从“挂起”蓝牙 python 连接中检测和恢复

Question

I have a bluetooth connection between a Raspberry Pi 3b+ and an Arduino Mega, using the RPi built-in module, and an HC-05 module on the Arduino. Bi-directional communication works like a charm, for minutes to sometimes, hours at a time.

Then, at seemingly random times, the python code hangs, blocked on the sock.recv() function. I can kill it via ctrl-c, and restart it, and it usually reconnects without a problem.

I know Bluetooth is a little finicky and so while any suggestions of how to make the communication more robust and extend the runtime-until-hanging are definitely appreciated, what I'm more interested in is how to detect this "hanging" and recover from it. ie: I want to just kill the connection and try to reconnect from within the Python program, rather than me having to see this myself and react to it.

This is what I have so far in python:

#!/usr/bin/python3

import datetime
import socket
import sys
import time

import bluetooth

COMMAND_START_CHAR = '<'
COMMAND_END_CHAR = '>'
LOGFILE = 'bt.log'


def SearchForFullCommand(buffer):
  """Puts fully formed commands from buffer into a list, returning the remaining buffer.

  We expect commands to be demarcated by COMMAND_START_CHAR and COMMAND_END_CHAR.  The
  buffer may have zero or more such commands. This function finds all demarcated commands,
  strips off those demarcations, and returns the remaining buffer.  Any text that arrives
  before a COMMAND_START_CHAR is discarded.

  Args:
    buffer: string representing the text received so far.

  Returns:
    A 2-tuple, where the first element is the remaining buffer, and the second element
    is a potentially empty list of identified commands.
  """
  commands = []
  while COMMAND_END_CHAR in buffer:
    end_pos = buffer.find(COMMAND_END_CHAR)
    if COMMAND_START_CHAR in buffer[:end_pos]:
      start_pos = buffer.find(COMMAND_START_CHAR) + len(COMMAND_START_CHAR)
      commands.append(buffer[start_pos:end_pos])
    buffer = buffer[end_pos+len(COMMAND_END_CHAR):]
  return (buffer, commands)  # no command found


def Log(s):
  """Appends message s to the logfile."""
  with open(LOGFILE, 'a') as f:
    f.write('%s\n' % s)


def ConnectBluetooth(address, port):
  """Attempts to make one connection to the given address and port."""
  sock = bluetooth.BluetoothSocket(bluetooth.RFCOMM)
  sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
  try:
    sock.connect((address, port))
  except (bluetooth.btcommon.BluetoothError) as e:
    Log('Failed to connect: %s' % e)
    return None
  return sock


def ConnectBluetoothRetry(address, port, seconds):
  """Attempts to make connections for a number of seconds, exiting program on fail."""
  second = 0
  while second < seconds:
    sock = ConnectBluetooth(address, port)
    if sock:
      Log('Connected after %d seconds' % second)
      return sock
    time.sleep(1)
    second += 1
  Log('Failed to connect after %d seconds' % second)
  sys.exit()


def main():
  """Sends sequential numbers over bluetooth, and receives & parses anything sent."""
  sys.stderr = open(LOGFILE, 'a')

  start = time.time()
  timestring = datetime.datetime.fromtimestamp(start).strftime('%Y-%m-%d %H:%M:%S')
  Log('Started at %s' % timestring)

  bd_addr = '98:D3:11:FC:42:16'
  port = 1
  sock = ConnectBluetoothRetry(bd_addr, port, 10)

  buffer = ''
  x = 0

  while True:
    try:
      recv = sock.recv(1024)
    except (bluetooth.btcommon.BluetoothError) as e:
      Log('Failed to receive: %s' % e)
      sock.close()
      sock = ConnectBluetoothRetry(bd_addr, port, 10)
    Log('.. %s (len=%d) after running for %.3f hours' % (
        recv, len(recv), (time.time() - start) / 60**2))
    buffer += recv.decode()
    buffer, commands = SearchForFullCommand(buffer)
    if commands:
      for n, command in enumerate(commands):
        Log('Received full command #%d: %s' % (n, command))

    send = COMMAND_START_CHAR+str(x)+COMMAND_END_CHAR
    try:
      sock.send(send)
    except (bluetooth.btcommon.BluetoothError) as e:
      Log('Failed to send %s: %s' % (send, e))
      sock.close()
      sock = ConnectBluetoothRetry(bd_addr, port, 10)
    Log('Sent %s' % send)

    x += 1
    time.sleep(1)


main()

When working well, the python log file looks like this:

.. b'646>' (len=4) after running for 0.843 hours
Received full command #0: 646
Sent <2526>
.. b'<647>' (len=5) after running for 0.843 hours
Received full command #0: 647
Sent <2527>
.. b'<' (len=1) after running for 0.844 hours
Sent <2528>
.. b'648>' (len=4) after running for 0.844 hours

Then, noticing it had stopped working, I killed it, and then restarted it:

KeyboardInterrupt
Started at 2020-05-03 11:15:07
Failed to connect: [Errno 16] Device or resource busy
Failed to connect: [Errno 16] Device or resource busy
Failed to connect: [Errno 16] Device or resource busy
Failed to connect: [Errno 16] Device or resource busy
Failed to connect: [Errno 16] Device or resource busy
Failed to connect: [Errno 16] Device or resource busy
Failed to connect: [Errno 16] Device or resource busy
Failed to connect: [Errno 16] Device or resource busy
Failed to connect: [Errno 16] Device or resource busy
Failed to connect: [Errno 16] Device or resource busy
Failed to connect after 10 seconds

I try again:

Started at 2020-05-03 11:15:42
Failed to connect: [Errno 112] Host is down
Failed to connect: [Errno 112] Host is down
Failed to connect: [Errno 112] Host is down
Connected after 3 seconds
.. b'1146><1147><1148><1149><1150><1151><1152><1153><1154><1155><1156><1157><1158><1159><1160><1161><1162><1163><1164><1165><1166><1' (len=127) after running for 0.005 hours
Received full command #0: 1147
Received full command #1: 1148
Received full command #2: 1149

... and it runs for another hour or two, before hanging again. I'm not physically moving either sender or receiver - they're within a foot of each other - so it's not range. Though I have tried disconnecting the Arduino, and repowering it, and they do reconnect without a problem within the still-running Python process.

The Arduino code, though I don't think its as relevant, is here:

long n = 1;

void setup() 
{
    Serial.begin(9600);

    // HC-05 default serial speed for communcation mode is 9600
    Serial1.begin(9600);  
}

void loop() 
{
    Serial1.print("<");
    Serial1.print(n);
    Serial1.print(">");
    if(Serial1.available() > 0){ // Checks whether data is comming from the serial port
      Serial.println(Serial1.readString());} // Reads the data from the serial port
    delay(1000);
    n++;
}

Thanks for any help or suggestions!

Answer 1

I could not get the socket connection to last more than a few hours despite a few days of different approaches & efforts; I only went down the socket rabbit hole because I was unable to figure out how to use pySerialTransfer, or even just serial, over bluetooth.

So, going back to the serial approach, after a bit more effort and investigation, I was ultimately able to get that approach working for a stable (over 1 day at this point) bluetooth connection between Raspberry Pi & HC-05 on Arduino.

Code is here .