UDP file transfer

client.c

#include <string.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <fcntl.h>

#define SERV_PORT 49312
#define MAXLINE   1024

char *END_FLAG = "================END";

int main(int argc, char **argv)
{
    int sockfd, n, fd;
    struct sockaddr_in servaddr;
    char buf[MAXLINE];
    char *target, *path;

    bzero(&servaddr, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_port = htons(SERV_PORT);
    inet_pton(AF_INET, argv[1], &servaddr.sin_addr);

    sockfd = socket(AF_INET, SOCK_DGRAM, 0);
    
    path = argv[2];
    target = argv[3];
    sendto(sockfd, target, strlen(target), 0, (struct sockaddr *) &servaddr, sizeof(servaddr));
    n = recvfrom(sockfd, buf, MAXLINE, 0, NULL, NULL);
    if (!strncmp(buf, "ok", 2)) {
        printf("Filename sent.\n");
    }
    
    fd = open(path, O_RDONLY);
    while ((n = read(fd, buf, MAXLINE)) > 0) {
        sendto(sockfd, buf, n, 0, (struct sockaddr *) &servaddr, sizeof(servaddr));
    }
    sendto(sockfd, END_FLAG, strlen(END_FLAG), 0, (struct sockaddr *) &servaddr, sizeof(servaddr));
    
    return 0;
}

server.c

#include <stdio.h>
#include <string.h>
#include <fcntl.h>
#include <arpa/inet.h>
#include <sys/socket.h>
  
#define SERV_PORT 49312
#define MAXLINE   1024
  
char *END_FLAG = "================END";

void run(int sockfd, struct sockaddr *cliaddr, socklen_t clilen)
{
    int n, fd;
    socklen_t len;
    char buf[MAXLINE];

    len = clilen;
    n = recvfrom(sockfd, buf, MAXLINE, 0, cliaddr, &len);
    buf[n] = 0;
    printf("Received from client: [%s]\n", buf);
    sendto(sockfd, "ok", strlen("ok"), 0, cliaddr, len);
    fd = open(buf, O_RDWR | O_CREAT, 0666);

    while ((n = recvfrom(sockfd, buf, MAXLINE, 0, cliaddr, &len))) {
        buf[n] = 0;
        printf("%s", buf);
        if (!(strcmp(buf, END_FLAG))) {
            break;
        }
        write(fd, buf, n);
    }
    close(fd);
}
         
int main(int argc, char **argv)
{
    int sockfd;
    struct sockaddr_in servaddr, cliaddr;

    sockfd = socket(AF_INET, SOCK_DGRAM, 0);
    bzero(&servaddr, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    servaddr.sin_port = htons(SERV_PORT);

    bind(sockfd, (struct sockaddr *) &servaddr, sizeof(servaddr));

    run(sockfd, (struct sockaddr *) &cliaddr, sizeof(cliaddr));

    return 0;
}

Would be awesome if it can be made to work with larger files (currently packets get lost on 15MB file...)