#include <stdio.h>//printf
#include <string.h>//字符串处理
#include <sys/socket.h>//套接字
#include <arpa/inet.h>//ip地址处理
#include <fcntl.h>//open系统调用
#include <unistd.h>//write系统调用
#include <netdb.h>//查询DNS
#include <stdlib.h>//exit函数
#include <sys/stat.h>//stat系统调用获取文件大小
#include <sys/time.h>//获取下载时间
//下载地址   http://dldir1.qq.com/qqfile/qq/QQ7.9/16638/QQ7.9.exe
struct HTTP_RES_HEADER//保持相应头信息
{int status_code;//HTTP/1.1 '200' OKchar content_type[128];//Content-Type: application/gziplong content_length;//Content-Length: 11683079
};void parse_url(const char *url, char *host, int *port, char *file_name)
{/*通过url解析出域名, 端口, 以及文件名*/int j = 0;int start = 0;*port = 80;char *patterns[] = {"http://", "https://", NULL};for (int i = 0; patterns[i]; i++)//分离下载地址中的http协议if (strncmp(url, patterns[i], strlen(patterns[i])) == 0)start = strlen(patterns[i]);//解析域名, 这里处理时域名后面的端口号会保留for (int i = start; url[i] != '/' && url[i] != '\0'; i++, j++)host[j] = url[i];host[j] = '\0';//解析端口号, 如果没有, 那么设置端口为80char *pos = strstr(host, ":");if (pos)sscanf(pos, ":%d", port);//删除域名端口号for (int i = 0; i < (int)strlen(host); i++){if (host[i] == ':'){host[i] = '\0';break;}}//获取下载文件名j = 0;for (int i = start; url[i] != '\0'; i++){if (url[i] == '/'){if (i !=  strlen(url) - 1)j = 0;continue;}elsefile_name[j++] = url[i];}file_name[j] = '\0';
}struct HTTP_RES_HEADER parse_header(const char *response)
{/*获取响应头的信息*/struct HTTP_RES_HEADER resp;char *pos = strstr(response, "HTTP/");if (pos)//获取返回代码sscanf(pos, "%*s %d", &resp.status_code);pos = strstr(response, "Content-Type:");if (pos)//获取返回文档类型sscanf(pos, "%*s %s", resp.content_type);pos = strstr(response, "Content-Length:");if (pos)//获取返回文档长度sscanf(pos, "%*s %ld", &resp.content_length);return resp;
}void get_ip_addr(char *host_name, char *ip_addr)
{/*通过域名得到相应的ip地址*/struct hostent *host = gethostbyname(host_name);//此函数将会访问DNS服务器if (!host){ip_addr = NULL;return;}for (int i = 0; host->h_addr_list[i]; i++){strcpy(ip_addr, inet_ntoa( * (struct in_addr*) host->h_addr_list[i]));break;}
}void progress_bar(long cur_size, long total_size, double speed)
{/*用于显示下载进度条*/float percent = (float) cur_size / total_size;const int numTotal = 50;int numShow = (int)(numTotal * percent);if (numShow == 0)numShow = 1;if (numShow > numTotal)numShow = numTotal;char sign[51] = {0};memset(sign, '=', numTotal);printf("\r%.2f%%[%-*.*s] %.2f/%.2fMB %4.0fkb/s", percent * 100, numTotal, numShow, sign, cur_size / 1024.0 / 1024.0, total_size / 1024.0 / 1024.0, speed);fflush(stdout);if (numShow == numTotal)printf("\n");
}unsigned long get_file_size(const char *filename)
{//通过系统调用直接得到文件的大小struct stat buf;if (stat(filename, &buf) < 0)return 0;return (unsigned long) buf.st_size;
}void download(int client_socket, char *file_name, long content_length)
{/*下载文件函数*/long hasrecieve = 0;//记录已经下载的长度struct timeval t_start, t_end;//记录一次读取的时间起点和终点, 计算速度int mem_size = 8192;//缓冲区大小8Kint buf_len = mem_size;//理想状态每次读取8K大小的字节流int len;//创建文件描述符int fd = open(file_name, O_CREAT | O_WRONLY, S_IRWXG | S_IRWXO | S_IRWXU);if (fd < 0){printf("文件创建失败!\n");exit(0);}char *buf = (char *) malloc(mem_size * sizeof(char));//从套接字流中读取文件流long diff = 0;int prelen = 0;double speed;while (hasrecieve < content_length){gettimeofday(&t_start, NULL ); //获取开始时间len = read(client_socket, buf, buf_len);write(fd, buf, len);gettimeofday(&t_end, NULL ); //获取结束时间hasrecieve += len;//更新已经下载的长度//计算速度if (t_end.tv_usec - t_start.tv_usec >= 0 &&  t_end.tv_sec - t_start.tv_sec >= 0)diff += 1000000 * ( t_end.tv_sec - t_start.tv_sec ) + (t_end.tv_usec - t_start.tv_usec);//usif (diff >= 1000000)//当一个时间段大于1s=1000000us时, 计算一次速度{speed = (double)(hasrecieve - prelen) / (double)diff * (1000000.0 / 1024.0);prelen = hasrecieve;//清零下载量diff = 0;//清零时间段长度}progress_bar(hasrecieve, content_length, speed);if (hasrecieve == content_length)break;}
}int main(int argc, char const *argv[])
{/* 命令行参数: 接收两个参数, 第一个是下载地址, 第二个是文件的保存位置和名字, 下载地址是必须的, 默认下载到当前目录* 示例: ./download http://www.baidu.com baidu.html*/char url[2048] = "127.0.0.1";//设置默认地址为本机,char host[64] = {0};//远程主机地址char ip_addr[16] = {0};//远程主机IP地址int port = 80;//远程主机端口, http默认80端口char file_name[256] = {0};//下载文件名if (argc == 1){printf("您必须给定一个http地址才能开始工作\n");exit(0);}elsestrcpy(url, argv[1]);puts("1: 正在解析下载地址...");parse_url(url, host, &port, file_name);//从url中分析出主机名, 端口号, 文件名if (argc == 3){printf("\t您已经将下载文件名指定为: %s\n", argv[2]);strcpy(file_name, argv[2]);}puts("2: 正在获取远程服务器IP地址...");get_ip_addr(host, ip_addr);//调用函数同访问DNS服务器获取远程主机的IPif (strlen(ip_addr) == 0){printf("错误: 无法获取到远程服务器的IP地址, 请检查下载地址的有效性\n");return 0;}puts("\n>>>>下载地址解析成功<<<<");printf("\t下载地址: %s\n", url);printf("\t远程主机: %s\n", host);printf("\tIP 地 址: %s\n", ip_addr);printf("\t主机PORT: %d\n", port);printf("\t 文件名 : %s\n\n", file_name);//设置http请求头信息char header[2048] = {0};sprintf(header, \"GET %s HTTP/1.1\r\n"\"Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8\r\n"\"User-Agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537(KHTML, like Gecko) Chrome/47.0.2526Safari/537.36\r\n"\"Host: %s\r\n"\"Connection: keep-alive\r\n"\"\r\n"\,url, host);puts("3: 创建网络套接字...");int client_socket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);if (client_socket < 0){printf("套接字创建失败: %d\n", client_socket);exit(-1);}//创建IP地址结构体struct sockaddr_in addr;memset(&addr, 0, sizeof(addr));addr.sin_family = AF_INET;addr.sin_addr.s_addr = inet_addr(ip_addr);addr.sin_port = htons(port);//连接远程主机puts("4: 正在连接远程主机...");int res = connect(client_socket, (struct sockaddr *) &addr, sizeof(addr));if (res == -1){printf("连接远程主机失败, error: %d\n", res);exit(-1);}puts("5: 正在发送http下载请求...");write(client_socket, header, strlen(header));//write系统调用, 将请求header发送给服务器int mem_size = 4096;int length = 0;int len;char *buf = (char *) malloc(mem_size * sizeof(char));char *response = (char *) malloc(mem_size * sizeof(char));//每次单个字符读取响应头信息puts("6: 正在解析http响应头...");while ((len = read(client_socket, buf, 1)) != 0){if (length + len > mem_size){//动态内存申请, 因为无法确定响应头内容长度mem_size *= 2;char * temp = (char *) realloc(response, sizeof(char) * mem_size);if (temp == NULL){printf("动态内存申请失败\n");exit(-1);}response = temp;}buf[len] = '\0';strcat(response, buf);//找到响应头的头部信息int flag = 0;for (int i = strlen(response) - 1; response[i] == '\n' || response[i] == '\r'; i--, flag++);if (flag == 4)//连续两个换行和回车表示已经到达响应头的头尾, 即将出现的就是需要下载的内容break;length += len;}struct HTTP_RES_HEADER resp = parse_header(response);printf("\n>>>>http响应头解析成功:<<<<\n");printf("\tHTTP响应代码: %d\n", resp.status_code);if (resp.status_code != 200){printf("文件无法下载, 远程主机返回: %d\n", resp.status_code);return 0;}printf("\tHTTP文档类型: %s\n", resp.content_type);printf("\tHTTP主体长度: %ld字节\n\n", resp.content_length);printf("7: 开始文件下载...\n");download(client_socket, file_name, resp.content_length);printf("8: 关闭套接字\n");if (resp.content_length == get_file_size(file_name))printf("\n文件%s下载成功! ^_^\n\n", file_name);else{remove(file_name);printf("\n文件下载中有字节缺失, 下载失败, 请重试!\n\n");}shutdown(client_socket, 2);//关闭套接字的接收和发送return 0;
}

运行效果：