expose ServerAPIVersion as a separate config option

server/db/mongodb/adapter.go

@@ -72,6 +72,9 @@ type configType struct {
 	TlsCertFile        string `json:"tls_cert_file,omitempty"`
 	TlsPrivateKey      string `json:"tls_private_key,omitempty"`
 	InsecureSkipVerify bool   `json:"tls_skip_verify,omitempty"`
+
+	// The only version supported at this time is "1".
+	APIVersion mdbopts.ServerAPIVersion `json:"api_version,omitempty"`
 }
 
 // Open initializes mongodb session
@@ -170,13 +173,15 @@ func (a *adapter) Open(jsonconfig json.RawMessage) error {
 		a.maxMessageResults = defaultMaxMessageResults
 	}
 
-	opts.SetServerAPIOptions(mdbopts.ServerAPI(mdbopts.ServerAPIVersion1))
-
 	// Connection string URI overrides any other options configured earlier.
 	if config.Uri != "" {
 		opts.ApplyURI(config.Uri)
 	}
 
+	if config.APIVersion != "" {
+		opts.SetServerAPIOptions(mdbopts.ServerAPI(config.APIVersion))
+	}
+
 	// Make sure the options are sane.
 	if err = opts.Validate(); err != nil {
 		return err

server/tinode.conf

@@ -252,16 +252,19 @@
 
 			// MongoDB configuration.
 			"mongodb": {
+				// Connection string https://www.mongodb.com/docs/manual/reference/connection-string/
+				// Options configured with the connection string override any other options.
+				"uri": "",
+				// The only supported server API version is "1". May or maynot be needed depending on server version.
+				"api_version": "",
+
 				// Address(es) of MongoDB node(s): either a string or an array of strings.
 				"addresses": "localhost:27017",
 				// Name of the main database.
 				"database": "tinode",
 				// Name of replica set of mongodb instance. Remove this line to use a standalone instance.
 				// If replica_set is disabled, transactions will be disabled as well.
 				"replica_set": "rs0",
-				// Connection string https://www.mongodb.com/docs/manual/reference/connection-string/
-				// Options configured with the connection string override any other options.
-				"uri": "",
 
 				// Authentication options. Uncomment if auth is configured on your MongoDB.