UDP文件传输程序在C中，而循环不会做任何事情

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <arpa/inet.h>

#define BUF_SIZE 1024

int main(int argc, char* argv[]) {
    if (argc != 3) {
        printf("Usage: %s <IP> <Port>\n", argv[0]);
        exit(1);
    }

    char* server_ip = argv[1];
    int server_port = atoi(argv[2]);

    // 创建UDP套接字
    int sockfd = socket(AF_INET, SOCK_DGRAM, 0);
    if (sockfd == -1) {
        perror("socket");
        exit(1);
    }

    struct sockaddr_in server_addr;
    memset(&server_addr, 0, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_addr.s_addr = inet_addr(server_ip);
    server_addr.sin_port = htons(server_port);

    // 读取文件内容并发送
    FILE* file = fopen("filename.txt", "rb");
    if (file == NULL) {
        perror("fopen");
        exit(1);
    }

    char buffer[BUF_SIZE];
    size_t len;
    while ((len = fread(buffer, 1, BUF_SIZE, file)) > 0) {
        // 发送数据包
        ssize_t send_len = sendto(sockfd, buffer, len, 0, (struct sockaddr*)&server_addr, sizeof(server_addr));
        if (send_len == -1) {
            perror("sendto");
            exit(1);
        }
    }

    // 关闭套接字和文件
    fclose(file);
    close(sockfd);

    return 0;
}