stats_httpd.py.in

#!@PYTHON@

# Copyright (C) 2011  Internet Systems Consortium.
#
# Permission to use, copy, modify, and distribute this software for any
# purpose with or without fee is hereby granted, provided that the above
# copyright notice and this permission notice appear in all copies.
#
# THE SOFTWARE IS PROVIDED "AS IS" AND INTERNET SYSTEMS CONSORTIUM
# DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL
# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL
# INTERNET SYSTEMS CONSORTIUM BE LIABLE FOR ANY SPECIAL, DIRECT,
# INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING
# FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
# NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION
# WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

"""
A standalone HTTP server for HTTP/XML interface of statistics in BIND 10

"""
import sys; sys.path.append ('@@PYTHONPATH@@')
import os
import time
import errno
import select
from optparse import OptionParser, OptionValueError
import http.server
import socket
import string
import xml.etree.ElementTree
import urllib.parse

import isc.cc
import isc.config
import isc.util.process

import isc.log
from isc.log_messages.stats_httpd_messages import *

isc.log.init("b10-stats-httpd")
logger = isc.log.Logger("stats-httpd")

# Some constants for debug levels.
DBG_STATHTTPD_INIT = logger.DBGLVL_START_SHUT
DBG_STATHTTPD_MESSAGING = logger.DBGLVL_COMMAND

# If B10_FROM_SOURCE is set in the environment, we use data files
# from a directory relative to that, otherwise we use the ones
# installed on the system
if "B10_FROM_SOURCE" in os.environ:
    BASE_LOCATION = os.environ["B10_FROM_SOURCE"] + os.sep + \
        "src" + os.sep + "bin" + os.sep + "stats"
else:
    PREFIX = "@prefix@"
    DATAROOTDIR = "@datarootdir@"
    BASE_LOCATION = "@datadir@" + os.sep + "@PACKAGE@"
    BASE_LOCATION = BASE_LOCATION.replace("${datarootdir}", DATAROOTDIR).replace("${prefix}", PREFIX)
SPECFILE_LOCATION = BASE_LOCATION + os.sep + "stats-httpd.spec"
XML_TEMPLATE_LOCATION = BASE_LOCATION + os.sep + "stats-httpd-xml.tpl"
XSD_TEMPLATE_LOCATION = BASE_LOCATION + os.sep + "stats-httpd-xsd.tpl"
XSL_TEMPLATE_LOCATION = BASE_LOCATION + os.sep + "stats-httpd-xsl.tpl"

# These variables are paths part of URL.
# eg. "http://${address}" + XXX_URL_PATH
XML_URL_PATH = '/bind10/statistics/xml'
XSD_URL_PATH = '/bind10/statistics/xsd'
XSL_URL_PATH = '/bind10/statistics/xsl'
# TODO: This should be considered later.
XSD_NAMESPACE = 'http://bind10.isc.org/bind10'

# Assign this process name
isc.util.process.rename()

class HttpHandler(http.server.BaseHTTPRequestHandler):
    """HTTP handler class for HttpServer class. The class inhrits the super
    class http.server.BaseHTTPRequestHandler. It implemets do_GET()
    and do_HEAD() and orverrides log_message()"""
    def do_GET(self):
        body = self.send_head()
        if body is not None:
            self.wfile.write(body.encode())

    def do_HEAD(self):
        self.send_head()

    def send_head(self):
        try:
            req_path = self.path
            req_path = urllib.parse.urlsplit(req_path).path
            req_path = urllib.parse.unquote(req_path)
            req_path = os.path.normpath(req_path)
            path_dirs = req_path.split('/')
            path_dirs = [ d for d in filter(None, path_dirs) ]
            module_name = None
            item_name = None
            # in case of /bind10/statistics/xxx/YYY/zzz/
            if len(path_dirs) >= 5:
                item_name = path_dirs[4]
            # in case of /bind10/statistics/xxx/YYY/
            if len(path_dirs) >= 4:
                module_name = path_dirs[3]
            if req_path.startswith(XML_URL_PATH):
                body = self.server.xml_handler(module_name, item_name)
            elif req_path.startswith(XSD_URL_PATH):
                body = self.server.xsd_handler(module_name, item_name)
            elif req_path.startswith(XSL_URL_PATH):
                body = self.server.xsl_handler(module_name, item_name)
            else:
                if req_path == '/' and 'Host' in self.headers.keys():
                    # redirect to XML URL only when requested with '/'
                    self.send_response(302)
                    self.send_header(
                        "Location",
                        "http://" + self.headers.get('Host') + XML_URL_PATH)
                    self.end_headers()
                    return None
                else:
                    # Couldn't find HOST
                    self.send_error(404)
                    return None
        except StatsHttpdError as err:
            self.send_error(500)
            logger.error(STATHTTPD_SERVER_ERROR, err)
            return None
        else:
            self.send_response(200)
            self.send_header("Content-type", "text/xml")
            self.send_header("Content-Length", len(body))
            self.end_headers()
            return body

class HttpServerError(Exception):
    """Exception class for HttpServer class. It is intended to be
    passed from the HttpServer object to the StatsHttpd object."""
    pass

class HttpServer(http.server.HTTPServer):
    """HTTP Server class. The class inherits the super
    http.server.HTTPServer. Some parameters are specified as
    arguments, which are xml_handler, xsd_handler, xsl_handler, and
    log_writer. These all are parameters which the StatsHttpd object
    has. The handler parameters are references of functions which
    return body of each document. The last parameter log_writer is
    reference of writer function to just write to
    sys.stderr.write. They are intended to be referred by HttpHandler
    object."""
    def __init__(self, server_address, handler,
                 xml_handler, xsd_handler, xsl_handler, log_writer):
        self.server_address = server_address
        self.xml_handler = xml_handler
        self.xsd_handler = xsd_handler
        self.xsl_handler = xsl_handler
        self.log_writer = log_writer
        http.server.HTTPServer.__init__(self, server_address, handler)

class StatsHttpdError(Exception):
    """Exception class for StatsHttpd class. It is intended to be
    thrown from the the StatsHttpd object to the HttpHandler object or
    main routine."""
    pass

class StatsHttpd:
    """The main class of HTTP server of HTTP/XML interface for
    statistics module. It handles HTTP requests, and command channel
    and config channel CC session. It uses select.select function
    while waiting for clients requests."""
    def __init__(self):
        self.running = False
        self.poll_intval = 0.5
        self.write_log = sys.stderr.write
        self.mccs = None
        self.httpd = []
        self.open_mccs()
        self.config = {}
        self.load_config()
        self.http_addrs = []
        self.mccs.start()
        self.open_httpd()

    def open_mccs(self):
        """Opens a ModuleCCSession object"""
        # create ModuleCCSession
        logger.debug(DBG_STATHTTPD_INIT, STATHTTPD_STARTING_CC_SESSION)
        self.mccs = isc.config.ModuleCCSession(
            SPECFILE_LOCATION, self.config_handler, self.command_handler)
        self.cc_session = self.mccs._session

    def close_mccs(self):
        """Closes a ModuleCCSession object"""
        if self.mccs is None:
            return

        logger.debug(DBG_STATHTTPD_INIT, STATHTTPD_CLOSING_CC_SESSION)
        self.mccs.close()
        self.mccs = None

    def load_config(self, new_config={}):
        """Loads configuration from spec file or new configuration
        from the config manager"""
        # load config
        if len(self.config) == 0:
            self.config = dict([
                (itm['item_name'], self.mccs.get_value(itm['item_name'])[0])
                for itm in self.mccs.get_module_spec().get_config_spec()
                ])
        self.config.update(new_config)
        # set addresses and ports for HTTP
        addrs = []
        if 'listen_on' in self.config:
            for cf in self.config['listen_on']:
                if 'address' in cf and 'port' in cf:
                    addrs.append((cf['address'], cf['port']))
        self.http_addrs = addrs

    def open_httpd(self):
        """Opens sockets for HTTP. Iterating each HTTP address to be
        configured in spec file"""
        for addr in self.http_addrs:
            self.httpd.append(self._open_httpd(addr))

    def _open_httpd(self, server_address):
        httpd = None
        try:
            # get address family for the server_address before
            # creating HttpServer object. If a specified address is
            # not numerical, gaierror may be thrown.
            address_family = socket.getaddrinfo(
                server_address[0], server_address[1], 0,
                socket.SOCK_STREAM, socket.IPPROTO_TCP, socket.AI_NUMERICHOST
                )[0][0]
            HttpServer.address_family = address_family
            httpd = HttpServer(
                server_address, HttpHandler,
                self.xml_handler, self.xsd_handler, self.xsl_handler,
                self.write_log)
            logger.info(STATHTTPD_STARTED, server_address[0],
                        server_address[1])
            return httpd
        except (socket.gaierror, socket.error,
                OverflowError, TypeError) as err:
           if httpd:
                httpd.server_close()
           raise HttpServerError(
               "Invalid address %s, port %s: %s: %s" %
               (server_address[0], server_address[1],
                err.__class__.__name__, err))

    def close_httpd(self):
        """Closes sockets for HTTP"""
        while len(self.httpd)>0:
            ht = self.httpd.pop()
            logger.info(STATHTTPD_CLOSING, ht.server_address[0],
                        ht.server_address[1])
            ht.server_close()

    def start(self):
        """Starts StatsHttpd objects to run. Waiting for client
        requests by using select.select functions"""
        self.running = True
        while self.running:
            try:
                (rfd, wfd, xfd) = select.select(
                    self.get_sockets(), [], [], self.poll_intval)
            except select.error as err:
                # select.error exception is caught only in the case of
                # EINTR, or in other cases it is just thrown.
                if err.args[0] == errno.EINTR:
                    (rfd, wfd, xfd) = ([], [], [])
                else:
                    raise
            # FIXME: This module can handle only one request at a
            # time. If someone sends only part of the request, we block
            # waiting for it until we time out.
            # But it isn't so big issue for administration purposes.
            for fd in rfd + xfd:
                if fd == self.mccs.get_socket():
                    self.mccs.check_command(nonblock=False)
                    continue
                for ht in self.httpd:
                    if fd == ht.socket:
                        ht.handle_request()
                        break
        self.stop()

    def stop(self):
        """Stops the running StatsHttpd objects. Closes CC session and
        HTTP handling sockets"""
        logger.info(STATHTTPD_SHUTDOWN)
        self.close_httpd()
        self.close_mccs()
        self.running = False

    def get_sockets(self):
        """Returns sockets to select.select"""
        sockets = []
        if self.mccs is not None:
            sockets.append(self.mccs.get_socket())
        if len(self.httpd) > 0:
            for ht in self.httpd:
                sockets.append(ht.socket)
        return sockets

    def config_handler(self, new_config):
        """Config handler for the ModuleCCSession object. It resets
        addresses and ports to listen HTTP requests on."""
        logger.debug(DBG_STATHTTPD_MESSAGING, STATHTTPD_HANDLE_CONFIG,
                   new_config)
        errors = []
        if not self.mccs.get_module_spec().\
                validate_config(False, new_config, errors):
                return isc.config.ccsession.create_answer(
                    1, ", ".join(errors))
        # backup old config
        old_config = self.config.copy()
        self.load_config(new_config)
        # If the http sockets aren't opened or
        # if new_config doesn't have'listen_on', it returns
        if len(self.httpd) == 0 or 'listen_on' not in new_config:
            return isc.config.ccsession.create_answer(0)
        self.close_httpd()
        try:
            self.open_httpd()
        except HttpServerError as err:
            logger.error(STATHTTPD_SERVER_ERROR, err)
            # restore old config
            self.load_config(old_config)
            self.open_httpd()
            return isc.config.ccsession.create_answer(1, str(err))
        else:
            return isc.config.ccsession.create_answer(0)

    def command_handler(self, command, args):
        """Command handler for the ModuleCCSesson object. It handles
        "status" and "shutdown" commands."""
        if command == "status":
            logger.debug(DBG_STATHTTPD_MESSAGING,
                         STATHTTPD_RECEIVED_STATUS_COMMAND)
            return isc.config.ccsession.create_answer(
                0, "Stats Httpd is up. (PID " + str(os.getpid()) + ")")
        elif command == "shutdown":
            logger.debug(DBG_STATHTTPD_MESSAGING,
                         STATHTTPD_RECEIVED_SHUTDOWN_COMMAND)
            self.running = False
            return isc.config.ccsession.create_answer(0)
        else:
            logger.debug(DBG_STATHTTPD_MESSAGING,
                         STATHTTPD_RECEIVED_UNKNOWN_COMMAND, command)
            return isc.config.ccsession.create_answer(
                1, "Unknown command: " + str(command))

    def get_stats_data(self, owner=None, name=None):
        """Requests statistics data to the Stats daemon and returns
        the data which obtains from it. args are owner and name."""
        param = {}
        if owner is None and name is None:
            param = None
        if owner is not None:
            param['owner'] = owner
        if name is not None:
            param['name'] = name
        try:
            seq = self.cc_session.group_sendmsg(
                isc.config.ccsession.create_command('show', param), 'Stats')
            (answer, env) = self.cc_session.group_recvmsg(False, seq)
            if answer:
                (rcode, value) = isc.config.ccsession.parse_answer(answer)
        except (isc.cc.session.SessionTimeout,
                isc.cc.session.SessionError) as err:
            raise StatsHttpdError("%s: %s" %
                                  (err.__class__.__name__, err))
        else:
            if rcode == 0:
                return value
            else:
                raise StatsHttpdError("Stats module: %s" % str(value))

    def get_stats_spec(self, owner=None, name=None):
        """Requests statistics data to the Stats daemon and returns
        the data which obtains from it. args are owner and name."""
        param = {}
        if owner is None and name is None:
            param = None
        if owner is not None:
            param['owner'] = owner
        if name is not None:
            param['name'] = name
        try:
            seq = self.cc_session.group_sendmsg(
                isc.config.ccsession.create_command('showschema', param), 'Stats')
            (answer, env) = self.cc_session.group_recvmsg(False, seq)
            if answer:
                (rcode, value) = isc.config.ccsession.parse_answer(answer)
                if rcode == 0:
                    return value
                else:
                    raise StatsHttpdError("Stats module: %s" % str(value))
        except (isc.cc.session.SessionTimeout,
                isc.cc.session.SessionError) as err:
            raise StatsHttpdError("%s: %s" %
                                  (err.__class__.__name__, err))


    def xml_handler(self, module_name=None, item_name=None):
        """Handler which requests to Stats daemon to obtain statistics
        data and returns the body of XML document"""

        def stats_data2xml(stats_spec, stats_data, xml_elem):
            """Internal use for xml_handler. Reads stats_data and
            stats_spec specified as first and second arguments, and
            modify the xml object specified as third
            argument. xml_elem must be modified and always returns
            None."""
            # assumed started with module_spec or started with
            # item_spec in statistics
            if type(stats_spec) is dict:
                # assumed started with module_spec
                if 'item_name' not in stats_spec \
                        and 'item_type' not in stats_spec:
                    for module_name in stats_spec.keys():
                        elem = xml.etree.ElementTree.Element(module_name)
                        stats_data2xml(stats_spec[module_name],
                                       stats_data[module_name], elem)
                        xml_elem.append(elem)
                # started with item_spec in statistics
                else:
                    elem = xml.etree.ElementTree.Element(stats_spec['item_name'])
                    if stats_spec['item_type'] == 'map':
                        stats_data2xml(stats_spec['map_item_spec'],
                                       stats_data,
                                       elem)
                    elif stats_spec['item_type'] == 'list':
                        for item in stats_data:
                            stats_data2xml(stats_spec['list_item_spec'],
                                           item, elem)
                    else:
                        elem.text = str(stats_data)
                    xml_elem.append(elem)
            # assumed started with stats_spec
            elif type(stats_spec) is list:
                for item_spec in stats_spec:
                    stats_data2xml(item_spec,
                                   stats_data[item_spec['item_name']],
                                   xml_elem)
            else:
                xml_elem.text = str(stats_data)
            return None

        stats_spec = self.get_stats_spec(module_name, item_name)
        stats_data = self.get_stats_data(module_name, item_name)
        xml_elem = xml.etree.ElementTree.Element(
            'bind10:statistics',
            attrib={ 'xsi:schemaLocation' : XSD_NAMESPACE + ' ' + XSD_URL_PATH,
                     'xmlns:bind10' : XSD_NAMESPACE,
                     'xmlns:xsi' : "http://www.w3.org/2001/XMLSchema-instance" })
        stats_data2xml(stats_spec, stats_data, xml_elem)
        # The coding conversion is tricky. xml..tostring() of Python 3.2
        # returns bytes (not string) regardless of the coding, while
        # tostring() of Python 3.1 returns a string.  To support both
        # cases transparently, we first make sure tostring() returns
        # bytes by specifying utf-8 and then convert the result to a
        # plain string (code below assume it).
        xml_string = str(xml.etree.ElementTree.tostring(xml_elem, encoding='utf-8'),
                         encoding='us-ascii')
        self.xml_body = self.open_template(XML_TEMPLATE_LOCATION).substitute(
            xml_string=xml_string,
            xsl_url_path=XSL_URL_PATH)
        assert self.xml_body is not None
        return self.xml_body

    def xsd_handler(self, module_name=None, item_name=None):
        """Handler which just returns the body of XSD document"""

        def stats_spec2xsd(stats_spec, xsd_elem):
            """Internal use for xsd_handler. Reads stats_spec
            specified as first arguments, and modify the xml object
            specified as second argument. xsd_elem must be
            modified. Always returns None with no exceptions."""
            # assumed module_spec or one stats_spec
            if type(stats_spec) is dict:
                # assumed module_spec
                if 'item_name' not in stats_spec:
                    for mod in stats_spec.keys():
                        elem = xml.etree.ElementTree.Element(
                            "element", { "name" : mod })
                        complextype = xml.etree.ElementTree.Element("complexType")
                        alltag = xml.etree.ElementTree.Element("all")
                        stats_spec2xsd(stats_spec[mod], alltag)
                        complextype.append(alltag)
                        elem.append(complextype)
                        xsd_elem.append(elem)
                # assumed stats_spec
                else:
                    if stats_spec['item_type'] == 'map':
                        alltag = xml.etree.ElementTree.Element("all")
                        stats_spec2xsd(stats_spec['map_item_spec'], alltag)
                        complextype = xml.etree.ElementTree.Element("complexType")
                        complextype.append(alltag)
                        elem = xml.etree.ElementTree.Element(
                            "element", { "name" : stats_spec["item_name"] })
                        elem.append(complextype)
                        xsd_elem.append(elem)
                    elif stats_spec['item_type'] == 'list':
                        alltag = xml.etree.ElementTree.Element("all")
                        stats_spec2xsd(stats_spec['list_item_spec'], alltag)
                        complextype = xml.etree.ElementTree.Element("complexType")
                        complextype.append(alltag)
                        elem = xml.etree.ElementTree.Element(
                            "element", { "name" : stats_spec["item_name"] })
                        elem.append(complextype)
                        xsd_elem.append(elem)
                    else:
                        elem = xml.etree.ElementTree.Element(
                            "element",
                            attrib={
                                'name' : stats_spec["item_name"],
                                'type' : stats_spec["item_type"] \
                                    if stats_spec["item_type"].lower() != 'real' \
                                    else 'float',
                                'minOccurs' : "1",
                                'maxOccurs' : "1"
                                }
                            )
                        annotation = xml.etree.ElementTree.Element("annotation")
                        appinfo = xml.etree.ElementTree.Element("appinfo")
                        documentation = xml.etree.ElementTree.Element("documentation")
                        if "item_title" in stats_spec:
                            appinfo.text = stats_spec["item_title"]
                        if "item_description" in stats_spec:
                            documentation.text = stats_spec["item_description"]
                        annotation.append(appinfo)
                        annotation.append(documentation)
                        elem.append(annotation)
                        xsd_elem.append(elem)
            # multiple stats_specs
            elif type(stats_spec) is list:
                for item_spec in stats_spec:
                    stats_spec2xsd(item_spec, xsd_elem)
            return None

        # for XSD
        stats_spec = self.get_stats_spec(module_name, item_name)
        alltag = xml.etree.ElementTree.Element("all")
        stats_spec2xsd(stats_spec, alltag)
        complextype = xml.etree.ElementTree.Element("complexType")
        complextype.append(alltag)
        documentation = xml.etree.ElementTree.Element("documentation")
        documentation.text = "A set of statistics data"
        annotation = xml.etree.ElementTree.Element("annotation")
        annotation.append(documentation)
        elem = xml.etree.ElementTree.Element(
            "element", attrib={ 'name' : 'statistics' })
        elem.append(annotation)
        elem.append(complextype)
        documentation = xml.etree.ElementTree.Element("documentation")
        documentation.text = "XML schema of the statistics data in BIND 10"
        annotation = xml.etree.ElementTree.Element("annotation")
        annotation.append(documentation)
        xsd_root = xml.etree.ElementTree.Element(
            "schema",
            attrib={ 'xmlns' : "http://www.w3.org/2001/XMLSchema",
                     'targetNamespace' : XSD_NAMESPACE,
                     'xmlns:bind10' : XSD_NAMESPACE })
        xsd_root.append(annotation)
        xsd_root.append(elem)
        # The coding conversion is tricky. xml..tostring() of Python 3.2
        # returns bytes (not string) regardless of the coding, while
        # tostring() of Python 3.1 returns a string.  To support both
        # cases transparently, we first make sure tostring() returns
        # bytes by specifying utf-8 and then convert the result to a
        # plain string (code below assume it).
        xsd_string = str(xml.etree.ElementTree.tostring(xsd_root, encoding='utf-8'),
                         encoding='us-ascii')
        self.xsd_body = self.open_template(XSD_TEMPLATE_LOCATION).substitute(
            xsd_string=xsd_string)
        assert self.xsd_body is not None
        return self.xsd_body

    def xsl_handler(self, module_name=None, item_name=None):
        """Handler which just returns the body of XSL document"""

        def stats_spec2xsl(stats_spec, xsl_elem):
            """Internal use for xsl_handler. Reads stats_spec
            specified as first arguments, and modify the xml object
            specified as second argument. xsl_elem must be
            modified. Always returns None with no exceptions."""
            # assumed module_spec or one stats_spec
            if type(stats_spec) is dict:
                # assumed module_spec
                if 'item_name' not in stats_spec:
                    table = xml.etree.ElementTree.Element("table")
                    tr = xml.etree.ElementTree.Element("tr")
                    th = xml.etree.ElementTree.Element("th")
                    th.text = "Module Names"
                    tr.append(th)
                    th = xml.etree.ElementTree.Element("th")
                    th.text = "Items"
                    tr.append(th)
                    table.append(tr)
                    for mod in stats_spec.keys():
                        foreach = xml.etree.ElementTree.Element(
                            "xsl:for-each", attrib={ "select" : mod })
                        tr = xml.etree.ElementTree.Element("tr")
                        td = xml.etree.ElementTree.Element("td")
                        td.text = mod
                        tr.append(td)
                        td = xml.etree.ElementTree.Element("td")
                        stats_spec2xsl(stats_spec[mod], td)
                        tr.append(td)
                        foreach.append(tr)
                        table.append(foreach)
                    xsl_elem.append(table)
                # assumed stats_spec
                else:
                    tr = xml.etree.ElementTree.Element("tr")
                    td = xml.etree.ElementTree.Element("td")
                    td.text = stats_spec["item_name"]
                    tr.append(td)
                    if stats_spec['item_type'] == 'map':
                        stats_spec2xsl(stats_spec['map_item_spec'], tr)
                    elif stats_spec['item_type'] == 'list':
                        stats_spec2xsl(stats_spec['list_item_spec'], tr)
                    else:
                        td = xml.etree.ElementTree.Element("td")
                        xsl_valueof = xml.etree.ElementTree.Element(
                            "xsl:value-of",
                            attrib={'select': stats_spec["item_name"]})
                        td.append(xsl_valueof)
                        tr.append(td)
                    xsl_elem.append(tr)
            # multiple stats_specs
            elif type(stats_spec) is list:
                table = xml.etree.ElementTree.Element("table")
                tr = xml.etree.ElementTree.Element("tr")
                th = xml.etree.ElementTree.Element("th")
                th.text = "Item Names"
                tr.append(th)
                th = xml.etree.ElementTree.Element("th")
                th.text = "Values"
                tr.append(th)
                table.append(tr)
                for item_spec in stats_spec:
                    stats_spec2xsl(item_spec, table)
                xsl_elem.append(table)
            return None

        # for XSL
        stats_spec = self.get_stats_spec(module_name, item_name)
        xsd_root = xml.etree.ElementTree.Element( # started with xml:template tag
            "xsl:template",
            attrib={'match': "bind10:statistics"})
        if module_name is not None and item_name is not None:
            stats_spec2xsl([ stats_spec ] , xsd_root)
        else:
            stats_spec2xsl(stats_spec, xsd_root)
        # The coding conversion is tricky. xml..tostring() of Python 3.2
        # returns bytes (not string) regardless of the coding, while
        # tostring() of Python 3.1 returns a string.  To support both
        # cases transparently, we first make sure tostring() returns
        # bytes by specifying utf-8 and then convert the result to a
        # plain string (code below assume it).
        xsl_string = str(xml.etree.ElementTree.tostring(xsd_root, encoding='utf-8'),
                         encoding='us-ascii')
        self.xsl_body = self.open_template(XSL_TEMPLATE_LOCATION).substitute(
            xsl_string=xsl_string,
            xsd_namespace=XSD_NAMESPACE)
        assert self.xsl_body is not None
        return self.xsl_body

    def open_template(self, file_name):
        """It opens a template file, and it loads all lines to a
        string variable and returns string. Template object includes
        the variable. Limitation of a file size isn't needed there."""
        f = open(file_name, 'r')
        lines = "".join(f.readlines())
        f.close()
        assert lines is not None
        return string.Template(lines)

if __name__ == "__main__":
    try:
        parser = OptionParser()
        parser.add_option(
            "-v", "--verbose", dest="verbose", action="store_true",
            help="display more about what is going on")
        (options, args) = parser.parse_args()
        if options.verbose:
            isc.log.init("b10-stats-httpd", "DEBUG", 99)
        stats_httpd = StatsHttpd()
        stats_httpd.start()
    except OptionValueError as ove:
        logger.fatal(STATHTTPD_BAD_OPTION_VALUE, ove)
        sys.exit(1)
    except isc.cc.session.SessionError as se:
        logger.fatal(STATHTTPD_CC_SESSION_ERROR, se)
        sys.exit(1)
    except HttpServerError as hse:
        logger.fatal(STATHTTPD_START_SERVER_INIT_ERROR, hse)
        sys.exit(1)
    except KeyboardInterrupt as kie:
        logger.info(STATHTTPD_STOPPED_BY_KEYBOARD)