kea/src/bin/stats/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) ]
            req_path = '/'+"/".join(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 == '/'.join([XML_URL_PATH] + path_dirs[3:5]):
                body = self.server.xml_handler(module_name, item_name)
            elif req_path == '/'.join([XSD_URL_PATH] + path_dirs[3:5]):
                body = self.server.xsd_handler(module_name, item_name)
            elif req_path == '/'.join([XSL_URL_PATH] + path_dirs[3:5]):
                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 StatsHttpdDataError as err:
            # Couldn't find neither specified module name nor
            # specified item name
            self.send_error(404)
            logger.error(STATHTTPD_SERVER_DATAERROR, err)
            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 StatsHttpdDataError(Exception):
    """Exception class for StatsHttpd class. The reason seems to be
    due to the data. 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
        self.mccs.send_stopping()

        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. The first argument is the
        module name which owns the statistics data, the second
        argument is one name of the statistics items which the the
        module owns. The second argument cannot be specified when the
        first argument is not specified. It returns the statistics
        data of the specified module or item. When the session timeout
        or the session error is occurred, it raises
        StatsHttpdError. When the stats daemon returns none-zero
        value, it raises StatsHttpdDataError."""
        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 StatsHttpdDataError("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. The first argument is the
        module name which owns the statistics data, the second
        argument is one name of the statistics items which the the
        module owns. The second argument cannot be specified when the
        first argument is not specified. It returns the statistics
        specification of the specified module or item. When the
        session timeout or the session error is occurred, it raises
        StatsHttpdError. When the stats daemon returns none-zero
        value, it raises StatsHttpdDataError."""
        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 StatsHttpdDataError("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):
        """Requests the specified statistics data and specification by
        using the functions get_stats_data and get_stats_spec
        respectively and loads the XML template file and returns the
        string of the XML document.The first argument is the module
        name which owns the statistics data, the second argument is
        one name of the statistics items which the the module
        owns. The second argument cannot be specified when the first
        argument is not specified."""

        # TODO: Separate the following recursive function by type of
        # the parameter. Because we should be sure what type there is
        # when we call it recursively.
        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)

        stats_spec = self.get_stats_spec(module_name, item_name)
        stats_data = self.get_stats_data(module_name, item_name)
        # make the path xxx/module/item if specified respectively
        path_info = ''
        if module_name is not None and item_name is not None:
            path_info = '/' + module_name + '/' + item_name
        elif module_name is not None:
            path_info = '/' + module_name
        xml_elem = xml.etree.ElementTree.Element(
            'bind10:statistics',
            attrib={ 'xsi:schemaLocation' : XSD_NAMESPACE + ' ' + XSD_URL_PATH + path_info,
                     '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).
        # FIXME: Non-ASCII characters might be lost here. Consider how
        # the whole system should handle non-ASCII characters.
        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 + path_info)
        assert self.xml_body is not None
        return self.xml_body

    def xsd_handler(self, module_name=None, item_name=None):
        """Requests the specified statistics specification by using
        the function get_stats_spec respectively and loads the XSD
        template file and returns the string of the XSD document.The
        first argument is the module name which owns the statistics
        data, the second argument is one name of the statistics items
        which the the module owns. The second argument cannot be
        specified when the first argument is not specified."""

        # TODO: Separate the following recursive function by type of
        # the parameter. Because we should be sure what type there is
        # when we call it recursively.
        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", attrib={ "name" : stats_spec["item_name"],
                                                "minOccurs": "0" \
                                                    if stats_spec["item_optional"] \
                                                    else "1",
                                                "maxOccurs": "unbounded" })
                        elem.append(complextype)
                        xsd_elem.append(elem)
                    elif stats_spec['item_type'] == 'list':
                        alltag = xml.etree.ElementTree.Element("sequence")
                        stats_spec2xsd(stats_spec['list_item_spec'], alltag)
                        complextype = xml.etree.ElementTree.Element("complexType")
                        complextype.append(alltag)
                        elem = xml.etree.ElementTree.Element(
                            "element", attrib={ "name" : stats_spec["item_name"],
                                                "minOccurs": "0" \
                                                    if stats_spec["item_optional"] \
                                                    else "1",
                                                "maxOccurs": "1" })
                        elem.append(complextype)
                        xsd_elem.append(elem)
                    else:
                        # determine the datatype of XSD
                        # TODO: Should consider other item_format types
                        datatype = stats_spec["item_type"] \
                            if stats_spec["item_type"].lower() != 'real' \
                            else 'float'
                        if "item_format" in stats_spec:
                            item_format = stats_spec["item_format"]
                            if datatype.lower() == 'string' \
                                    and item_format.lower() == 'date-time':
                                 datatype = 'dateTime'
                            elif datatype.lower() == 'string' \
                                    and (item_format.lower() == 'date' \
                                             or item_format.lower() == 'time'):
                                 datatype = item_format.lower()
                        elem = xml.etree.ElementTree.Element(
                            "element",
                            attrib={
                                'name' : stats_spec["item_name"],
                                'type' : datatype,
                                'minOccurs' : "0" \
                                    if stats_spec["item_optional"] \
                                    else "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)

        # 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).
        # FIXME: Non-ASCII characters might be lost here. Consider how
        # the whole system should handle non-ASCII characters.
        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):
        """Requests the specified statistics specification by using
        the function get_stats_spec respectively and loads the XSL
        template file and returns the string of the XSL document.The
        first argument is the module name which owns the statistics
        data, the second argument is one name of the statistics items
        which the the module owns. The second argument cannot be
        specified when the first argument is not specified."""

        # TODO: Separate the following recursive function by type of
        # the parameter. Because we should be sure what type there is
        # when we call it recursively.
        def stats_spec2xsl(stats_spec, xsl_elem, path=XML_URL_PATH):
            """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. The third argument is a base path used for
            making anchor tag in XSL. 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 Name"
                    tr.append(th)
                    th = xml.etree.ElementTree.Element("th")
                    th.text = "Module Item"
                    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")
                        a = xml.etree.ElementTree.Element(
                            "a", attrib={ "href": urllib.parse.quote(path + "/" + mod) })
                        a.text = mod
                        td.append(a)
                        tr.append(td)
                        td = xml.etree.ElementTree.Element("td")
                        stats_spec2xsl(stats_spec[mod], td,
                                       path + "/" + mod)
                        tr.append(td)
                        foreach.append(tr)
                        table.append(foreach)
                    xsl_elem.append(table)
                # assumed stats_spec
                else:
                    if stats_spec['item_type'] == 'map':
                        table = xml.etree.ElementTree.Element("table")
                        tr = xml.etree.ElementTree.Element("tr")
                        th = xml.etree.ElementTree.Element("th")
                        th.text = "Item Name"
                        tr.append(th)
                        th = xml.etree.ElementTree.Element("th")
                        th.text = "Item Value"
                        tr.append(th)
                        table.append(tr)
                        foreach = xml.etree.ElementTree.Element(
                            "xsl:for-each", attrib={ "select" : stats_spec['item_name'] })
                        tr = xml.etree.ElementTree.Element("tr")
                        td = xml.etree.ElementTree.Element(
                            "td",
                            attrib={ "class" : "title",
                                     "title" : stats_spec["item_description"] \
                                         if "item_description" in stats_spec \
                                         else "" })
                        # TODO: Consider whether we should always use
                        # the identical name "item_name" for the
                        # user-visible name in XSL.
                        td.text = stats_spec[ "item_title" if "item_title" in stats_spec else "item_name" ]
                        tr.append(td)
                        td = xml.etree.ElementTree.Element("td")
                        stats_spec2xsl(stats_spec['map_item_spec'], td,
                                       path + "/" + stats_spec["item_name"])
                        tr.append(td)
                        foreach.append(tr)
                        table.append(foreach)
                        xsl_elem.append(table)
                    elif stats_spec['item_type'] == 'list':
                        stats_spec2xsl(stats_spec['list_item_spec'], xsl_elem,
                                       path + "/" + stats_spec["item_name"])
                    else:
                        xsl_valueof = xml.etree.ElementTree.Element(
                            "xsl:value-of",
                            attrib={'select': stats_spec["item_name"]})
                        xsl_elem.append(xsl_valueof)

            # 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 Name"
                tr.append(th)
                th = xml.etree.ElementTree.Element("th")
                th.text = "Item Value"
                tr.append(th)
                table.append(tr)
                for item_spec in stats_spec:
                    tr = xml.etree.ElementTree.Element("tr")
                    td = xml.etree.ElementTree.Element(
                        "td",
                        attrib={ "class" : "title",
                                 "title" : item_spec["item_description"] \
                                     if "item_description" in item_spec \
                                     else "" })
                    # if the path length is equal to or shorter than
                    # XML_URL_PATH + /Module/Item, add the anchor tag.
                    if len(path.split('/')) <= len((XML_URL_PATH + '/Module/Item').split('/')):
                        a = xml.etree.ElementTree.Element(
                            "a", attrib={ "href": urllib.parse.quote(path + "/" + item_spec["item_name"]) })
                        a.text = item_spec[ "item_title" if "item_title" in item_spec else "item_name" ]
                        td.append(a)
                    else:
                        td.text = item_spec[ "item_title" if "item_title" in item_spec else "item_name" ]
                    tr.append(td)
                    td = xml.etree.ElementTree.Element("td")
                    stats_spec2xsl(item_spec, td, path)
                    tr.append(td)
                    if item_spec['item_type'] == 'list':
                        foreach = xml.etree.ElementTree.Element(
                            "xsl:for-each", attrib={ "select" : item_spec['item_name'] })
                        foreach.append(tr)
                        table.append(foreach)
                    else:
                        table.append(tr)
                xsl_elem.append(table)

        # 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"})
        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).
        # FIXME: Non-ASCII characters might be lost here. Consider how
        # the whole system should handle non-ASCII characters.
        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)