examples/port_publisher.py

#! /usr/bin/env python
"""\
Multi-port serial<->TCP/IP forwarder.
- RFC 2217
- check existence of serial port periodically
- start/stop forwarders
- each forwarder creates a server socket and opens the serial port
- serial ports are opened only once. network connect/disconnect
  does not influence serial port
- only one client per connection
"""
import os
import select
import socket
import sys
import time
import traceback

import serial
import serial.rfc2217

import avahi
import dbus

class ZeroconfService:
    """\
    A simple class to publish a network service with zeroconf using avahi.
    """

    def __init__(self, name, port, stype="_http._tcp",
                 domain="", host="", text=""):
        self.name = name
        self.stype = stype
        self.domain = domain
        self.host = host
        self.port = port
        self.text = text
        self.group = None

    def publish(self):
        bus = dbus.SystemBus()
        server = dbus.Interface(
            bus.get_object(
                avahi.DBUS_NAME,
                avahi.DBUS_PATH_SERVER
            ),
            avahi.DBUS_INTERFACE_SERVER
        )

        g = dbus.Interface(
            bus.get_object(
                avahi.DBUS_NAME,
                server.EntryGroupNew()
            ),
            avahi.DBUS_INTERFACE_ENTRY_GROUP
        )

        g.AddService(avahi.IF_UNSPEC, avahi.PROTO_UNSPEC, dbus.UInt32(0),
                     self.name, self.stype, self.domain, self.host,
                     dbus.UInt16(self.port), self.text)

        g.Commit()
        self.group = g

    def unpublish(self):
        if self.group is not None:
            self.group.Reset()
            self.group = None

    def __str__(self):
        return "%r @ %s:%s (%s)" % (self.name, self.host, self.port, self.stype)



class Forwarder(ZeroconfService):
    """\
    Single port serial<->TCP/IP forarder that depends on an external select
    loop.
    - Buffers for serial -> network and network -> serial
    - RFC 2217 state
    - Zeroconf publish/unpublish on open/close.
    """

    def __init__(self, device, name, network_port, on_close=None):
        ZeroconfService.__init__(self, name, network_port, stype='_serial_port._tcp')
        self.alive = False
        self.network_port = network_port
        self.on_close = on_close
        self.device = device
        self.serial = serial.Serial()
        self.serial.port = device
        self.serial.baudrate = 115200
        self.serial.timeout = 0
        self.socket = None
        self.server_socket = None
        self.rfc2217 = None # instantiate later, when connecting

    def __del__(self):
        try:
            if self.alive: self.close()
        except:
            pass # XXX errors on shutdown

    def open(self):
        """open serial port, start network server and publish service"""
        self.buffer_net2ser = ''
        self.buffer_ser2net = ''

        # open serial port
        try:
            self.serial.open()
            self.serial.setRTS(False)
        except Exception as msg:
            self.handle_serial_error(msg)

        self.serial_settings_backup = self.serial.getSettingsDict()

        # start the socket server
        self.server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        self.server_socket.setsockopt(
            socket.SOL_SOCKET,
            socket.SO_REUSEADDR,
            self.server_socket.getsockopt(
                socket.SOL_SOCKET,
                socket.SO_REUSEADDR
            ) | 1
        )
        self.server_socket.setblocking(0)
        try:
            self.server_socket.bind( ('', self.network_port) )
            self.server_socket.listen(1)
        except socket.error as msg:
            self.handle_server_error()
            #~ raise
        if not options.quiet:
            print "%s: Waiting for connection on %s..." % (self.device, self.network_port)

        # zeroconfig
        self.publish()

        # now we are ready
        self.alive = True

    def close(self):
        """Close all resources and unpublish service"""
        if not options.quiet:
            print("%s: closing..." % (self.device, ))
        self.alive = False
        self.unpublish()
        if self.server_socket: self.server_socket.close()
        if self.socket:
            self.handle_disconnect()
        self.serial.close()
        if self.on_close is not None:
            # ensure it is only called once
            callback = self.on_close
            self.on_close = None
            callback(self)

    def write(self, data):
        """the write method is used by serial.rfc2217.PortManager. it has to
        write to the network."""
        self.buffer_ser2net += data

    def update_select_maps(self, read_map, write_map, error_map):
        """Update dictionaries for select call. insert fd->callback mapping"""
        if self.alive:
            # always handle serial port reads
            read_map[self.serial] = self.handle_serial_read
            error_map[self.serial] = self.handle_serial_error
            # handle serial port writes if buffer is not empty
            if self.buffer_net2ser:
                write_map[self.serial] = self.handle_serial_write
            # handle network
            if self.socket is not None:
                # handle socket if connected
                # only read from network if the internal buffer is not
                # already filled. the TCP flow control will hold back data
                if len(self.buffer_net2ser) < 2048:
                    read_map[self.socket] = self.handle_socket_read
                # only check for write readiness when there is data
                if self.buffer_ser2net:
                    write_map[self.socket] = self.handle_socket_write
                error_map[self.socket] = self.handle_socket_error
            else:
                # no connection, ensure clear buffer
                self.buffer_ser2net = ''
            # check the server socket
            read_map[self.server_socket] = self.handle_connect
            error_map[self.server_socket] = self.handle_server_error


    def handle_serial_read(self):
        """Reading from serial port"""
        try:
            data = os.read(self.serial.fileno(), 1024)
            if data:
                # store data in buffer if there is a client connected
                if self.socket is not None:
                    # escape outgoing data when needed (Telnet IAC (0xff) character)
                    if self.rfc2217:
                        data = serial.to_bytes(self.rfc2217.escape(data))
                    self.buffer_ser2net += data
            else:
                self.handle_serial_error()
        except Exception as msg:
            self.handle_serial_error(msg)

    def handle_serial_write(self):
        """Writing to serial port"""
        try:
            # write a chunk
            n = os.write(self.serial.fileno(), self.buffer_net2ser)
            # and see how large that chunk was, remove that from buffer
            self.buffer_net2ser = self.buffer_net2ser[n:]
        except Exception as msg:
            self.handle_serial_error(msg)

    def handle_serial_error(self, error=None):
        """Serial port error"""
        # terminate connection
        self.close()

    def handle_socket_read(self):
        """Read from socket"""
        try:
            # read a chunk from the serial port
            data = self.socket.recv(1024)
            if data:
                # Process RFC 2217 stuff when enabled
                if self.rfc2217:
                    data = serial.to_bytes(self.rfc2217.filter(data))
                # add data to buffer
                self.buffer_net2ser += data
            else:
                # empty read indicates disconnection
                self.handle_disconnect()
        except socket.error:
            self.handle_socket_error()

    def handle_socket_write(self):
        """Write to socket"""
        try:
            # write a chunk
            count = self.socket.send(self.buffer_ser2net)
            # and remove the sent data from the buffer
            self.buffer_ser2net = self.buffer_ser2net[count:]
        except socket.error:
            self.handle_socket_error()

    def handle_socket_error(self):
        """Socket connection fails"""
        self.handle_disconnect()

    def handle_connect(self):
        """Server socket gets a connection"""
        # accept a connection in any case, close connection
        # below if already busy
        connection, addr = self.server_socket.accept()
        if self.socket is None:
            self.socket = connection
            self.socket.setblocking(0)
            self.socket.setsockopt(socket.IPPROTO_TCP, socket.TCP_NODELAY, 1)
            if not options.quiet:
                print('%s: Connected by %s:%s' % (self.device, addr[0], addr[1]))
            self.serial.setRTS(True)
            self.serial.setDTR(True)
            self.rfc2217 = serial.rfc2217.PortManager(self.serial, self)
        else:
            # reject connection if there is already one
            connection.close()
            if not options.quiet:
                print('%s: Rejecting connect from %s:%s' % (self.device, addr[0], addr[1]))

    def handle_server_error(self):
        """Socket server fails"""
        self.close()

    def handle_disconnect(self):
        """Socket gets disconnected"""
        # signal disconnected terminal with control lines
        try:
            self.serial.setRTS(False)
            self.serial.setDTR(False)
        finally:
            # restore original port configuration in case it was changed
            self.serial.applySettingsDict(self.serial_settings_backup)
            # stop RFC 2217 state machine
            self.rfc2217 = None
            # clear send buffer
            self.buffer_ser2net = ''
            # close network connection
            if self.socket is not None:
                self.socket.close()
                self.socket = None
                if not options.quiet:
                    print('%s: Disconnected' % self.device)


def test():
    service = ZeroconfService(name="TestService", port=3000)
    service.publish()
    raw_input("Press any key to unpublish the service ")
    service.unpublish()


if __name__ == '__main__':
    import optparse

    parser = optparse.OptionParser(usage="""\
%prog [options]

Announce the existence of devices using zeroconf and provide
a TCP/IP <-> serial port gateway (implements RFC 2217).

Note that the TCP/IP server is not protected. Everyone can connect
to it!

If running as daemon, write to syslog. Otherwise write to stdout.
""")

    parser.add_option("-q", "--quiet", dest="quiet", action="store_true",
        help="suppress non error messages", default=False)

    parser.add_option("-o", "--logfile", dest="log_file",
        help="write messages file instead of stdout", default=None, metavar="FILE")

    parser.add_option("-d", "--daemon", dest="daemonize", action="store_true",
            help="start as daemon", default=False)

    parser.add_option("", "--pidfile", dest="pid_file",
        help="specify a name for the PID file", default=None, metavar="FILE")

    (options, args) = parser.parse_args()

    # redirect output if specified
    if options.log_file is not None:
        class WriteFlushed:
            def __init__(self, fileobj):
                self.fileobj = fileobj
            def write(self, s):
                self.fileobj.write(s)
                self.fileobj.flush()
            def close(self):
                self.fileobj.close()
                sys.stdout = sys.stderr = WriteFlushed(open(options.log_file, 'a'))
        # atexit.register(lambda: sys.stdout.close())

    if options.daemonize:
        # if running as daemon is requested, do the fork magic
        # options.quiet = True
        import pwd
        # do the UNIX double-fork magic, see Stevens' "Advanced
        # Programming in the UNIX Environment" for details (ISBN 0201563177)
        try:
            pid = os.fork()
            if pid > 0:
                # exit first parent
                sys.exit(0)
        except OSError as e:
            sys.stderr.write("fork #1 failed: %d (%s)\n" % (e.errno, e.strerror))
            sys.exit(1)

        # decouple from parent environment
        os.chdir("/")   # don't prevent unmounting....
        os.setsid()
        os.umask(0)

        # do second fork
        try:
            pid = os.fork()
            if pid > 0:
                # exit from second parent, print eventual PID before
                # print "Daemon PID %d" % pid
                if options.pid_file is not None:
                    open(options.pid_file,'w').write("%d"%pid)
                sys.exit(0)
        except OSError as e:
            sys.stderr.write("fork #2 failed: %d (%s)\n" % (e.errno, e.strerror))
            sys.exit(1)

        if options.log_file is None:
            import syslog
            syslog.openlog("serial port publisher")
            # redirect output to syslog
            class WriteToSysLog:
                def __init__(self):
                    self.buffer = ''
                def write(self, s):
                    self.buffer += s
                    if '\n' in self.buffer:
                        output, self.buffer = self.buffer.split('\n', 1)
                        syslog.syslog(output)
                def flush(self):
                    syslog.syslog(self.buffer)
                    self.buffer = ''
                def close(self):
                    self.flush()
            sys.stdout = sys.stderr = WriteToSysLog()

            # ensure the that the daemon runs a normal user, if run as root
        #if os.getuid() == 0:
            #    name, passwd, uid, gid, desc, home, shell = pwd.getpwnam('someuser')
            #    os.setgid(gid)     # set group first
            #    os.setuid(uid)     # set user

    # keep the published stuff in a dictionary
    published = {}
    # prepare list of device names (hard coded)
    device_list = ['/dev/ttyUSB%d' % p for p in range(8)]
    # get a nice hostname
    hostname = socket.gethostname()

    def unpublish(forwarder):
        """when forwarders die, we need to unregister them"""
        try:
            del published[forwarder.device]
        except KeyError:
            pass
        else:
            if not options.quiet: print("unpublish: %s" % (forwarder))

    alive = True
    next_check = 0
    # main loop
    while alive:
        try:
            # if it is time, check for serial port devices
            now = time.time()
            if now > next_check:
                next_check = now + 5
                # check each device
                for device in device_list:
                    # if it appeared
                    if os.path.exists(device):
                        if device not in published:
                            num = int(device[-1])
                            published[device] = Forwarder(
                                device,
                                "%s on %s" % (device, hostname),
                                7000+num,
                                on_close=unpublish
                            )
                            if not options.quiet: print("publish: %s" % (published[device]))
                            published[device].open()
                    else:
                        # or when it disappeared
                        if device in published:
                            if not options.quiet: print("unpublish: %s" % (published[device]))
                            published[device].close()
                            try:
                                del published[device]
                            except KeyError:
                                pass

            # select_start = time.time()
            read_map = {}
            write_map = {}
            error_map = {}
            for publisher in published.values():
                publisher.update_select_maps(read_map, write_map, error_map)
            try:
                readers, writers, errors = select.select(
                    read_map.keys(),
                    write_map.keys(),
                    error_map.keys(),
                    5
                )
            except select.error as err:
                if err[0] != EINTR:
                    raise
            # select_end = time.time()
            # print "select used %.3f s" % (select_end - select_start)
            for reader in readers:
                read_map[reader]()
            for writer in writers:
                write_map[writer]()
            for error in errors:
                error_map[error]()
            # print "operation used %.3f s" % (time.time() - select_end)
        except KeyboardInterrupt:
            alive = False
        except SystemExit:
            raise
        except:
            #~ raise
            traceback.print_exc()