[enh] add PostgreSQL engine

Slightly modified merge of [22079ff] from searx.

[22079ff] https://github.com/searx/searx/commit/22079ffdefb07cf69486a232e823797e737014e9

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

searx/engines/postgresql.py

@@ -0,0 +1,69 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
+# lint: pylint
+# pylint: disable=missing-function-docstring
+"""PostgreSQL database (offline)
+
+"""
+
+# import error is ignored because the admin has to install mysql manually to use
+# the engine
+import psycopg2  # pylint: disable=import-error
+
+engine_type = 'offline'
+host = "127.0.0.1"
+port = "5432"
+database = ""
+username = ""
+password = ""
+query_str = ""
+limit = 10
+paging = True
+result_template = 'key-value.html'
+_connection = None
+
+def init(engine_settings):
+    global _connection  # pylint: disable=global-statement
+
+    if 'query_str' not in engine_settings:
+        raise ValueError('query_str cannot be empty')
+
+    if not engine_settings['query_str'].lower().startswith('select '):
+        raise ValueError('only SELECT query is supported')
+
+    _connection = psycopg2.connect(
+        database = database,
+        user = username,
+        password = password,
+        host = host,
+        port = port,
+    )
+
+def search(query, params):
+    query_params = {'query': query}
+    query_to_run = (
+        query_str
+        + ' LIMIT {0} OFFSET {1}'.format(limit, (params['pageno'] - 1) * limit)
+    )
+
+    with _connection:
+        with _connection.cursor() as cur:
+            cur.execute(query_to_run, query_params)
+            return _fetch_results(cur)
+
+def _fetch_results(cur):
+    results = []
+    titles = []
+
+    try:
+        titles = [column_desc.name for column_desc in cur.description]
+
+        for res in cur:
+            result = dict(zip(titles, map(str, res)))
+            result['template'] = result_template
+            results.append(result)
+
+    # no results to fetch
+    except psycopg2.ProgrammingError:
+        pass
+
+    return results

searx/settings.yml

@@ -854,6 +854,16 @@ engines:
     url: https://thepiratebay.org/
     timeout : 3.0
 
+# Required dependency: psychopg2
+#  - name : postgresql
+#    engine : postgresql
+#    database : postgres
+#    username : postgres
+#    password : postgres
+#    limit : 10
+#    query_str : 'SELECT * from my_table WHERE my_column = %(query)s'
+#    shortcut : psql
+
   - name : pubmed
     engine : pubmed
     shortcut : pub