gajim-plural/src/common/logger.py

## logger.py
##
## Copyright (C) 2005-2006 Nikos Kouremenos <kourem@gmail.com>
## Copyright (C) 2005-2006 Yann Leboulanger <asterix@lagaule.org>
##
## This file is part of Gajim.
##
## Gajim is free software; you can redistribute it and/or modify
## it under the terms of the GNU General Public License as published
## by the Free Software Foundation; version 3 only.
##
## Gajim is distributed in the hope that it will be useful,
## but WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
## GNU General Public License for more details.
##
## You should have received a copy of the GNU General Public License
## along with Gajim.  If not, see <http://www.gnu.org/licenses/>.
##

''' This module allows to access the on-disk database of logs. '''

import os
import sys
import time
import datetime
from gzip import GzipFile
from cStringIO import StringIO

import exceptions
import gajim

try:
	import sqlite3 as sqlite # python 2.5
except ImportError:
	try:
		from pysqlite2 import dbapi2 as sqlite
	except ImportError:
		raise exceptions.PysqliteNotAvailable

import configpaths
LOG_DB_PATH = configpaths.gajimpaths['LOG_DB']
LOG_DB_FOLDER, LOG_DB_FILE = os.path.split(LOG_DB_PATH)

class Constants:
	def __init__(self):
		(
			self.JID_NORMAL_TYPE,
			self.JID_ROOM_TYPE
		) = range(2)

		(
			self.KIND_STATUS,
			self.KIND_GCSTATUS,
			self.KIND_GC_MSG,
			self.KIND_SINGLE_MSG_RECV,
			self.KIND_CHAT_MSG_RECV,
			self.KIND_SINGLE_MSG_SENT,
			self.KIND_CHAT_MSG_SENT,
			self.KIND_ERROR
		) = range(8)

		(
			self.SHOW_ONLINE,
			self.SHOW_CHAT,
			self.SHOW_AWAY,
			self.SHOW_XA,
			self.SHOW_DND,
			self.SHOW_OFFLINE
		) = range(6)

		(
			self.TYPE_AIM,
			self.TYPE_GG,
			self.TYPE_HTTP_WS,
			self.TYPE_ICQ,
			self.TYPE_MSN,
			self.TYPE_QQ,
			self.TYPE_SMS,
			self.TYPE_SMTP,
			self.TYPE_TLEN,
			self.TYPE_YAHOO,
			self.TYPE_NEWMAIL,
			self.TYPE_RSS,
			self.TYPE_WEATHER,
		) = range(13)

constants = Constants()

class Logger:
	def __init__(self):
		self.jids_already_in = [] # holds jids that we already have in DB
		self.con = None

		if not os.path.exists(LOG_DB_PATH):
			# this can happen only the first time (the time we create the db)
			# db is not created here but in src/common/checks_paths.py
			return
		self.init_vars()

	def close_db(self):
		if self.con:
			self.con.close()
		self.con = None
		self.cur = None

	def open_db(self):
		self.close_db()

		# FIXME: sqlite3_open wants UTF8 strings. So a path with
		# non-ascii chars doesn't work. See #2812 and
		# http://lists.initd.org/pipermail/pysqlite/2005-August/000134.html
		back = os.getcwd()
		os.chdir(LOG_DB_FOLDER)

		# if locked, wait up to 20 sec to unlock
		# before raise (hopefully should be enough)

		self.con = sqlite.connect(LOG_DB_FILE, timeout = 20.0,
			isolation_level = 'IMMEDIATE')
		os.chdir(back)
		self.cur = self.con.cursor()
		self.set_synchronous(False)

	def set_synchronous(self, sync):
		try:
			if sync:
				self.cur.execute("PRAGMA synchronous = NORMAL")
			else:
				self.cur.execute("PRAGMA synchronous = OFF")
		except sqlite.Error, e:
			gajim.log.debug("Failed to set_synchronous(%s): %s" % (sync, str(e)))

	def init_vars(self):
		self.open_db()
		self.get_jids_already_in_db()

	def simple_commit(self, sql_to_commit):
		'''helper to commit'''
		self.cur.execute(sql_to_commit)
		try:
			self.con.commit()
		except sqlite.OperationalError, e:
			print >> sys.stderr, str(e)

	def get_jids_already_in_db(self):
		try:
			self.cur.execute('SELECT jid FROM jids')
			rows = self.cur.fetchall() # list of tupples: [(u'aaa@bbb',), (u'cc@dd',)]
		except sqlite.DatabaseError:
			raise exceptions.DatabaseMalformed
		self.jids_already_in = []
		for row in rows:
			# row[0] is first item of row (the only result here, the jid)
			if row[0] == '':
				# malformed jid, ignore line
				pass
			else:
				self.jids_already_in.append(row[0])

	def get_jids_in_db(self):
		return self.jids_already_in

	def jid_is_from_pm(self, jid):
		'''if jid is gajim@conf/nkour it's likely a pm one, how we know
		gajim@conf is not a normal guy and nkour is not his resource?
		we ask if gajim@conf is already in jids (with type room jid)
		this fails if user disables logging for room and only enables for
		pm (so higly unlikely) and if we fail we do not go chaos
		(user will see the first pm as if it was message in room's public chat)
		and after that all okay'''
		
		if jid.find('/') > -1: 
			possible_room_jid, possible_nick = jid.split('/', 1)
			return self.jid_is_room_jid(possible_room_jid)
		else:
			# it's not a full jid, so it's not a pm one
			return False

	def jid_is_room_jid(self, jid):
		self.cur.execute('SELECT jid_id FROM jids WHERE jid=?  AND type=?',
			(jid, constants.JID_ROOM_TYPE))
		row = self.cur.fetchone()
		if row is None:
			return False
		else:
			return True

	def get_jid_id(self, jid, typestr = None):
		'''jids table has jid and jid_id
		logs table has log_id, jid_id, contact_name, time, kind, show, message
		so to ask logs we need jid_id that matches our jid in jids table
		this method wants jid and returns the jid_id for later sql-ing on logs
		typestr can be 'ROOM' or anything else depending on the type of JID
		and is only needed to be specified when the JID is new in DB
		'''
		if jid.find('/') != -1: # if it has a /
			jid_is_from_pm = self.jid_is_from_pm(jid)
			if not jid_is_from_pm: # it's normal jid with resource
				jid = jid.split('/', 1)[0] # remove the resource
		if jid in self.jids_already_in: # we already have jids in DB
			self.cur.execute('SELECT jid_id FROM jids WHERE jid=?', [jid])
			row = self.cur.fetchone()
			if row:
				return row[0]
		# oh! a new jid :), we add it now
		if typestr == 'ROOM':
			typ = constants.JID_ROOM_TYPE
		else:
			typ = constants.JID_NORMAL_TYPE
		try:
			self.cur.execute('INSERT INTO jids (jid, type) VALUES (?, ?)', (jid,
				typ))
		except sqlite.IntegrityError, e:
			# Jid already in DB, maybe added by another instance. re-read DB
			self.get_jids_already_in_db()
			return self.get_jid_id(jid, typestr)
		try:
			self.con.commit()
		except sqlite.OperationalError, e:
			print >> sys.stderr, str(e)
		jid_id = self.cur.lastrowid
		self.jids_already_in.append(jid)
		return jid_id

	def convert_human_values_to_db_api_values(self, kind, show):
		'''coverts from string style to constant ints for db'''
		if kind == 'status':
			kind_col = constants.KIND_STATUS
		elif kind == 'gcstatus':
			kind_col = constants.KIND_GCSTATUS
		elif kind == 'gc_msg':
			kind_col = constants.KIND_GC_MSG
		elif kind == 'single_msg_recv':
			kind_col = constants.KIND_SINGLE_MSG_RECV
		elif kind == 'single_msg_sent':
			kind_col = constants.KIND_SINGLE_MSG_SENT
		elif kind == 'chat_msg_recv':
			kind_col = constants.KIND_CHAT_MSG_RECV
		elif kind == 'chat_msg_sent':
			kind_col = constants.KIND_CHAT_MSG_SENT
		elif kind == 'error':
			kind_col = constants.KIND_ERROR

		if show == 'online':
			show_col = constants.SHOW_ONLINE
		elif show == 'chat':
			show_col = constants.SHOW_CHAT
		elif show == 'away':
			show_col = constants.SHOW_AWAY
		elif show == 'xa':
			show_col = constants.SHOW_XA
		elif show == 'dnd':
			show_col = constants.SHOW_DND
		elif show == 'offline':
			show_col = constants.SHOW_OFFLINE
		elif show is None:
			show_col = None
		else: # invisible in GC when someone goes invisible
			# it's a RFC violation .... but we should not crash
			show_col = 'UNKNOWN'

		return kind_col, show_col

	def convert_human_transport_type_to_db_api_values(self, type_):
		'''converts from string style to constant ints for db'''
		if type_ == 'aim':
			return constants.TYPE_AIM
		if type_ == 'gadu-gadu':
			return constants.TYPE_GG
		if type_ == 'http-ws':
			return constants.TYPE_HTTP_WS
		if type_ == 'icq':
			return constants.TYPE_ICQ
		if type_ == 'msn':
			return constants.TYPE_MSN
		if type_ == 'qq':
			return constants.TYPE_QQ
		if type_ == 'sms':
			return constants.TYPE_SMS
		if type_ == 'smtp':
			return constants.TYPE_SMTP
		if type_ in ('tlen', 'x-tlen'):
			return constants.TYPE_TLEN
		if type_ == 'yahoo':
			return constants.TYPE_YAHOO
		if type_ == 'newmail':
			return constants.TYPE_NEWMAIL
		if type_ == 'rss':
			return constants.TYPE_RSS
		if type_ == 'weather':
			return constants.TYPE_WEATHER
		return None

	def convert_api_values_to_human_transport_type(self, type_id):
		'''converts from constant ints for db to string style'''
		if type_id == constants.TYPE_AIM:
			return 'aim'
		if type_id == constants.TYPE_GG:
			return 'gadu-gadu'
		if type_id == constants.TYPE_HTTP_WS:
			return 'http-ws'
		if type_id == constants.TYPE_ICQ:
			return 'icq'
		if type_id == constants.TYPE_MSN:
			return 'msn'
		if type_id == constants.TYPE_QQ:
			return 'qq'
		if type_id == constants.TYPE_SMS:
			return 'sms'
		if type_id == constants.TYPE_SMTP:
			return 'smtp'
		if type_id == constants.TYPE_TLEN:
			return 'tlen'
		if type_id == constants.TYPE_YAHOO:
			return 'yahoo'
		if type_id == constants.TYPE_NEWMAIL:
			return 'newmail'
		if type_id == constants.TYPE_RSS:
			return 'rss'
		if type_id == constants.TYPE_WEATHER:
			return 'weather'

	def commit_to_db(self, values, write_unread = False):
		sql = 'INSERT INTO logs (jid_id, contact_name, time, kind, show, message, subject) VALUES (?, ?, ?, ?, ?, ?, ?)'
		try:
			self.cur.execute(sql, values)
		except sqlite.DatabaseError:
			raise exceptions.DatabaseMalformed 
		except sqlite.OperationalError, e:
			raise exceptions.PysqliteOperationalError(str(e))
		message_id = None
		try:
			self.con.commit()
			if write_unread:
				message_id = self.cur.lastrowid
		except sqlite.OperationalError, e:
			print >> sys.stderr, str(e)
		if message_id:
			self.insert_unread_events(message_id, values[0])
		return message_id

	def insert_unread_events(self, message_id, jid_id):
		''' add unread message with id: message_id'''
		sql = 'INSERT INTO unread_messages VALUES (%d, %d)' % (message_id, jid_id)
		self.simple_commit(sql)

	def set_read_messages(self, message_ids):
		''' mark all messages with ids in message_ids as read'''
		ids = ','.join([str(i) for i in message_ids])
		sql = 'DELETE FROM unread_messages WHERE message_id IN (%s)' % ids
		self.simple_commit(sql)

	def get_unread_msgs(self):
		''' get all unread messages '''
		all_messages = []
		try:
			self.cur.execute(
				'SELECT message_id from unread_messages')
			results = self.cur.fetchall()
		except:
			pass
		for message in results:
			msg_id = message[0]
			# here we get infos for that message, and related jid from jids table
			# do NOT change order of SELECTed things, unless you change function(s) 
			# that called this function
			self.cur.execute('''
				SELECT logs.log_line_id, logs.message, logs.time, logs.subject,
				jids.jid
				FROM logs, jids
				WHERE logs.log_line_id = %d AND logs.jid_id = jids.jid_id
				''' % msg_id
				)
			results = self.cur.fetchall()
			if len(results) == 0:
				# Log line is no more in logs table. remove it from unread_messages
				self.set_read_messages([msg_id])
				continue
			all_messages.append(results[0])
		return all_messages

	def write(self, kind, jid, message = None, show = None, tim = None,
	subject = None):
		'''write a row (status, gcstatus, message etc) to logs database
		kind can be status, gcstatus, gc_msg, (we only recv for those 3),
		single_msg_recv, chat_msg_recv, chat_msg_sent, single_msg_sent
		we cannot know if it is pm or normal chat message, we try to guess
		see jid_is_from_pm()

		we analyze jid and store it as follows:
		jids.jid text column will hold JID if TC-related, room_jid if GC-related,
		ROOM_JID/nick if pm-related.'''

		if self.jids_already_in == []: # only happens if we just created the db
			self.open_db()

		contact_name_col = None # holds nickname for kinds gcstatus, gc_msg
		# message holds the message unless kind is status or gcstatus,
		# then it holds status message
		message_col = message
		subject_col = subject
		if tim:
			time_col = int(float(time.mktime(tim)))
		else:
			time_col = int(float(time.time()))

		kind_col, show_col = self.convert_human_values_to_db_api_values(kind,
			show)

		write_unread = False

		# now we may have need to do extra care for some values in columns
		if kind == 'status': # we store (not None) time, jid, show, msg
			# status for roster items
			jid_id = self.get_jid_id(jid)
			if show is None: # show is None (xmpp), but we say that 'online'
				show_col = constants.SHOW_ONLINE

		elif kind == 'gcstatus':
			# status in ROOM (for pm status see status)
			if show is None: # show is None (xmpp), but we say that 'online'
				show_col = constants.SHOW_ONLINE
			jid, nick = jid.split('/', 1)
			jid_id = self.get_jid_id(jid, 'ROOM') # re-get jid_id for the new jid
			contact_name_col = nick

		elif kind == 'gc_msg':
			if jid.find('/') != -1: # if it has a /
				jid, nick = jid.split('/', 1)
			else:
				# it's server message f.e. error message
				# when user tries to ban someone but he's not allowed to
				nick = None
			jid_id = self.get_jid_id(jid, 'ROOM') # re-get jid_id for the new jid
			contact_name_col = nick
		else:
			jid_id = self.get_jid_id(jid)
			if kind == 'chat_msg_recv':
				if not self.jid_is_from_pm(jid):
					# Save in unread table only if it's not a pm
					write_unread = True

		if show_col == 'UNKNOWN': # unknown show, do not log
			return

		values = (jid_id, contact_name_col, time_col, kind_col, show_col,
			message_col, subject_col)
		return self.commit_to_db(values, write_unread)

	def get_last_conversation_lines(self, jid, restore_how_many_rows,
		pending_how_many, timeout, account):
		'''accepts how many rows to restore and when to time them out (in minutes)
		(mark them as too old) and number of messages that are in queue
		and are already logged but pending to be viewed,
		returns a list of tupples containg time, kind, message,
		list with empty tupple if nothing found to meet our demands'''
		jid_id = self.get_jid_id(jid)
		where_sql = self._build_contact_where(account, jid)

		now = int(float(time.time()))
		timed_out = now - (timeout * 60) # before that they are too old
		# so if we ask last 5 lines and we have 2 pending we get
		# 3 - 8 (we avoid the last 2 lines but we still return 5 asked)
		try:
			self.cur.execute('''
				SELECT time, kind, message FROM logs
				WHERE (%s) AND kind IN (%d, %d, %d, %d, %d) AND time > %d
				ORDER BY time DESC LIMIT %d OFFSET %d
				''' % (where_sql, constants.KIND_SINGLE_MSG_RECV,
					constants.KIND_CHAT_MSG_RECV, constants.KIND_SINGLE_MSG_SENT,
					constants.KIND_CHAT_MSG_SENT, constants.KIND_ERROR,
					timed_out, restore_how_many_rows, pending_how_many)
				)

			results = self.cur.fetchall()
		except sqlite.DatabaseError:
			raise exceptions.DatabaseMalformed
		results.reverse()
		return results

	def get_unix_time_from_date(self, year, month, day):
		# year (fe 2005), month (fe 11), day (fe 25)
		# returns time in seconds for the second that starts that date since epoch
		# gimme unixtime from year month day:
		d = datetime.date(year, month, day)
		local_time = d.timetuple() # time tupple (compat with time.localtime())
		# we have time since epoch baby :)
		start_of_day = int(time.mktime(local_time))
		return start_of_day

	def get_conversation_for_date(self, jid, year, month, day, account):
		'''returns contact_name, time, kind, show, message
		for each row in a list of tupples,
		returns list with empty tupple if we found nothing to meet our demands'''
		jid_id = self.get_jid_id(jid)
		where_sql = self._build_contact_where(account, jid)

		start_of_day = self.get_unix_time_from_date(year, month, day)
		seconds_in_a_day = 86400 # 60 * 60 * 24
		last_second_of_day = start_of_day + seconds_in_a_day - 1

		self.cur.execute('''
			SELECT contact_name, time, kind, show, message FROM logs
			WHERE (%s)
			AND time BETWEEN %d AND %d
			ORDER BY time
			''' % (where_sql, start_of_day, last_second_of_day))

		results = self.cur.fetchall()
		return results

	def get_search_results_for_query(self, jid, query, account):
		'''returns contact_name, time, kind, show, message
		for each row in a list of tupples,
		returns list with empty tupple if we found nothing to meet our demands'''
		jid_id = self.get_jid_id(jid)

		if False: #query.startswith('SELECT '): # it's SQL query (FIXME)
			try:
				self.cur.execute(query)
			except sqlite.OperationalError, e:
				results = [('', '', '', '', str(e))]
				return results

		else: # user just typed something, we search in message column
			where_sql = self._build_contact_where(account, jid)
			like_sql = '%' + query.replace("'", "''") + '%'
			self.cur.execute('''
				SELECT contact_name, time, kind, show, message, subject FROM logs
				WHERE (%s) AND message LIKE '%s'
				ORDER BY time
				''' % (where_sql, like_sql))

		results = self.cur.fetchall()
		return results

	def get_days_with_logs(self, jid, year, month, max_day, account):
		'''returns the list of days that have logs (not status messages)'''
		jid_id = self.get_jid_id(jid)
		days_with_logs = []
		where_sql = self._build_contact_where(account, jid)

		# First select all date of month whith logs we want
		start_of_month = self.get_unix_time_from_date(year, month, 1)
		seconds_in_a_day = 86400 # 60 * 60 * 24
		last_second_of_month = start_of_month + (seconds_in_a_day * max_day) - 1

		self.cur.execute('''
			SELECT time FROM logs
			WHERE (%s)
			AND time BETWEEN %d AND %d
			AND kind NOT IN (%d, %d)
			ORDER BY time
			''' % (where_sql, start_of_month, last_second_of_month,
			constants.KIND_STATUS, constants.KIND_GCSTATUS))
		result = self.cur.fetchall()

		# Copy all interesting times in a temporary table
		self.cur.execute('CREATE TEMPORARY TABLE temp_table(time,INTEGER)')
		for line in result:
			self.cur.execute('''
				INSERT INTO temp_table (time) VALUES (%d)
				''' % (line[0]))

		# then search in this small temp table for each day
		for day in xrange(1, max_day + 1):  # count from 1 to 28 or to 30 or to 31
			start_of_day = self.get_unix_time_from_date(year, month, day)
			last_second_of_day = start_of_day + seconds_in_a_day - 1

			# just ask one row to see if we have sth for this date
			self.cur.execute('''
				SELECT time FROM temp_table
				WHERE time BETWEEN %d AND %d
				LIMIT 1
				''' % (start_of_day, last_second_of_day))
			result = self.cur.fetchone()
			if result:
				days_with_logs[0:0]=[day]

		# Delete temporary table
		self.cur.execute('DROP TABLE temp_table')
		result = self.cur.fetchone()
		return days_with_logs

	def get_last_date_that_has_logs(self, jid, account = None, is_room = False):
		'''returns last time (in seconds since EPOCH) for which
		we had logs (excluding statuses)'''
		where_sql = ''
		if not is_room:
			where_sql = self._build_contact_where(account, jid)
		else:
			jid_id = self.get_jid_id(jid, 'ROOM')
			where_sql = 'jid_id = %s' % jid_id
		self.cur.execute('''
			SELECT MAX(time) FROM logs
			WHERE (%s)
			AND kind NOT IN (%d, %d)
			''' % (where_sql, constants.KIND_STATUS, constants.KIND_GCSTATUS))

		results = self.cur.fetchone()
		if results is not None:
			result = results[0]
		else:
			result = None
		return result

	def get_room_last_message_time(self, jid):
		'''returns FASTLY last time (in seconds since EPOCH) for which
		we had logs for that room from rooms_last_message_time table'''
		jid_id = self.get_jid_id(jid, 'ROOM')
		where_sql = 'jid_id = %s' % jid_id
		self.cur.execute('''
			SELECT time FROM rooms_last_message_time
			WHERE (%s)
			''' % (where_sql))

		results = self.cur.fetchone()
		if results is not None:
			result = results[0]
		else:
			result = None
		return result

	def set_room_last_message_time(self, jid, time):
		'''set last time (in seconds since EPOCH) for which
		we had logs for that room in rooms_last_message_time table'''
		jid_id = self.get_jid_id(jid, 'ROOM')
		# jid_id is unique in this table, create or update :
		sql = 'REPLACE INTO rooms_last_message_time VALUES (%d, %d)' % \
			(jid_id, time)
		self.simple_commit(sql)

	def _build_contact_where(self, account, jid):
		'''build the where clause for a jid, including metacontacts
		jid(s) if any'''
		where_sql = ''
		# will return empty list if jid is not associated with
		# any metacontacts
		family = gajim.contacts.get_metacontacts_family(account, jid)
		if family:
			for user in family:
				jid_id = self.get_jid_id(user['jid'])
				where_sql += 'jid_id = %s' % jid_id
				if user != family[-1]:
					where_sql += ' OR '
		else: # if jid was not associated with metacontacts
			jid_id = self.get_jid_id(jid)
			where_sql = 'jid_id = %s' % jid_id
		return where_sql

	def save_transport_type(self, jid, type_):
		'''save the type of the transport in DB'''
		type_id = self.convert_human_transport_type_to_db_api_values(type_)
		if not type_id:
			# unknown type
			return
		self.cur.execute(
			'SELECT type from transports_cache WHERE transport = "%s"' % jid)
		results = self.cur.fetchall()
		if results:
			result = results[0][0]
			if result == type_id:
				return
			sql = 'UPDATE transports_cache SET type = %d WHERE transport = "%s"' %\
				(type_id, jid)
			self.simple_commit(sql)
			return
		sql = 'INSERT INTO transports_cache VALUES ("%s", %d)' % (jid, type_id)
		self.simple_commit(sql)

	def get_transports_type(self):
		'''return all the type of the transports in DB'''
		self.cur.execute(
			'SELECT * from transports_cache')
		results = self.cur.fetchall()
		if not results:
			return {}
		answer = {}
		for result in results:
			answer[result[0]] = self.convert_api_values_to_human_transport_type(
				result[1])
		return answer

	# A longer note here:
	# The database contains a blob field. Pysqlite seems to need special care for such fields.
	# When storing, we need to convert string into buffer object (1).
	# When retrieving, we need to convert it back to a string to decompress it. (2)
	# GzipFile needs a file-like object, StringIO emulates file for plain strings.
	def iter_caps_data(self):
		''' Iterate over caps cache data stored in the database.
		The iterator values are pairs of (node, ver, ext, identities, features):
		identities == {'category':'foo', 'type':'bar', 'name':'boo'},
		features being a list of feature namespaces. '''

		# get data from table
		# the data field contains binary object (gzipped data), this is a hack
		# to get that data without trying to convert it to unicode
		#tmp, self.con.text_factory = self.con.text_factory, str
		try:
			self.cur.execute('''SELECT node, ver, ext, data FROM caps_cache;''');
		except sqlite.OperationalError:
			# might happen when there's no caps_cache table yet
			# -- there's no data to read anyway then
			#self.con.text_factory = tmp
			return
		#self.con.text_factory = tmp

		for node, ver, ext, data in self.cur:
			# for each row: unpack the data field
			# (format: (category, type, name, category, type, name, ...
			#   ..., 'FEAT', feature1, feature2, ...).join(' '))
			# NOTE: if there's a need to do more gzip, put that to a function
			data=GzipFile(fileobj=StringIO(str(data))).read().split('\0')
			i=0
			identities=set()
			features=set()
			while i<(len(data)-2) and data[i]!='FEAT':
				category=data[i]
				type=data[i+1]
				name=data[i+2]
				identities.add((category,type,name))
				i+=3
			i+=1
			while i<len(data):
				features.add(data[i])
				i+=1
			if not ext: ext=None	# to make '' a None

			# yield the row
			yield node, ver, ext, identities, features

	def add_caps_entry(self, node, ver, ext, identities, features):
		data=[]
		for identity in identities:
			# there is no FEAT category
			if identity[0]=='FEAT': return
			if len(identity)<2 or not identity[2]:
				data.extend((identity[0], identity[1], ''))
			else:
				data.extend(identity)
		data.append('FEAT')
		data.extend(features)
		data = '\0'.join(data)
		# if there's a need to do more gzip, put that to a function
		string = StringIO()
		gzip=GzipFile(fileobj=string, mode='w')
		gzip.write(data)
		gzip.close()
		data = string.getvalue()
		self.cur.execute('''
			INSERT INTO caps_cache ( node, ver, ext, data )
			VALUES (?, ?, ?, ?);
			''', (node, ver, ext, buffer(data))) # (1) -- note above
		try:
			self.con.commit()
		except sqlite.OperationalError, e:
			print >> sys.stderr, str(e)