MM-32133 shared channel username collisions (#17347)

Support for handling username collisions between remote clusters. Users belonging to remote clusters have their username changed to include the remote name e.g. wiggin becomes wiggin:mattermost.

@mentions are also modified so the munged username is replaced with the original username when the post is sync'd with the remote the user belongs to.

When adding remote users:
- append the remote name to the username with colon separator
- append the remote name to the email address with colon separator
- store the original username and email address in user props
- when resolving @mentions replace with the stored original username

model/remote_cluster.go

@@ -11,16 +11,24 @@ import (
 	"encoding/json"
 	"io"
 	"net/http"
+	"regexp"
 	"strings"
 )
 
 const (
 	RemoteOfflineAfterMillis = 1000 * 60 * 5 // 5 minutes
+	RemoteNameMinLength      = 1
+	RemoteNameMaxLength      = 64
+)
+
+var (
+	validRemoteNameChars = regexp.MustCompile(`^[a-zA-Z0-9\.\-\_]+$`)
 )
 
 type RemoteCluster struct {
 	RemoteId     string `json:"remote_id"`
 	RemoteTeamId string `json:"remote_team_id"`
+	Name         string `json:"name"`
 	DisplayName  string `json:"display_name"`
 	SiteURL      string `json:"site_url"`
 	CreateAt     int64  `json:"create_at"`
@@ -36,6 +44,14 @@ func (rc *RemoteCluster) PreSave() {
 		rc.RemoteId = NewId()
 	}
 
+	if rc.DisplayName == "" {
+		rc.DisplayName = rc.Name
+	}
+
+	rc.Name = SanitizeUnicode(rc.Name)
+	rc.DisplayName = SanitizeUnicode(rc.DisplayName)
+	rc.Name = NormalizeRemoteName(rc.Name)
+
 	if rc.Token == "" {
 		rc.Token = NewId()
 	}
@@ -51,8 +67,8 @@ func (rc *RemoteCluster) IsValid() *AppError {
 		return NewAppError("RemoteCluster.IsValid", "model.cluster.is_valid.id.app_error", nil, "id="+rc.RemoteId, http.StatusBadRequest)
 	}
 
-	if rc.DisplayName == "" {
-		return NewAppError("RemoteCluster.IsValid", "model.cluster.is_valid.name.app_error", nil, "display_name empty", http.StatusBadRequest)
+	if !IsValidRemoteName(rc.Name) {
+		return NewAppError("RemoteCluster.IsValid", "model.cluster.is_valid.name.app_error", nil, "name="+rc.Name, http.StatusBadRequest)
 	}
 
 	if rc.CreateAt == 0 {
@@ -65,7 +81,21 @@ func (rc *RemoteCluster) IsValid() *AppError {
 	return nil
 }
 
+func IsValidRemoteName(s string) bool {
+	if len(s) < RemoteNameMinLength || len(s) > RemoteNameMaxLength {
+		return false
+	}
+	return validRemoteNameChars.MatchString(s)
+}
+
 func (rc *RemoteCluster) PreUpdate() {
+	if rc.DisplayName == "" {
+		rc.DisplayName = rc.Name
+	}
+
+	rc.Name = SanitizeUnicode(rc.Name)
+	rc.DisplayName = SanitizeUnicode(rc.DisplayName)
+	rc.Name = NormalizeRemoteName(rc.Name)
 	rc.fixTopics()
 }
 
@@ -105,12 +135,17 @@ func (rc *RemoteCluster) ToJSON() (string, error) {
 
 func (rc *RemoteCluster) ToRemoteClusterInfo() RemoteClusterInfo {
 	return RemoteClusterInfo{
+		Name:        rc.Name,
 		DisplayName: rc.DisplayName,
 		CreateAt:    rc.CreateAt,
 		LastPingAt:  rc.LastPingAt,
 	}
 }
 
+func NormalizeRemoteName(name string) string {
+	return strings.ToLower(name)
+}
+
 func RemoteClusterFromJSON(data io.Reader) (*RemoteCluster, *AppError) {
 	var rc RemoteCluster
 	err := json.NewDecoder(data).Decode(&rc)
@@ -122,6 +157,7 @@ func RemoteClusterFromJSON(data io.Reader) (*RemoteCluster, *AppError) {
 
 // RemoteClusterInfo provides a subset of RemoteCluster fields suitable for sending to clients.
 type RemoteClusterInfo struct {
+	Name        string `json:"name"`
 	DisplayName string `json:"display_name"`
 	CreateAt    int64  `json:"create_at"`
 	LastPingAt  int64  `json:"last_ping_at"`