在 Python 中通过套接字发送大量数据的正确方法是什么？

Question

最近我写了一些代码（客户端和服务器）来发送图像 - 客户端只是将图像上传到服务器，只是使用 socket 模块： Sending image over sockets (ONLY) in Python, image cannot开放。

然而，图像发送部分现在是我关心的。这是我正在使用的原始图像：

在我的服务器代码（接收图像）中，我有这些行：

 myfile = open(basename % imgcounter, 'wb')
myfile.write(data)

data = sock.recv(40960000)
if not data:
     myfile.close()
     break
myfile.write(data)
myfile.close()

sock.sendall("GOT IMAGE")
sock.shutdown()

但我认为这不是最好的方法。我想我应该改为实现服务器，以便它以块的形式接收数据：

 #!/usr/bin/env python

import random
import socket, select
from time import gmtime, strftime
from random import randint

imgcounter = 1
basename = "image%s.png"

HOST = '127.0.0.1'
PORT = 2905

connected_clients_sockets = []

server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

server_socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
server_socket.bind((HOST, PORT))
server_socket.listen(10)

connected_clients_sockets.append(server_socket)

while True:

    read_sockets, write_sockets, error_sockets = select.select(connected_clients_sockets, [], [])

    for sock in read_sockets:

        if sock == server_socket:

            sockfd, client_address = server_socket.accept()
            connected_clients_sockets.append(sockfd)

        else:
            try:

                data = sock.recv(4096)
                txt = str(data)

                if data:

                    if data.startswith('SIZE'):
                        tmp = txt.split()
                        size = int(tmp[1])

                        print 'got size %s' % size

                        sock.sendall("GOT SIZE")

                    elif data.startswith('BYE'):
                        sock.shutdown()

                    else :

                        myfile = open(basename % imgcounter, 'wb')
                        myfile.write(data)

                        amount_received = 0
                        while amount_received < size:
                            data = sock.recv(4096)
                            amount_received += len(data)

                            print amount_received

                            if not data:
                                break
                            myfile.write(data)
                        myfile.close()

                        sock.sendall("GOT IMAGE")
                        sock.shutdown()
            except:
                sock.close()
                connected_clients_sockets.remove(sock)
                continue
        imgcounter += 1
server_socket.close()

但是当我这样做时，服务器会打印：

 got size 54674
4096
8192
12288
16384
20480
24576
28672
32768
36864
40960
45056
49152
50578

然后似乎挂了，客户端也挂了。但是，在服务器端，我只能看到客户端想要发送的图像的一部分：

似乎缺少一些字节。仅使用套接字发送大量数据（图像，其他类型的文件）的正确方法是什么？

原文由 yak 发布，翻译遵循 CC BY-SA 4.0 许可协议

Answer 1

我假设您有特殊原因使用裸套接字执行此操作，例如自我教育，这意味着我不会回答说“您不小心忘记了只使用 HTTP 和 Twisted”，也许您已经 之前听说过:-P。但实际上你应该在某个时候看看更高级别的库，因为它们要容易得多！

定义协议

如果您只想发送图像，那么它可以很简单：

1. Client -> server: 8 bytes ：大端，图像长度。
2. Client -> server: length bytes : 所有图像数据。
3. （ Client <- server: 1 byte, value 0 ：表示接收到传输 - 可选步骤你可能不关心你是否使用 TCP，只是假设它是可靠的。）

编码吧

服务器.py

 import os
from socket import *
from struct import unpack

class ServerProtocol:

    def __init__(self):
        self.socket = None
        self.output_dir = '.'
        self.file_num = 1

    def listen(self, server_ip, server_port):
        self.socket = socket(AF_INET, SOCK_STREAM)
        self.socket.bind((server_ip, server_port))
        self.socket.listen(1)

    def handle_images(self):

        try:
            while True:
                (connection, addr) = self.socket.accept()
                try:
                    bs = connection.recv(8)
                    (length,) = unpack('>Q', bs)
                    data = b''
                    while len(data) < length:
                        # doing it in batches is generally better than trying
                        # to do it all in one go, so I believe.
                        to_read = length - len(data)
                        data += connection.recv(
                            4096 if to_read > 4096 else to_read)

                    # send our 0 ack
                    assert len(b'\00') == 1
                    connection.sendall(b'\00')
                finally:
                    connection.shutdown(SHUT_WR)
                    connection.close()

                with open(os.path.join(
                        self.output_dir, '%06d.jpg' % self.file_num), 'w'
                ) as fp:
                    fp.write(data)

                self.file_num += 1
        finally:
            self.close()

    def close(self):
        self.socket.close()
        self.socket = None

        # could handle a bad ack here, but we'll assume it's fine.

if __name__ == '__main__':
    sp = ServerProtocol()
    sp.listen('127.0.0.1', 55555)
    sp.handle_images()

客户端.py

 from socket import *
from struct import pack

class ClientProtocol:

    def __init__(self):
        self.socket = None

    def connect(self, server_ip, server_port):
        self.socket = socket(AF_INET, SOCK_STREAM)
        self.socket.connect((server_ip, server_port))

    def close(self):
        self.socket.shutdown(SHUT_WR)
        self.socket.close()
        self.socket = None

    def send_image(self, image_data):

        # use struct to make sure we have a consistent endianness on the length
        length = pack('>Q', len(image_data))

        # sendall to make sure it blocks if there's back-pressure on the socket
        self.socket.sendall(length)
        self.socket.sendall(image_data)

        ack = self.socket.recv(1)

        # could handle a bad ack here, but we'll assume it's fine.

if __name__ == '__main__':
    cp = ClientProtocol()

    image_data = None
    with open('IMG_0077.jpg', 'r') as fp:
        image_data = fp.read()

    assert(len(image_data))
    cp.connect('127.0.0.1', 55555)
    cp.send_image(image_data)
    cp.close()

原文由 daphtdazz 发布，翻译遵循 CC BY-SA 3.0 许可协议

Answer 2

一种简单的方法是将数据大小作为数据的前 4 个字节发送，然后一次性读取完整数据。在客户端和服务器端使用以下函数发送和接收数据。

 def send_data(conn, data):
    serialized_data = pickle.dumps(data)
    conn.sendall(struct.pack('>I', len(serialized_data)))
    conn.sendall(serialized_data)

def receive_data(conn):
    data_size = struct.unpack('>I', conn.recv(4))[0]
    received_payload = b""
    reamining_payload_size = data_size
    while reamining_payload_size != 0:
        received_payload += conn.recv(reamining_payload_size)
        reamining_payload_size = data_size - len(received_payload)
    data = pickle.loads(received_payload)

    return data

你可以在 https://github.com/vijendra1125/Python-Socket-Programming.git 找到示例程序

原文由 Vijendra1125 发布，翻译遵循 CC BY-SA 4.0 许可协议