[fix] calculator: call python using subprocess.Popen

call Python directly with -S and -I parameters to skip loading
of the standard library and the SearXNG module.

The actual calculator is moved to a standalone script: calculator_process.py

searx/plugins/calculator/__init__.py

@@ -0,0 +1,107 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
+"""Calculate mathematical expressions using ack#eval
+"""
+
+import re
+import sys
+import subprocess
+from pathlib import Path
+
+import flask
+import babel
+from flask_babel import gettext
+
+from searx.plugins import logger
+
+name = "Basic Calculator"
+description = gettext("Calculate mathematical expressions via the search bar")
+default_on = True
+
+preference_section = 'general'
+plugin_id = 'calculator'
+
+logger = logger.getChild(plugin_id)
+
+
+def call_calculator(query_py_formatted, timeout):
+    calculator_process_py_path = Path(__file__).parent.absolute() / "calculator_process.py"
+    # see https://docs.python.org/3/using/cmdline.html
+    # -S Disable the import of the module site and the site-dependent manipulations
+    #    of sys.path that it entails. Also disable these manipulations if site is
+    #    explicitly imported later (call site.main() if you want them to be triggered).
+    # -I Run Python in isolated mode. This also implies -E, -P and -s options.
+    # -E Ignore all PYTHON* environment variables, e.g. PYTHONPATH and PYTHONHOME, that might be set.
+    # -P Don’t prepend a potentially unsafe path to sys.path
+    # -s Don’t add the user site-packages directory to sys.path.
+    process = subprocess.Popen(  # pylint: disable=R1732
+        [sys.executable, "-S", "-I", calculator_process_py_path, query_py_formatted],
+        stdout=subprocess.PIPE,
+        stderr=subprocess.PIPE,
+        text=True,
+    )
+    try:
+        stdout, stderr = process.communicate(timeout=timeout)
+        if process.returncode == 0 and not stderr:
+            return stdout
+        logger.debug("calculator exited with stderr %s", stderr)
+        return None
+    except subprocess.TimeoutExpired:
+        process.terminate()
+        try:
+            # Give the process a grace period to terminate
+            process.communicate(timeout=2)
+        except subprocess.TimeoutExpired:
+            # Forcefully kill the process
+            process.kill()
+            process.communicate()
+        logger.debug("calculator terminated after timeout")
+        # Capture any remaining output
+        return None
+    finally:
+        # Ensure the process is fully cleaned up
+        if process.poll() is None:  # If still running
+            process.kill()
+            process.communicate()
+
+
+def post_search(_request, search):
+
+    # only show the result of the expression on the first page
+    if search.search_query.pageno > 1:
+        return True
+
+    query = search.search_query.query
+    # in order to avoid DoS attacks with long expressions, ignore long expressions
+    if len(query) > 100:
+        return True
+
+    # replace commonly used math operators with their proper Python operator
+    query = query.replace("x", "*").replace(":", "/")
+
+    # use UI language
+    ui_locale = babel.Locale.parse(flask.request.preferences.get_value('locale'), sep='-')
+
+    # parse the number system in a localized way
+    def _decimal(match: re.Match) -> str:
+        val = match.string[match.start() : match.end()]
+        val = babel.numbers.parse_decimal(val, ui_locale, numbering_system="latn")
+        return str(val)
+
+    decimal = ui_locale.number_symbols["latn"]["decimal"]
+    group = ui_locale.number_symbols["latn"]["group"]
+    query = re.sub(f"[0-9]+[{decimal}|{group}][0-9]+[{decimal}|{group}]?[0-9]?", _decimal, query)
+
+    # only numbers and math operators are accepted
+    if any(str.isalpha(c) for c in query):
+        return True
+
+    # in python, powers are calculated via **
+    query_py_formatted = query.replace("^", "**")
+
+    # Prevent the runtime from being longer than 50 ms
+    result = call_calculator(query_py_formatted, 0.05)
+    if result is None or result == "":
+        return True
+    result = babel.numbers.format_decimal(result, locale=ui_locale)
+    search.result_container.answers['calculate'] = {'answer': f"{search.search_query.query} = {result}"}
+    return True

searx/plugins/calculator/calculator_process.py

@@ -0,0 +1,58 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
+"""Standalone script to actually calculate mathematical expressions using ast
+
+This is not a module, the SearXNG modules are not available here
+"""
+
+import ast
+import sys
+import operator
+from typing import Callable
+
+
+operators: dict[type, Callable] = {
+    ast.Add: operator.add,
+    ast.Sub: operator.sub,
+    ast.Mult: operator.mul,
+    ast.Div: operator.truediv,
+    ast.Pow: operator.pow,
+    ast.BitXor: operator.xor,
+    ast.USub: operator.neg,
+}
+
+
+def _eval_expr(expr):
+    """
+    >>> _eval_expr('2^6')
+    4
+    >>> _eval_expr('2**6')
+    64
+    >>> _eval_expr('1 + 2*3**(4^5) / (6 + -7)')
+    -5.0
+    """
+    try:
+        return _eval(ast.parse(expr, mode='eval').body)
+    except ZeroDivisionError:
+        # This is undefined
+        return ""
+
+
+def _eval(node):
+    if isinstance(node, ast.Constant) and isinstance(node.value, (int, float)):
+        return node.value
+
+    if isinstance(node, ast.BinOp):
+        return operators[type(node.op)](_eval(node.left), _eval(node.right))
+
+    if isinstance(node, ast.UnaryOp):
+        return operators[type(node.op)](_eval(node.operand))
+
+    raise TypeError(node)
+
+
+def main():
+    print(_eval_expr(sys.argv[1]), end="")
+
+
+if __name__ == "__main__":
+    main()