From 2465739c7014098b8d39dc6ea3a4883bbd115253 Mon Sep 17 00:00:00 2001
From: "claude[bot]" <41898282+claude[bot]@users.noreply.github.com>
Date: Wed, 21 Oct 2026 09:46:34 +0000
Subject: [PATCH] Raise ParseError for truncated stoch plane arrays

Closes #145

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 source_modelling/stoch.py | 54 +++++++++++++++++++++++++++------------
 tests/test_stoch.py       | 15 +++++++++++
 2 files changed, 53 insertions(+), 16 deletions(-)

diff --git a/source_modelling/stoch.py b/source_modelling/stoch.py
index 0952e3b..1c7dbbe 100644
--- a/source_modelling/stoch.py
+++ b/source_modelling/stoch.py
@@ -117,6 +117,38 @@ def _read_stoch_header(handle: TextIO) -> StochHeader:
     )
 
 
+def _read_array(handle: TextIO, header: StochHeader, label: str) -> FloatArray2D:
+    """
+    Read a single (ny, nx) data array of a stochastic plane.
+
+    Parameters
+    ----------
+    handle : TextIO
+        Text file handle positioned at the start of the array.
+    header : StochHeader
+        Header of the plane, giving the array dimensions.
+    label : str
+        Name of the array being read, used in error messages.
+
+    Returns
+    -------
+    FloatArray2D
+        The array, with shape (ny, nx).
+
+    Raises
+    ------
+    parse_utils.ParseError
+        If fewer than nx * ny values could be read.
+    """
+    n = header.nx * header.ny
+    array = np.fromfile(handle, dtype=np.float32, sep=" ", count=n)
+    if array.size != n:
+        raise parse_utils.ParseError(
+            f"Expected {n} values for {label}, got {array.size}"
+        )
+    return cast(FloatArray2D, array.reshape((header.ny, header.nx)))
+
+
 def _read_stoch_plane(handle: TextIO) -> StochPlane:
     """
     Read a complete stochastic plane from a file.
@@ -132,20 +164,9 @@ def _read_stoch_plane(handle: TextIO) -> StochPlane:
         Named tuple containing the plane's header and data arrays (slip, rise, trup).
     """
     header = _read_stoch_header(handle)
-    slip_array = np.fromfile(
-        handle, dtype=np.float32, sep=" ", count=header.nx * header.ny
-    ).reshape((header.ny, header.nx))
-    slip = cast(FloatArray2D, slip_array)
-
-    rise_array = np.fromfile(
-        handle, dtype=np.float32, sep=" ", count=header.nx * header.ny
-    ).reshape((header.ny, header.nx))
-    rise = cast(FloatArray2D, rise_array)
-
-    trup_array = np.fromfile(
-        handle, dtype=np.float32, sep=" ", count=header.nx * header.ny
-    ).reshape((header.ny, header.nx))
-    trup = cast(FloatArray2D, trup_array)
+    slip = _read_array(handle, header, "slip")
+    rise = _read_array(handle, header, "rise")
+    trup = _read_array(handle, header, "trup")
 
     return StochPlane(header, slip, rise, trup)
 
@@ -192,8 +213,9 @@ def from_file(cls, filename: Path) -> Self:
 
         Raises
         ------
-        ValueError
-            If the number of planes specified in the file is not a positive integer.
+        parse_utils.ParseError
+            If the number of planes specified in the file is not a positive
+            integer, or if the file contains truncated or malformed data.
         """
         filename = Path(filename)
         with open(filename, "r") as handle:
diff --git a/tests/test_stoch.py b/tests/test_stoch.py
index 42ca856..5dc1d97 100644
--- a/tests/test_stoch.py
+++ b/tests/test_stoch.py
@@ -327,6 +327,21 @@ def test_stoch_file_truncated_raises_instead_of_hanging(truncated_stoch_file: Pa
     assert "Unexpected end of file" in queue.get()
 
 
+def test_stoch_file_truncated_array_raises_parse_error(tmp_path: Path):
+    """A stoch file truncated inside a plane's arrays should raise ParseError
+    naming the array, rather than a bare reshape ValueError."""
+    stoch_filepath = tmp_path / "truncated_array_stoch_file"
+    stoch_filepath.write_text(
+        "1\n"
+        "174.5 -41.3 2 2 1.0 1.0 45 60 90 0.5 2.5 1.5\n"
+        "1.0 2.0 3.0 4.0\n"
+        "0.1 0.2 0.3 0.4\n"
+        "0.01 0.02 0.03\n"
+    )
+    with pytest.raises(parse_utils.ParseError, match="Expected 4 values for trup"):
+        StochFile.from_file(stoch_filepath)
+
+
 def dump_and_reload(stoch_file: StochFile, tmp_path: Path) -> StochFile:
     """Dump a StochFile and read the result back in."""
     dumped = tmp_path / "dumped.stoch"