// udp.c —— 原书 Figure 48.2：一个简单的 UDP 库
#include <netdb.h>
#include <stdio.h>
#include <string.h>
#include <strings.h>
#include <unistd.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include "udp.h"

int UDP_Open(int port) {
    int sd;
    if ((sd = socket(AF_INET, SOCK_DGRAM, 0)) == -1)   // SOCK_DGRAM = UDP 数据报
        return -1;
    struct sockaddr_in myaddr;
    bzero(&myaddr, sizeof(myaddr));
    myaddr.sin_family = AF_INET;
    myaddr.sin_port = htons(port);                      // 端口号转成网络字节序（大端）
    myaddr.sin_addr.s_addr = INADDR_ANY;
    if (bind(sd, (struct sockaddr *) &myaddr, sizeof(myaddr)) == -1) {
        close(sd);
        return -1;
    }
    return sd;
}

int UDP_FillSockAddr(struct sockaddr_in *addr, char *hostname, int port) {
    bzero(addr, sizeof(struct sockaddr_in));
    addr->sin_family = AF_INET;          // host byte order
    addr->sin_port = htons(port);        // network byte order
    struct in_addr *in_addr;
    struct hostent *host_entry;
    if ((host_entry = gethostbyname(hostname)) == NULL)   // 命名：主机名 → IP 地址
        return -1;
    in_addr = (struct in_addr *) host_entry->h_addr;
    addr->sin_addr = *in_addr;
    return 0;
}

int UDP_Write(int sd, struct sockaddr_in *addr, char *buffer, int n) {
    int addr_len = sizeof(struct sockaddr_in);
    return sendto(sd, buffer, n, 0, (struct sockaddr *) addr, addr_len);
}

int UDP_Read(int sd, struct sockaddr_in *addr, char *buffer, int n) {
    socklen_t len = sizeof(struct sockaddr_in);
    return recvfrom(sd, buffer, n, 0, (struct sockaddr *) addr, &len);
}

int UDP_Close(int sd) { return close(sd); }