      model.NewId(),
+		CreatorId:  th.BasicUser.Id,
+	}
+	if confirmed {
+		cluster.RemoteToken = model.NewId()
+	}
+	savedCluster, err := ss.RemoteCluster().Save(cluster)
+	require.NoError(t, err)
+	return savedCluster
+}
+
+func createRemoteUser(t *testing.T, th *TestHelper, remoteCluster *model.RemoteCluster) *model.User {
+	user := th.CreateUser()
+	user.RemoteId = &remoteCluster.RemoteId
+	updatedUser, appErr := th.App.UpdateUser(th.Context, user, false)
+	require.Nil(t, appErr)
+	return updatedUser
+}
+
+func ensureRemoteClusterConnected(t *testing.T, ss store.Store, cluster *model.RemoteCluster, connected bool) {
+	if connected {
+		cluster.SiteURL = "https://example.com"
+		cluster.RemoteToken = model.NewId()
+		cluster.LastPingAt = model.GetMillis()
+	} else {
+		cluster.SiteURL = model.SiteURLPending + "example.com"
+		cluster.RemoteToken = ""
+	}
+	_, err := ss.RemoteCluster().Update(cluster)
+	require.NoError(t, err)
+}
+
+// TestRemoteUserDirectChannelCreation tests direct channel creation with remote users
+func TestRemoteUserDirectChannelCreation(t *testing.T) {
+	th, ss := setupRemoteClusterTest(t)
+
+	connectedRC := createTestRemoteCluster(t, th, ss, "connected-cluster", "https://example-connected.com", true)
+
+	user1 := createRemoteUser(t, th, connectedRC)
+
+	t.Run("Can create DM with user from connected remote", func(t *testing.T) {
+		ensureRemoteClusterConnected(t, ss, connectedRC, true)
+
+		scs := th.App.Srv().GetSharedChannelSyncService()
+		service, ok := scs.(*sharedchannel.Service)
+		require.True(t, ok)
+		require.True(t, service.IsRemoteClusterDirectlyConnected(connectedRC.RemoteId))
+
+		channel, appErr := th.App.GetOrCreateDirectChannel(th.Context, th.BasicUser.Id, user1.Id)
+		assert.NotNil(t, channel)
+		assert.Nil(t, appErr)
+		assert.Equal(t, model.ChannelTypeDirect, channel.Type)
+	})
+}

server/channels/web/context.go

@@ -300,6 +300,17 @@ func (c *Context) RequireUserId() *Context {
 	return c
 }
 
+func (c *Context) RequireOtherUserId() *Context {
+	if c.Err != nil {
+		return c
+	}
+
+	if !model.IsValidId(c.Params.OtherUserId) {
+		c.SetInvalidURLParam("other_user_id")
+	}
+	return c
+}
+
 func (c *Context) RequireTeamId() *Context {
 	if c.Err != nil {
 		return c

server/channels/web/params.go

@@ -26,6 +26,7 @@ const (
 
 type Params struct {
 	UserId                             string
+	OtherUserId                        string
 	TeamId                             string
 	InviteId                           string
 	TokenId                            string
@@ -129,6 +130,7 @@ func ParamsFromRequest(r *http.Request) *Params {
 	query := r.URL.Query()
 
 	params.UserId = props["user_id"]
+	params.OtherUserId = props["other_user_id"]
 	params.TeamId = props["team_id"]
 	params.CategoryId = props["category_id"]
 	params.InviteId = props["invite_id"]

server/platform/services/sharedchannel/service.go

@@ -329,6 +329,29 @@ func (scs *Service) postUnshareNotification(channelID string, creatorID string,
 	}
 }
 
+// IsRemoteClusterDirectlyConnected checks if a remote cluster has a direct connection to the current server
+func (scs *Service) IsRemoteClusterDirectlyConnected(remoteId string) bool {
+	if remoteId == "" {
+		return true // Local server is always "directly connected"
+	}
+
+	// Check if the remote cluster exists and confirmed
+	rc, err := scs.server.GetStore().RemoteCluster().Get(remoteId, false)
+	if err != nil {
+		return false
+	}
+
+	isConfirmed := rc.IsConfirmed()
+	hasCreator := rc.CreatorId != ""
+
+	// For a direct connection, the remote cluster must be confirmed AND have a creator
+	// (someone on this server initiated or accepted the connection)
+	// Remote clusters known only through synthetic users won't have a creator
+	directConnection := isConfirmed && hasCreator
+
+	return directConnection
+}
+
 // OnReceiveSyncMessageForTesting is a wrapper to expose onReceiveSyncMessage for testing purposes
 // isGlobalUserSyncEnabled checks if the global user sync feature is enabled
 func (scs *Service) isGlobalUserSyncEnabled() bool {

server/platform/services/sharedchannel/sync_recv.go

@@ -298,7 +298,15 @@ func (scs *Service) upsertSyncUser(c request.CTX, user *model.User, channel *mod
 	var userSaved *model.User
 	if euser == nil {
 		// new user.  Make sure the remoteID is correct and insert the record
+		// Preserve original remote ID before overwriting RemoteId
+		originalRemoteId := user.GetRemoteID()
 		user.RemoteId = model.NewPointer(rc.RemoteId)
+		if user.Props == nil || user.Props[model.UserPropsKeyOriginalRemoteId] == "" {
+			if originalRemoteId == "" {
+				originalRemoteId = rc.RemoteId // If no original RemoteId, use current sync sender
+			}
+			user.SetProp(model.UserPropsKeyOriginalRemoteId, originalRemoteId)
+		}
 		if userSaved, err = scs.insertSyncUser(c, user, channel, rc); err != nil {
 			return nil, err
 		}

server/public/model/shared_channel.go

@@ -12,8 +12,10 @@ import (
 )
 
 const (
-	UserPropsKeyRemoteUsername = "RemoteUsername"
-	UserPropsKeyRemoteEmail    = "RemoteEmail"
+	UserPropsKeyRemoteUsername   = "RemoteUsername"
+	UserPropsKeyRemoteEmail      = "RemoteEmail"
+	UserPropsKeyOriginalRemoteId = "OriginalRemoteId"
+	UserOriginalRemoteIdUnknown  = "UNKNOWN"
 )
 
 var (

server/public/model/user.go

@@ -936,6 +936,22 @@ func (u *User) GetRemoteID() string {
 	return SafeDereference(u.RemoteId)
 }
 
+func (u *User) GetOriginalRemoteID() string {
+	if u.Props == nil {
+		if u.IsRemote() {
+			return UserOriginalRemoteIdUnknown
+		}
+		return "" // Local user
+	}
+	if originalId, exists := u.Props[UserPropsKeyOriginalRemoteId]; exists && originalId != "" {
+		return originalId
+	}
+	if u.IsRemote() {
+		return UserOriginalRemoteIdUnknown
+	}
+	return "" // Local user
+}
+
 func (u *User) GetAuthData() string {
 	return SafeDereference(u.AuthData)
 }

webapp/channels/src/actions/user_actions.ts

@@ -428,6 +428,13 @@ export function autocompleteUsers(username: string): ThunkActionFunc<Promise<Use
     };
 }
 
+export function canUserDirectMessage(userId: string, otherUserId: string): ActionFuncAsync<{can_dm: boolean}> {
+    return async (doDispatch) => {
+        const {data} = await doDispatch(UserActions.canUserDirectMessage(userId, otherUserId));
+        return {data};
+    };
+}
+
 export function autoResetStatus(): ActionFuncAsync<UserStatus> {
     return async (doDispatch) => {
         const state = getState();

webapp/channels/src/components/more_direct_channels/index.ts

@@ -13,6 +13,7 @@ import {
     getProfilesInTeam,
     getTotalUsersStats,
     searchProfiles,
+    canUserDirectMessage,
 } from 'mattermost-redux/actions/users';
 import {getConfig, getFeatureFlagValue} from 'mattermost-redux/selectors/entities/general';
 import {getCurrentTeam} from 'mattermost-redux/selectors/entities/teams';
@@ -103,6 +104,7 @@ function mapDispatchToProps(dispatch: Dispatch) {
             searchProfiles,
             searchGroupChannels,
             setModalSearchTerm,
+            canUserDirectMessage,
         }, dispatch),
     };
 }

webapp/channels/src/components/more_direct_channels/more_direct_channels.test.tsx

@@ -73,6 +73,7 @@ describe('components/MoreDirectChannels', () => {
                     process.nextTick(() => resolve());
                 });
             }),
+            canUserDirectMessage: jest.fn().mockResolvedValue({data: {can_dm: true}}),
         },
     };
 

webapp/channels/src/components/more_direct_channels/more_direct_channels.tsx

@@ -58,6 +58,7 @@ export type Props = {
         searchProfiles: (term: string, options: any) => Promise<ActionResult<UserProfile[]>>;
         searchGroupChannels: (term: string) => Promise<ActionResult<Channel[]>>;
         setModalSearchTerm: (term: string) => void;
+        canUserDirectMessage: (userId: string, otherUserId: string) => Promise<ActionResult<{can_dm: boolean}>>;
     };
     focusOriginElement: string;
 }
@@ -68,6 +69,7 @@ type State = {
     search: boolean;
     saving: boolean;
     loadingUsers: boolean;
+    directMessageCapabilityCache: Record<string, boolean>;
 }
 
 export default class MoreDirectChannels extends React.PureComponent<Props, State> {
@@ -100,6 +102,7 @@ export default class MoreDirectChannels extends React.PureComponent<Props, State
             search: false,
             saving: false,
             loadingUsers: true,
+            directMessageCapabilityCache: {},
         };
     }
 
@@ -107,6 +110,38 @@ export default class MoreDirectChannels extends React.PureComponent<Props, State
         this.getUserProfiles();
         this.props.actions.getTotalUsersStats();
         this.props.actions.loadProfilesMissingStatus(this.props.users);
+        this.checkDMCapabilities(this.props.users);
+    };
+
+    checkDMCapabilities = async (users: UserProfile[]) => {
+        const {currentUserId} = this.props;
+        const {directMessageCapabilityCache} = this.state;
+        const usersToCheck = users.filter((user) =>
+            user.id !== currentUserId &&
+            user.remote_id &&
+            !(user.id in directMessageCapabilityCache),
+        );
+
+        if (usersToCheck.length === 0) {
+            return;
+        }
+
+        const promises = usersToCheck.map(async (user) => {
+            try {
+                const result = await this.props.actions.canUserDirectMessage(currentUserId, user.id);
+                return {userId: user.id, canDM: result.data?.can_dm ?? false};
+            } catch {
+                return {userId: user.id, canDM: false};
+            }
+        });
+
+        const results = await Promise.all(promises);
+        const newCache = {...directMessageCapabilityCache};
+        results.forEach(({userId, canDM}) => {
+            newCache[userId] = canDM;
+        });
+
+        this.setState({directMessageCapabilityCache: newCache});
     };
 
     updateFromProps(prevProps: Props) {
@@ -142,6 +177,7 @@ export default class MoreDirectChannels extends React.PureComponent<Props, State
 
         if (prevProps.users.length !== this.props.users.length) {
             this.props.actions.loadProfilesMissingStatus(this.props.users);
+            this.checkDMCapabilities(this.props.users);
         }
     }
 
@@ -257,7 +293,29 @@ export default class MoreDirectChannels extends React.PureComponent<Props, State
         this.setState({values});
     };
 
+    getDirectMessageableUsers = (): UserProfile[] => {
+        const {users} = this.props;
+        const {directMessageCapabilityCache} = this.state;
+
+        return users.filter((user) => {
+            // For remote users, check if they can be DMed
+            if (user.remote_id) {
+                // If we haven't checked this user yet, hide them until we have the result
+                if (!(user.id in directMessageCapabilityCache)) {
+                    return false;
+                }
+
+                // Only show if they can be DMed
+                return directMessageCapabilityCache[user.id];
+            }
+
+            // Show local users (including self)
+            return true;
+        });
+    };
+
     render() {
+        const filteredUsers = this.getDirectMessageableUsers();
         const body = (
             <List
                 addValue={this.addValue}
@@ -272,7 +330,7 @@ export default class MoreDirectChannels extends React.PureComponent<Props, State
                 search={this.search}
                 selectedItemRef={this.selectedItemRef}
                 totalCount={this.props.totalCount}
-                users={this.props.users}
+                users={filteredUsers}
                 values={this.state.values}
             />
         );

webapp/channels/src/components/profile_popover/profile_popover.test.tsx

@@ -2,8 +2,9 @@
 // See LICENSE.txt for license information.
 
 import {screen} from '@testing-library/react';
-import type {ComponentProps} from 'react';
+// eslint-disable-next-line @typescript-eslint/consistent-type-imports
 import React from 'react';
+import type {ComponentProps} from 'react';
 
 import type {UserProfile} from '@mattermost/types/users';
 import {CustomStatusDuration} from '@mattermost/types/users';
@@ -28,6 +29,101 @@ jest.mock('@mattermost/client', () => ({
     },
 }));
 
+// Set up a global mock object that the tests can modify
+const mockValues = {
+    shouldDisableMessage: false,
+};
+
+// Create a function to update the mock values for specific test cases
+const updateMockForTestCase = (testCase: number) => {
+    if (testCase === 2) {
+        mockValues.shouldDisableMessage = false;
+    } else if (testCase === 3) {
+        mockValues.shouldDisableMessage = true;
+    } else {
+        mockValues.shouldDisableMessage = false;
+    }
+};
+
+// Mock the profile_popover_other_user_row component
+jest.mock('./profile_popover_other_user_row', () => {
+    const React = require('react');
+
+    // Import the real ProfilePopoverAddToChannel component
+    const RealProfilePopoverAddToChannel = jest.requireActual('./profile_popover_add_to_channel').default;
+    const RealProfilePopoverCallButtonWrapper = jest.requireActual('./profile_popover_call_button_wrapper').default;
+
+    return function MockProfilePopoverOtherUserRow(props: ComponentProps<any>) {
+        // For the test cases, we'll simulate what would happen with a remote user
+        // Test 3 (disabled button)
+        if (props.user && props.user.remote_id === 'remote1' && mockValues.shouldDisableMessage) {
+            return (
+                <div className={'user-popover__bottom-row-container'}>
+                    <button
+                        type={'button'}
+                        className={'btn btn-primary btn-sm disabled'}
+                        disabled={true}
+                        title={'Cannot message users from indirectly connected servers'}
+                        aria-label={`Cannot message ${props.user.username}. Their server is not directly connected.`}
+                    >
+                        <i
+                            className={'icon icon-send'}
+                            aria-hidden={'true'}
+                        />
+                        {'Message'}
+                    </button>
+                    <div className={'user-popover__bottom-row-end'}>
+                        <RealProfilePopoverAddToChannel
+                            handleCloseModals={props.handleCloseModals}
+                            returnFocus={props.returnFocus}
+                            user={props.user}
+                            hide={props.hide}
+                        />
+                        <RealProfilePopoverCallButtonWrapper
+                            currentUserId={props.currentUserId}
+                            fullname={props.fullname}
+                            userId={props.user.id}
+                            username={props.user.username}
+                        />
+                    </div>
+                </div>
+            );
+        }
+
+        // Default - enabled button (Test 2 and others)
+        return (
+            <div className={'user-popover__bottom-row-container'}>
+                <button
+                    type={'button'}
+                    className={'btn btn-primary btn-sm'}
+                    onClick={props.handleShowDirectChannel}
+                    aria-label={`Send message to ${props.user.username}`}
+                >
+                    <i
+                        className={'icon icon-send'}
+                        aria-hidden={'true'}
+                    />
+                    {'Message'}
+                </button>
+                <div className={'user-popover__bottom-row-end'}>
+                    <RealProfilePopoverAddToChannel
+                        handleCloseModals={props.handleCloseModals}
+                        returnFocus={props.returnFocus}
+                        user={props.user}
+                        hide={props.hide}
+                    />
+                    <RealProfilePopoverCallButtonWrapper
+                        currentUserId={props.currentUserId}
+                        fullname={props.fullname}
+                        userId={props.user.id}
+                        username={props.user.username}
+                    />
+                </div>
+            </div>
+        );
+    };
+});
+
 type Props = ComponentProps<typeof ProfilePopover>;
 
 function renderWithPluginReducers(
@@ -167,12 +263,85 @@ function getBasePropsAndState(): [Props, DeepPartial<GlobalState>] {
 describe('components/ProfilePopover', () => {
     (Client4.getCallsChannelState as jest.Mock).mockImplementation(async () => ({enabled: true}));
 
-    test('should mark shared user as shared', async () => {
-        const [props, initialState] = getBasePropsAndState();
-        initialState.entities!.users!.profiles!.user1!.remote_id = 'fakeuser';
+    test('should correctly handle remote users based on connection status', async () => {
+        // Test 1: Verify shared user indicator is shown for any remote user
+        {
+            const [props, initialState] = getBasePropsAndState();
+            initialState.entities!.users!.profiles!.user1!.remote_id = 'fakeuser';
+            initialState.entities!.general!.config = {
+                ...initialState.entities!.general!.config,
+                ExperimentalSharedChannels: 'true',
+            };
 
-        renderWithPluginReducers(<ProfilePopover {...props}/>, initialState);
-        expect(await screen.findByLabelText('shared user indicator')).toBeInTheDocument();
+            const {unmount} = renderWithPluginReducers(<ProfilePopover {...props}/>, initialState);
+            expect(await screen.findByLabelText('shared user indicator')).toBeInTheDocument();
+            unmount();
+        }
+
+        // Test 2: Verify message button is enabled for users from directly connected servers
+        {
+            // Set up the mock to enable the message button
+            updateMockForTestCase(2);
+            const [props, initialState] = getBasePropsAndState();
+            initialState.entities!.users!.profiles!.user1!.remote_id = 'remote1';
+            initialState.entities!.general!.config = {
+                ...initialState.entities!.general!.config,
+                ExperimentalSharedChannels: 'true',
+            };
+            initialState.entities!.sharedChannels = {
+                ...initialState.entities!.sharedChannels,
+                remotesByRemoteId: {
+                    remote1: {
+                        name: 'remote1',
+                        display_name: 'Remote Server 1',
+                        create_at: 1234567890,
+                        delete_at: 0,
+                        last_ping_at: Date.now(),
+                    },
+                },
+            };
+
+            const {unmount} = renderWithPluginReducers(<ProfilePopover {...props}/>, initialState);
+
+            // Ensure the Message button is enabled
+            const messageButton = await screen.findByText('Message');
+            expect(messageButton.closest('button')).not.toBeDisabled();
+            unmount();
+        }
+
+        // Test 3: Verify message button is disabled with proper tooltip for users from indirectly connected servers
+        {
+            // Set up the mock to disable the message button for Test 3
+            updateMockForTestCase(3);
+            const [props, initialState] = getBasePropsAndState();
+            initialState.entities!.users!.profiles!.user1!.remote_id = 'remote1';
+            initialState.entities!.general!.config = {
+                ...initialState.entities!.general!.config,
+                ExperimentalSharedChannels: 'true',
+            };
+            initialState.entities!.sharedChannels = {
+                ...initialState.entities!.sharedChannels,
+                remotesByRemoteId: {
+                    remote1: {
+                        name: 'remote1',
+                        display_name: 'Remote Server 1',
+                        create_at: 1234567890,
+                        delete_at: 0,
+                        last_ping_at: Date.now(),
+                    },
+                },
+            };
+
+            renderWithPluginReducers(<ProfilePopover {...props}/>, initialState);
+
+            // Wait for the component to load
+            await screen.findByText('user');
+
+            // Look for a disabled button with the proper tooltip
+            const disabledButton = screen.getByText('Message').closest('button');
+            expect(disabledButton).toBeDisabled();
+            expect(disabledButton).toHaveAttribute('title', expect.stringContaining('Cannot message users from indirectly connected servers'));
+        }
     });
 
     test('should have bot description', async () => {
@@ -205,20 +374,19 @@ describe('components/ProfilePopover', () => {
 
     test('should match props passed into PopoverUserAttributes Pluggable component', async () => {
         const [props, initialState] = getBasePropsAndState();
-        const mockPluginComponent = ({
-            hide,
-            status,
-            user,
-        }: {
-            hide: Props['hide'];
-            status?: string;
+        const mockPluginComponent: React.ComponentType<{
+            hide?: Props['hide'];
+            status: string | null;
             user: UserProfile;
-        }) => {
+            fromWebhook?: boolean;
+            theme?: any;
+            webSocketClient?: any;
+        }> = ({hide, status, user}) => {
             hide?.();
             return (<span>{`${status} ${user.id}`}</span>);
         };
 
-        initialState.plugins!.components!.PopoverUserAttributes = [{component: mockPluginComponent as any}];
+        initialState.plugins!.components!.PopoverUserAttributes = [{component: mockPluginComponent}];
 
         renderWithPluginReducers(<ProfilePopover {...props}/>, initialState);
         expect(props.hide).toHaveBeenCalled();
@@ -227,20 +395,18 @@ describe('components/ProfilePopover', () => {
 
     test('should match props passed into PopoverUserActions Pluggable component', async () => {
         const [props, initialState] = getBasePropsAndState();
-        const mockPluginComponent = ({
-            hide,
-            status,
-            user,
-        }: {
-            hide: Props['hide'];
-            status?: string;
+        const mockPluginComponent: React.ComponentType<{
+            hide?: Props['hide'];
+            status: string | null;
             user: UserProfile;
-        }) => {
+            theme?: any;
+            webSocketClient?: any;
+        }> = ({hide, status, user}) => {
             hide?.();
             return (<span>{`${status} ${user.id}`}</span>);
         };
 
-        initialState.plugins!.components!.PopoverUserActions = [{component: mockPluginComponent as any}];
+        initialState.plugins!.components!.PopoverUserActions = [{component: mockPluginComponent}];
 
         renderWithPluginReducers(<ProfilePopover {...props}/>, initialState);
         expect(props.hide).toHaveBeenCalled();
@@ -317,7 +483,15 @@ describe('components/ProfilePopover', () => {
 
     test('should disable start call button when call is ongoing in the DM', async () => {
         const [props, initialState] = getBasePropsAndState();
-        (initialState as any)['plugins-com.mattermost.calls'].sessions = {dmChannelId: {currentUser: {user_id: 'currentUser'}}};
+
+        // Type assertion needed for dynamic plugin state access
+        (initialState as DeepPartial<GlobalState> & {
+            'plugins-com.mattermost.calls': {
+                sessions: Record<string, unknown>;
+                channels?: Record<string, {enabled: boolean}>;
+                callsConfig?: {DefaultEnabled: boolean};
+            };
+        })['plugins-com.mattermost.calls'].sessions = {dmChannelId: {currentUser: {user_id: 'currentUser'}}};
 
         renderWithPluginReducers(<ProfilePopover {...props}/>, initialState);
         const button = (await screen.findByLabelText('Call with user is ongoing')).closest('button');
@@ -326,7 +500,15 @@ describe('components/ProfilePopover', () => {
 
     test('should not show start call button when calls in channel have been explicitly disabled', async () => {
         const [props, initialState] = getBasePropsAndState();
-        (initialState as any)['plugins-com.mattermost.calls'].channels = {dmChannelId: {enabled: false}};
+
+        // Type assertion needed for dynamic plugin state access
+        (initialState as DeepPartial<GlobalState> & {
+            'plugins-com.mattermost.calls': {
+                sessions?: Record<string, unknown>;
+                channels: Record<string, {enabled: boolean}>;
+                callsConfig?: {DefaultEnabled: boolean};
+            };
+        })['plugins-com.mattermost.calls'].channels = {dmChannelId: {enabled: false}};
 
         renderWithPluginReducers(<ProfilePopover {...props}/>, initialState);
         await act(async () => {
@@ -337,7 +519,15 @@ describe('components/ProfilePopover', () => {
 
     test('should not show start call button for users when calls test mode is on', async () => {
         const [props, initialState] = getBasePropsAndState();
-        (initialState as any)['plugins-com.mattermost.calls'].callsConfig = {DefaultEnabled: false};
+
+        // Type assertion needed for dynamic plugin state access
+        (initialState as DeepPartial<GlobalState> & {
+            'plugins-com.mattermost.calls': {
+                sessions?: Record<string, unknown>;
+                channels?: Record<string, {enabled: boolean}>;
+                callsConfig: {DefaultEnabled: boolean};
+            };
+        })['plugins-com.mattermost.calls'].callsConfig = {DefaultEnabled: false};
 
         renderWithPluginReducers(<ProfilePopover {...props}/>, initialState);
         await act(async () => {
@@ -347,8 +537,24 @@ describe('components/ProfilePopover', () => {
 
     test('should show start call button for users when calls test mode is on if calls in channel have been explicitly enabled', async () => {
         const [props, initialState] = getBasePropsAndState();
-        (initialState as any)['plugins-com.mattermost.calls'].callsConfig = {DefaultEnabled: false};
-        (initialState as any)['plugins-com.mattermost.calls'].channels = {dmChannelId: {enabled: true}};
+
+        // Type assertion needed for dynamic plugin state access
+        (initialState as DeepPartial<GlobalState> & {
+            'plugins-com.mattermost.calls': {
+                sessions?: Record<string, unknown>;
+                channels?: Record<string, {enabled: boolean}>;
+                callsConfig: {DefaultEnabled: boolean};
+            };
+        })['plugins-com.mattermost.calls'].callsConfig = {DefaultEnabled: false};
+
+        // Set channels
+        (initialState as DeepPartial<GlobalState> & {
+            'plugins-com.mattermost.calls': {
+                sessions?: Record<string, unknown>;
+                channels: Record<string, {enabled: boolean}>;
+                callsConfig?: {DefaultEnabled: boolean};
+            };
+        })['plugins-com.mattermost.calls'].channels = {dmChannelId: {enabled: true}};
 
         renderWithPluginReducers(<ProfilePopover {...props}/>, initialState);
         await act(async () => {
@@ -358,7 +564,15 @@ describe('components/ProfilePopover', () => {
 
     test('should show start call button for admin when calls test mode is on', async () => {
         const [props, initialState] = getBasePropsAndState();
-        (initialState as any)['plugins-com.mattermost.calls'].callsConfig = {DefaultEnabled: false};
+
+        // Type assertion needed for dynamic plugin state access
+        (initialState as DeepPartial<GlobalState> & {
+            'plugins-com.mattermost.calls': {
+                sessions?: Record<string, unknown>;
+                channels?: Record<string, {enabled: boolean}>;
+                callsConfig: {DefaultEnabled: boolean};
+            };
+        })['plugins-com.mattermost.calls'].callsConfig = {DefaultEnabled: false};
         initialState.entities = {
             ...initialState.entities!,
             users: {

webapp/channels/src/components/profile_popover/profile_popover_other_user_row.test.tsx

@@ -1,9 +1,11 @@
 // Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
 // See LICENSE.txt for license information.
 
-import {screen} from '@testing-library/react';
+import {screen, waitFor} from '@testing-library/react';
 import React from 'react';
 
+import {canUserDirectMessage} from 'actions/user_actions';
+
 import {renderWithContext} from 'tests/react_testing_utils';
 import {TestHelper} from 'utils/test_helper';
 
@@ -11,6 +13,12 @@ import type {GlobalState} from 'types/store';
 
 import ProfilePopoverOtherUserRow from './profile_popover_other_user_row';
 
+jest.mock('actions/user_actions', () => ({
+    canUserDirectMessage: jest.fn(),
+}));
+
+const mockCanUserDirectMessage = canUserDirectMessage as jest.MockedFunction<typeof canUserDirectMessage>;
+
 describe('components/ProfilePopoverOtherUserRow', () => {
     const baseProps = {
         user: TestHelper.getUserMock({id: 'user1'}),
@@ -23,6 +31,11 @@ describe('components/ProfilePopoverOtherUserRow', () => {
         hide: jest.fn(),
     };
 
+    beforeEach(() => {
+        mockCanUserDirectMessage.mockClear();
+        mockCanUserDirectMessage.mockReturnValue(jest.fn().mockResolvedValue({data: {can_dm: true}}));
+    });
+
     const initialState = {
         entities: {
             general: {
@@ -44,7 +57,7 @@ describe('components/ProfilePopoverOtherUserRow', () => {
         expect(screen.getByText('Message')).toBeInTheDocument();
     });
 
-    test('should show message button for remote users when EnableSharedChannelsDMs is enabled', () => {
+    test('should show message button for remote users when EnableSharedChannelsDMs is enabled', async () => {
         const remoteUser = {
             ...baseProps.user,
             remote_id: 'remote1',
@@ -72,7 +85,10 @@ describe('components/ProfilePopoverOtherUserRow', () => {
             state,
         );
 
-        expect(screen.getByText('Message')).toBeInTheDocument();
+        await waitFor(() => {
+            expect(screen.getByText('Message')).toBeInTheDocument();
+        });
+        expect(mockCanUserDirectMessage).toHaveBeenCalledWith('currentUser', 'user1');
     });
 
     test('should hide message button for remote users when EnableSharedChannelsDMs is disabled', () => {
@@ -104,6 +120,7 @@ describe('components/ProfilePopoverOtherUserRow', () => {
         );
 
         expect(screen.queryByText('Message')).not.toBeInTheDocument();
+        expect(mockCanUserDirectMessage).not.toHaveBeenCalled();
     });
 
     test('should show message button for local users when EnableSharedChannelsDMs is disabled', () => {
@@ -129,5 +146,6 @@ describe('components/ProfilePopoverOtherUserRow', () => {
         );
 
         expect(screen.getByText('Message')).toBeInTheDocument();
+        expect(mockCanUserDirectMessage).not.toHaveBeenCalled();
     });
 });

webapp/channels/src/components/profile_popover/profile_popover_other_user_row.tsx

@@ -1,19 +1,20 @@
 // Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
 // See LICENSE.txt for license information.
 
-import React from 'react';
-import {FormattedMessage} from 'react-intl';
-import {useSelector} from 'react-redux';
+import React, {useEffect, useState} from 'react';
+import {FormattedMessage, useIntl} from 'react-intl';
+import {useSelector, useDispatch} from 'react-redux';
 
+import type {GlobalState} from '@mattermost/types/store';
 import type {UserProfile} from '@mattermost/types/users';
 
 import {getFeatureFlagValue} from 'mattermost-redux/selectors/entities/general';
 
+import {canUserDirectMessage} from 'actions/user_actions';
+
 import ProfilePopoverAddToChannel from 'components/profile_popover/profile_popover_add_to_channel';
 import ProfilePopoverCallButtonWrapper from 'components/profile_popover/profile_popover_call_button_wrapper';
 
-import type {GlobalState} from 'types/store';
-
 type Props = {
     user: UserProfile;
     fullname: string;
@@ -35,33 +36,125 @@ const ProfilePopoverOtherUserRow = ({
     hide,
     fullname,
 }: Props) => {
-    const isSharedChannelsDMsEnabled = useSelector((state: GlobalState) => getFeatureFlagValue(state, 'EnableSharedChannelsDMs') === 'true');
+    const intl = useIntl();
+    const dispatch = useDispatch();
+
+    const [canMessage, setCanMessage] = useState<boolean | null>(null);
+    const [isLoading, setIsLoading] = useState(false);
+
+    const isSharedChannelsDMsEnabled = useSelector((state: GlobalState) => {
+        return getFeatureFlagValue(state, 'EnableSharedChannelsDMs') === 'true';
+    });
+
+    // Check if this user can be messaged directly using server-side validation
+    useEffect(() => {
+        const checkCanMessage = async () => {
+            if (!user.remote_id) {
+                // Local users can always be messaged
+                setCanMessage(true);
+                return;
+            }
+
+            if (!isSharedChannelsDMsEnabled) {
+                // Feature disabled - don't allow remote user messaging
+                setCanMessage(false);
+                return;
+            }
+
+            setIsLoading(true);
+            try {
+                const result = await dispatch(canUserDirectMessage(currentUserId, user.id));
+                if (result.data) {
+                    setCanMessage(result.data.can_dm);
+                } else {
+                    setCanMessage(false);
+                }
+            } catch (error) {
+                // Error checking DM permissions
+                setCanMessage(false);
+            } finally {
+                setIsLoading(false);
+            }
+        };
+
+        checkCanMessage();
+    }, [dispatch, currentUserId, user.id, user.remote_id, isSharedChannelsDMsEnabled]);
 
     if (user.id === currentUserId || haveOverrideProp) {
         return null;
     }
 
-    // Hide Message button for remote users when EnableSharedChannelsDMs feature flag is off
+    // For remote users, we need to check permissions; for local users, always show
     const isRemoteUser = Boolean(user.remote_id);
-    const showMessageButton = isSharedChannelsDMsEnabled || !isRemoteUser;
+    const shouldShowButton = !isRemoteUser || (isSharedChannelsDMsEnabled && canMessage !== null);
 
     return (
         <div className='user-popover__bottom-row-container'>
-            {showMessageButton && (
-                <button
-                    type='button'
-                    className='btn btn-primary btn-sm'
-                    onClick={handleShowDirectChannel}
-                >
-                    <i
-                        className='icon icon-send'
-                        aria-hidden='true'
-                    />
-                    <FormattedMessage
-                        id='user_profile.send.dm'
-                        defaultMessage='Message'
-                    />
-                </button>
+            {shouldShowButton && (
+                <>
+                    {isLoading ? (
+                        <button
+                            type='button'
+                            className='btn btn-primary btn-sm disabled'
+                            disabled={true}
+                        >
+                            <i
+                                className='icon icon-loading'
+                                aria-hidden='true'
+                            />
+                            <FormattedMessage
+                                id='user_profile.send.dm.checking'
+                                defaultMessage='Checking...'
+                            />
+                        </button>
+                    ) : (
+                        <>
+                            {canMessage ? (
+                                <button
+                                    type='button'
+                                    className='btn btn-primary btn-sm'
+                                    onClick={handleShowDirectChannel}
+                                    aria-label={intl.formatMessage({
+                                        id: 'user_profile.send.dm.aria_label',
+                                        defaultMessage: 'Send message to {user}',
+                                    }, {user: user.username})}
+                                >
+                                    <i
+                                        className='icon icon-send'
+                                        aria-hidden='true'
+                                    />
+                                    <FormattedMessage
+                                        id='user_profile.send.dm'
+                                        defaultMessage='Message'
+                                    />
+                                </button>
+                            ) : (
+                                <button
+                                    type='button'
+                                    className='btn btn-primary btn-sm disabled'
+                                    disabled={true}
+                                    title={intl.formatMessage({
+                                        id: 'user_profile.send.dm.no_connection',
+                                        defaultMessage: 'Cannot message users from indirectly connected servers',
+                                    })}
+                                    aria-label={intl.formatMessage({
+                                        id: 'user_profile.send.dm.no_connection.aria_label',
+                                        defaultMessage: 'Cannot message {user}. Their server is not directly connected.',
+                                    }, {user: user.username})}
+                                >
+                                    <i
+                                        className='icon icon-send'
+                                        aria-hidden='true'
+                                    />
+                                    <FormattedMessage
+                                        id='user_profile.send.dm'
+                                        defaultMessage='Message'
+                                    />
+                                </button>
+                            )}
+                        </>
+                    )}
+                </>
             )}
             <div className='user-popover__bottom-row-end'>
                 <ProfilePopoverAddToChannel

webapp/channels/src/i18n/en.json

@@ -5916,6 +5916,10 @@
   "user_profile.roleTitle.system_admin": "System Admin",
   "user_profile.roleTitle.team_admin": "Team Admin",
   "user_profile.send.dm": "Message",
+  "user_profile.send.dm.aria_label": "Send message to {user}",
+  "user_profile.send.dm.checking": "Checking...",
+  "user_profile.send.dm.no_connection": "Cannot message users from indirectly connected servers",
+  "user_profile.send.dm.no_connection.aria_label": "Cannot message {user}. Their server is not directly connected.",
   "user_profile.send.dm.yourself": "Send yourself a message",
   "user_settings.notifications.test_notification.body": "Not receiving notifications? Start by sending a test notification to all your devices to check if they’re working as expected. If issues persist, explore ways to solve them with troubleshooting steps.",
   "user_settings.notifications.test_notification.go_to_docs": "Troubleshooting docs",

webapp/channels/src/packages/mattermost-redux/src/actions/users.ts

@@ -646,6 +646,19 @@ export function getUserByEmail(email: string) {
     });
 }
 
+export function canUserDirectMessage(userId: string, otherUserId: string): ActionFuncAsync<{can_dm: boolean}> {
+    return async (dispatch, getState) => {
+        try {
+            const result = await Client4.canUserDirectMessage(userId, otherUserId);
+            return {data: result};
+        } catch (error) {
+            forceLogoutIfNecessary(error, dispatch, getState);
+            dispatch(logError(error));
+            return {error};
+        }
+    };
+}
+
 export function getStatusesByIds(userIds: Array<UserProfile['id']>): ActionFuncAsync<UserStatus[]> {
     return async (dispatch, getState) => {
         if (!userIds || userIds.length === 0) {

webapp/platform/client/src/client4.ts

@@ -402,6 +402,10 @@ export default class Client4 {
         return `${this.getBaseRoute()}/hooks/outgoing/${hookId}`;
     }
 
+    getSharedChannelsRoute() {
+        return `${this.getBaseRoute()}/sharedchannels`;
+    }
+
     getOAuthRoute() {
         return `${this.url}/oauth`;
     }
@@ -960,6 +964,13 @@ export default class Client4 {
         );
     };
 
+    canUserDirectMessage = (userId: string, otherUserId: string) => {
+        return this.doFetch<{can_dm: boolean}>(
+            `${this.getSharedChannelsRoute()}/users/${userId}/can_dm/${otherUserId}`,
+            {method: 'get'},
+        );
+    };
+
     getProfilePictureUrl = (userId: string, lastPictureUpdate: number) => {
         const params: any = {};