databricks
diff --git a/‎lib/DBSQLClient.ts‎
Lines changed: 78 additions & 64 deletions b/‎lib/DBSQLClient.ts‎
Lines changed: 78 additions & 64 deletions
@@ -1,10 +1,8 @@
 import thrift from 'thrift';
-import Int64 from 'node-int64';
 import os from 'os';
 
 import { EventEmitter } from 'events';
 import TCLIService from '../thrift/TCLIService';
-import { TProtocolVersion } from '../thrift/TCLIService_types';
 import IDBSQLClient, { ClientOptions, ConnectionOptions, OpenSessionRequest } from './contracts/IDBSQLClient';
 import IDriver from './contracts/IDriver';
 import IClientContext, { ClientConfig } from './contracts/IClientContext';
@@ -15,9 +13,12 @@ import IDBSQLSession from './contracts/IDBSQLSession';
 import IAuthentication from './connection/contracts/IAuthentication';
 import HttpConnection from './connection/connections/HttpConnection';
 import IConnectionOptions from './connection/contracts/IConnectionOptions';
-import Status from './dto/Status';
 import HiveDriverError from './errors/HiveDriverError';
-import { buildUserAgentString, definedOrError, serializeQueryTags } from './utils';
+import { buildUserAgentString } from './utils';
+import IBackend from './contracts/IBackend';
+import { InternalConnectionOptions } from './contracts/InternalConnectionOptions';
+import ThriftBackend from './thrift-backend/ThriftBackend';
+import SeaBackend from './sea/SeaBackend';
 import PlainHttpAuthentication from './connection/auth/PlainHttpAuthentication';
 import DatabricksOAuth, { OAuthFlow } from './connection/auth/DatabricksOAuth';
 import {
@@ -47,19 +48,6 @@ function prependSlash(str: string): string {
   return str;
 }
 
-function getInitialNamespaceOptions(catalogName?: string, schemaName?: string) {
-  if (!catalogName && !schemaName) {
-    return {};
-  }
-
-  return {
-    initialNamespace: {
-      catalogName,
-      schemaName,
-    },
-  };
-}
-
 export type ThriftLibrary = Pick<typeof thrift, 'createClient'>;
 
 /**
@@ -111,6 +99,8 @@ export default class DBSQLClient extends EventEmitter implements IDBSQLClient, I
 
   private readonly sessions = new CloseableCollection<DBSQLSession>();
 
+  private backend?: IBackend;
+
   // Telemetry components — `telemetryClient` is the shared per-host owner
   // (process-wide via TelemetryClientProvider). The exporter, aggregator,
   // circuit-breaker registry and feature-flag cache live on it. Each
@@ -633,34 +623,35 @@ export default class DBSQLClient extends EventEmitter implements IDBSQLClient, I
 
     this.connectionProvider = this.createConnectionProvider(options);
 
-    const thriftConnection = await this.connectionProvider.getThriftConnection();
+    // M0: `useSEA` is consumed via a non-exported internal-options cast so it
+    // doesn't ship in the public `.d.ts`. Mirrors Python's `kwargs.get("use_sea")`
+    // pattern (see databricks-sql-python/src/databricks/sql/session.py).
+    const internalOptions = options as ConnectionOptions & InternalConnectionOptions;
+    const backend = internalOptions.useSEA
+      ? new SeaBackend()
+      : new ThriftBackend({
+          context: this,
+          onConnectionEvent: (event, payload) => this.forwardConnectionEvent(event, payload),
+        });
 
-    thriftConnection.on('error', (error: Error) => {
-      // Error.stack already contains error type and message, so log stack if available,
-      // otherwise fall back to just error type + message
-      this.logger.log(LogLevel.error, error.stack || `${error.name}: ${error.message}`);
+    // Publish `this.backend` only after a successful `connect()`. Otherwise a
+    // failed connect would leave a half-initialized backend in place, and the
+    // next `openSession()` would slip past the `!this.backend` guard and
+    // surface a misleading "backend not implemented" / partial-state error
+    // instead of the accurate "DBSQLClient: not connected".
+    try {
+      await backend.connect(options);
+    } catch (err) {
+      // `IBackend.close()` is documented as safe on a partially-initialized
+      // backend; best-effort cleanup so we don't leak sockets / state.
       try {
-        this.emit('error', error);
-      } catch (e) {
-        // EventEmitter will throw unhandled error when emitting 'error' event.
-        // Since we already logged it few lines above, just suppress this behaviour
+        await backend.close();
+      } catch (closeErr) {
+        // Swallow; the original error is what the caller needs to see.
       }
-    });
-
-    thriftConnection.on('reconnecting', (params: { delay: number; attempt: number }) => {
-      this.logger.log(LogLevel.debug, `Reconnecting, params: ${JSON.stringify(params)}`);
-      this.emit('reconnecting', params);
-    });
-
-    thriftConnection.on('close', () => {
-      this.logger.log(LogLevel.debug, 'Closing connection.');
-      this.emit('close');
-    });
-
-    thriftConnection.on('timeout', () => {
-      this.logger.log(LogLevel.debug, 'Connection timed out.');
-      this.emit('timeout');
-    });
+      throw err;
+    }
+    this.backend = backend;
 
     // Initialize telemetry if enabled. The env var DATABRICKS_TELEMETRY_DISABLED
     // is a hard kill switch for ops/IT teams who can't redeploy app code.
@@ -691,6 +682,41 @@ export default class DBSQLClient extends EventEmitter implements IDBSQLClient, I
     return this;
   }
 
+  private forwardConnectionEvent(event: 'error' | 'reconnecting' | 'close' | 'timeout', payload?: unknown): void {
+    switch (event) {
+      case 'error': {
+        // `payload` is typed `unknown` because the cross-backend
+        // `IBackend.onConnectionEvent` doesn't constrain the error shape.
+        // Normalize to `Error` so the stack/name/message access below is safe
+        // for any backend that emits a non-Error value (e.g. a bare string).
+        const error = payload instanceof Error ? payload : new Error(String(payload));
+        this.logger.log(LogLevel.error, error.stack || `${error.name}: ${error.message}`);
+        try {
+          this.emit('error', error);
+        } catch (e) {
+          // EventEmitter throws when 'error' has no listeners; we've already logged it.
+        }
+        return;
+      }
+      case 'reconnecting':
+        this.logger.log(LogLevel.debug, `Reconnecting, params: ${JSON.stringify(payload)}`);
+        this.emit('reconnecting', payload);
+        return;
+      case 'close':
+        this.logger.log(LogLevel.debug, 'Closing connection.');
+        this.emit('close');
+        return;
+      case 'timeout':
+        this.logger.log(LogLevel.debug, 'Connection timed out.');
+        this.emit('timeout');
+        // Explicit return mirrors the other cases and protects against
+        // fall-through if a new event is added below.
+        // eslint-disable-next-line no-useless-return
+        return;
+      // no default
+    }
+  }
+
   /**
    * Starts new session
    * @public
@@ -701,6 +727,10 @@ export default class DBSQLClient extends EventEmitter implements IDBSQLClient, I
    * const session = await client.openSession();
    */
   public async openSession(request: OpenSessionRequest = {}): Promise<IDBSQLSession> {
+    if (!this.backend) {
+      throw new HiveDriverError('DBSQLClient: not connected');
+    }
+
     // Track connection open latency
     const startTime = Date.now();
 
@@ -711,30 +741,11 @@ export default class DBSQLClient extends EventEmitter implements IDBSQLClient, I
     if (this.config.enableMetricViewMetadata) {
       configuration['spark.sql.thriftserver.metadata.metricview.enabled'] = 'true';
     }
-
-    // Serialize queryTags dict and set in configuration; takes precedence over configuration.QUERY_TAGS
-    if (request.queryTags !== undefined) {
-      const serialized = serializeQueryTags(request.queryTags);
-      if (serialized) {
-        configuration.QUERY_TAGS = serialized;
-      } else {
-        delete configuration.QUERY_TAGS;
-      }
-    }
-
-    const response = await this.driver.openSession({
-      client_protocol_i64: new Int64(TProtocolVersion.SPARK_CLI_SERVICE_PROTOCOL_V8),
-      ...getInitialNamespaceOptions(request.initialCatalog, request.initialSchema),
+    const sessionBackend = await this.backend.openSession({
+      ...request,
       configuration,
-      canUseMultipleCatalogs: true,
-    });
-
-    Status.assert(response.status);
-    const session = new DBSQLSession({
-      handle: definedOrError(response.sessionHandle),
-      context: this,
-      serverProtocolVersion: response.serverProtocolVersion,
     });
+    const session = new DBSQLSession({ backend: sessionBackend, context: this });
     this.sessions.add(session);
 
     // Emit connection.open telemetry event. The DriverConfiguration blob
@@ -772,6 +783,9 @@ export default class DBSQLClient extends EventEmitter implements IDBSQLClient, I
    */
   public async close(): Promise<void> {
     await this.sessions.closeAll();
+    await this.backend?.close();
+
+    this.backend = undefined;
 
     // Cleanup telemetry. Releasing our refcount on the shared TelemetryClient
     // is awaited because the underlying close() drains the final HTTP POST —