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+++ b/examples/trac/trac/db/api.py
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+# -*- coding: utf-8 -*-
+#
+# Copyright (C) 2005 Edgewall Software
+# Copyright (C) 2005 Christopher Lenz <cmlenz@gmx.de>
+# All rights reserved.
+#
+# This software is licensed as described in the file COPYING, which
+# you should have received as part of this distribution. The terms
+# are also available at http://trac.edgewall.com/license.html.
+#
+# This software consists of voluntary contributions made by many
+# individuals. For the exact contribution history, see the revision
+# history and logs, available at http://projects.edgewall.com/trac/.
+#
+# Author: Christopher Lenz <cmlenz@gmx.de>
+
+import os
+import urllib
+
+from trac.config import Option
+from trac.core import *
+from trac.db.pool import ConnectionPool
+
+
+def get_column_names(cursor):
+    return cursor.description and \
+           [(isinstance(d[0], str) and [unicode(d[0], 'utf-8')] or [d[0]])[0]
+            for d in cursor.description] or []
+
+
+class IDatabaseConnector(Interface):
+    """Extension point interface for components that support the connection to
+    relational databases."""
+
+    def get_supported_schemes():
+        """Return the connection URL schemes supported by the connector, and
+        their relative priorities as an iterable of `(scheme, priority)` tuples.
+        """
+
+    def get_connection(**kwargs):
+        """Create a new connection to the database."""
+        
+    def init_db(**kwargs):
+        """Initialize the database."""
+
+    def to_sql(table):
+        """Return the DDL statements necessary to create the specified table,
+        including indices."""
+
+
+class DatabaseManager(Component):
+
+    connectors = ExtensionPoint(IDatabaseConnector)
+
+    connection_uri = Option('trac', 'database', 'sqlite:db/trac.db',
+        """Database connection
+        [wiki:TracEnvironment#DatabaseConnectionStrings string] for this
+        project""")
+
+    def __init__(self):
+        self._cnx_pool = None
+
+    def init_db(self):
+        connector, args = self._get_connector()
+        connector.init_db(**args)
+
+    def get_connection(self):
+        if not self._cnx_pool:
+            connector, args = self._get_connector()
+            self._cnx_pool = ConnectionPool(5, connector, **args)
+        return self._cnx_pool.get_cnx()
+
+    def shutdown(self):
+        if self._cnx_pool:
+            self._cnx_pool.shutdown()
+            self._cnx_pool = None
+
+    def _get_connector(self): ### FIXME: Make it public?
+        scheme, args = _parse_db_str(self.connection_uri)
+        candidates = {}
+        connector = None
+        for connector in self.connectors:
+            for scheme_, priority in connector.get_supported_schemes():
+                if scheme_ != scheme:
+                    continue
+                highest = candidates.get(scheme_, (None, 0))[1]
+                if priority > highest:
+                    candidates[scheme] = (connector, priority)
+            connector = candidates.get(scheme, [None])[0]
+        if not connector:
+            raise TracError, 'Unsupported database type "%s"' % scheme
+
+        if scheme == 'sqlite':
+            # Special case for SQLite to support a path relative to the
+            # environment directory
+            if args['path'] != ':memory:' and \
+                   not args['path'].startswith('/'):
+                args['path'] = os.path.join(self.env.path,
+                                            args['path'].lstrip('/'))
+
+        return connector, args
+
+
+def _parse_db_str(db_str):
+    scheme, rest = db_str.split(':', 1)
+
+    if not rest.startswith('/'):
+        if scheme == 'sqlite':
+            # Support for relative and in-memory SQLite connection strings
+            host = None
+            path = rest
+        else:
+            raise TracError, 'Database connection string %s must start with ' \
+                             'scheme:/' % db_str
+    else:
+        if rest.startswith('/') and not rest.startswith('//'):
+            host = None
+            rest = rest[1:]
+        elif rest.startswith('///'):
+            host = None
+            rest = rest[3:]
+        else:
+            rest = rest[2:]
+            if rest.find('/') == -1:
+                host = rest
+                rest = ''
+            else:
+                host, rest = rest.split('/', 1)
+        path = None
+
+    if host and host.find('@') != -1:
+        user, host = host.split('@', 1)
+        if user.find(':') != -1:
+            user, password = user.split(':', 1)
+        else:
+            password = None
+    else:
+        user = password = None
+    if host and host.find(':') != -1:
+        host, port = host.split(':')
+        port = int(port)
+    else:
+        port = None
+
+    if not path:
+        path = '/' + rest
+    if os.name == 'nt':
+        # Support local paths containing drive letters on Win32
+        if len(rest) > 1 and rest[1] == '|':
+            path = "%s:%s" % (rest[0], rest[2:])
+
+    params = {}
+    if path.find('?') != -1:
+        path, qs = path.split('?', 1)
+        qs = qs.split('&')
+        for param in qs:
+            name, value = param.split('=', 1)
+            value = urllib.unquote(value)
+            params[name] = value
+
+    args = zip(('user', 'password', 'host', 'port', 'path', 'params'),
+               (user, password, host, port, path, params))
+    return scheme, dict([(key, value) for key, value in args if value])