Question

我创建了一个简单的C ++服务器，该服务器试图通过套接字将vector<uint8_t>的字节发送给Python客户端。我的所有服务器和客户端连接正常，但是数据在python中错误地输出。我首先发送一个整数，描述期望的字节数，然后发送字节。但是，当我运行python脚本并在套接字上调用recv时，有时我得到的字节数值不正确。

我已经调试了C ++和Python代码，并且显示出一些奇怪的行为。首先，我意识到在调试Python代码时，它运行良好。事实证明，在我的Python脚本中，如果我在读取整数头的前4个字节与读取其余字节之间的时间之间调用sleep(1)，则它起作用。但是，当我不睡觉就进行多个recv通话时，事情就会出错。我还检查了字节尾数是否正确。我什至在服务器和客户端之间添加了一个握手过程，以确保它们可以很好地协同工作。

对于C ++：设置套接字：

int Server::setup_socket(int port){
    int server_fd, new_socket; 
    struct sockaddr_in address; 
    int opt = 1; 
    int addrlen = sizeof(address); 

    // Creating socket file descriptor 
    if ((server_fd = socket(AF_INET, SOCK_STREAM, 0)) == 0){ 
        perror("socket failed"); 
        exit(EXIT_FAILURE); 
    } 

    // Forcefully attaching socket to the port 
    if (setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR | SO_REUSEPORT, &opt, sizeof(opt))){ 
        perror("setsockopt"); 
        exit(EXIT_FAILURE); 
    } 
    address.sin_family = AF_INET; 
    address.sin_addr.s_addr = INADDR_ANY; 
    address.sin_port = htons(port); 

    // Forcefully attaching socket to the port 
    if (bind(server_fd, (struct sockaddr *)&address, sizeof(address))<0){ 
        perror("bind failed"); 
        exit(EXIT_FAILURE); 
    } 
    if (listen(server_fd, 3) < 0){ 
        perror("listen"); 
        exit(EXIT_FAILURE); 
    } 
    printf("Successfully connected to port %d\n", port);
    if ((new_socket = accept(server_fd, (struct sockaddr *)&address, (socklen_t*)&addrlen))<0){ 
        perror("accept"); 
        exit(EXIT_FAILURE); 
    } 

    return new_socket;
}

发送数据和握手方法：

void Server::send_image(cv::Mat &image) {
    std::vector<uint8_t> buf;
    std::vector<int> param(2);
    param[0] = cv::IMWRITE_JPEG_QUALITY;
    param[1] = 80; //default(95) 0-100
    cv::imencode(".jpg", image, buf, param);

    int length = buf.size();
    printf("Sending image of size: %d\n", length);
    write(data_socket, &length, sizeof(length));
    write(data_socket, buf.data(), length);
}

void Server::confirm_sent(){
    uint8_t confirmation[1];
    write(conf_socket, confirmation, 1);
}

void Server::confirm_received(){
    uint8_t confirmation[1];
    read(conf_socket, confirmation, 1);
}

Python代码：

data_sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)  # For sending data
conf_sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)  # For hand shaking

# Connect the socket to the port where the server is listening
data_address = ('192.168.1.146', 2323)
conf_address = ('192.168.1.146', 2324)
print('connecting to %s port %s' % data_address)
data_sock.connect(data_address)
time.sleep(1)
print('connecting to %s port %s' % conf_address)
conf_sock.connect(conf_address)

while True:
    conf_sock.recv(1)  # Confirm sent
    size1 = int.from_bytes(data_sock.recv(4), byteorder="big") 
    size2 = socket.ntohl(size1) # Fixes endian problems
    # time.sleep(1) # Inserting this fixes things, but I don't want the delay
    data = np.frombuffer(data_sock.recv(size2), dtype=np.uint8)
    print(f"{size1}, {size2}, {data.shape}")
    conf_sock.send(bytes(1))

C ++输出和预期大小：

Max speed spi is 8000000
OV5642 detected.
Successfully connected to port 2323
Successfully connected to port 2324
Sending image of size: 134966
Sending image of size: 135072
Sending image of size: 134628
Sending image of size: 134846
Sending image of size: 134704
Sending image of size: 134885
Sending image of size: 133942

Python收到的大小：

connecting to 192.168.1.146 port 2323
connecting to 192.168.1.146 port 2324
906953216, 134966, (95568,)
1224436735, 4285266760, (45190,)
2585803520, 3874970, (137968,)
939478527, 4283301687, (137524,)
103119361, 24782086, (136294,)
1526714366, 4275044186, (127464,)
469746175, 4290903835, (136333,)

Answer 1

网络数据可能会缓慢到达，socket.recv()将为您提供个请求的字节数，但是如果缓冲区中没有足够的数据，则字节数会减少。

您需要继续调用recv()，直到所有字节到达为止。这很常见，您希望函数为您处理重复的调用：

def socket_read(sock, expected):
    """Read expected number of bytes from sock

    Will repeatedly call recv until all expected data is received

    """
    buffer = b''
    while len(buffer) < expected:
        buffer += sock.recv(expected - len(buffer))
    return buffer

并使用该功能接收您的数据：

message_size = int.from_bytes(socket_read(data_sock, 4), byteorder="little")
data = np.frombuffer(socket_read(data_sock, message_size), dtype=np.uint8)

有关字节顺序的说明：服务器必须以特定的字节顺序发送数据。 TCP / IP连接上的网络顺序是大端的，因此您的C ++代码需要使用该顺序，并使用int.from_bytes(..., byteorder="big")使用socket.ntohl() 不。 byteorder参数与平台无关，使用此方法将字节解释为整数，不受平台差异的影响。

现在，您的C ++代码根本不处理字节顺序；在服务器代码中使用htonl() function，以确保写出正确的字节顺序：

write(data_socket, &(htonl(length)), sizeof(length));

，然后在Python中使用int.from_bytes(..., byteorder="big")。

通过套接字从C ++服务器向Python客户端发送数据时出现问题

1 个答案: