Communicating via Bluetooth serial with Python

How do you process and receive serial data via Bluetooth and Python?

I’m trying to make a simple Python server that access data via Bluetooth as explained here.

My server.py file, which sends a random number when sent the text “temp”, is:

#!/usr/bin/env python

import os
import glob
import time
import random

from bluetooth import *

def read_temp():
    return random.random()

server_sock=BluetoothSocket( RFCOMM )
server_sock.bind(("",PORT_ANY))
server_sock.listen(1)

port = server_sock.getsockname()[1]

uuid = "94f39d29-7d6d-437d-973b-fba39e49d4ee"

advertise_service( server_sock, "TestServer",
                   service_id = uuid,
                   service_classes = [ uuid, SERIAL_PORT_CLASS ],
                   profiles = [ SERIAL_PORT_PROFILE ], 
#                   protocols = [ OBEX_UUID ] 
                    )
while True:          
    print "Waiting for connection on RFCOMM channel %d" % port

    client_sock, client_info = server_sock.accept()
    print "Accepted connection from ", client_info

    try:
        data = client_sock.recv(1024)
        if len(data) == 0: break
        print "received [%s]" % data

        if data == 'temp':
            data = str(read_temp())+'!'
            client_sock.send(data)
        else:
            data = 'WTF!' 
            client_sock.send(data)
        print "sending [%s]" % data

    except IOError:
        pass

    except KeyboardInterrupt:

        print "disconnected"

        client_sock.close()
        server_sock.close()
        print "all done"

        break

When I first ran this, I was getting the error:

bluetooth.btcommon.BluetoothError: (2, 'No such file or directory')

which Googled showed could be fixed by enabling compatibility mode and loading the serial profile by editing file /lib/systemd/system/bluetooth.service and changing line:

ExecStart=/usr/lib/bluetooth/bluetoothd

to:

ExecStart=/usr/lib/bluetooth/bluetoothd -C

and then running sudo sdptool add SP.

Now python server.py seems to run without error, and I can pair the machine running it to my Android phone. However, it seems it’s unable to receive any data.

I’ve tried using bluetooth terminal emulation apps like BlueTerm, BT Simple Terminal, and Arduino BT, but when I connect to the server enter text and press enter, there’s no response from server.py. It will initially report a “Accepted connection…” and having received and empty string, but it receives nothing after that.

Since there’s no explicit error being reported, I’m not sure how to diagnose the problem. How would I determine if the problem lies in my Python code? Or the bluetooth configuration on the server? Or my Android phone?

Answer

The correct code is:

#!/usr/bin/env python
"""
A simple test server that returns a random number when sent the text "temp" via Bluetooth serial.
"""

import os
import glob
import time
import random

from bluetooth import *

server_sock = BluetoothSocket( RFCOMM )
server_sock.bind(("",PORT_ANY))
server_sock.listen(1)

port = server_sock.getsockname()[1]

uuid = "94f39d29-7d6d-437d-973b-fba39e49d4ee"

advertise_service( server_sock, "TestServer",
                   service_id = uuid,
                   service_classes = [ uuid, SERIAL_PORT_CLASS ],
                   profiles = [ SERIAL_PORT_PROFILE ], 
#                   protocols = [ OBEX_UUID ] 
                    )

print "Waiting for connection on RFCOMM channel %d" % port
client_sock, client_info = server_sock.accept()
print "Accepted connection from ", client_info

while True:          

    try:
        req = client_sock.recv(1024)
        if len(req) == 0:
            break
        print "received [%s]" % req

        data = None
        if req in ('temp', '*temp'):
            data = str(random.random())+'!'
        else:
            pass

        if data:
            print "sending [%s]" % data
            client_sock.send(data)

    except IOError:
        pass

    except KeyboardInterrupt:

        print "disconnected"

        client_sock.close()
        server_sock.close()
        print "all done"

        break