基于C语言的传输协议封包、发包实现

前言：本实例中以APDU协议为例进行封包和发包（这里的发包以一个报文为单位，在实际工作中应该是以实际带宽决定吧）。

#include 
#include 
#include 

//SYS
#define MTU_DATA 16
#define MTU (MTU_DATA + 6)

//USER
#define RAW_LEN 100

//APDU Format
#define CLA 0
#define INS 1
#define P1 2
#define P2 3
#define Lc 4
#define Le(data_len) (5 + (data_len))

//example:apdu
//CLA INS P1 P2 | Lc data Le
int
warp_packet(char *rawdata, int raw_len, char **newdata, int *new_len, int *count)
{
    int loop, apdu_count, data_len;

    *new_len = 0;
    *count = 0;
    loop = raw_len;
    apdu_count = (raw_len/MTU_DATA) + (((raw_len%MTU_DATA) > 0) ? 1:0);
    *count = (apdu_count > 0)?apdu_count:1;
    *newdata = malloc( sizeof(char) * MTU * (*count) );
    if(*newdata == NULL){
        printf("malloc is failed\n");
        return -1;
    }
    memset(*newdata, 0, sizeof(char) * MTU * (*count));
    for(int i = 0; i < *count; ++i){
        //head fill
        (*newdata)[CLA + MTU*i] = 0x00;
        (*newdata)[INS + MTU*i] = 0x01;
        (*newdata)[P1 + MTU*i] = 0x02;
        (*newdata)[P2 + MTU*i] = 0x03;

        //body fill
        data_len = (loop > MTU_DATA)?MTU_DATA:(loop%MTU_DATA);
        (*newdata)[Lc + MTU*i] = data_len;
        memcpy(*newdata + Lc + MTU*i + 1, rawdata + i*MTU_DATA, data_len);
        (*newdata)[Le(data_len) + i*MTU] = data_len;
        
        loop -= MTU_DATA;
        *new_len += 6 + data_len;
    }

    return 0;
}

void 
send(char *buff, int len)
{
    printf("send:");
    for(int i = 0; i < len; ++i)
        printf("%x ", buff[i]);
    printf("\n");
}

void 
multi_send(char *data, int len, int count)
{
    for(int i = 0; i < count; ++i){
        if(i == (count-1))
            send(data + MTU*i, len%MTU);
        else
            send(data + MTU*i, MTU);
    }
}
void
gen_data(char *array, int n)
{
    for(int i = 0; i < n; ++i)
        array[i] = i;
}
int 
main(int argc, char const *argv[])
{
    char rawdata[RAW_LEN];
    char *newdata;
    int new_len, count;

    gen_data(rawdata, RAW_LEN);
    for(int i = 0; i < RAW_LEN; ++i){
        printf("%x ", rawdata[i]);
    }
    printf("\n");

    warp_packet(rawdata, RAW_LEN, &newdata, &new_len, &count);
    printf("count:%d new_len:%d \n", count, new_len);
    for(int i = 0; i < new_len; ++i){
        printf("%x ", newdata[i]);
        if((i+1)%MTU == 0)
            printf("\n");
    }
    printf("\n");

    multi_send(newdata, new_len, count);

    return 0;
}