使用“C”在套接字編程中發送數據

Question

我之前發布了一個關於相同的問題，但是在這里我想要我的代碼的指導。 使用我嘗試創建的人的提示來發送數據包。 我的最大數據包結構以及 header 和有效負載為 16 個字節。如果可能，請瀏覽發送和接收代碼並建議我哪里出錯了。 基本上我的客戶一直在向服務器發送數據，它只是沒有結束，服務器沒有顯示結果。

客戶：

int main(int argc, char *argv[])
{
    int sockfd, portno, n;
    struct sockaddr_in serv_addr;
    struct hostent *server;
    struct packet
    { 
        long int srcID;
        long int destID;
        long int pver;
        long int profiles;
        char length;
        long int data;
    };
    if (argc < 3) {
        fprintf(stderr,"usage: %s hostname port\n", argv[0]);
        exit(0);
    }
    portno = atoi(argv[2]); //Convert ASCII to integer
    sockfd = socket(AF_INET, SOCK_STREAM, 0); // socket file descriptor

    if (sockfd < 0) 
        error("ERROR DETECTED !!! Problem in opening socket\n");

    server = gethostbyname(argv[1]);
    if (server == NULL) {
        fprintf(stderr,"ERROR DETECTED !!!, no such server found \n");
        exit(0);
    }

    bzero((char *) &serv_addr, sizeof(serv_addr)); //clear the memory for server address

    serv_addr.sin_family = AF_INET;    
    bcopy((char *)server->h_addr, 
    (char *)&serv_addr.sin_addr.s_addr,
    server->h_length);

    serv_addr.sin_port = htons(portno);

    printf("Client 1 trying to connect with server host %s on port %d\n", argv[1], portno); 

    if (connect(sockfd,(struct sockaddr *)&serv_addr,sizeof(serv_addr)) < 0) 
    error("ERROR in connection");

    printf("SUCCESS !!! Connection established \n");

    char buffer[128];
    struct packet *pkt = (struct packet *) buffer;
    char *payload = buffer + sizeof(struct packet);
    long int packet_size;

    printf("Started Creating packet\n");
    pkt->srcID = 0x01;
    pkt->destID = 0x02;
    pkt->pver = 0x01;
    pkt->profiles = 0x01;
    pkt->length = 128;
    pkt->data = 1; 2; 3; 4; 5; 6; 7; 8;


    if (send(sockfd,pkt,sizeof(packet_size),0) <0)
        printf ("error\n");
    else
        printf ("packet send done");
    return 0;
}

服務器：

int main(int argc, char *argv[])
{
    int sockfd, newsockfd, portno, clilen;
    struct sockaddr_in serv_addr, cli_addr;
    int n;
    char wish;

    long int SrcID;
    long int DestID;
    long int Pver;
    long int Profiles;
    long int Data;
    char Length;
    char bytes_to_receive;
    char received_bytes;
    struct packet
    { 
        long int srcID;
        long int destID;
        long int pver;
        long int profiles;
        char length;
        long int data;
    };

    if (argc < 2) {
        fprintf(stderr,"usage: %s port_number1",argv[0]);
        exit(1);
    }
    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0) 
        error("ERROR DETECTED !!! Problem in opening socket");

    bzero((char *) &serv_addr, sizeof(serv_addr));
    portno = atoi(argv[1]);

    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
    serv_addr.sin_port = htons(portno);

    if (bind(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) < 0) 
        error("ERROR DETECTED !!! There was a problem in binding");

    listen(sockfd, 10);
    clilen = sizeof(cli_addr);

    printf("Server listening on port number %d...\n", serv_addr.sin_port); 

    newsockfd = accept(sockfd,(struct sockaddr *) &cli_addr, &clilen);

    if (newsockfd < 0) 
        error("ERROR DETECTED !!! the connection request was not accepted");

    char buffer[128];
    struct packet *pkt = (struct packet *) buffer;
    char *payload = buffer + sizeof(struct packet);
    long int packet_size;

    bytes_to_receive = sizeof(pkt);
    received_bytes = 0;

    if (recv(newsockfd, pkt, sizeof(pkt), 0) < 0)
        error("ERROR DETECTED !!! There was a problem in reading the data");
    else
    { 
        do {
            received_bytes += (buffer + received_bytes, bytes_to_receive - received_bytes);
        } while (received_bytes != bytes_to_receive);

        SrcID = pkt->srcID;
        DestID = pkt->destID;
        Pver = pkt->pver ;
        Profiles = pkt->profiles;
        Length = pkt->length;
        Data = pkt->data;
        printf("Data Received from Client_1 are :\n");
        printf("Source ID: %l\n", SrcID);
        printf("Destination ID: %l\n", DestID);
        printf("profile Version: %l\n", Pver);
        printf("No of Profiles: %l\n", Profiles);
        printf("Length: %l\n", Length);
        printf("data : %l\n", Data);
    }
    if (close(newsockfd) == -1) {
        error("Error closing connection with client 1");
    }

    printf("Connection with client 1 has been closed\n");
    return 0; 
}

服務器沒有顯示任何 o/p。 客戶說它已經發送了數據包。 在編譯服務器代碼時，我看到四個警告，說明服務器代碼中所有 printf 語句的格式為未知轉換類型字符 0xa。 我想我在服務器代碼端的某個地方出錯了，但我無法遵循“序列化”。 請用您的輸入更新我，這將有很大幫助。

Answer 1

這是我發現的幾個問題：

1. 您的客戶一直在發送包裹，因為它處於無限循環中。
2. 您傳遞了錯誤的 recv function 的 len 參數。 現在您傳遞的 sizeof(packet_size) 等於 sizeof(long int) （在 32 位操作系統上為 4 個字節），但您的意圖可能是使用 sizeof(packet) （16 個字節）。

3. 您沒有檢查 recv function 真正讀取了多少字節。 使用 TCP 您不能保證您讀取了所有 16 個字節的結構數據包。 因此，有時您可以讀取更少的字節，並且您的數據包將不完整。 這是一些偽代碼中的示例，您應該如何接收整個數據包：

    bytes_to_receive = sizeof(packet) received_bytes = 0; do { received_bytes += recv(buffer + received_bytes, bytes_to_receive - received_bytes) } while (received_bytes != bytes_to_receive)

4. 您在客戶端和服務器中的結構packet是不同的。 在一個中，您使用char length; 在第二個long int length;

5. 我認為服務器中的這種分配也沒有意義pkt->srcID = SrcID; 應該是這樣的SrcID = pkt->srcID;

Answer 2

客戶端不斷發送的問題是因為您只是將其置於循環中。 縮進固定后，發生了什么就很清楚了：

while (1)
{
    if (send(sockfd,pkt,sizeof(packet_size),0) <0)
        printf ("error\n");
    else
        printf ("packet send done");
}

Answer 3

addr_size = sizeof serverAddr;

連接(clientSocket, (struct sockaddr *) &serverAddr, addr_size);