ENH: Ensure lib._format_impl.read_array handles file reading errors. (numpy#28330)

* BUG:  Ensure ``lib._format_impl.read_array`` handles file reading errors.

* ENH: improve error messages in``lib._format_impl.read_array``

* TST: add tests for file read failures in ``read_array``

* ENH: improve the phrasing of the error message in ``lib._format_impl.read_array``

* TST: fix some issues in ``test_file_truncated``

* Update numpy/lib/tests/test_format.py

---------

Co-authored-by: Sebastian Berg <[email protected]>

Author: WAAutoMaton

numpy/lib/_format_impl.py

@@ -872,6 +872,14 @@ def read_array(fp, allow_pickle=False, pickle_kwargs=None, *,
                     data = _read_bytes(fp, read_size, "array data")
                     array[i:i + read_count] = numpy.frombuffer(data, dtype=dtype,
                                                              count=read_count)
+        
+        if array.size != count:
+            raise ValueError(
+                "Failed to read all data for array. "
+                f"Expected {shape} = {count} elements, "
+                f"could only read {array.size} elements. "
+                "(file seems not fully written?)"
+            )
 
         if fortran_order:
             array.shape = shape[::-1]

numpy/lib/tests/test_format.py

@@ -428,7 +428,6 @@ def roundtrip_truncated(arr):
     arr2 = format.read_array(f2)
     return arr2
 
-
 def assert_equal_(o1, o2):
     assert_(o1 == o2)
 
@@ -451,6 +450,30 @@ def test_roundtrip_truncated():
         if arr.dtype != object:
             assert_raises(ValueError, roundtrip_truncated, arr)
 
+def test_file_truncated(tmp_path):
+    path = tmp_path / "a.npy"
+    for arr in basic_arrays:
+        if arr.dtype != object:
+            with open(path, 'wb') as f:
+                format.write_array(f, arr)
+            #truncate the file by one byte
+            with open(path, 'rb+') as f:
+                f.seek(-1, os.SEEK_END)
+                f.truncate()
+            with open(path, 'rb') as f:
+                with pytest.raises(
+                    ValueError, 
+                    match = (
+                        r"EOF: reading array header, "
+                        r"expected (\d+) bytes got (\d+)"
+                    ) if arr.size == 0 else (
+                        r"Failed to read all data for array\. "
+                        r"Expected \(.*?\) = (\d+) elements, "
+                        r"could only read (\d+) elements\. "
+                        r"\(file seems not fully written\?\)"
+                    )
+                ):
+                    _ = format.read_array(f)
 
 def test_long_str():
     # check items larger than internal buffer size, gh-4027