For Leptonica 1.79+ use leptSetStderrHandler

Lock free and considerably less dangerous to stderr messages.

src/ocrmypdf/leptonica.py

@@ -24,7 +24,9 @@ import argparse
 import logging
 import os
 import sys
+import threading
 import warnings
+from collections import deque
 from collections.abc import Sequence
 from contextlib import suppress
 from ctypes.util import find_library
@@ -75,7 +77,7 @@ except ffi.error as e:
     ) from e
 
 
-class _LeptonicaErrorTrap:
+class _LeptonicaErrorTrap_Redirect:
     """
     Context manager to trap errors reported by Leptonica.
 
@@ -155,6 +157,62 @@ class _LeptonicaErrorTrap:
         return False
 
 
+tls = threading.local()
+tls.trap = None
+
+
+@ffi.callback("void(char *)")
+def _stderr_handler(cstr):
+    msg = ffi.string(cstr).decode(errors='replace')
+    if msg.startswith("Error"):
+        logger.error(msg)
+    elif msg.startswith("Warning"):
+        logger.warning(msg)
+    else:
+        logger.debug(msg)
+    if tls.trap is not None:
+        tls.trap.append(msg)
+    return
+
+
+class _LeptonicaErrorTrap_Queue:
+    def __init__(self):
+        self.queue = deque()
+
+    def __enter__(self):
+        self.queue.clear()
+        tls.trap = self.queue
+
+    def __exit__(self, exc_type, exc_value, traceback):
+        tls.trap = None
+        output = ''.join(self.queue)
+        self.queue.clear()
+
+        # If there are Python errors, record them
+        if exc_type:
+            logger.warning(output)
+
+        if 'Error' in output:
+            if 'image file not found' in output:
+                raise FileNotFoundError()
+            if 'pixWrite: stream not opened' in output:
+                raise LeptonicaIOError()
+            if 'index not valid' in output:
+                raise IndexError()
+            raise LeptonicaError(output)
+        return False
+
+
+try:
+    lept.leptSetStderrHandler(_stderr_handler)
+except ffi.error:
+    # Pre-1.79 Leptonica does not have leptSetStderrHandler
+    _LeptonicaErrorTrap = _LeptonicaErrorTrap_Redirect
+else:
+    # 1.79 have this new symbol
+    _LeptonicaErrorTrap = _LeptonicaErrorTrap_Queue
+
+
 class LeptonicaError(Exception):
     pass
 

src/ocrmypdf/lib/compile_leptonica.py

@@ -509,6 +509,8 @@ void selDestroy ( SEL **psel );
 l_int32
 setMsgSeverity(l_int32 newsev);
 
+void
+leptSetStderrHandler(void (*handler)(const char *));
 """
 )
 

tests/test_lept.py

@@ -16,27 +16,25 @@
 # along with OCRmyPDF.  If not, see <http://www.gnu.org/licenses/>.
 
 
-import os
 from os import fspath
 from pickle import dumps, loads
-from unittest.mock import patch
 
 import pytest
 from PIL import Image, ImageChops
 
-import ocrmypdf.leptonica as lept
+from ocrmypdf import leptonica as lp
 
 
 def test_colormap_backgroundnorm(resources):
     # Issue #262 - unclear how to reproduce exactly, so just ensure leptonica
     # can handle that case
-    pix = lept.Pix.open(resources / 'baiona_colormapped.png')
+    pix = lp.Pix.open(resources / 'baiona_colormapped.png')
     pix.background_norm()
 
 
 @pytest.fixture
 def crom_pix(resources):
-    pix = lept.Pix.open(resources / 'crom.png')
+    pix = lp.Pix.open(resources / 'crom.png')
     im = Image.open(resources / 'crom.png')
     yield pix, im
     im.close()
@@ -64,17 +62,17 @@ def test_pix_otsu(crom_pix):
 
 
 @pytest.mark.skipif(
-    lept.get_leptonica_version() < 'leptonica-1.76',
+    lp.get_leptonica_version() < 'leptonica-1.76',
     reason="needs new leptonica for API change",
 )
 def test_crop(resources):
-    pix = lept.Pix.open(resources / 'linn.png')
+    pix = lp.Pix.open(resources / 'linn.png')
     foreground = pix.crop_to_foreground()
     assert foreground.width < pix.width
 
 
 def test_clean_bg(resources):
-    pix = lept.Pix.open(resources / 'congress.jpg')
+    pix = lp.Pix.open(resources / 'congress.jpg')
     imbg = pix.clean_background_to_white()
 
 
@@ -96,4 +94,12 @@ def test_leptonica_compile(tmp_path):
 
 def test_file_not_found():
     with pytest.raises(FileNotFoundError):
-        lept.Pix.open("does_not_exist1")
+        lp.Pix.open("does_not_exist1")
+
+
+def test_error_trap():
+    with pytest.raises(lp.LeptonicaError, match=r"Error in pixReadMem"):
+        with lp._LeptonicaErrorTrap():
+            lp.Pix(lp.lept.pixReadMem(lp.ffi.NULL, 0))
+        with lp._LeptonicaErrorTrap_Redirect():
+            lp.Pix(lp.lept.pixReadMem(lp.ffi.NULL, 0))