[feat] plugins: new calculator plugin

3 files changed, 90 insertions, 1 deletions

diff --git a/searx/plugins/calculator.py b/searx/plugins/calculator.py
new file mode 100644
index 000000000..cb5425e90
--- /dev/null
+++ b/searx/plugins/calculator.py
@@ -0,0 +1,88 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
+"""Calculate mathematical expressions using ack#eval
+"""
+
+import ast
+import operator
+
+from flask_babel import gettext
+from searx import settings
+
+name = "Basic Calculator"
+description = gettext("Calculate mathematical expressions via the search bar")
+default_on = False
+
+preference_section = 'general'
+plugin_id = 'calculator'
+
+operators = {
+    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
+    """
+    return _eval(ast.parse(expr, mode='eval').body)
+
+
+def _eval(node):
+    if isinstance(node, ast.Constant) and isinstance(node.value, int):
+        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 post_search(_request, search):
+    # don't run on public instances due to possible attack surfaces
+    if settings['server']['public_instance']:
+        return True
+
+    # 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(":", "/")
+
+    # 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("^", "**")
+    try:
+        result = str(_eval_expr(query_py_formatted))
+        if result != query:
+            search.result_container.answers['calculate'] = {'answer': f"{query} = {result}"}
+    except (TypeError, SyntaxError, ArithmeticError):
+        pass
+
+    return True
+
+
+def is_allowed():
+    return not settings['server']['public_instance']
diff --git a/searx/settings.yml b/searx/settings.yml
index f26c3904d..8f1df1801 100644
--- a/searx/settings.yml
+++ b/searx/settings.yml
@@ -220,6 +220,7 @@ outgoing:
 #   - 'Ahmia blacklist'  # activation depends on outgoing.using_tor_proxy
 #   # these plugins are disabled if nothing is configured ..
 #   - 'Hostname replace'  # see hostname_replace configuration below
+#   - 'Calculator plugin'
 #   - 'Open Access DOI rewrite'
 #   - 'Tor check plugin'
 #   # Read the docs before activate: auto-detection of the language could be
diff --git a/searx/templates/simple/preferences.html b/searx/templates/simple/preferences.html
index 9dab84fd1..0145dcd0f 100644
--- a/searx/templates/simple/preferences.html
+++ b/searx/templates/simple/preferences.html
@@ -38,7 +38,7 @@
 
 {%- macro plugin_preferences(section) -%}
 {%- for plugin in plugins -%}
-{%- if plugin.preference_section == section -%}
+{%- if plugin.preference_section == section and (plugin.is_allowed() if plugin.is_allowed else True) -%}
 <fieldset>{{- '' -}}
     <legend>{{ _(plugin.name) }}</legend>{{- '' -}}
     <div class="value">