通过python套接字接收ctypes`c_wchar_p`的问题（python 3.7.7）答案

【问题标题】：Problem with receiving ctypes `c_wchar_p` over python socket (python 3.7.7)通过python套接字接收ctypes`c_wchar_p`的问题（python 3.7.7）
【发布时间】：2021-01-06 21:58:36
【问题描述】：

（Windows 10、x64、PyCharm）

短篇小说：我在 python 服务器脚本中遇到了 payload_in.event 和 payload_out.event 的问题。两者都来自c_wchar_p 类型，后者来自ctypes。

长篇大论：我目前正在使用 python 开发客户端和服务器。它们通过 127.0.01:6666 上的 TCP/IP 套接字进行通信。我正在使用模块 Ctypes 来发送和接收类似 c 的结构。一切正常，我可以发送/接收数组、整数、浮点数并在两侧使用它们，但我发现在 python 服务器脚本中打印 payload_in.event 和 payload_out.event 时存在错误，两者都是 @987654327 类型@。

在客户端脚本中，我可以完美地访问和打印payload_in.event 和payload_out.event ***但是即使代码相同，我的服务器脚本也不能。 . .

在服务器脚本中，打印 payload_in.event 和 payload_out.event 会导致两个程序暂停 10 秒左右，然后客户端控制台告诉我与服务器的连接已关闭。

如果我在 python 服务器脚本中注释掉 payload_in.event 和 payload_out.event 的打印，一切正常。我不知道如何解决此问题，如果有人可以帮助我，我会很高兴。

beagleServer.py

import socket
from ctypes import *


class Struct(Structure):
    _fields_ = [("id", c_uint32),  # 4B
                ("prio", c_uint32),  # 4B
                ("event", c_wchar_p),  # 8B
                ("data", c_float * 10)]  # 40B


def main():
    BUFFSIZE = sizeof(Struct)
    host = '127.0.0.1'
    port = 6666

    beagleServer = socket.socket()
    beagleServer.bind((host, port))
    beagleServer.listen(1)

    print("Server is listening on " + host + ":" + str(port) + "!")
    client, clientAddress = beagleServer.accept()
    print("Connection from: " + str(clientAddress[0]) + ":" + str(clientAddress[1]))

    # receiving payload
    buffer = client.recv(BUFFSIZE)
    payload_in = Struct.from_buffer_copy(buffer)
    print("\nPayload of ", sizeof(payload_in), " Bytes has been received successfully: ", payload_in,
          "\nPayload.id: ", payload_in.id,
          "\nPayload.prio: ", payload_in.prio,
          "\nPayload.event: ", payload_in.event,
          "\nPayload.data: ", list(payload_in.data),
          "\nReceived buffer: ", buffer)

    # sending back payload
    payload_out = payload_in
    transferredBytes = client.send(payload_out)
    print("\nPayload of ", transferredBytes, " Bytes has been sent successfully: ", payload_out,
          "\nPayload.id: ", payload_out.id,
          "\nPayload.prio: ", payload_out.prio,
          "\nPayload.event: ", payload_out.event,
          "\nPayload.data: ", list(payload_out.data))

    print("Closing server socket!")
    client.close()

if __name__ == '__main__':
    main()

beagleClient.py

import socket
from ctypes import *


class Struct(Structure):
    _fields_ = [("id", c_uint32),  # 4B
                ("prio", c_uint32),  # 4B
                ("event", c_wchar_p),  # 8B
                ("data", c_float * 10)]  # 40B


beagleServer = ('127.0.0.1', 6666)
beagleClient = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
beagleClient.connect(beagleServer)
print("Connection with server has been established!")

# Creating the Struct
payload_out = Struct(390897,
                     0,
                     "activateMode1",
                     (3.12, 4.21, 1.23))
print("\nPayload of ", sizeof(payload_out), " Bytes has been created successfully: ", payload_out,
      "\nPayload.id: ", payload_out.id,
      "\nPayload.prio: ", payload_out.prio,
      "\nPayload.event: ", payload_out.event,
      "\nPayload.data: ", list(payload_out.data))

# Sending
bytesTransferred = beagleClient.send(payload_out)
print("\nPayload of ", bytesTransferred, " Bytes has been sent!")

# Receiving
BUFFSIZE = sizeof(Struct)
buffer = beagleClient.recv(BUFFSIZE)
payload_in = Struct.from_buffer_copy(buffer)
print("\nPayload of ", sizeof(payload_in), " Bytes has been received successfully: ", payload_in,
      "\nPayload.id: ", payload_in.id,
      "\nPayload.prio: ", payload_in.prio,
      "\nPayload.event: ", payload_in.event,
      "\nPayload.data: ", list(payload_in.data))

print("Closing the connection to ", beagleServer, "!")
beagleClient.close()

【问题讨论】：

c_wchar_p 是 pointer 类型。通过网络传输这个 64 位值并不会神奇地授予接收者读取指向的数据的能力，这些数据位于发送进程的内存空间中的某个位置。您需要将实际字符放入结构中，而不是指向它们的指针。
正如 jasonharper 所说... python 有指针。您的代码阻塞，因为它试图读取提供的地址（甚至可能不存在于服务器内存空间中）。
谢谢大家，现在我明白了！

标签： python ctypes python-sockets

【解决方案1】：

Struct.event 是一个指针。在两个进程之间传输的指针只是一个地址，在另一个进程中没有任何意义。改用数组：

("event", c_wchar * 80)

它仍然可以以相同的方式初始化，但不能超过传输字符串的数组大小。此外c_wchar 的大小因架构而异，因此您可能希望使用c_char * 80，然后对字符串进行编码/解码，例如payload.event = 'some string'.encode()（或只使用字节串：b'some string'）。

【讨论】：