def _process_request(self, req_data, req_addr):
# The TFTP specification (RFC 1350) says that a request that is denied
# should result in an error packet being sent. It also specifies that an
# invalid packet received as part of a connection should result in an
# error packet being sent. However, it does not specify what should
# happen if an invalid packet is sent to the request port.
# Most other implementations seem to ignore requests with an invalid
# opcode, so we choose to do the same. We still log a debug message in
# these cases.
# A request must have at least two bytes for the opcode.
if len(req_data) < 2:
logger.debug('Invalid request from %s: The request was too short.',
socket_address_to_str(req_addr))
return
(opcode_num, ) = struct.unpack_from('!H', req_data)
try:
opcode = Opcode(opcode_num)
except Exception:
logger.debug(
'Invalid request from %s: Opcode %s is not recognized.',
socket_address_to_str(req_addr), opcode_num)
return
if opcode == Opcode.READ_REQUEST:
self._process_read_request(req_data, req_addr)
elif opcode == Opcode.WRITE_REQUEST:
self._process_write_request(req_data, req_addr)
else:
self._process_invalid_request(opcode, req_addr)
def _process_write_request(self, req_data, req_addr):
logger.error(
'Received write request from %s, but this server only supports '
'read requests', socket_address_to_str(req_addr))
data = error_packet(ErrorCode.ACCESS_VIOLATION,
'Write requests are not allowed by this server.')
self._socket.sendto(data, req_addr)
def _delegate_request(self):
try:
response_started = False
# No sane HTTP client will ever send a request path that does
# not start with a slash or contains a null byte. We do not
# check that the request path does not contain a null byte after
# decoding, this is the job of the handler that does the
# decoding.
if (not self.path.startswith('/')) or ('\0' in self.path):
response_started = True
self.send_error(http.HTTPStatus.BAD_REQUEST)
return
for handler in self.server.real_request_handlers:
context = handler.prepare_context(self.path)
if handler.can_handle(self.path, context):
try:
(status, headers, body) = handler.handle(
self.path,
self.command,
self.headers,
self.rfile,
self.client_address,
context)
except Exception:
logger.exception(
'Request handler for %s request for file "%s" '
'from client %s raised an exception.',
self.command,
self.path,
socket_address_to_str(self.client_address))
response_started = True
self.send_error(
http.HTTPStatus.INTERNAL_SERVER_ERROR)
return
# If status is an error code and there is neither a body
# nor are there headers, we use send_error instead of
# send_response.
response_started = True
if ((status.value >= 400)
and (not headers)
and (body is None)):
self.send_error(status)
return
self.send_response(status)
if headers is not None:
for header_name, header_value in headers.items():
self.send_header(header_name, header_value)
self.end_headers()
if body is not None:
shutil.copyfileobj(body, self.wfile)
return
self.send_error(http.HTTPStatus.NOT_FOUND)
except Exception:
# We do not want a problem with a request to bubble up into the
# calling code, so we log the problem and continue.
logger.exception('Request processing failed.')
if not response_started:
self.send_error(http.HTTPStatus.INTERNAL_SERVER_ERROR)
return
def _process_invalid_request(self, opcode, req_addr):
logger.debug(
'Received request from %s with opcode %s, but only READ or WRITE '
'requests are allowed on this server port.',
socket_address_to_str(req_addr), opcode)
data = error_packet(
ErrorCode.ILLEGAL_OPERATION,
'Only read or write requests are allowed on this port.')
self._socket.sendto(data, req_addr)
def _handle_read(self, filename, transfer_mode, options, client_address,
handler_function, handler_context):
# If debugging is enabled, we make the info message more verbose.
if logger.isEnabledFor(logging.DEBUG):
logger.info(
'Received read request for file "%s" from client %s using mode '
'%s and options %s.', filename,
socket_address_to_str(client_address), transfer_mode, options)
else:
logger.info('Handling read request for file "%s" from client %s.',
filename, socket_address_to_str(client_address))
# Constructing the request object is sufficient for handling the
# request. The actual request handling is done by a daemon thread that
# is created when constructing the object.
_TftpReadRequest(filename, transfer_mode, options, client_address,
handler_function, handler_context,
self._default_timeout, self._max_timeout,
self._max_retries, self._max_block_size,
self._block_counter_wrap_value)
def _process_read_request(self, req_data, req_addr):
try:
(filename, transfer_mode, options) = decode_read_request(req_data)
except Exception:
# If we cannot decode the read request, this is an error, but in the
# client, not the server, so we log it with a level of INFO.
logger.info(
'Decoding read request from %s resulted in an exception.',
socket_address_to_str(req_addr))
data = error_packet(ErrorCode.ILLEGAL_OPERATION,
'Malformed read request.')
self._socket.sendto(data, req_addr)
return
# The mail transfer mode is only valid for write requests (and we do not
# support it anyway).
if transfer_mode == TransferMode.MAIL:
# If the client requests transfer mode "mail" this is not an error
# in the server, so we log it with a level of INFO.
logger.info(
'Read request from %s requested unsupported transfer mode '
'"mail".', socket_address_to_str(req_addr))
data = error_packet(
ErrorCode.ILLEGAL_OPERATION,
'Transfer mode mail is not allowed for read requests.')
self._socket.sendto(data, req_addr)
return
# We try the request handlers in order until we find one that can handle
# the request.
for request_handler in self._request_handlers:
handler_context = request_handler.prepare_context(filename)
if request_handler.can_handle(filename, handler_context):
self._handle_read(filename, transfer_mode, options, req_addr,
request_handler.handle, handler_context)
return
# If we cannot find such a request handler, we tell the client that the
# file does not exist.
logger.info(
'No handler can fulfill request for file "%s" from client %s.',
filename, socket_address_to_str(req_addr))
data = error_packet(ErrorCode.FILE_NOT_FOUND,
'The requested file does not exist.')
self._socket.sendto(data, req_addr)
def _receive(self):
self._set_socket_timeout()
(data, from_addr) = self._socket.recvfrom(MAX_REQUEST_PACKET_SIZE)
# The TFTP specification demands that we send an error packet to each
# client that sends a packet to a port that belongs to the connection
# of a different client. For this connection, we are supposed to ignore
# such a packet and continue waiting for a packet from the right client.
while from_addr != self._client_address:
logger.debug(
'Received unexpected packet from %s on socket handling '
'connection from %s.', socket_address_to_str(from_addr),
socket_address_to_str(self._client_address))
data = error_packet(
ErrorCode.UNKNOWN_TRANSFER_ID,
'This port is associated with a different client connection.')
self._socket.sendto(data, from_addr)
# Some time has already passed, so we have to reset the socket
# timeout.
self._set_socket_timeout()
(data, from_addr) = self._socket.recvfrom(MAX_REQUEST_PACKET_SIZE)
return data
def start(self):
"""
Starts this server instance. This opens the server socket, binds it, and
creates a deamon thread that processes requests.
If the server is already running, this method does nothing.
"""
with self._running_lock:
if self._running:
return
self._socket = socket.socket(family=socket.AF_INET6,
type=socket.SOCK_DGRAM)
try:
self._socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR,
1)
# This timeout specifies how quickly we can shutdown the server.
self._socket.settimeout(0.1)
# socket.IPPROTO_IPV6 is not available when running on Windows
# and using Python < 3.8, so we fall back to a fixed value if it
# is not available.
try:
ipproto_ipv6 = socket.IPPROTO_IPV6
except AttributeError:
ipproto_ipv6 = 41
# socket.IPV6_V6ONLY, on the other hand, should be available on
# Windows, at least for the Python versions we care about
# (>= 3.5). If it is not available or if the call to setsockopt
# fails, we log a warning, but continue.
try:
self._socket.setsockopt(ipproto_ipv6, socket.IPV6_V6ONLY,
0)
except Exception:
logger.warning(
'Cannot set IPV6_V6ONLY socket option to 0, socket '
'might not be reachable via IPv4.')
self._socket.bind((self._bind_address, self._bind_port))
logger.info(
'TFTP server is listening on %s.',
socket_address_to_str(
(self._bind_address, self._bind_port)))
self._main_thread = threading.Thread(target=self._run,
daemon=True)
self._main_thread.start()
self._running = True
except BaseException:
self._socket.close()
self._socket = None
raise
def start(self):
"""
Start this server instance.
If the server is already running, this method does nothing.
"""
with self._running_lock:
if self._running:
return
self._server = self._ThreadingHTTPServer(
(self._bind_address, self._bind_port),
self._DelegatingRequestHandler)
logger.info(
'HTTP server is listening on %s.',
socket_address_to_str((self._bind_address, self._bind_port)))
self._server.real_request_handlers = self._request_handlers
self._main_thread = threading.Thread(target=self._run, daemon=True)
self._main_thread.start()
self._running = True
def _send_options_ack(self):
data = options_ack_packet(self._options)
tries_left = self._max_retries + 1
ack_received = False
while not ack_received and tries_left > 0:
# With each try, we have to reset the timeout.
self._reset_timeout()
logger.debug('Sending OACK with options %s to %s.', self._options,
socket_address_to_str(self._client_address))
self._send(data)
try:
while not ack_received:
block_number = self._receive_ack()
# The ACK for the options ACK has to use a block number of
# zero.
ack_received = (block_number == 0)
except socket.timeout:
if tries_left > 0:
tries_left -= 1
else:
raise
def _send_data_block(self, block_number, data):
packet_data = data_packet(block_number, data)
tries_left = self._max_retries + 1
ack_received = False
while not ack_received and tries_left > 0:
# With each try, we have to reset the timeout.
self._reset_timeout()
logger.debug(
'Sending DATA with block # %s and %s bytes of data to %s.',
block_number, len(data),
socket_address_to_str(self._client_address))
try:
self._send(packet_data)
while not ack_received:
ack_block_number = self._receive_ack()
# The block number in the ACK packet has to match the
# block number in the DATA packet.
ack_received = (ack_block_number == block_number)
except socket.timeout:
if tries_left > 0:
tries_left -= 1
else:
raise
def _receive_ack(self):
data = self._receive()
if len(data) < 2:
raise _TftpReadRequest._InvalidPacket('Short packet received.')
(opcode_num, ) = struct.unpack_from('!H', data)
try:
opcode = Opcode(opcode_num)
except ValueError:
raise _TftpReadRequest._InvalidPacket(
'Received packet with invalid opcode %s.', opcode_num)
if opcode == Opcode.ACK:
try:
block_number = decode_ack(data)
logger.debug('Received ACK for block # %s from %s.',
block_number,
socket_address_to_str(self._client_address))
return block_number
except ValueError:
raise _TftpReadRequest._InvalidPacket(
'Received malformed ACK packet.')
elif opcode == Opcode.ERROR:
(error_code, error_message) = decode_error(data)
if error_code == ErrorCode.TRANSFER_ABORTED:
raise _TftpReadRequest._TransferAborted()
if error_code is not None and error_message:
raise _TftpReadRequest._ClientError(
'Error code {0}: {1}'.format(error_code.value,
error_message))
elif error_code is not None:
raise _TftpReadRequest._ClientError('Error code {0}.'.format(
error_code.value))
elif error_message:
raise _TftpReadRequest._ClientError(
'Error code unknown: {0}'.format(error_message))
else:
raise _TftpReadRequest._ClientError('Unknown error.')
def _run(self):
try:
self._socket = socket.socket(family=socket.AF_INET6,
type=socket.SOCK_DGRAM)
except Exception:
logger.exception(
'Error creating socket for read request for file "%s" from '
'client %s.', self._filename,
socket_address_to_str(self._client_address))
return
# We want to make sure that we always close the socket, so we use it in
# a with statement.
with self._socket:
self._socket.settimeout(self._timeout)
# socket.IPPROTO_IPV6 is not available when running on Windows and
# using Python < 3.8, so we fall back to a fixed value if it is not
# available.
try:
ipproto_ipv6 = socket.IPPROTO_IPV6
except AttributeError:
ipproto_ipv6 = 41
# socket.IPV6_V6ONLY, on the other hand, should be available on
# Windows, at least for the Python versions we care about (>= 3.5).
# If it is not available or if the call to setsockopt fails, we do
# not even log a warning because we most likely already logged that
# warning for the main socket.
try:
self._socket.setsockopt(ipproto_ipv6, socket.IPV6_V6ONLY, 0)
except Exception:
pass
try:
self._file = self._handler_function(self._filename,
self._client_address,
self._handler_context)
except TftpError as e:
# A TftpError is not necessarily a "real" error, so we only log
# it with a level of info.
logger.info(
'Request handler for read request for file "%s" from '
'client %s signalled an error with error code %s and '
'message "%s".', self._filename,
socket_address_to_str(self._client_address), e.error_code,
e.message)
data = error_packet(e.error_code, e.message)
# When sending the error, we want to use a fresh timeout value.
self._socket.settimeout(self._timeout)
self._send(data)
return
except Exception:
logger.exception(
'Request handler for read request for file "%s" from '
'client %s raised an exception.', self._filename,
socket_address_to_str(self._client_address))
data = error_packet(
ErrorCode.NOT_DEFINED,
'An internal error occurred while trying to fulfill the '
'request.')
# When sending the error, we want to use a fresh timeout value.
self._socket.settimeout(self._timeout)
self._send(data)
return
# We always want to close the file-like object, so we use it in a
# with statement.
with self._file:
# If the client requested the file size, we tell it if possible.
# We do this here because we need access to the file in order to
# determine its size.
self._process_transfer_size_option()
if self._netascii_mode:
self._file_reader = _TftpReadRequest._NetasciiReader(
self._file)
else:
self._file_reader = _TftpReadRequest._OctetReader(
self._file)
self._process_request()
def _process_request(self):
try:
if self._options:
self._send_options_ack()
self._send_data()
except socket.timeout:
# If we got a timeout the max. number of retries has been reached
# and we give up.
logger.info('Request for file "%s" from client %s timed out.',
self._filename,
socket_address_to_str(self._client_address))
except _TftpReadRequest._BlockCounterOverflow:
# This exception is raised if a file is so large that the limit of
# the block counter is reached, but wrapping of the counter is not
# allowed.
logger.error(
'Processing of request for file "%s" from client %s was '
'aborted due the block counter reaching its limit.',
self._filename, socket_address_to_str(self._client_address))
# When sending the error, we want to use a fresh timeout value.
self._socket.settimeout(self._timeout)
self._send(
error_packet(ErrorCode.NOT_DEFINED,
'File is too large to complete the transfer.'))
except _TftpReadRequest._ClientError as e:
# If the client sent an error message, we log it and abort this
# connection.
logger.info(
'Processing of request for file "%s" from client %s was '
'aborted due to a client error: %s', self._filename,
socket_address_to_str(self._client_address), e.args[0])
except _TftpReadRequest._InvalidPacket as e:
message = e.args[0]
# If we received an invalid packet, we log this, send an error to
# the client, and abort this connection.
logger.info(
'Processing of request for file "%s" from client %s was '
'aborted due to an invalid client packet: %s', self._filename,
socket_address_to_str(self._client_address), message)
# When sending the error, we want to use a fresh timeout value.
self._socket.settimeout(self._timeout)
self._send(error_packet(ErrorCode.NOT_DEFINED, message))
except _TftpReadRequest._TransferAborted:
# The client aborting a transfer is not an error, but we log a
# simple informational message.
logger.info(
'Processing of request for file "%s" from client %s was '
'aborted on client request.', self._filename,
socket_address_to_str(self._client_address))
except Exception:
# Otherwise, there must be some kind of internal error, so we log
# the exception and send an error code to the client.
logger.exception(
'Exception while processing read request for file "%s" from '
'client %s.', self._filename,
socket_address_to_str(self._client_address))
data = error_packet(
ErrorCode.NOT_DEFINED,
'An internal error occurred while trying to fulfill the '
'request.')
# When sending the error, we want to use a fresh timeout value.
self._socket.settimeout(self._timeout)
self._send(data)
