Fix perform_fft ignoring get_window failure and transforming uninitialized memory

.github/workflows/run_unix.yml

@@ -354,6 +354,8 @@ jobs:
       run: sudo -H python3 $GITHUB_WORKSPACE/python_package/examples/tests/transforms.py
     - name: Downsampling Python
       run: sudo -H python3 $GITHUB_WORKSPACE/python_package/examples/tests/downsampling.py
+    - name: FFT Window Error Python
+      run: sudo -H python3 $GITHUB_WORKSPACE/python_package/examples/tests/fft_window_error.py
     - name: ICA Python
       run: sudo -H python3 $GITHUB_WORKSPACE/python_package/examples/tests/ica.py
     - name: CSP Python

python_package/examples/tests/fft_window_error.py

@@ -0,0 +1,46 @@
+import numpy as np
+
+from brainflow.data_filter import DataFilter, DataHandlerDLL, WindowOperations
+from brainflow.exit_codes import BrainFlowError, BrainFlowExitCodes
+
+
+def main():
+    data_len = 64
+    data = np.arange(data_len, dtype=np.float64)
+
+    # Call the native entry point directly rather than DataFilter.perform_fft, because the
+    # wrapper allocates the output buffers itself and raises before returning them. Filling
+    # them with sentinels here is what makes "left untouched" observable.
+    original = np.copy(data)
+    real = np.full(data_len // 2 + 1, -12345.0)
+    imag = np.full(data_len // 2 + 1, -54321.0)
+
+    invalid_window = 999
+    res = DataHandlerDLL.get_instance().perform_fft(data, data_len, invalid_window, real, imag)
+
+    assert res == BrainFlowExitCodes.INVALID_ARGUMENTS_ERROR.value, res
+    # perform_fft used to ignore the get_window failure and transform the uninitialized
+    # window buffer, so both outputs were written with values derived from garbage.
+    assert np.all(real == -12345.0), real
+    assert np.all(imag == -54321.0), imag
+    assert np.array_equal(data, original), data
+
+    # The same failure through the public wrapper, which turns the code into an exception.
+    try:
+        DataFilter.perform_fft(np.arange(data_len, dtype=np.float64), invalid_window)
+    except BrainFlowError as err:
+        assert err.exit_code == BrainFlowExitCodes.INVALID_ARGUMENTS_ERROR.value, err.exit_code
+    else:
+        raise AssertionError('an invalid window function must not be accepted')
+
+    # A valid window still round-trips, so the early return did not shadow the normal path.
+    restored = DataFilter.perform_ifft(
+        DataFilter.perform_fft(np.copy(original), WindowOperations.NO_WINDOW.value)
+    )
+    assert np.allclose(restored, original), restored
+
+    print('fft window error regression passed')
+
+
+if __name__ == '__main__':
+    main()

src/data_handler/data_handler.cpp

@@ -788,7 +788,12 @@ int perform_fft (
     }
 
     double *windowed_data = new double[data_len];
-    get_window (window_function, data_len, windowed_data);
+    int window_res = get_window (window_function, data_len, windowed_data);
+    if (window_res != (int)BrainFlowExitCodes::STATUS_OK)
+    {
+        delete[] windowed_data;
+        return window_res;
+    }
     for (int i = 0; i < data_len; i++)
     {
         windowed_data[i] *= data[i];