通过UDP发送时丢失数据

Question

我编写了一个UDP发送/接收函数来发送一个结构并监听另一个结构.字节必须按特定顺序发送,但这正好我正在使用#pragma pack(1).我现在唯一的问题是,如果结构中出现任何Null值(0x00),则Null消失后的其余数据.

我想有一些相当简单的事情,我做错了,但这是我的代码:

typedef u_int8_t NN;
typedef u_int8_t X;
typedef int32_t S;
typedef u_int32_t U;
typedef char C;

typedef struct{
    X test;
    NN test2[2];
    C test3[4];
    S test4;
} Test;

int main(int argc, char** argv)
{
    Test t;
    memset( &t, 0, sizeof(t));
    t.test = 0xde;
    t.test2[0]=0xad; t.test2[1]=0x00;
    t.test3[0]=0xbe; t.test3[1]=0xef; t.test3[2]=0xde; t.test3[3]=0xca;
    t.test4=0xde; 

    LogOnResponse response;

    udp_send_receive(&t, &response);

    return 0;
}

这是我的发送/接收功能:

int send_and_receive(void* message, void* reply, int do_send, int expect_reply)
{
    struct sockaddr_in serv_addr;
    int sockfd, i, slen=sizeof(serv_addr);
    int buflen = BUFLEN;
    void* buf = NULL;
    struct timeval tv;
    int n_timeouts=1;
    int recv_retval;

//  printf("Message Size: %d\n", strlen(message));

    if ( (strlen(message)) >= BUFLEN)
        err("Message too big");

    buf = malloc(buflen);

    if ((sockfd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP))==-1)
        err("socket");

    tv.tv_sec = timeout_seconds;
    tv.tv_usec = timeout_microseconds;
    if( setsockopt(sockfd, SOL_SOCKET, SO_RCVTIMEO,&tv,sizeof(tv)) < 0 ){
        err("Setting Timout"); 
    }

    bzero(&serv_addr, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(PORT);
    if (inet_aton(IP_ADDRESS, &serv_addr.sin_addr)==0)
        err("inet_aton() failed\n");

    //---Timeout Send/Receive loop

    do{
    if(do_send == TRUE){
        strcpy(buf, message);
        if (sendto(sockfd, buf, buflen, 0, (struct sockaddr*)&serv_addr, slen)==-1)
            err("sendto()");
    }

    if (expect_reply == TRUE){
        if( (recv_retval = recvfrom(sockfd, buf, buflen, 0, (struct sockaddr*)&serv_addr, &slen)) == -1){
            itercount++;    
        }
    }

    }while ((itercount < itermax) && (recv_retval == -1));

    if ( itercount != itermax ){
        memcpy(reply, buf, BUFLEN);
    }
    else{
        reply=NULL;
    }

    close(sockfd);
    free(buf);
    return 0;
}

void udp_send_receive(void* message, void* reply)
{
    send_and_receive(message, reply, TRUE, TRUE);
}

运行上面的代码并使用show捕获数据包WireShark:

Data: DEAD000000000000000000....

我希望它显示:

Data: DEAD00BEEFDECADE

我真的很感激这方面的一些指示.

Answer 1

您不能对二进制数据使用字符串函数(如strlen或strcpy).这是因为字符串以值零(字符'\0')终止.

例如,您使用strcpy复制数据,但一看到字符串终止符就会停止,这意味着它不会复制所有数据.