Python ptyprocess读取缺失末尾两行数据问题求助

问题现象 #

真实终端中执行bluetoothctl操作能得到包含18个值和末尾“OK”的完整响应，但通过ptyprocess的read方法只能获取13个值，丢失末尾的“OK”行，同时还会返回一个ESC字符。

相关代码 #

@staticmethod
def communicate(write_uuid, read_uuid, data):
    
    # Requires a writable and a readable GATT uuid and data to be written
    # The method returns the data retrieved from the readable GATT uuid
    
    hex_string = ''
    for char in data:
        hex_string += hex(ord(char)) + ' '

    timeout = .1
    read_process = ptyprocess.PtyProcessUnicode.spawn(['/bin/bash'])
    commands = ['bluetoothctl', 'menu gatt', f'select-attribute {read_uuid}', 'notify on']
    for command in commands:
        read_process.write(command + '\n')
        time.sleep(timeout)
        read_process.read(1)

    write_process = ptyprocess.PtyProcessUnicode.spawn(['/bin/bash'])
    commands = f'bluetoothctl <<EOF\nmenu gatt\nselect-attribute {write_uuid}\nwrite "{hex_string}"\nEOF\n'
    write_process.write(commands)
    time.sleep(timeout)
    write_process.read(1)
    time.sleep(timeout)

    hex_values = []
    pattern = re.compile(r'\b[0-9a-fA-F]{2}\b')
    lines = read_process.read(size=10000).splitlines()
    for line in lines:
        print(line)

实际读取到的响应 #

[CHG] Attribute /org/bluez/hci0/dev_CE_EE_A8_9B_17_AC/service000b/char000e Value:
[Device:/service000b/char000e]#                                              
  30 2e 30 2c 20 30 2e 30 2c 20 30 2e 30 2c 20 30  0.0, 0.0, 0.0, 0
[Device:/service000b/char000e]#                                              
  2e 30 2c 20 30 2e 30 2c 20 30 2e 30 2c 20 30 2e  .0, 0.0, 0.0, 0.
[Device:/service000b/char000e]#                                              
  30 2c 20 30 2e 30 2c 20 30 2e 30 2c 20 30 2e 30  0, 0.0, 0.0, 0.0
[Device:/service000b/char000e]#                                              
  2c 20 30 2e 30 2c 20 30 2e 30 2c 20 30 2e 30 2c  , 0.0, 0.0, 0.0,
[Device:/service000b/char000e][

预期完整响应 #

[Device:/service000b/char000e]# [CHG] Attribute /org/bluez/hci0/dev_CE_EE_A8_9B_17_AC/service000b/char000e Value:
[Device:/service000b/char000e]#   30 2e 30 2c 20 30 2e 30 2c 20 30 2e 30 2c 20 30  0.0, 0.0, 0.0, 0
[Device:/service000b/char000e]#   2e 30 2c 20 30 2e 30 2c 20 30 2e 30 2c 20 30 2e  .0, 0.0, 0.0, 0.
[Device:/service000b/char000e]#   30 2c 20 30 2e 30 2c 20 30 2e 30 2c 20 30 2e 30  0, 0.0, 0.0, 0.0
[Device:/service000b/char000e]#   2c 20 30 2e 30 2c 20 30 2e 30 2c 20 30 2e 30 2c  , 0.0, 0.0, 0.0,
[Device:/service000b/char000e]#   20 30 2e 30 2c 20 30 2e 30 2c 20 30 2e 30 2c 20   0.0, 0.0, 0.0, 
[Device:/service000b/char000e]#   30 2e 30 2c 20 30 2e 30 20 4f 4b 0a              0.0, 0.0 OK.   

解决方案 #

1. 调整等待逻辑与读取方式 #

问题核心是等待时间不足，导致bluetoothctl未输出完所有内容就开始读取；同时单次固定大小的read可能提前终止。修改方案如下：

@staticmethod
def communicate(write_uuid, read_uuid, data):
    hex_string = ' '.join(hex(ord(char)) for char in data)

    # 合并为单个进程处理，减少时序干扰
    process = ptyprocess.PtyProcessUnicode.spawn(['bluetoothctl'])
    time.sleep(0.2)
    
    # 执行GATT相关命令
    commands = [
        'menu gatt',
        f'select-attribute {read_uuid}',
        'notify on',
        f'select-attribute {write_uuid}',
        f'write "{hex_string}"'
    ]
    
    for cmd in commands:
        process.write(cmd + '\n')
        time.sleep(0.2)
        # 清空当前命令的输出缓冲区，避免残留数据干扰后续读取
        while process.readable():
            try:
                process.read_nonblocking(size=1024, timeout=0.1)
            except ptyprocess.PtyProcessTimeout:
                break
    
    # 循环读取直到捕获到"OK"标记，确保获取完整响应
    full_output = ""
    while True:
        try:
            chunk = process.read_nonblocking(size=1024, timeout=0.5)
            full_output += chunk
            if "OK" in full_output:
                break
        except ptyprocess.PtyProcessTimeout:
            break
    
    # 过滤ESC字符（ASCII码27）并输出
    cleaned_output = full_output.replace('\x1b', '')
    lines = cleaned_output.splitlines()
    for line in lines:
        print(line)
    
    process.close()

2. 关键优化点 #

• 合并进程：避免多进程同步问题，用单个进程处理所有bluetoothctl操作
• 延长等待时间：根据蓝牙设备响应速度调整sleep时长，确保命令执行完成
• 非阻塞读取：配合超时机制循环读取，确保捕获所有输出直到目标标记出现
• 清理异常字符：直接替换ESC字符（\x1b），净化输出内容

内容的提问来源于stack exchange，提问作者sonus89