Python Socket数据传输：深度解析recv的陷阱与完整数据接收策略

import socket
import os

if __name__ == '__main__':
    file_path = 'vid.mp4' # 确保此文件存在
    if not os.path.exists(file_path):
        print(f"Error: File '{file_path}' not found.")
        exit()

    with open(file_path, 'rb') as f:
        data = f.read()

    server_soc = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    server_soc.bind(('localhost', 1234))
    server_soc.listen()
    print("Server listening on localhost:1234")

    client_soc, addr = server_soc.accept()
    print(f"Accepted connection from {addr}")

    # 发送数据长度，固定16位长度，用'0'填充
    data_len_str = str(len(data)).rjust(16, '0').encode()
    client_soc.send(data_len_str)
    print(f"Sent data length: {len(data)}")

    # 发送所有文件数据
    client_soc.sendall(data)
    print("Finished sending file data.")
    client_soc.close()
    server_soc.close()

import socket

if __name__ == '__main__':
    # 请替换为实际的ngrok地址和端口
    # soc = socket.socket()
    # soc.connect(('6.tcp.eu.ngrok.io', 19717))

    # 假设连接到本地服务器
    soc = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    soc.connect(('localhost', 1234))
    print("Connected to server.")

    # 接收数据长度
    data_len_bytes = b''
    while len(data_len_bytes) < 16:
        packet = soc.recv(16 - len(data_len_bytes))
        if not packet:
            print("Error: Server disconnected while receiving length.")
            break
        data_len_bytes += packet

    if len(data_len_bytes) < 16:
        print("Failed to receive complete data length.")
        exit()

    data_len = int(data_len_bytes.decode())
    print(f"Expected data length: {data_len}")

    # 接收文件数据
    with open('new.mp4', 'wb') as f:
        read_bytes = 0
        while read_bytes < data_len:
            # 错误假设：soc.recv(4096) 总是返回 4096 字节
            f.write(soc.recv(4096))
            read_bytes += 4096 # 错误：这里应该累加实际接收的字节数
    print("File reception finished (possibly incomplete).")
    soc.close()

import socket
import os

if __name__ == '__main__':
    # 请替换为实际的ngrok地址和端口，或本地服务器地址
    # soc = socket.socket()
    # soc.connect(('6.tcp.eu.ngrok.io', 19717))

    soc = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    try:
        soc.connect(('localhost', 1234))
        print("Connected to server.")

        # 接收数据长度，确保完整接收16字节
        data_len_bytes = b''
        while len(data_len_bytes) < 16:
            packet = soc.recv(16 - len(data_len_bytes))
            if not packet:
                print("Error: Server disconnected while receiving length.")
                raise ConnectionError("Server closed connection prematurely.")
            data_len_bytes += packet

        data_len = int(data_len_bytes.decode())
        print(f"Expected data length: {data_len} bytes.")

        # 接收文件数据
        output_file_name = 'new_complete.mp4'
        with open(output_file_name, 'wb') as f:
            read_bytes = 0
            while read_bytes < data_len:
                # 接收数据，最多4096字节
                chunk = soc.recv(min(4096, data_len - read_bytes)) 

                # 检查是否收到数据，如果为空则表示对端已关闭连接
                if not chunk:
                    print(f"Warning: Server disconnected before receiving all data. Expected {data_len}, got {read_bytes}.")
                    break

                f.write(chunk)
                read_bytes += len(chunk) # 关键：累加实际接收的字节数

                # 可选：打印进度
                # print(f"\rReceived {read_bytes}/{data_len} bytes ({read_bytes/data_len:.2%})", end='')

        print(f"\nFile reception finished. Received {read_bytes} bytes to '{output_file_name}'.")
        if read_bytes == data_len:
            print("File received completely.")
        else:
            print("File received incompletely due to server disconnection.")

    except ConnectionRefusedError:
        print("Error: Connection refused. Is the server running?")
    except ConnectionError as e:
        print(f"Connection error: {e}")
    except Exception as e:
        print(f"An unexpected error occurred: {e}")
    finally:
        soc.close()