chore: Improve error message for Read-only transaction with bounded staleness

src/database.ts

@@ -85,7 +85,7 @@
   LongRunningCallback,
   NormalCallback,
   PagedOptionsWithFilter,
   CLOUD_RESOURCE_HEADER,
   PagedResponse,
   RequestCallback,
   ResourceCallback,
@@ -2095,6 +2095,19 @@
         ? (optionsOrCallback as TimestampBounds)
         : {};
 
+    if (options !=null && (options['maxStaleness'] != null || options['minReadTimestamp'] != null)) {
+      const error = Object.assign(
+        new Error(
+          'maxStaleness / minReadTimestamp is not supported for multi-use read-only transactions.'
+        ),
+        {
+          code: 3, // invalid argument
+        }
+      ) as ServiceError;
+      callback!(error);
+      return;
+    }
+
     return startTrace('Database.getSnapshot', this._traceConfig, span => {
       this.pool_.getSession((err, session) => {
         if (err) {

test/database.ts

@@ -2307,6 +2307,39 @@ describe('Database', () => {
       assert.strictEqual(bounds, fakeTimestampBounds);
     });
 
+    it('should throw error if maxStaleness is passed in the timestamp bounds to the snapshot', () => {
+      const fakeTimestampBounds = {maxStaleness: 10};
+
+      database.getSnapshot(fakeTimestampBounds, err => {
+        assert.strictEqual(err.code, 3);
+        assert.strictEqual(
+          err.message,
+          'maxStaleness / minReadTimestamp is not supported for multi-use read-only transactions.'
+        );
+      });
+    });
+
+    it('should throw error if minReadTimestamp is passed in the timestamp bounds to the snapshot', () => {
+      const fakeTimestampBounds = {minReadTimestamp: 10};
+
+      database.getSnapshot(fakeTimestampBounds, err => {
+        assert.strictEqual(err.code, 3);
+        assert.strictEqual(
+          err.message,
+          'maxStaleness / minReadTimestamp is not supported for multi-use read-only transactions.'
+        );
+      });
+    });
+
+    it('should pass when maxStaleness is undefined', () => {
+      const fakeTimestampBounds = {minReadTimestamp: undefined};
+
+      database.getSnapshot(fakeTimestampBounds, assert.ifError);
+
+      const bounds = snapshotStub.lastCall.args[0];
+      assert.strictEqual(bounds, fakeTimestampBounds);
+    });
+
     it('should begin a snapshot', () => {
       beginSnapshotStub.callsFake(() => {});