Question

我的教授指示我们手动制作UDP请求并发送。我到目前为止构建了UDP头和内容指针..问题是sendto函数需要数据结构sockaddr而我所拥有的只是指示目标ipv4的字符串..

那么任何想法如何将此字符串转换为该结构或是否有不同的发送消息？

#include <errno.h>
#include <unistd.h>
#include <netdb.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdio.h>
#include <stdarg.h>
#include <stdlib.h>
#include <string.h>

static void die (const char * format, ...)
{
    va_list vargs;
    va_start (vargs, format);
    vfprintf (stderr, format, vargs);
    fprintf (stderr, ".\n");
    exit (1);
}
void copy_lower_16_int(void * dest,int value)
{
    size_t sz  =sizeof(value);
    if(sz == 2)
        memcpy(dest,&value,2);
    else if (sz >2)
    {
        memcpy(dest,(&value)+sz-2,2);
    }
}
int sendTo(void * message,size_t size ,char * destinationIP,unsigned short  destinationPort)
{


    // Get the target transport protocol number
    const char* protocol_name="udp";
    struct protoent* protocol=getprotobyname(protocol_name);
    if (!protocol) {
        die("Protocol %s not found",protocol_name);
    }
    int protocol_number=protocol->p_proto;

    printf(" Protocol %s has number of %d \n",protocol_name,protocol_number);

    // Create raw socket for usage with IPv4 & the specified transport protocol (UDP)
    int fd=socket(AF_INET,SOCK_RAW,protocol_number);
    if (fd==-1) {
        die("Failed to create a raw socket, error : %s",strerror(errno));
    }

    // Construct the UDP datagram

    //Calculate total size ( message size + 8 byte for the headers)
    size_t total_size = size + 8;
    // Calculate the checksum 
    int checksum = 0x53AF;  

    void * content = (void*) malloc(total_size);
    const int sourcePort = 1524;


    copy_lower_16_int(content,sourcePort);
    copy_lower_16_int(content+2,destinationPort);
    copy_lower_16_int(content+4,total_size);

    copy_lower_16_int(content+6,checksum);


    memcpy(content+8,message,size);

}
void main(){
    printf("Size of int is %d",sizeof(2));
    sendTo("Cx",2,"127.0.0.1",5405);
}

Answer 1

我使用getaddrinfo作为以下

解决了我的问题

struct addrinfo *addr_result;
struct addrinfo hints;


memset(&hints, 0, sizeof(struct addrinfo));
hints.ai_family = AF_INET;    /* Allow IPv4 or IPv6 */
hints.ai_socktype = SOCK_RAW; /* Datagram socket */
hints.ai_flags = AI_PASSIVE;    /* For wildcard IP address */
hints.ai_protocol = protocol_number;          /* Any protocol */
hints.ai_canonname = NULL;
hints.ai_addr = NULL;
hints.ai_next = NULL;
getaddrinfo(destinationIP,NULL,&hints,&addr_result);

//Send the damn message
ssize_t sentsz = sendto(fd,content,total_size,0,addr_result->ai_addr,addr_result->ai_addrlen);
if (sentsz == -1)
{
        printf("It failed to send !!");
}
else {
        printf("It did send %d bytes",sentsz);
}
// free allocated memory

free(content);
freeaddrinfo(addr_result);

在C中发送手动制作的UDP数据报？

1 个答案: