# Python implementation of the MySQL client-server protocol
# http://dev.mysql.com/doc/internals/en/client-server-protocol.html
# Error codes:
# http://dev.mysql.com/doc/refman/5.5/en/error-messages-client.html
from __future__ import print_function
from ._compat import PY2, range_type, text_type, str_type, JYTHON, IRONPYTHON

import errno
from functools import partial
import hashlib
import io
import os
import socket
import struct
import sys
import traceback
import warnings

from .charset import MBLENGTH, charset_by_name, charset_by_id
from .constants import CLIENT, COMMAND, CR, FIELD_TYPE, SERVER_STATUS
from .converters import escape_item, escape_string, through, conversions as _conv
from .cursors import Cursor
from .optionfile import Parser
from .util import byte2int, int2byte
from . import err

try:
    import ssl
    SSL_ENABLED = True
except ImportError:
    ssl = None
    SSL_ENABLED = False

try:
    import getpass
    DEFAULT_USER = getpass.getuser()
    del getpass
except (ImportError, KeyError):
    # KeyError occurs when there's no entry in OS database for a current user.
    DEFAULT_USER = None


DEBUG = False

_py_version = sys.version_info[:2]


# socket.makefile() in Python 2 is not usable because very inefficient and
# bad behavior about timeout.
# XXX: ._socketio doesn't work under IronPython.
if _py_version == (2, 7) and not IRONPYTHON:
    # read method of file-like returned by sock.makefile() is very slow.
    # So we copy io-based one from Python 3.
    from ._socketio import SocketIO

    def _makefile(sock, mode):
        return io.BufferedReader(SocketIO(sock, mode))
elif _py_version == (2, 6):
    # Python 2.6 doesn't have fast io module.
    # So we make original one.
    class SockFile(object):
        def __init__(self, sock):
            self._sock = sock

        def read(self, n):
            read = self._sock.recv(n)
            if len(read) == n:
                return read
            while True:
                data = self._sock.recv(n-len(read))
                if not data:
                    return read
                read += data
                if len(read) == n:
                    return read

    def _makefile(sock, mode):
        assert mode == 'rb'
        return SockFile(sock)
else:
    # socket.makefile in Python 3 is nice.
    def _makefile(sock, mode):
        return sock.makefile(mode)


TEXT_TYPES = set([
    FIELD_TYPE.BIT,
    FIELD_TYPE.BLOB,
    FIELD_TYPE.LONG_BLOB,
    FIELD_TYPE.MEDIUM_BLOB,
    FIELD_TYPE.STRING,
    FIELD_TYPE.TINY_BLOB,
    FIELD_TYPE.VAR_STRING,
    FIELD_TYPE.VARCHAR,
    FIELD_TYPE.GEOMETRY])

sha_new = partial(hashlib.new, 'sha1')

NULL_COLUMN = 251
UNSIGNED_CHAR_COLUMN = 251
UNSIGNED_SHORT_COLUMN = 252
UNSIGNED_INT24_COLUMN = 253
UNSIGNED_INT64_COLUMN = 254

DEFAULT_CHARSET = 'latin1'

MAX_PACKET_LEN = 2**24-1


def dump_packet(data): # pragma: no cover
    def is_ascii(data):
        if 65 <= byte2int(data) <= 122:
            if isinstance(data, int):
                return chr(data)
            return data
        return '.'

    try:
        print("packet length:", len(data))
        for i in range(1, 6):
            f = sys._getframe(i)
            print("call[%d]: %s (line %d)" % (i, f.f_code.co_name, f.f_lineno))
        print("-" * 66)
    except ValueError:
        pass
    dump_data = [data[i:i+16] for i in range_type(0, min(len(data), 256), 16)]
    for d in dump_data:
        print(' '.join(map(lambda x: "{:02X}".format(byte2int(x)), d)) +
              '   ' * (16 - len(d)) + ' ' * 2 +
              ''.join(map(lambda x: "{}".format(is_ascii(x)), d)))
    print("-" * 66)
    print()


def _scramble(password, message):
    if not password:
        return b''
    if DEBUG: print('password=' + str(password))
    stage1 = sha_new(password).digest()
    stage2 = sha_new(stage1).digest()
    s = sha_new()
    s.update(message)
    s.update(stage2)
    result = s.digest()
    return _my_crypt(result, stage1)


def _my_crypt(message1, message2):
    length = len(message1)
    result = b''
    for i in range_type(length):
        x = (struct.unpack('B', message1[i:i+1])[0] ^
             struct.unpack('B', message2[i:i+1])[0])
        result += struct.pack('B', x)
    return result

# old_passwords support ported from libmysql/password.c
SCRAMBLE_LENGTH_323 = 8


class RandStruct_323(object):
    def __init__(self, seed1, seed2):
        self.max_value = 0x3FFFFFFF
        self.seed1 = seed1 % self.max_value
        self.seed2 = seed2 % self.max_value

    def my_rnd(self):
        self.seed1 = (self.seed1 * 3 + self.seed2) % self.max_value
        self.seed2 = (self.seed1 + self.seed2 + 33) % self.max_value
        return float(self.seed1) / float(self.max_value)


def _scramble_323(password, message):
    hash_pass = _hash_password_323(password)
    hash_message = _hash_password_323(message[:SCRAMBLE_LENGTH_323])
    hash_pass_n = struct.unpack(">LL", hash_pass)
    hash_message_n = struct.unpack(">LL", hash_message)

    rand_st = RandStruct_323(hash_pass_n[0] ^ hash_message_n[0],
                             hash_pass_n[1] ^ hash_message_n[1])
    outbuf = io.BytesIO()
    for _ in range_type(min(SCRAMBLE_LENGTH_323, len(message))):
        outbuf.write(int2byte(int(rand_st.my_rnd() * 31) + 64))
    extra = int2byte(int(rand_st.my_rnd() * 31))
    out = outbuf.getvalue()
    outbuf = io.BytesIO()
    for c in out:
        outbuf.write(int2byte(byte2int(c) ^ byte2int(extra)))
    return outbuf.getvalue()


def _hash_password_323(password):
    nr = 1345345333
    add = 7
    nr2 = 0x12345671

    # x in py3 is numbers, p27 is chars
    for c in [byte2int(x) for x in password if x not in (' ', '\t', 32, 9)]:
        nr ^= (((nr & 63) + add) * c) + (nr << 8) & 0xFFFFFFFF
        nr2 = (nr2 + ((nr2 << 8) ^ nr)) & 0xFFFFFFFF
        add = (add + c) & 0xFFFFFFFF

    r1 = nr & ((1 << 31) - 1)  # kill sign bits
    r2 = nr2 & ((1 << 31) - 1)
    return struct.pack(">LL", r1, r2)


def pack_int24(n):
    return struct.pack('<I', n)[:3]

# https://dev.mysql.com/doc/internals/en/integer.html#packet-Protocol::LengthEncodedInteger
def lenenc_int(i):
    if (i < 0):
        raise ValueError("Encoding %d is less than 0 - no representation in LengthEncodedInteger" % i)
    elif (i < 0xfb):
        return int2byte(i)
    elif (i < (1 << 16)):
        return b'\xfc' + struct.pack('<H', i)
    elif (i < (1 << 24)):
        return b'\xfd' + struct.pack('<I', i)[:3]
    elif (i < (1 << 64)):
        return b'\xfe' + struct.pack('<Q', i)
    else:
        raise ValueError("Encoding %x is larger than %x - no representation in LengthEncodedInteger" % (i, (1 << 64)))

class MysqlPacket(object):
    """Representation of a MySQL response packet.

    Provides an interface for reading/parsing the packet results.
    """
    __slots__ = ('_position', '_data')

    def __init__(self, data, encoding):
        self._position = 0
        self._data = data

    def get_all_data(self):
        return self._data

    def read(self, size):
        """Read the first 'size' bytes in packet and advance cursor past them."""
        result = self._data[self._position:(self._position+size)]
        if len(result) != size:
            error = ('Result length not requested length:\n'
                     'Expected=%s.  Actual=%s.  Position: %s.  Data Length: %s'
                     % (size, len(result), self._position, len(self._data)))
            if DEBUG:
                print(error)
                self.dump()
            raise AssertionError(error)
        self._position += size
        return result

    def read_all(self):
        """Read all remaining data in the packet.

        (Subsequent read() will return errors.)
        """
        result = self._data[self._position:]
        self._position = None  # ensure no subsequent read()
        return result

    def advance(self, length):
        """Advance the cursor in data buffer 'length' bytes."""
        new_position = self._position + length
        if new_position < 0 or new_position > len(self._data):
            raise Exception('Invalid advance amount (%s) for cursor.  '
                            'Position=%s' % (length, new_position))
        self._position = new_position

    def rewind(self, position=0):
        """Set the position of the data buffer cursor to 'position'."""
        if position < 0 or position > len(self._data):
            raise Exception("Invalid position to rewind cursor to: %s." % position)
        self._position = position

    def get_bytes(self, position, length=1):
        """Get 'length' bytes starting at 'position'.

        Position is start of payload (first four packet header bytes are not
        included) starting at index '0'.

        No error checking is done.  If requesting outside end of buffer
        an empty string (or string shorter than 'length') may be returned!
        """
        return self._data[position:(position+length)]

    if PY2:
        def read_uint8(self):
            result = ord(self._data[self._position])
            self._position += 1
            return result
    else:
        def read_uint8(self):
            result = self._data[self._position]
            self._position += 1
            return result

    def read_uint16(self):
        result = struct.unpack_from('<H', self._data, self._position)[0]
        self._position += 2
        return result

    def read_uint24(self):
        low, high = struct.unpack_from('<HB', self._data, self._position)
        self._position += 3
        return low + (high << 16)

    def read_uint32(self):
        result = struct.unpack_from('<I', self._data, self._position)[0]
        self._position += 4
        return result

    def read_uint64(self):
        result = struct.unpack_from('<Q', self._data, self._position)[0]
        self._position += 8
        return result

    def read_string(self):
        end_pos = self._data.find(b'\0', self._position)
        if end_pos < 0:
            return None
        result = self._data[self._position:end_pos]
        self._position = end_pos + 1
        return result

    def read_length_encoded_integer(self):
        """Read a 'Length Coded Binary' number from the data buffer.

        Length coded numbers can be anywhere from 1 to 9 bytes depending
        on the value of the first byte.
        """
        c = self.read_uint8()
        if c == NULL_COLUMN:
            return None
        if c < UNSIGNED_CHAR_COLUMN:
            return c
        elif c == UNSIGNED_SHORT_COLUMN:
            return self.read_uint16()
        elif c == UNSIGNED_INT24_COLUMN:
            return self.read_uint24()
        elif c == UNSIGNED_INT64_COLUMN:
            return self.read_uint64()

    def read_length_coded_string(self):
        """Read a 'Length Coded String' from the data buffer.

        A 'Length Coded String' consists first of a length coded
        (unsigned, positive) integer represented in 1-9 bytes followed by
        that many bytes of binary data.  (For example "cat" would be "3cat".)
        """
        length = self.read_length_encoded_integer()
        if length is None:
            return None
        return self.read(length)

    def read_struct(self, fmt):
        s = struct.Struct(fmt)
        result = s.unpack_from(self._data, self._position)
        self._position += s.size
        return result

    def is_ok_packet(self):
        # https://dev.mysql.com/doc/internals/en/packet-OK_Packet.html
        return self._data[0:1] == b'\0' and len(self._data) >= 7

    def is_eof_packet(self):
        # http://dev.mysql.com/doc/internals/en/generic-response-packets.html#packet-EOF_Packet
        # Caution: \xFE may be LengthEncodedInteger.
        # If \xFE is LengthEncodedInteger header, 8bytes followed.
        return self._data[0:1] == b'\xfe' and len(self._data) < 9

    def is_auth_switch_request(self):
        # http://dev.mysql.com/doc/internals/en/connection-phase-packets.html#packet-Protocol::AuthSwitchRequest
        return self._data[0:1] == b'\xfe'

    def is_resultset_packet(self):
        field_count = ord(self._data[0:1])
        return 1 <= field_count <= 250

    def is_load_local_packet(self):
        return self._data[0:1] == b'\xfb'

    def is_error_packet(self):
        return self._data[0:1] == b'\xff'

    def check_error(self):
        if self.is_error_packet():
            self.rewind()
            self.advance(1)  # field_count == error (we already know that)
            errno = self.read_uint16()
            if DEBUG: print("errno =", errno)
            err.raise_mysql_exception(self._data)

    def dump(self):
        dump_packet(self._data)


class FieldDescriptorPacket(MysqlPacket):
    """A MysqlPacket that represents a specific column's metadata in the result.

    Parsing is automatically done and the results are exported via public
    attributes on the class such as: db, table_name, name, length, type_code.
    """

    def __init__(self, data, encoding):
        MysqlPacket.__init__(self, data, encoding)
        self._parse_field_descriptor(encoding)

    def _parse_field_descriptor(self, encoding):
        """Parse the 'Field Descriptor' (Metadata) packet.

        This is compatible with MySQL 4.1+ (not compatible with MySQL 4.0).
        """
        self.catalog = self.read_length_coded_string()
        self.db = self.read_length_coded_string()
        self.table_name = self.read_length_coded_string().decode(encoding)
        self.org_table = self.read_length_coded_string().decode(encoding)
        self.name = self.read_length_coded_string().decode(encoding)
        self.org_name = self.read_length_coded_string().decode(encoding)
        self.charsetnr, self.length, self.type_code, self.flags, self.scale = (
            self.read_struct('<xHIBHBxx'))
        # 'default' is a length coded binary and is still in the buffer?
        # not used for normal result sets...

    def description(self):
        """Provides a 7-item tuple compatible with the Python PEP249 DB Spec."""
        return (
            self.name,
            self.type_code,
            None,  # TODO: display_length; should this be self.length?
            self.get_column_length(),  # 'internal_size'
            self.get_column_length(),  # 'precision'  # TODO: why!?!?
            self.scale,
            self.flags % 2 == 0)

    def get_column_length(self):
        if self.type_code == FIELD_TYPE.VAR_STRING:
            mblen = MBLENGTH.get(self.charsetnr, 1)
            return self.length // mblen
        return self.length

    def __str__(self):
        return ('%s %r.%r.%r, type=%s, flags=%x'
                % (self.__class__, self.db, self.table_name, self.name,
                   self.type_code, self.flags))


class OKPacketWrapper(object):
    """
    OK Packet Wrapper. It uses an existing packet object, and wraps
    around it, exposing useful variables while still providing access
    to the original packet objects variables and methods.
    """

    def __init__(self, from_packet):
        if not from_packet.is_ok_packet():
            raise ValueError('Cannot create ' + str(self.__class__.__name__) +
                             ' object from invalid packet type')

        self.packet = from_packet
        self.packet.advance(1)

        self.affected_rows = self.packet.read_length_encoded_integer()
        self.insert_id = self.packet.read_length_encoded_integer()
        self.server_status, self.warning_count = self.read_struct('<HH')
        self.message = self.packet.read_all()
        self.has_next = self.server_status & SERVER_STATUS.SERVER_MORE_RESULTS_EXISTS

    def __getattr__(self, key):
        return getattr(self.packet, key)


class EOFPacketWrapper(object):
    """
    EOF Packet Wrapper. It uses an existing packet object, and wraps
    around it, exposing useful variables while still providing access
    to the original packet objects variables and methods.
    """

    def __init__(self, from_packet):
        if not from_packet.is_eof_packet():
            raise ValueError(
                "Cannot create '{0}' object from invalid packet type".format(
                    self.__class__))

        self.packet = from_packet
        self.warning_count, self.server_status = self.packet.read_struct('<xhh')
        if DEBUG: print("server_status=", self.server_status)
        self.has_next = self.server_status & SERVER_STATUS.SERVER_MORE_RESULTS_EXISTS

    def __getattr__(self, key):
        return getattr(self.packet, key)


class LoadLocalPacketWrapper(object):
    """
    Load Local Packet Wrapper. It uses an existing packet object, and wraps
    around it, exposing useful variables while still providing access
    to the original packet objects variables and methods.
    """

    def __init__(self, from_packet):
        if not from_packet.is_load_local_packet():
            raise ValueError(
                "Cannot create '{0}' object from invalid packet type".format(
                    self.__class__))

        self.packet = from_packet
        self.filename = self.packet.get_all_data()[1:]
        if DEBUG: print("filename=", self.filename)

    def __getattr__(self, key):
        return getattr(self.packet, key)


class Connection(object):
    """
    Representation of a socket with a mysql server.

    The proper way to get an instance of this class is to call
    connect().
    """

    _sock = None
    _auth_plugin_name = ''
    _closed = False

    def __init__(self, host=None, user=None, password="",
                 database=None, port=0, unix_socket=None,
                 charset='', sql_mode=None,
                 read_default_file=None, conv=None, use_unicode=None,
                 client_flag=0, cursorclass=Cursor, init_command=None,
                 connect_timeout=10, ssl=None, read_default_group=None,
                 compress=None, named_pipe=None, no_delay=None,
                 autocommit=False, db=None, passwd=None, local_infile=False,
                 max_allowed_packet=16*1024*1024, defer_connect=False,
                 auth_plugin_map={}, read_timeout=None, write_timeout=None,
                 bind_address=None):
        """
        Establish a connection to the MySQL database. Accepts several
        arguments:

        host: Host where the database server is located
        user: Username to log in as
        password: Password to use.
        database: Database to use, None to not use a particular one.
        port: MySQL port to use, default is usually OK. (default: 3306)
        bind_address: When the client has multiple network interfaces, specify
            the interface from which to connect to the host. Argument can be
            a hostname or an IP address.
        unix_socket: Optionally, you can use a unix socket rather than TCP/IP.
        charset: Charset you want to use.
        sql_mode: Default SQL_MODE to use.
        read_default_file:
            Specifies  my.cnf file to read these parameters from under the [client] section.
        conv:
            Conversion dictionary to use instead of the default one.
            This is used to provide custom marshalling and unmarshaling of types.
            See converters.
        use_unicode:
            Whether or not to default to unicode strings.
            This option defaults to true for Py3k.
        client_flag: Custom flags to send to MySQL. Find potential values in constants.CLIENT.
        cursorclass: Custom cursor class to use.
        init_command: Initial SQL statement to run when connection is established.
        connect_timeout: Timeout before throwing an exception when connecting.
            (default: 10, min: 1, max: 31536000)
        ssl:
            A dict of arguments similar to mysql_ssl_set()'s parameters.
            For now the capath and cipher arguments are not supported.
        read_default_group: Group to read from in the configuration file.
        compress; Not supported
        named_pipe: Not supported
        autocommit: Autocommit mode. None means use server default. (default: False)
        local_infile: Boolean to enable the use of LOAD DATA LOCAL command. (default: False)
        max_allowed_packet: Max size of packet sent to server in bytes. (default: 16MB)
            Only used to limit size of "LOAD LOCAL INFILE" data packet smaller than default (16KB).
        defer_connect: Don't explicitly connect on contruction - wait for connect call.
            (default: False)
        auth_plugin_map: A dict of plugin names to a class that processes that plugin.
            The class will take the Connection object as the argument to the constructor.
            The class needs an authenticate method taking an authentication packet as
            an argument.  For the dialog plugin, a prompt(echo, prompt) method can be used
            (if no authenticate method) for returning a string from the user. (experimental)
        db: Alias for database. (for compatibility to MySQLdb)
        passwd: Alias for password. (for compatibility to MySQLdb)
        """
        if no_delay is not None:
            warnings.warn("no_delay option is deprecated", DeprecationWarning)

        if use_unicode is None and sys.version_info[0] > 2:
            use_unicode = True

        if db is not None and database is None:
            database = db
        if passwd is not None and not password:
            password = passwd

        if compress or named_pipe:
            raise NotImplementedError("compress and named_pipe arguments are not supported")

        self._local_infile = bool(local_infile)
        if self._local_infile:
            client_flag |= CLIENT.LOCAL_FILES

        if read_default_group and not read_default_file:
            if sys.platform.startswith("win"):
                read_default_file = "c:\\my.ini"
            else:
                read_default_file = "/etc/my.cnf"

        if read_default_file:
            if not read_default_group:
                read_default_group = "client"

            cfg = Parser()
            cfg.read(os.path.expanduser(read_default_file))

            def _config(key, arg):
                if arg:
                    return arg
                try:
                    return cfg.get(read_default_group, key)
                except Exception:
                    return arg

            user = _config("user", user)
            password = _config("password", password)
            host = _config("host", host)
            database = _config("database", database)
            unix_socket = _config("socket", unix_socket)
            port = int(_config("port", port))
            bind_address = _config("bind-address", bind_address)
            charset = _config("default-character-set", charset)
            if not ssl:
                ssl = {}
            if isinstance(ssl, dict):
                for key in ["ca", "capath", "cert", "key", "cipher"]:
                    value = _config("ssl-" + key, ssl.get(key))
                    if value:
                        ssl[key] = value

        self.ssl = False
        if ssl:
            if not SSL_ENABLED:
                raise NotImplementedError("ssl module not found")
            self.ssl = True
            client_flag |= CLIENT.SSL
            self.ctx = self._create_ssl_ctx(ssl)

        self.host = host or "localhost"
        self.port = port or 3306
        self.user = user or DEFAULT_USER
        self.password = password or ""
        self.db = database
        self.unix_socket = unix_socket
        self.bind_address = bind_address
        if not (0 < connect_timeout <= 31536000):
            raise ValueError("connect_timeout should be >0 and <=31536000")
        self.connect_timeout = connect_timeout or None
        if read_timeout is not None and read_timeout <= 0:
            raise ValueError("read_timeout should be >= 0")
        self._read_timeout = read_timeout
        if write_timeout is not None and write_timeout <= 0:
            raise ValueError("write_timeout should be >= 0")
        self._write_timeout = write_timeout
        if charset:
            self.charset = charset
            self.use_unicode = True
        else:
            self.charset = DEFAULT_CHARSET
            self.use_unicode = False

        if use_unicode is not None:
            self.use_unicode = use_unicode

        self.encoding = charset_by_name(self.charset).encoding

        client_flag |= CLIENT.CAPABILITIES
        if self.db:
            client_flag |= CLIENT.CONNECT_WITH_DB
        self.client_flag = client_flag

        self.cursorclass = cursorclass

        self._result = None
        self._affected_rows = 0
        self.host_info = "Not connected"

        #: specified autocommit mode. None means use server default.
        self.autocommit_mode = autocommit

        if conv is None:
            conv = _conv
        # Need for MySQLdb compatibility.
        self.encoders = dict([(k, v) for (k, v) in conv.items() if type(k) is not int])
        self.decoders = dict([(k, v) for (k, v) in conv.items() if type(k) is int])
        self.sql_mode = sql_mode
        self.init_command = init_command
        self.max_allowed_packet = max_allowed_packet
        self._auth_plugin_map = auth_plugin_map
        if defer_connect:
            self._sock = None
        else:
            self.connect()

    def _create_ssl_ctx(self, sslp):
        if isinstance(sslp, ssl.SSLContext):
            return sslp
        ca = sslp.get('ca')
        capath = sslp.get('capath')
        hasnoca = ca is None and capath is None
        ctx = ssl.create_default_context(cafile=ca, capath=capath)
        ctx.check_hostname = not hasnoca and sslp.get('check_hostname', True)
        ctx.verify_mode = ssl.CERT_NONE if hasnoca else ssl.CERT_REQUIRED
        if 'cert' in sslp:
            ctx.load_cert_chain(sslp['cert'], keyfile=sslp.get('key'))
        if 'cipher' in sslp:
            ctx.set_ciphers(sslp['cipher'])
        ctx.options |= ssl.OP_NO_SSLv2
        ctx.options |= ssl.OP_NO_SSLv3
        return ctx

    def close(self):
        """Send the quit message and close the socket"""
        if self._closed:
            raise err.Error("Already closed")
        self._closed = True
        if self._sock is None:
            return
        send_data = struct.pack('<iB', 1, COMMAND.COM_QUIT)
        try:
            self._write_bytes(send_data)
        except Exception:
            pass
        finally:
            self._force_close()

    @property
    def open(self):
        return self._sock is not None

    def _force_close(self):
        """Close connection without QUIT message"""
        if self._sock:
            try:
                self._sock.close()
            except:
                pass
        self._sock = None
        self._rfile = None

    __del__ = _force_close

    def autocommit(self, value):
        self.autocommit_mode = bool(value)
        current = self.get_autocommit()
        if value != current:
            self._send_autocommit_mode()

    def get_autocommit(self):
        return bool(self.server_status &
                    SERVER_STATUS.SERVER_STATUS_AUTOCOMMIT)

    def _read_ok_packet(self):
        pkt = self._read_packet()
        if not pkt.is_ok_packet():
            raise err.OperationalError(2014, "Command Out of Sync")
        ok = OKPacketWrapper(pkt)
        self.server_status = ok.server_status
        return ok

    def _send_autocommit_mode(self):
        """Set whether or not to commit after every execute()"""
        self._execute_command(COMMAND.COM_QUERY, "SET AUTOCOMMIT = %s" %
                              self.escape(self.autocommit_mode))
        self._read_ok_packet()

    def begin(self):
        """Begin transaction."""
        self._execute_command(COMMAND.COM_QUERY, "BEGIN")
        self._read_ok_packet()

    def commit(self):
        """Commit changes to stable storage"""
        self._execute_command(COMMAND.COM_QUERY, "COMMIT")
        self._read_ok_packet()

    def rollback(self):
        """Roll back the current transaction"""
        self._execute_command(COMMAND.COM_QUERY, "ROLLBACK")
        self._read_ok_packet()

    def show_warnings(self):
        """SHOW WARNINGS"""
        self._execute_command(COMMAND.COM_QUERY, "SHOW WARNINGS")
        result = MySQLResult(self)
        result.read()
        return result.rows

    def select_db(self, db):
        """Set current db"""
        self._execute_command(COMMAND.COM_INIT_DB, db)
        self._read_ok_packet()

    def escape(self, obj, mapping=None):
        """Escape whatever value you pass to it.
        
        Non-standard, for internal use; do not use this in your applications.
        """
        if isinstance(obj, str_type):
            return "'" + self.escape_string(obj) + "'"
        return escape_item(obj, self.charset, mapping=mapping)

    def literal(self, obj):
        """Alias for escape()
        
        Non-standard, for internal use; do not use this in your applications.
        """
        return self.escape(obj, self.encoders)

    def escape_string(self, s):
        if (self.server_status &
                SERVER_STATUS.SERVER_STATUS_NO_BACKSLASH_ESCAPES):
            return s.replace("'", "''")
        return escape_string(s)

    def cursor(self, cursor=None):
        """Create a new cursor to execute queries with"""
        if cursor:
            return cursor(self)
        return self.cursorclass(self)

    def __enter__(self):
        """Context manager that returns a Cursor"""
        return self.cursor()

    def __exit__(self, exc, value, traceback):
        """On successful exit, commit. On exception, rollback"""
        if exc:
            self.rollback()
        else:
            self.commit()

    # The following methods are INTERNAL USE ONLY (called from Cursor)
    def query(self, sql, unbuffered=False):
        # if DEBUG:
        #     print("DEBUG: sending query:", sql)
        if isinstance(sql, text_type) and not (JYTHON or IRONPYTHON):
            if PY2:
                sql = sql.encode(self.encoding)
            else:
                sql = sql.encode(self.encoding, 'surrogateescape')
        self._execute_command(COMMAND.COM_QUERY, sql)
        self._affected_rows = self._read_query_result(unbuffered=unbuffered)
        return self._affected_rows

    def next_result(self, unbuffered=False):
        self._affected_rows = self._read_query_result(unbuffered=unbuffered)
        return self._affected_rows

    def affected_rows(self):
        return self._affected_rows

    def kill(self, thread_id):
        arg = struct.pack('<I', thread_id)
        self._execute_command(COMMAND.COM_PROCESS_KILL, arg)
        return self._read_ok_packet()

    def ping(self, reconnect=True):
        """Check if the server is alive"""
        if self._sock is None:
            if reconnect:
                self.connect()
                reconnect = False
            else:
                raise err.Error("Already closed")
        try:
            self._execute_command(COMMAND.COM_PING, "")
            return self._read_ok_packet()
        except Exception:
            if reconnect:
                self.connect()
                return self.ping(False)
            else:
                raise

    def set_charset(self, charset):
        # Make sure charset is supported.
        encoding = charset_by_name(charset).encoding

        self._execute_command(COMMAND.COM_QUERY, "SET NAMES %s" % self.escape(charset))
        self._read_packet()
        self.charset = charset
        self.encoding = encoding

    def connect(self, sock=None):
        self._closed = False
        try:
            if sock is None:
                if self.unix_socket and self.host in ('localhost', '127.0.0.1'):
                    sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
                    sock.settimeout(self.connect_timeout)
                    sock.connect(self.unix_socket)
                    self.host_info = "Localhost via UNIX socket"
                    if DEBUG: print('connected using unix_socket')
                else:
                    kwargs = {}
                    if self.bind_address is not None:
                        kwargs['source_address'] = (self.bind_address, 0)
                    while True:
                        try:
                            sock = socket.create_connection(
                                (self.host, self.port), self.connect_timeout,
                                **kwargs)
                            break
                        except (OSError, IOError) as e:
                            if e.errno == errno.EINTR:
                                continue
                            raise
                    self.host_info = "socket %s:%d" % (self.host, self.port)
                    if DEBUG: print('connected using socket')
                    sock.setsockopt(socket.IPPROTO_TCP, socket.TCP_NODELAY, 1)
                sock.settimeout(None)
                sock.setsockopt(socket.SOL_SOCKET, socket.SO_KEEPALIVE, 1)
            self._sock = sock
            self._rfile = _makefile(sock, 'rb')
            self._next_seq_id = 0

            self._get_server_information()
            self._request_authentication()

            if self.sql_mode is not None:
                c = self.cursor()
                c.execute("SET sql_mode=%s", (self.sql_mode,))

            if self.init_command is not None:
                c = self.cursor()
                c.execute(self.init_command)
                c.close()
                self.commit()

            if self.autocommit_mode is not None:
                self.autocommit(self.autocommit_mode)
        except BaseException as e:
            self._rfile = None
            if sock is not None:
                try:
                    sock.close()
                except:
                    pass

            if isinstance(e, (OSError, IOError, socket.error)):
                exc = err.OperationalError(
                        2003,
                        "Can't connect to MySQL server on %r (%s)" % (
                            self.host, e))
                # Keep original exception and traceback to investigate error.
                exc.original_exception = e
                exc.traceback = traceback.format_exc()
                if DEBUG: print(exc.traceback)
                raise exc

            # If e is neither DatabaseError or IOError, It's a bug.
            # But raising AssertionError hides original error.
            # So just reraise it.
            raise

    def write_packet(self, payload):
        """Writes an entire "mysql packet" in its entirety to the network
        addings its length and sequence number.
        """
        # Internal note: when you build packet manualy and calls _write_bytes()
        # directly, you should set self._next_seq_id properly.
        data = pack_int24(len(payload)) + int2byte(self._next_seq_id) + payload
        if DEBUG: dump_packet(data)
        self._write_bytes(data)
        self._next_seq_id = (self._next_seq_id + 1) % 256

    def _read_packet(self, packet_type=MysqlPacket):
        """Read an entire "mysql packet" in its entirety from the network
        and return a MysqlPacket type that represents the results.
        """
        buff = b''
        while True:
            packet_header = self._read_bytes(4)
            if DEBUG: dump_packet(packet_header)

            btrl, btrh, packet_number = struct.unpack('<HBB', packet_header)
            bytes_to_read = btrl + (btrh << 16)
            if packet_number != self._next_seq_id:
                self._force_close()
                if packet_number == 0:
                    # MariaDB sends error packet with seqno==0 when shutdown
                    raise err.OperationalError(
                        CR.CR_SERVER_LOST,
                        "Lost connection to MySQL server during query")
                raise err.InternalError(
                    "Packet sequence number wrong - got %d expected %d"
                    % (packet_number, self._next_seq_id))
            self._next_seq_id = (self._next_seq_id + 1) % 256

            recv_data = self._read_bytes(bytes_to_read)
            if DEBUG: dump_packet(recv_data)
            buff += recv_data
            # https://dev.mysql.com/doc/internals/en/sending-more-than-16mbyte.html
            if bytes_to_read == 0xffffff:
                continue
            if bytes_to_read < MAX_PACKET_LEN:
                break

        packet = packet_type(buff, self.encoding)
        packet.check_error()
        return packet

    def _read_bytes(self, num_bytes):
        self._sock.settimeout(self._read_timeout)
        while True:
            try:
                data = self._rfile.read(num_bytes)
                break
            except (IOError, OSError) as e:
                if e.errno == errno.EINTR:
                    continue
                self._force_close()
                raise err.OperationalError(
                    CR.CR_SERVER_LOST,
                    "Lost connection to MySQL server during query (%s)" % (e,))
        if len(data) < num_bytes:
            self._force_close()
            raise err.OperationalError(
                CR.CR_SERVER_LOST, "Lost connection to MySQL server during query")
        return data

    def _write_bytes(self, data):
        self._sock.settimeout(self._write_timeout)
        try:
            self._sock.sendall(data)
        except IOError as e:
            self._force_close()
            raise err.OperationalError(
                CR.CR_SERVER_GONE_ERROR,
                "MySQL server has gone away (%r)" % (e,))

    def _read_query_result(self, unbuffered=False):
        if unbuffered:
            try:
                result = MySQLResult(self)
                result.init_unbuffered_query()
            except:
                result.unbuffered_active = False
                result.connection = None
                raise
        else:
            result = MySQLResult(self)
            result.read()
        self._result = result
        if result.server_status is not None:
            self.server_status = result.server_status
        return result.affected_rows

    def insert_id(self):
        if self._result:
            return self._result.insert_id
        else:
            return 0

    def _execute_command(self, command, sql):
        if not self._sock:
            raise err.InterfaceError("(0, '')")

        # If the last query was unbuffered, make sure it finishes before
        # sending new commands
        if self._result is not None:
            if self._result.unbuffered_active:
                warnings.warn("Previous unbuffered result was left incomplete")
                self._result._finish_unbuffered_query()
            while self._result.has_next:
                self.next_result()
            self._result = None

        if isinstance(sql, text_type):
            sql = sql.encode(self.encoding)

        packet_size = min(MAX_PACKET_LEN, len(sql) + 1)  # +1 is for command

        # tiny optimization: build first packet manually instead of
        # calling self..write_packet()
        prelude = struct.pack('<iB', packet_size, command)
        packet = prelude + sql[:packet_size-1]
        self._write_bytes(packet)
        if DEBUG: dump_packet(packet)
        self._next_seq_id = 1

        if packet_size < MAX_PACKET_LEN:
            return

        sql = sql[packet_size-1:]
        while True:
            packet_size = min(MAX_PACKET_LEN, len(sql))
            self.write_packet(sql[:packet_size])
            sql = sql[packet_size:]
            if not sql and packet_size < MAX_PACKET_LEN:
                break

    def _request_authentication(self):
        # https://dev.mysql.com/doc/internals/en/connection-phase-packets.html#packet-Protocol::HandshakeResponse
        if int(self.server_version.split('.', 1)[0]) >= 5:
            self.client_flag |= CLIENT.MULTI_RESULTS

        if self.user is None:
            raise ValueError("Did not specify a username")

        charset_id = charset_by_name(self.charset).id
        if isinstance(self.user, text_type):
            self.user = self.user.encode(self.encoding)

        data_init = struct.pack('<iIB23s', self.client_flag, 1, charset_id, b'')

        if self.ssl and self.server_capabilities & CLIENT.SSL:
            self.write_packet(data_init)

            self._sock = self.ctx.wrap_socket(self._sock, server_hostname=self.host)
            self._rfile = _makefile(self._sock, 'rb')

        data = data_init + self.user + b'\0'

        authresp = b''
        if self._auth_plugin_name in ('', 'mysql_native_password'):
            authresp = _scramble(self.password.encode('latin1'), self.salt)

        if self.server_capabilities & CLIENT.PLUGIN_AUTH_LENENC_CLIENT_DATA:
            data += lenenc_int(len(authresp)) + authresp
        elif self.server_capabilities & CLIENT.SECURE_CONNECTION:
            data += struct.pack('B', len(authresp)) + authresp
        else:  # pragma: no cover - not testing against servers without secure auth (>=5.0)
            data += authresp + b'\0'

        if self.db and self.server_capabilities & CLIENT.CONNECT_WITH_DB:
            if isinstance(self.db, text_type):
                self.db = self.db.encode(self.encoding)
            data += self.db + b'\0'

        if self.server_capabilities & CLIENT.PLUGIN_AUTH:
            name = self._auth_plugin_name
            if isinstance(name, text_type):
                name = name.encode('ascii')
            data += name + b'\0'

        self.write_packet(data)
        auth_packet = self._read_packet()

        # if authentication method isn't accepted the first byte
        # will have the octet 254
        if auth_packet.is_auth_switch_request():
            # https://dev.mysql.com/doc/internals/en/connection-phase-packets.html#packet-Protocol::AuthSwitchRequest
            auth_packet.read_uint8() # 0xfe packet identifier
            plugin_name = auth_packet.read_string()
            if self.server_capabilities & CLIENT.PLUGIN_AUTH and plugin_name is not None:
                auth_packet = self._process_auth(plugin_name, auth_packet)
            else:
                # send legacy handshake
                data = _scramble_323(self.password.encode('latin1'), self.salt) + b'\0'
                self.write_packet(data)
                auth_packet = self._read_packet()

    def _process_auth(self, plugin_name, auth_packet):
        plugin_class = self._auth_plugin_map.get(plugin_name)
        if not plugin_class:
            plugin_class = self._auth_plugin_map.get(plugin_name.decode('ascii'))
        if plugin_class:
            try:
                handler = plugin_class(self)
                return handler.authenticate(auth_packet)
            except AttributeError:
                if plugin_name != b'dialog':
                    raise err.OperationalError(2059, "Authentication plugin '%s'" \
                              " not loaded: - %r missing authenticate method" % (plugin_name, plugin_class))
            except TypeError:
                raise err.OperationalError(2059, "Authentication plugin '%s'" \
                    " not loaded: - %r cannot be constructed with connection object" % (plugin_name, plugin_class))
        else:
            handler = None
        if plugin_name == b"mysql_native_password":
            # https://dev.mysql.com/doc/internals/en/secure-password-authentication.html#packet-Authentication::Native41
            data = _scramble(self.password.encode('latin1'), auth_packet.read_all()) + b'\0'
        elif plugin_name == b"mysql_old_password":
            # https://dev.mysql.com/doc/internals/en/old-password-authentication.html
            data = _scramble_323(self.password.encode('latin1'), auth_packet.read_all()) + b'\0'
        elif plugin_name == b"mysql_clear_password":
            # https://dev.mysql.com/doc/internals/en/clear-text-authentication.html
            data = self.password.encode('latin1') + b'\0'
        elif plugin_name == b"dialog":
            pkt = auth_packet
            while True:
                flag = pkt.read_uint8()
                echo = (flag & 0x06) == 0x02
                last = (flag & 0x01) == 0x01
                prompt = pkt.read_all()

                if prompt == b"Password: ":
                    self.write_packet(self.password.encode('latin1') + b'\0')
                elif handler:
                    resp = 'no response - TypeError within plugin.prompt method'
                    try:
                        resp = handler.prompt(echo, prompt)
                        self.write_packet(resp + b'\0')
                    except AttributeError:
                        raise err.OperationalError(2059, "Authentication plugin '%s'" \
                                  " not loaded: - %r missing prompt method" % (plugin_name, handler))
                    except TypeError:
                        raise err.OperationalError(2061, "Authentication plugin '%s'" \
                                  " %r didn't respond with string. Returned '%r' to prompt %r" % (plugin_name, handler, resp, prompt))
                else:
                    raise err.OperationalError(2059, "Authentication plugin '%s' (%r) not configured" % (plugin_name, handler))
                pkt = self._read_packet()
                pkt.check_error()
                if pkt.is_ok_packet() or last:
                    break
            return pkt
        else:
            raise err.OperationalError(2059, "Authentication plugin '%s' not configured" % plugin_name)

        self.write_packet(data)
        pkt = self._read_packet()
        pkt.check_error()
        return pkt

    # _mysql support
    def thread_id(self):
        return self.server_thread_id[0]

    def character_set_name(self):
        return self.charset

    def get_host_info(self):
        return self.host_info

    def get_proto_info(self):
        return self.protocol_version

    def _get_server_information(self):
        i = 0
        packet = self._read_packet()
        data = packet.get_all_data()

        if DEBUG: dump_packet(data)
        self.protocol_version = byte2int(data[i:i+1])
        i += 1

        server_end = data.find(b'\0', i)
        self.server_version = data[i:server_end].decode('latin1')
        i = server_end + 1

        self.server_thread_id = struct.unpack('<I', data[i:i+4])
        i += 4

        self.salt = data[i:i+8]
        i += 9  # 8 + 1(filler)

        self.server_capabilities = struct.unpack('<H', data[i:i+2])[0]
        i += 2

        if len(data) >= i + 6:
            lang, stat, cap_h, salt_len = struct.unpack('<BHHB', data[i:i+6])
            i += 6
            self.server_language = lang
            self.server_charset = charset_by_id(lang).name

            self.server_status = stat
            if DEBUG: print("server_status: %x" % stat)

            self.server_capabilities |= cap_h << 16
            if DEBUG: print("salt_len:", salt_len)
            salt_len = max(12, salt_len - 9)

        # reserved
        i += 10

        if len(data) >= i + salt_len:
            # salt_len includes auth_plugin_data_part_1 and filler
            self.salt += data[i:i+salt_len]
            i += salt_len

        i+=1
        # AUTH PLUGIN NAME may appear here.
        if self.server_capabilities & CLIENT.PLUGIN_AUTH and len(data) >= i:
            # Due to Bug#59453 the auth-plugin-name is missing the terminating
            # NUL-char in versions prior to 5.5.10 and 5.6.2.
            # ref: https://dev.mysql.com/doc/internals/en/connection-phase-packets.html#packet-Protocol::Handshake
            # didn't use version checks as mariadb is corrected and reports
            # earlier than those two.
            server_end = data.find(b'\0', i)
            if server_end < 0: # pragma: no cover - very specific upstream bug
                # not found \0 and last field so take it all
                self._auth_plugin_name = data[i:].decode('latin1')
            else:
                self._auth_plugin_name = data[i:server_end].decode('latin1')

    def get_server_info(self):
        return self.server_version

    Warning = err.Warning
    Error = err.Error
    InterfaceError = err.InterfaceError
    DatabaseError = err.DatabaseError
    DataError = err.DataError
    OperationalError = err.OperationalError
    IntegrityError = err.IntegrityError
    InternalError = err.InternalError
    ProgrammingError = err.ProgrammingError
    NotSupportedError = err.NotSupportedError


class MySQLResult(object):

    def __init__(self, connection):
        """
        :type connection: Connection
        """
        self.connection = connection
        self.affected_rows = None
        self.insert_id = None
        self.server_status = None
        self.warning_count = 0
        self.message = None
        self.field_count = 0
        self.description = None
        self.rows = None
        self.has_next = None
        self.unbuffered_active = False

    def __del__(self):
        if self.unbuffered_active:
            self._finish_unbuffered_query()

    def read(self):
        try:
            first_packet = self.connection._read_packet()

            if first_packet.is_ok_packet():
                self._read_ok_packet(first_packet)
            elif first_packet.is_load_local_packet():
                self._read_load_local_packet(first_packet)
            else:
                self._read_result_packet(first_packet)
        finally:
            self.connection = None

    def init_unbuffered_query(self):
        self.unbuffered_active = True
        first_packet = self.connection._read_packet()

        if first_packet.is_ok_packet():
            self._read_ok_packet(first_packet)
            self.unbuffered_active = False
            self.connection = None
        elif first_packet.is_load_local_packet():
            self._read_load_local_packet(first_packet)
            self.unbuffered_active = False
            self.connection = None
        else:
            self.field_count = first_packet.read_length_encoded_integer()
            self._get_descriptions()

            # Apparently, MySQLdb picks this number because it's the maximum
            # value of a 64bit unsigned integer. Since we're emulating MySQLdb,
            # we set it to this instead of None, which would be preferred.
            self.affected_rows = 18446744073709551615

    def _read_ok_packet(self, first_packet):
        ok_packet = OKPacketWrapper(first_packet)
        self.affected_rows = ok_packet.affected_rows
        self.insert_id = ok_packet.insert_id
        self.server_status = ok_packet.server_status
        self.warning_count = ok_packet.warning_count
        self.message = ok_packet.message
        self.has_next = ok_packet.has_next

    def _read_load_local_packet(self, first_packet):
        if not self.connection._local_infile:
            raise RuntimeError(
                "**WARN**: Received LOAD_LOCAL packet but local_infile option is false.")
        load_packet = LoadLocalPacketWrapper(first_packet)
        sender = LoadLocalFile(load_packet.filename, self.connection)
        try:
            sender.send_data()
        except:
            self.connection._read_packet()  # skip ok packet
            raise

        ok_packet = self.connection._read_packet()
        if not ok_packet.is_ok_packet(): # pragma: no cover - upstream induced protocol error
            raise err.OperationalError(2014, "Commands Out of Sync")
        self._read_ok_packet(ok_packet)

    def _check_packet_is_eof(self, packet):
        if not packet.is_eof_packet():
            return False
        #TODO: Support CLIENT.DEPRECATE_EOF
        # 1) Add DEPRECATE_EOF to CAPABILITIES
        # 2) Mask CAPABILITIES with server_capabilities
        # 3) if server_capabilities & CLIENT.DEPRECATE_EOF: use OKPacketWrapper instead of EOFPacketWrapper
        wp = EOFPacketWrapper(packet)
        self.warning_count = wp.warning_count
        self.has_next = wp.has_next
        return True

    def _read_result_packet(self, first_packet):
        self.field_count = first_packet.read_length_encoded_integer()
        self._get_descriptions()
        self._read_rowdata_packet()

    def _read_rowdata_packet_unbuffered(self):
        # Check if in an active query
        if not self.unbuffered_active:
            return

        # EOF
        packet = self.connection._read_packet()
        if self._check_packet_is_eof(packet):
            self.unbuffered_active = False
            self.connection = None
            self.rows = None
            return

        row = self._read_row_from_packet(packet)
        self.affected_rows = 1
        self.rows = (row,)  # rows should tuple of row for MySQL-python compatibility.
        return row

    def _finish_unbuffered_query(self):
        # After much reading on the MySQL protocol, it appears that there is,
        # in fact, no way to stop MySQL from sending all the data after
        # executing a query, so we just spin, and wait for an EOF packet.
        while self.unbuffered_active:
            packet = self.connection._read_packet()
            if self._check_packet_is_eof(packet):
                self.unbuffered_active = False
                self.connection = None  # release reference to kill cyclic reference.

    def _read_rowdata_packet(self):
        """Read a rowdata packet for each data row in the result set."""
        rows = []
        while True:
            packet = self.connection._read_packet()
            if self._check_packet_is_eof(packet):
                self.connection = None  # release reference to kill cyclic reference.
                break
            rows.append(self._read_row_from_packet(packet))

        self.affected_rows = len(rows)
        self.rows = tuple(rows)

    def _read_row_from_packet(self, packet):
        row = []
        for encoding, converter in self.converters:
            try:
                data = packet.read_length_coded_string()
            except IndexError:
                # No more columns in this row
                # See https://github.com/PyMySQL/PyMySQL/pull/434
                break
            if data is not None:
                if encoding is not None:
                    data = data.decode(encoding)
                if DEBUG: print("DEBUG: DATA = ", data)
                if converter is not None:
                    data = converter(data)
            row.append(data)
        return tuple(row)

    def _get_descriptions(self):
        """Read a column descriptor packet for each column in the result."""
        self.fields = []
        self.converters = []
        use_unicode = self.connection.use_unicode
        conn_encoding = self.connection.encoding
        description = []

        for i in range_type(self.field_count):
            field = self.connection._read_packet(FieldDescriptorPacket)
            self.fields.append(field)
            description.append(field.description())
            field_type = field.type_code
            if use_unicode:
                if field_type == FIELD_TYPE.JSON:
                    # When SELECT from JSON column: charset = binary
                    # When SELECT CAST(... AS JSON): charset = connection encoding
                    # This behavior is different from TEXT / BLOB.
                    # We should decode result by connection encoding regardless charsetnr.
                    # See https://github.com/PyMySQL/PyMySQL/issues/488
                    encoding = conn_encoding  # SELECT CAST(... AS JSON) 
                elif field_type in TEXT_TYPES:
                    if field.charsetnr == 63:  # binary
                        # TEXTs with charset=binary means BINARY types.
                        encoding = None
                    else:
                        encoding = conn_encoding
                else:
                    # Integers, Dates and Times, and other basic data is encoded in ascii
                    encoding = 'ascii'
            else:
                encoding = None
            converter = self.connection.decoders.get(field_type)
            if converter is through:
                converter = None
            if DEBUG: print("DEBUG: field={}, converter={}".format(field, converter))
            self.converters.append((encoding, converter))

        eof_packet = self.connection._read_packet()
        assert eof_packet.is_eof_packet(), 'Protocol error, expecting EOF'
        self.description = tuple(description)


class LoadLocalFile(object):
    def __init__(self, filename, connection):
        self.filename = filename
        self.connection = connection

    def send_data(self):
        """Send data packets from the local file to the server"""
        if not self.connection._sock:
            raise err.InterfaceError("(0, '')")
        conn = self.connection

        try:
            with open(self.filename, 'rb') as open_file:
                packet_size = min(conn.max_allowed_packet, 16*1024)  # 16KB is efficient enough
                while True:
                    chunk = open_file.read(packet_size)
                    if not chunk:
                        break
                    conn.write_packet(chunk)
        except IOError:
            raise err.OperationalError(1017, "Can't find file '{0}'".format(self.filename))
        finally:
            # send the empty packet to signify we are done sending data
            conn.write_packet(b'')
