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#!/usr/bin/env python3
#
# Experimental implementation of asyncio support.
#
# This file is part of pySerial. https://github.com/pyserial/pyserial
# (C) 2015 Chris Liechti <cliechti@gmx.net>
#
# SPDX-License-Identifier: BSD-3-Clause
"""\
Support asyncio with serial ports. EXPERIMENTAL
Posix platforms only, Python 3.4+ only.
Windows event loops can not wait for serial ports with the current
implementation. It should be possible to get that working though.
"""
import asyncio
import serial
class SerialTransport(asyncio.Transport):
"""An asyncio transport model of a serial communication channel.
A transport class is an abstraction of a communication channel.
This allows protocol implementations to be developed against the
transport abstraction without needing to know the details of the
underlying channel, such as whether it is a pipe, a socket, or
indeed a serial port.
You generally won’t instantiate a transport yourself; instead, you
will call `create_serial_connection` which will create the
transport and try to initiate the underlying communication channel,
calling you back when it succeeds.
"""
def __init__(self, loop, protocol, serial_instance):
super().__init__()
self._loop = loop
self._protocol = protocol
self._serial = serial_instance
self._closing = False
self._protocol_paused = False
self._max_read_size = 1024
self._write_buffer = []
self._set_write_buffer_limits()
self._has_reader = False
self._has_writer = False
# XXX how to support url handlers too
# Asynchronous I/O requires non-blocking devices
self._serial.timeout = 0
self._serial.write_timeout = 0
# These two callbacks will be enqueued in a FIFO queue by asyncio
loop.call_soon(protocol.connection_made, self)
loop.call_soon(self._ensure_reader)
@property
def serial(self):
"""The underlying Serial instance."""
return self._serial
def __repr__(self):
return '{self.__class__.__name__}({self._loop}, {self._protocol}, {self.serial})'.format(self=self)
def is_closing(self):
"""Return True if the transport is closing or closed."""
return self._closing
def close(self):
"""Close the transport gracefully.
Any buffered data will be written asynchronously. No more data
will be received and further writes will be silently ignored.
After all buffered data is flushed, the protocol's
connection_lost() method will be called with None as its
argument.
"""
if not self._closing:
self._close(None)
def _read_ready(self):
try:
data = self._serial.read(self._max_read_size)
except serial.SerialException as e:
self._close(exc=e)
else:
if data:
self._protocol.data_received(data)
def write(self, data):
"""Write some data to the transport.
This method does not block; it buffers the data and arranges
for it to be sent out asynchronously. Writes made after the
transport has been closed will be ignored."""
if self._closing:
return
if self.get_write_buffer_size() == 0:
# Attempt to send it right away first
try:
n = self._serial.write(data)
except serial.SerialException as exc:
self._fatal_error(exc, 'Fatal write error on serial transport')
return
if n == len(data):
return # Whole request satisfied
assert n > 0
data = data[n:]
self._ensure_writer()
self._write_buffer.append(data)
self._maybe_pause_protocol()
def can_write_eof(self):
"""Serial ports do not support the concept of end-of-file.
Always returns False.
"""
return False
def pause_reading(self):
"""Pause the receiving end of the transport.
No data will be passed to the protocol’s data_received() method
until resume_reading() is called.
"""
self._remove_reader()
def resume_reading(self):
"""Resume the receiving end of the transport.
Incoming data will be passed to the protocol's data_received()
method until pause_reading() is called.
"""
self._ensure_reader()
def set_write_buffer_limits(self, high=None, low=None):
"""Set the high- and low-water limits for write flow control.
These two values control when call the protocol’s
pause_writing()and resume_writing() methods are called. If
specified, the low-water limit must be less than or equal to
the high-water limit. Neither high nor low can be negative.
"""
self._set_write_buffer_limits(high=high, low=low)
self._maybe_pause_protocol()
def get_write_buffer_size(self):
"""The number of bytes in the write buffer.
This buffer is unbounded, so the result may be larger than the
the high water mark.
"""
return sum(map(len, self._write_buffer))
def write_eof(self):
raise NotImplementedError("Serial connections do not support end-of-file")
def abort(self):
"""Close the transport immediately.
Pending operations will not be given opportunity to complete,
and buffered data will be lost. No more data will be received
and further writes will be ignored. The protocol's
connection_lost() method will eventually be called.
"""
self._abort(None)
def _maybe_pause_protocol(self):
"""To be called whenever the write-buffer size increases.
Tests the current write-buffer size against the high water
mark configured for this transport. If the high water mark is
exceeded, the protocol is instructed to pause_writing().
"""
if self.get_write_buffer_size() <= self._high_water:
return
if not self._protocol_paused:
self._protocol_paused = True
try:
self._protocol.pause_writing()
except Exception as exc:
self._loop.call_exception_handler({
'message': 'protocol.pause_writing() failed',
'exception': exc,
'transport': self,
'protocol': self._protocol,
})
def _maybe_resume_protocol(self):
"""To be called whenever the write-buffer size decreases.
Tests the current write-buffer size against the low water
mark configured for this transport. If the write-buffer
size is below the low water mark, the protocol is
instructed that is can resume_writing().
"""
if (self._protocol_paused and
self.get_write_buffer_size() <= self._low_water):
self._protocol_paused = False
try:
self._protocol.resume_writing()
except Exception as exc:
self._loop.call_exception_handler({
'message': 'protocol.resume_writing() failed',
'exception': exc,
'transport': self,
'protocol': self._protocol,
})
def _write_ready(self):
"""Asynchronously write buffered data.
This method is called back asynchronously as a writer
registered with the asyncio event-loop against the
underlying file descriptor for the serial port.
Should the write-buffer become empty if this method
is invoked while the transport is closing, the protocol's
connection_lost() method will be called with None as its
argument.
"""
data = b''.join(self._write_buffer)
num_bytes = len(data)
assert data, 'Write buffer should not be empty'
self._write_buffer.clear()
try:
n = self._serial.write(data)
except (BlockingIOError, InterruptedError):
self._write_buffer.append(data)
except serial.SerialException as exc:
self._fatal_error(exc, 'Fatal write error on serial transport')
else:
if n == len(data):
assert self._flushed()
self._remove_writer()
self._maybe_resume_protocol() # May cause further writes
# _write_ready may have been invoked by the event loop
# after the transport was closed, as part of the ongoing
# process of flushing buffered data. If the buffer
# is now empty, we can close the connection
if self._closing and self._flushed():
self._close()
return
assert n > 0
data = data[n:]
self._write_buffer.append(data) # Try again later
self._maybe_resume_protocol()
assert self._has_writer
def _ensure_reader(self):
if (not self._has_reader) and (not self._closing):
self._loop.add_reader(self._serial.fd, self._read_ready)
self._has_reader = True
def _remove_reader(self):
if self._has_reader:
self._loop.remove_reader(self._serial.fd)
self._has_reader = False
def _ensure_writer(self):
if (not self._has_writer) and (not self._closing):
self._loop.add_writer(self._serial.fd, self._write_ready)
self._has_writer = True
def _remove_writer(self):
if self._has_writer:
self._loop.remove_writer(self._serial.fd)
self._has_writer = False
def _set_write_buffer_limits(self, high=None, low=None):
"""Ensure consistent write-buffer limits."""
if high is None:
high = 64 * 1024 if low is None else 4 * low
if low is None:
low = high // 4
if not high >= low >= 0:
raise ValueError('high (%r) must be >= low (%r) must be >= 0' %
(high, low))
self._high_water = high
self._low_water = low
def _fatal_error(self, exc, message='Fatal error on serial transport'):
"""Report a fatal error to the event-loop and abort the transport."""
self._loop.call_exception_handler({
'message': message,
'exception': exc,
'transport': self,
'protocol': self._protocol,
})
self._abort(exc)
def _flushed(self):
"""True if the write buffer is empty, otherwise False."""
return self.get_write_buffer_size() == 0
def _close(self, exc=None):
"""Close the transport gracefully.
If the write buffer is already empty, writing will be
stopped immediately and a call to the protocol's
connection_lost() method scheduled.
If the write buffer is not already empty, the
asynchronous writing will continue, and the _write_ready
method will call this _close method again when the
buffer has been flushed completely.
"""
self._closing = True
self._remove_reader()
if self._flushed():
self._remove_writer()
self._loop.call_soon(self._call_connection_lost, exc)
def _abort(self, exc):
"""Close the transport immediately.
Pending operations will not be given opportunity to complete,
and buffered data will be lost. No more data will be received
and further writes will be ignored. The protocol's
connection_lost() method will eventually be called with the
passed exception.
"""
self._closing = True
self._remove_reader()
self._remove_writer() # Pending buffered data will not be written
self._loop.call_soon(self._call_connection_lost, exc)
def _call_connection_lost(self, exc):
"""Close the connection.
Informs the protocol through connection_lost() and clears
pending buffers and closes the serial connection.
"""
assert self._closing
assert not self._has_writer
assert not self._has_reader
self._serial.flush()
try:
self._protocol.connection_lost(exc)
finally:
self._write_buffer.clear()
self._serial.close()
self._serial = None
self._protocol = None
self._loop = None
@asyncio.coroutine
def create_serial_connection(loop, protocol_factory, *args, **kwargs):
ser = serial.serial_for_url(*args, **kwargs)
protocol = protocol_factory()
transport = SerialTransport(loop, protocol, ser)
return (transport, protocol)
@asyncio.coroutine
def open_serial_connection(**kwargs):
"""A wrapper for create_serial_connection() returning a (reader,
writer) pair.
The reader returned is a StreamReader instance; the writer is a
StreamWriter instance.
The arguments are all the usual arguments to Serial(). Additional
optional keyword arguments are loop (to set the event loop instance
to use) and limit (to set the buffer limit passed to the
StreamReader.
This function is a coroutine.
"""
# in order to avoid errors when pySerial is installed under Python 2,
# avoid Pyhthon 3 syntax here. So do not use this function as a good
# example!
loop = kwargs.get('loop', asyncio.get_event_loop())
limit = kwargs.get('limit', asyncio.streams._DEFAULT_LIMIT)
reader = asyncio.StreamReader(limit=limit, loop=loop)
protocol = asyncio.StreamReaderProtocol(reader, loop=loop)
# in Python 3 we would write "yield transport, _ from c()"
for transport, _ in create_serial_connection(
loop=loop,
protocol_factory=lambda: protocol,
**kwargs):
yield transport, _
writer = asyncio.StreamWriter(transport, protocol, reader, loop)
# in Python 3 we would write "return reader, writer"
raise StopIteration(reader, writer)
# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
# test
if __name__ == '__main__':
class Output(asyncio.Protocol):
def connection_made(self, transport):
self.transport = transport
print('port opened', transport)
transport.serial.rts = False
transport.write(b'hello world\n')
def data_received(self, data):
print('data received', repr(data))
if b'\n' in data:
self.transport.close()
def connection_lost(self, exc):
print('port closed')
asyncio.get_event_loop().stop()
def pause_writing(self):
print('pause writing')
print(self.transport.get_write_buffer_size())
def resume_writing(self):
print(self.transport.get_write_buffer_size())
print('resume writing')
loop = asyncio.get_event_loop()
coro = create_serial_connection(loop, Output, '/dev/ttyUSB0', baudrate=115200)
loop.run_until_complete(coro)
loop.run_forever()
loop.close()
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