BUG: Fix SEGY cube export producing non-UTF8 byte in binary header (#1543)

Author: GibranAlfa

src/xtgeo/cube/_cube_export.py

@@ -88,6 +88,9 @@ def export_segy(cube: Cube, sfile: str) -> None:
         f.bin[segyio.BinField.SortingCode] = 4  # trace sorting from C: needed?
         # TODO: Make this read from cube._measurement (or something)
         f.bin[segyio.BinField.MeasurementSystem] = 1
+        text_header = bytearray(f.text[0])
+        text_header[-1] = 0x20  # ASCII space
+        f.text[0] = bytes(text_header)
 
 
 def export_rmsreg(self, sfile):

tests/test_cube/test_cube.py

@@ -242,6 +242,24 @@ def test_segy_export_to_bytesio_raises():
         cube.to_file(stream, fformat="segy")
 
 
+def test_segy_export_sanitizes_text_header_last_byte(
+    tmp_path: pathlib.Path,
+) -> None:
+    """Text header last byte is a safe EBCDIC space after export."""
+    cube = xtgeo.Cube(ncol=3, nrow=2, nlay=5, xinc=10, yinc=10, zinc=1)
+    cube.values = list(range(30))
+    outfile = tmp_path / "cube_text_header_sanitized.segy"
+
+    cube.to_file(outfile, fformat="segy")
+    raw = outfile.read_bytes()
+    assert raw[3199] == 0x40  # EBCDIC space
+    assert raw[3199] != 0x80
+
+    with segyio.open(outfile, "r") as seg:
+        assert seg.bin[segyio.BinField.Interval] == 1000
+        assert seg.bin[segyio.BinField.Samples] == 5
+
+
 def test_cube_resampling(loadsfile1):
     """Import a cube, then make a smaller and resample, then export the new"""