C语言 HTTP 下载文件

C语言 HTTP协议下载文件，实现断点续传，socket通讯，目前只支持ip和port方式连接，有兴趣的读者可完善域名方式。
      代码分为 http.c： 实现http协议下载文件 ，socket.c： 封装linux socket函数，移植时只需修改socket.c中的函数即可。
     希望对大家有帮助，本人亲测可用！
http.c

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 //http.c
 //作者：王振
 #include <stdio.h>
 #include <stdlib.h>
 #include <errno.h>
 #include <string.h>

 #include <sys/types.h>
 #include <sys/stat.h>
 #include <fcntl.h>

 #include "socket.h"
 #include "http.h"


 #define MAX_RECV_SIZE    1440//硬件单包最大的接收字节数
 char g_host[URL_LEN];
 char g_ip[URL_LEN+1];//ip/域名
 char g_port[5+1];

 char g_buf_send[4*1024];//发送数据暂存区
 char g_buf_recv[10*1024];//接收数据暂存区

 BreakPoint_ST g_break_point;

 /*
 功能:判断断点有效性,现在校验url是否一致
 参数:
 返回:
 >0---------有效,已下载文件大小
 -1----------无效
 */
 int Get_Breakpoint_Available(BreakPoint_ST *breakpoint,char *url,char *file_crc)
 {

     //判断断点是否有效,后续加入文件校验码
     if((memcmp(breakpoint->url,url,strlen(url))== 0)&&(breakpoint->recv_size== MAX_RECV_SIZE))
         return breakpoint->download_size;
     else
     {
         return -1;
     }

 }


 /*
 功能:判断要下载文件是否存在断点
 参数:
 filename---要下载的文件名
 file_crc----服务器返回下载文件的校验码
 返回:
 0---------无断点
 >0--------有断点,已下载文件大小
 */
 int Get_Breakpoint(char *url,char *filename,char *file_crc)
 {
     char filename_bp[64];
     int fd = -1;
     int ret;
     BreakPoint_ST break_point;

     //断点文件名 filename+bp
     sprintf(filename_bp,"%s.bp",filename);

     //检测是否存在filename断点文件
     fd = open(filename_bp,O_RDONLY,S_IRUSR|S_IWUSR);
     if(fd == -1)
     {
         #ifdef DEBUG_HTTP
         printf("no exsit %s\n",filename_bp);
         #endif
         return 0;
     }

     //存在断点
     ret = read(fd,&break_point,sizeof(break_point));
     if(ret != sizeof(break_point))
     {
         perror("ERR:Get_Breakpoint read");
         exit(-1);
     }

     close(fd);

     //判断断点是否有效
     ret = Get_Breakpoint_Available(&break_point,url,file_crc);
     if(ret > 0)
         return ret;
     else
     {

         printf("%s not available\n",filename_bp);
         remove(filename);
         remove(filename_bp);
         return 0;

     }
 }

 /*
 功能:保存断点信息,文件名filename.bp
 参数:
 filename---要下载的文件名
 file_crc----服务器返回下载文件的校验码
 返回:
 0---------成功
 >0--------有断点,已下载文件大小
 */
 int Save_Breakpoint(char *url,char *filename,int download_size,char *file_crc)
 {
     int fd;
     BreakPoint_ST breakpoint;
     char filename_bp[128];//断点信息文件名，包含路径

     sprintf(filename_bp,"%s.bp",filename);
     /* 创建目的文件 */
     if((fd=open(filename_bp,O_WRONLY|O_CREAT,S_IRUSR|S_IWUSR))==-1)
     {
         fprintf(stderr,"Open %s Error：%s\n",filename_bp,strerror(errno));
         exit(1);
     }
     memset(&breakpoint,0x0,sizeof(breakpoint));
     strcpy(breakpoint.url,url);
     //strcpy(breakpoint.crc,file_crc);
     strcpy(breakpoint.filename,filename);
     breakpoint.download_size = download_size;
     breakpoint.recv_size= MAX_RECV_SIZE;

     //xu tioa zheng wei fen ci xie ru
     if(write(fd,&breakpoint,sizeof(breakpoint)) != sizeof(breakpoint))
     {
         perror("ERR:Save_Breakpoint");
         exit(1);
     }

     close(fd);

     return 0;



 }

 /*
 功能:保存文件,追加写
 参数:
 返回:
 0---------成功
 */

 int Save_File(char *filebuf,int filelength,char *filename)
 {
     int fd;
     /* 创建目的文件追加写 */
     if((fd=open(filename,O_WRONLY|O_CREAT|O_APPEND,S_IRUSR|S_IWUSR))==-1)
     {
         fprintf(stderr,"Open %s Error：%s\n",filename,strerror(errno));
         exit(1);
     }
     //xu tioa zheng wei fen ci xie ru
     if(write(fd,filebuf,filelength) != filelength)
     {
         perror("ERR:Save_File");
         exit(1);
     }

     close(fd);

     return 0;


 }


 int HTTP_GetResponseCode(void)
 {


 }

  /*
 功能:读取http返回的协议实体主体长度
 参数:
 revbuf--------接收到的返回值
 返回值:
 >=0---------内容(实体主体)的长度
 -1-----------数据返回错误
 */
 int HTTP_GetRecvLength(char *revbuf)
 {
     char *p1 = NULL;
     int HTTP_Body = 0;//内容体长度
     int HTTP_Head = 0;//HTTP 协议头长度


     HTTP_Body = HTTP_GetContentLength(revbuf);
     if(HTTP_Body == -1)
         return -1;

     p1=strstr(revbuf,"\r\n\r\n");
     if(p1==NULL)
         return -1;
     else
     {
         HTTP_Head = p1- revbuf +4;// 4是\r\n\r\n的长度
         return HTTP_Body+HTTP_Head;
     }


 }


 /*
 功能:读取http返回的Content-Length长度
 参数:
 revbuf--------接收到的数据
 返回值:
 >=0---------Content-Length长度
 -1-----------数据返回错误
 */
 int HTTP_GetContentLength(char *revbuf)
 {
     char *p1 = NULL, *p2 = NULL;
     int HTTP_Body = 0;//内容体长度

     p1 = strstr(revbuf,"Content-Length");
     if(p1 == NULL)
         return -1;
     else
     {
         p2 = p1+strlen("Content-Length")+ 2;
         HTTP_Body = atoi(p2);
         return HTTP_Body;
     }

 }

  /*
  功能:
  参数:
  sockfd--------接收到的返回值
  返回值:
  >0---------接收到长度
  -1----------失败
  =0---------服务端断开连接
  注:内部接收缓冲10k
  */

 int HTTP_Recv(int sockfd,char *buf_recv)
 {
     int ret;
     int recvlen=0;
     int downloadlen = 0;
     //int contentlen=0;
     char buf_recv_tmp[10*1024+1];

     memset(buf_recv_tmp,0x0,sizeof(buf_recv_tmp));
     while(1)
     {
         ret = Recv(sockfd,buf_recv_tmp+recvlen,sizeof(buf_recv_tmp)-1,0);

         if(ret <= 0)//下载失败
         {
             perror("ERR:recv fail");
             return ret;
         }


         if(recvlen == 0)
         {
             #ifdef DEBUG_HTTP_RECV
             printf("recv len = %d\n", ret);
              printf("recv = %s\n", buf_recv_tmp);
             #endif
             //获取需要下载长度;
             downloadlen = HTTP_GetRecvLength(buf_recv_tmp);


             #ifdef DEBUG_HTTP_RECV
             printf("downloadlen = %d\n",downloadlen);
             #endif
         }

         recvlen += ret;
         #ifdef DEBUG_HTTP_RECV
         printf("total recvlen = %d\n",recvlen);
         #endif

         if(downloadlen == recvlen)//下载完成
             break;


     }
     memcpy(buf_recv,buf_recv_tmp,downloadlen);
     return recvlen;

 }

 /*
 功能:获取下载url中的文件名,最后一个/后的字符
 参数:
 返回值:
 0-----------成功
 -1----------失败
 注:内部接收缓冲10k
 */

 int HTTP_GetFileName(char *url,char *filename)
 {
     //提取url中最后一个/后的内容
     int len;
     int i;

     len = strlen(url);
     for(i=len-1;i>0;i--)
     {
         if(url[i] == '/')
             break;
     }
     if(i == 0)//下载地址错误
     {
         printf("url not contain '/'\n");
         return -1;
     }
     else
     {

         strcpy(filename,url+i+1);
         #ifdef DEBUG_HTTP
         printf("filename=%s\n",filename);
         #endif
         return 0;
     }
 }

 /*
 功能:获取下载url中的路径,第一个/后的字符
 参数:
 返回值:
 0-----------成功
 -1----------失败
 注:url ex "http://host:port/path"
 */
 int HTTP_GetPath(char *url,char *path)
 {
     char *p;

     p = strstr(url,"http://");
     if(p == NULL)
     {
         p = strchr(url,'/');
         if(p == NULL)
             return -1;
         else
         {
             strcpy(path,p);
             return 0;
         }
     }
     else
     {
         p = strchr(url+strlen("http://"),'/');
         if(p == NULL)
             return -1;
         else
         {
             strcpy(path,p);
             return 0;
         }
     }

 }
 /*
 功能:获取下载url中的ip和port,ip支持域名,端口默认为80
 参数:
 返回值:
 1-----------域名式
 2-----------ip port式
 -1----------失败
 注:url ex "http://host:port/path"
 */

 int HTTP_Get_IP_PORT(char *url,char *ip,char *port)
 {
     char *p = NULL;
     int offset = 0;
     char DOMAIN_NAME[128];

     p = strstr(url,"http://");
     if(p == NULL)
     {
         offset = 0;
     }
     else
     {
         offset = strlen("http://");
     }

     p = strchr(url+offset,'/');
     if(p == NULL)
     {
         printf("url:%s format error\n",url);
         return -1;

     }
     else
     {

         memset(DOMAIN_NAME,0x0,sizeof(DOMAIN_NAME));
         memcpy(DOMAIN_NAME,url+offset,(p-url-offset));
         p = strchr(DOMAIN_NAME,':');
         if(p == NULL)
         {
             strcpy(ip,DOMAIN_NAME);
             strcpy(port,"80");
             //printf("ip %p,port %p\n",ip,port);

             #ifdef DEBUG_HTTP
             printf("ip=%s,port=%s\n",ip,port);//debug info
             #endif
             return 1;

         }
         else
         {
             *p = '\0';

             strcpy(ip,DOMAIN_NAME);
             strcpy(port,p+1);

             #ifdef DEBUG_HTTP
             printf("ip=%s,port=%s\n",ip,port);//debug info
             #endif
             return 2;

         }


         return 0;
     }

 }
 void Package_Url_Get_File(char *path, char *range)
 {
     char buf[64];
     memset(g_buf_send,0x0,sizeof(g_buf_send));
     sprintf(g_buf_send, "GET %s",path);


     //HTTP/1.1\r\n 前面需要一个空格
     strcat(g_buf_send," HTTP/1.1\r\n");
     strcat(g_buf_send, "Host: ");
     strcat(g_buf_send, g_host);
     //strcat(g_buf_send, ":");
     //strcat(g_buf_send, PORT);

     sprintf(buf, "\r\nRange: bytes=%s",range);
     strcat(g_buf_send,buf);
     strcat(g_buf_send, "\r\nKeep-Alive: 200");
     strcat(g_buf_send,"\r\nConnection: Keep-Alive\r\n\r\n");


 }

 int Package_Url_Get_FileSize(char *url)
 {

     memset(g_buf_send,0x0,sizeof(g_buf_send));
     sprintf(g_buf_send, "HEAD %s",url);

         //HTTP/1.1\r\n 前面需要一个空格
     strcat(g_buf_send," HTTP/1.1\r\n");
     strcat(g_buf_send, "Host: ");
     strcat(g_buf_send, g_host);
     //strcat(g_buf_send, ":");
     //strcat(g_buf_send, PORT);
     strcat(g_buf_send,"\r\nConnection: Keep-Alive\r\n\r\n");

     return 0;
 }


 int HTTP_GetFileSize(int sockfd,char *path)
 {
     int ret = -1;
     char buf_recv_tmp[10*1024+1];

     Package_Url_Get_FileSize(path);
 #ifdef DEBUG_HTTP
     printf("send = %s \n",g_buf_send);
 #endif

     Send(sockfd, g_buf_send, strlen(g_buf_send), 0);

     memset(buf_recv_tmp,0x0,sizeof(buf_recv_tmp));
     ret = Recv(sockfd,buf_recv_tmp,sizeof(buf_recv_tmp)-1,0);
 #ifdef DEBUG_HTTP
     printf("recv len = %d\n", ret);
     printf("recv = %s\n", buf_recv_tmp);
 #endif
     if(ret <= 0)
     {
         perror("ERR:recv fail GetFileSize()");
         return -1;

     }
     ret = HTTP_GetContentLength(buf_recv_tmp);
     if(ret <= 0)
         return -1;
     else
         return ret;


 }




 /*
 功能:分段下载文件
 参数:
 返回值:
 >0----------已下载文件大小(不包含上次下载)
 -1----------失败
 */
 int HTTP_GetFile(int sockfd,char *path,int filelength,int download_size,char *filebuf)
 {
     int count;
     char range[32];
     int i;
     int j = 0;//成功下载次数
     int ret = -1;
     char *p = NULL;
     int download_index;//下载开始索引

     count = (filelength%MAX_RECV_SIZE)?(filelength/MAX_RECV_SIZE +1):(filelength/MAX_RECV_SIZE);

     download_index = download_size/MAX_RECV_SIZE;

     for(i=download_index;i<count;i++)
     {
         //if(i == 20)//测试断点
             //break;


         if((i == (count-1))&&(filelength%MAX_RECV_SIZE))
             sprintf(range,"%d-%d",i*MAX_RECV_SIZE,filelength-1);
         else
             sprintf(range,"%d-%d",i*MAX_RECV_SIZE,(i+1)*MAX_RECV_SIZE-1);


         Package_Url_Get_File(path,range);
         #ifdef DEBUG_HTTP
          printf("send = %s \n",g_buf_send);
         #endif
          Send(sockfd, g_buf_send, strlen(g_buf_send), 0);

         /*需改为提取http 返回协议头和协议体总长,然后定长接收*/
         memset(g_buf_recv,0x0,sizeof(g_buf_recv));
         ret = HTTP_Recv(sockfd,g_buf_recv);
         if(ret < 0)
             break;
         if(ret == 0 )//服务端断开连接
         {
             sockfd = Socket_Connect(g_ip,g_port);
              i--;
             continue;
         }
         /*提取协议体数据,保存在filebuf中*/
         p = strstr(g_buf_recv,"\r\n\r\n");
         if(p == NULL)//jia ru duan dian baocun
         {
             printf("ERR:g_buf_recv not contain end flag\n");
             break;
         }
          else
          {
              memcpy(filebuf+j*MAX_RECV_SIZE,p+4,MAX_RECV_SIZE);
              j++;

          }
     }
     if(i == count)
         return (filelength-download_size);
     else
         return (i*MAX_RECV_SIZE-download_size);
 }

 /*
 功能:HTTP下载文件
 参数:
 返回值:
 0----------下载完成
 -1---------失败
 -2---------部分下载完成
 注:保存文件到bin所在目录
 */
 int HTTP_DownloadFile(char *url,char *save_path)
 {
     int ret;
     int sockfd;
     int filesize;
     int download_size;
     char filename[FILENAME_LEN+1];
     char filename_bp[FILENAME_LEN+3+1];
     char *filebuf;
     char save_file_path[FILENAME_LEN+1];//保存下载文件的路径+文件名

     char path[PATH_LEN+1];//url中的path

     //提取ip和port或url(url 暂不实现,需要gethostbyname linux)
     ret = HTTP_Get_IP_PORT(url,g_ip,g_port);
     if(ret == -1)
         return -1;
     else
     {
         sprintf(g_host,"%s:%s",g_ip,g_port);
     }
     //提取下载文件名
     ret = HTTP_GetFileName(url,filename);
     if(ret == -1)
         return -1;

     ret = HTTP_GetPath(url,path);
     if(ret == -1)
         return -1;
     //sleep(3);//debug info
     //建立连接
     sockfd = Socket_Connect(g_ip,g_port);

     //获取下载文件总大小
     filesize = HTTP_GetFileSize(sockfd,path);
     if(filesize == -1)
         return -1;
     //#ifdef DEBUG_HTTP
     printf("http need download size %d\n",filesize);
     //#endif
     //malloc分配存储文件空间
     filebuf = (char *)malloc(filesize);
     if(filebuf == NULL)
     {
         perror("malloc filebuf fail");
         return -1;
     }
     else
         memset(filebuf,0x0,filesize);

     download_size = Get_Breakpoint(url,filename,NULL);
     #ifdef DEBUG_HTTP
     printf("breakpoint download_size=%d\n",download_size);//debug info
     sleep(3);//debug info
     #endif
     //分段下载文件
     ret = HTTP_GetFile(sockfd,path,filesize,download_size,filebuf);
     Close(sockfd);
     if(ret < 0)
     {
         free(filebuf);
         return -1;
     }
     else
     {

         sprintf(save_file_path,"%s%s",save_path,filename);

         #ifdef DEBUG_HTTP
         printf("save_path=%s\n",save_path);
         printf("filename=%s\n",filename);
         printf("save_file_path=%s\n",save_file_path);
         printf("download_size = %d\n",ret);
         #endif
         Save_File(filebuf,ret,save_file_path);
         free(filebuf);
         if((ret+download_size) == filesize)//全部下载完成
         {
             sprintf(filename_bp,"%s.bp",filename);
             remove(filename_bp);

      printf("download success\n");
             return 0;
         }
         else//部分下载完成
         {
             printf("part download success\n");
             //保存断点信息
             Save_Breakpoint(url,save_file_path,ret+download_size,NULL);
             return -2;
         }
     }

 }

socket . c  

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 //socket.c
 //作者：王振

 #include <stdio.h>
 #include <stdlib.h>
 #include <errno.h>
 #include <string.h>
 #include <sys/types.h>
 #include <netinet/in.h>
 #include <sys/socket.h>
 #include <sys/wait.h>

 #include "socket.h"

 int Connect(int fd, struct sockaddr *addr, socklen_t len)
 {
     int result;
     if ((result = connect(fd, addr, len)) == -1) {
         perror("connect");
         exit(EXIT_FAILURE);
     }
     return 0;
 }

 int Socket_Connect(char *ip,char *port)
 {
     struct sockaddr_in addr;

     int sockfd;
     int len;


     addr.sin_family = AF_INET;
     addr.sin_addr.s_addr = inet_addr(ip);//127.0.0.1为本机ip
     addr.sin_port = htons(atoi(port));
     len = sizeof(addr);

     sockfd = socket(AF_INET, SOCK_STREAM, 0);
     Connect(sockfd, (struct sockaddr*)&addr, len);
     return sockfd;

 }


 /*
 功能:向socketfd发送数据,内部实现了循环发送len长度
 参数:
 sockfd 是代表你与远程程序连接的套接字描述符。
 msg 是一个指针，指向你想发送的信息的地址。
 len 是你想发送信息的长度。
 flags 发送标记。一般都设为0
 返回:
 0-------- 成功
 退出---失败
 修改:
 备注:
 王振
 */
 int Send(int sockfd, char *sendbuf, int len, int flags)
 {
     int sendlen = 0;
     int ret = -1;

     while(sendlen < len)
     {
         ret = send(sockfd, sendbuf+sendlen, len-sendlen, flags);
         if(-1 == ret)
         {
             perror("send");
             exit(EXIT_FAILURE);
         }
         else
             sendlen += ret;

     }

     return 0;

 }

 int Close(int sockfd)
 {
     return close(sockfd);


 }
 int Recv(int sockfd, char *recvbuf, int len, int flags)
 {
     int recv_len;

     if ((recv_len = recv(sockfd, recvbuf, len, flags)) < 0)
     {
         perror("recv error");
         exit(EXIT_FAILURE);
     }

     return recv_len;
 }

很早就有这个想法了，知道今天才实现了一下，参考了周立发的《《C语言实现HTTP下载例子》》和林超旗整理的《《HTTP协议详解》》，特此谢谢！由于今天时间有限，所以大概的实现了一下(目前只在ubuntu环境下测试的)，跨平台部分还需要完善，后面会陆续整理出完整的版本。代码如下：

头文件

/*
	$Id: httpdownload.h, v1.0.0, 2011.6.28, YellowBug $
	$@@: http下载 
*/
#ifndef PENQ_HTTP_DOWNLOAD_H_
#define PENQ_HTTP_DOWNLOAD_H_
#include 
#include 
#include 
#include 
#if defined(__GNUC__)
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#define PATH_SPLIT			'/'
typedef int	HSOCKET;
#define closesocket(s)		close(s)
#elif defined(_WIN32)
#include 
#include 
#define PATH_SPLIT			'//'	
typedef SOCKET HSOCKET;
#endif

#define DEF_HTTP_PORT			80
#define HTTP_MAX_PATH			260
#define HTTP_MAX_REQUESTHEAD	1024
#define HTTP_MAX_RESPONSEHEAD	2048
#define HTTP_DOWN_PERSIZE		128	
#define HTTP_FLUSH_BLOCK		1024

/*
	$@@ 下载状态
	$@ HDL_URLERR: 提供的url非法
	$@ HDL_SERVERFAL: 根据host地址无法找到主机 
	$@ HDL_TIMEOUT: 连接下载地址超时
	$@ HDL_READYOK: 连接下载地址成功,准备下载
	$@ HDL_DOWNING: 正在下载
	$@ HDL_DISCONN: 断开连接了
	$@ HDL_FINISH: 下载完成
*/
enum 
{
	HDL_URLERR = 0xe0,
	HDL_SERVERFAL = 0xe1,
	HDL_SOCKFAL = 0xe2,
	HDL_SNDREQERR = 0xe3,
	HDL_SERVERERR = 0xe4,
	HDL_CRLOCFILEFAL = 0xe5,
	HDL_TIMEOUT = 0x100,
	HDL_NORESPONSE = 0x101,
	HDL_READYOK = 0x104,
	HDL_DOWNING = 0x105,
	HDL_DISCONN = 0x106,
	HDL_FINISH = 0x107
};

/*
	$@@ 下载回调函数,主要用于监听下载过程
	$@ 第一个参数: 下载标识符号(上面枚举中的值)
	$@ 第二个参数: 需要下载的总字节数
	$@ 第三个参数: 已经下载的总字节数
	$@ 第四个参数: 距离上一次下载的时间戳(毫秒)
	$@ 返回值: 下次下载的字节数(0: 表示默认值, 小于0则下载中断, 大于0则位下次下载指定的字节)
*/
typedef int (*HTTPDOWNLOAD_CALLBACK)(int, unsigned int, unsigned int, unsigned int);

/*
	$@@ 通过指定的url下载资源
	$@ url: 下载资源地址
	$@ filepath: 存储在本地的路径(如果为NULL则存储在当前目录)
	$@ filename: 存储的文件名(如果为NULL则位url中分析的文件名)
	$@ http_func: 下载过程监听函数(如果为NULL则不监听下载过程)
*/
void pq_http_download(const char *url, const char *filepath, const char *filename, HTTPDOWNLOAD_CALLBACK http_func);
#endif /* #ifndef PENQ_HTTP_DOWNLOAD_H_ */
/* END */

实现:

/*
	$Id: httpdownload.c, v1.0.0, 2011.6.28, YellowBug $
	$@@: http下载 
*/
#include "httpdownload.h"

#define HERROR(exp, err)	do {														 /
								if (exp) {												 /
									printf("(%s,%d) %s/n", __FILE__, __LINE__, #exp);	 /
									if(S_http_callback) S_http_callback((err), 0, 0, 0); /
									exit(1);                                             /
								}                                                        /
							} while(0)							

#define HCALLBACK(a, b, c, d)		(S_http_callback ? S_http_callback((a), (b), (c), (d)) : 0)
/*
	$@@ 文件域的局部变量
*/
static HTTPDOWNLOAD_CALLBACK 	S_http_callback = NULL;
static const char * S_request_head = "GET %s HTTP/1.1/r/n" /
							  		 "Accept: */*/r/n" /
							  		 "Accept-Language: zh-cn/r/n" /
							  		 "User-Agent: Molliza/4.0(compatible;MSIE6.0;windows NT 5.0)/r/n" /
							  		 "Host: %s/r/n" /
							  		 "Connection: close/r/n/r/n";

#if defined(__GNUC__)
unsigned int get_tick() 
{
	struct timeval tv;
	gettimeofday(&tv, NULL);
	return (unsigned int)(tv.tv_sec*1000+tv.tv_usec/1000);
}
#elif defined(_WIN32)
#define get_tick()		GetTickCount()
#endif

/*
	$@@ 从指定长度(len0)的字符串的右端开始找到第一个位ch的字符
*/
static char * r_strchr(const char *p, int len, char ch)
{
	int last_pos = -1;
	int i = 0;
	while ( *(p+i) != '/0' ) {
		if ( *(p+i) == ch ) last_pos = i;
		if ( ++i >= len ) break;	
	}
	return last_pos >= 0 ? (char *)(p+last_pos) : NULL;
}

/*
 	$@@ 解析url，分析出web地址,端口号,下载的资源名称
*/
static void parse_url(const char *url, char *web, int *port, char *filepath, char *filename)
{
	int web_len = 0;
	int web_start = 0;
	int file_len = 0;
	int file_start = 0;
	int path_len = 0;
	int path_start = 0;
	char *pa = NULL;
	char *pb = NULL;
	if ( !strncmp(url, "http://", 7) ) web_start = 7;
	else if ( !strncmp(url, "https://", 8) ) web_start = 8;
	
	pa = strchr(url+web_start, '/');
	pb = strchr(url+web_start, ':');
	
	/* 获取web */	
	if ( pa ) {
		web_len = (int)(pa - (url+web_start));
	} else {
		if ( pb ) web_len = pb - (url+web_start);
		else web_len = strlen(url+web_start);		
	}
	HERROR(0 == web_len, HDL_URLERR);
	memcpy(web, url+web_start, web_len);
	web[web_len] = '/0';		
	/* 获取filename */
	if ( pb ) {
		pa = r_strchr(url+web_start, (int)(pb-(url+web_start)), '/');
		file_len = (int)(pb - pa - 1);
		file_start = (int)(pa + 1 - url);
		*port = atoi(pb+1);
	} else {
		pa = r_strchr(url+web_start, strlen(url+web_start), '/');
		HERROR(NULL == pa, HDL_URLERR);
		file_len = strlen(pa+1);
		file_start = (int)(pa + 1 - url);
		*port = DEF_HTTP_PORT;
	}
	HERROR(NULL == pa, HDL_URLERR);
	memcpy(filename, url+file_start, file_len);
	filename[file_len] = '/0';
	
	/* 获取filepath */
	path_start = web_start + web_len;
	path_len = file_start - path_start + file_len;
	memcpy(filepath, url+web_start+web_len, file_start - path_start + file_len);
	filepath[path_len] = '/0';
}

/*
	$@@ 封装request报头
*/
int package_request(char *request, const char *web, const char *filepath)
{
	int n = sprintf(request, S_request_head, filepath, web);
	request[n] = '/0';
	return n;
}
/*
	$@@ 发送请求报头
*/
int send_request(HSOCKET sock, const char *buf, int n)
{
	int already_bytes = 0;
	int per_bytes = 0;	
	
	while ( already_bytes < n ) {
		per_bytes = send(sock, buf+already_bytes, n-already_bytes, 0);
		if ( per_bytes < 0 ) {
			break;
		} else if ( 0 == per_bytes ) {
			HCALLBACK(HDL_DISCONN, 0, 0, 0);
			break;
		} else
			already_bytes += per_bytes;	
	}
	return already_bytes;
}

/*
	$@@ 获取响应报头(状态行和消息报头)
*/
int get_response_head(HSOCKET sock, char *response, int max)
{
	int total_bytes = 0;
	int per_bytes = 0;
	int over_flag = 0;
	char ch;
	
	do {		
		per_bytes = recv(sock, &ch, 1, 0);
		if ( per_bytes < 0 ) break;
		else if ( 0 == per_bytes ) {
			HCALLBACK(HDL_DISCONN, 0, 0, 0);
			break;
		} else {
			if ( '/r' == ch || '/n' == ch ) over_flag++;
			else over_flag = 0;
			
			response[total_bytes] = ch;			
			if ( total_bytes >= max ) break;
			else total_bytes += per_bytes;
		}
	} while ( over_flag < 4 );
	response[total_bytes] = '/0';
	return total_bytes;
}
void parse_response_head(char *response, int n, int *server_status, unsigned int *down_total)
{
	int i = 1;
	char *pstatus = strstr(response, "HTTP/1.1");
	char *plen = strstr(response, "Content-Length:");	
	printf("%s/n", response);
	
	if ( pstatus ) {
		pstatus += strlen("HTTP/1.1");
		i = 1;	
		while ( *(pstatus+i) == ' ' ) ++i;
		*server_status = atoi(pstatus+i);
	} else
		*server_status = 0;
	if ( plen ) {
		plen += strlen("Content-Length:");
		i = 1;
		while ( *(plen+i) == ' ' ) ++i;
		*down_total = (unsigned int)atoi(plen+i); 
	} else
		*down_total = 0;
	printf("status: %d/n", *server_status);
	printf("total: %u/n", *down_total);
}
/*
	$@@ 创建本地文件
*/
FILE * create_local_file(const char *local_path, const char *local_file, const char *remote_file)
{
	int len = strlen(local_path);
	static char filename[HTTP_MAX_PATH+1];
	if ( local_path[len-1] != PATH_SPLIT ) {
		if ( local_file ) len = sprintf(filename, "%s%c%s", local_path, PATH_SPLIT, local_file);	
		else len = sprintf(filename, "%s%c%s", local_path, PATH_SPLIT, remote_file);		
 	} else {
		if ( local_file ) len = sprintf(filename, "%s%s", local_path, local_file);	
		else len = sprintf(filename, "%s%s", local_path, remote_file);	
	}
	filename[len] = '/0'; 
	printf("ready to create local file: %s/n", filename);
	return fopen(filename, "wb+");
}
/*
	$@@ 开始下载
*/
void start_download(HSOCKET sock, unsigned int total_bytes, FILE *stream)
{
	unsigned int already_bytes;
	int per_bytes;
	int flush_bytes;
	unsigned int total_tim;
	unsigned int per_tim;
	static char buf[HTTP_DOWN_PERSIZE];
	
	do {
		per_tim = get_tick();
		per_bytes = recv(sock, buf, HTTP_DOWN_PERSIZE, 0);
		per_tim = get_tick() - per_tim;
		if ( per_bytes < 0 ) break;
		else if ( 0 == per_bytes ) {
			HCALLBACK(HDL_DISCONN, total_bytes, already_bytes, 0);
			break;		
		} else {
			fwrite(buf, 1, per_bytes, stream);
			already_bytes += (unsigned int)per_bytes;
			
			flush_bytes += per_bytes;
			if ( flush_bytes >= HTTP_FLUSH_BLOCK ) {
				fflush(stream);
				flush_bytes = 0;	
			}
			HCALLBACK(HDL_DOWNING, total_bytes, already_bytes, per_tim);
		}
	} while ( already_bytes < total_bytes );
	
	if ( flush_bytes > 0 )
		fflush(stream);

	HCALLBACK(HDL_FINISH, total_bytes, already_bytes, total_tim);
}

void pq_http_download(const char *url, const char *local_path, const char *local_file, HTTPDOWNLOAD_CALLBACK http_func)
{
	int port;
	char web[HTTP_MAX_PATH+1];
	char remote_path[HTTP_MAX_PATH+1];
	char remote_file[HTTP_MAX_PATH+1];
	char request[HTTP_MAX_REQUESTHEAD+1];
	char response_head[HTTP_MAX_RESPONSEHEAD+1];
	int request_len = 0;
	int response_len = 0;
	unsigned int down_total = 0;
	int server_status = 404;
	HSOCKET sock = -1;
	struct hostent *host = NULL;
	struct sockaddr_in server_addr;	
	FILE *stream = NULL;
	S_http_callback = http_func;
	parse_url(url, web, &port, remote_path, remote_file);
	request_len = package_request(request, web, remote_path);
	host = gethostbyname(web);
	HERROR(NULL==host, HDL_SERVERFAL);
	
	sock = socket(AF_INET, SOCK_STREAM, 0);
	HERROR(-1==sock, HDL_SOCKFAL);
	
	memset(&server_addr, 0, sizeof(server_addr));
	server_addr.sin_family = AF_INET;
	server_addr.sin_port = htons(port);
	server_addr.sin_addr = *((struct in_addr *)host->h_addr);
	HERROR(-1==connect(sock, (struct sockaddr *)&server_addr, sizeof(struct sockaddr)), HDL_TIMEOUT);
	HERROR(request_len != send_request(sock, request, request_len), HDL_SNDREQERR);
	response_len = get_response_head(sock, response_head, HTTP_MAX_RESPONSEHEAD);
	HERROR(response_len <= 0, HDL_NORESPONSE);
	parse_response_head(response_head, response_len, &server_status, &down_total);
	switch ( server_status ) {
		case 200:
			if ( down_total > 0 ) {
				stream = create_local_file(local_path, local_file, remote_file);
				HERROR(NULL == stream, HDL_CRLOCFILEFAL);
				HCALLBACK(HDL_READYOK, down_total, 0, 0);
				start_download(sock, down_total, stream);
				fclose(stream);		
			} else {
				HCALLBACK(HDL_FINISH, 0, 0, 0);
			}
		default:
			HCALLBACK(HDL_SERVERERR, 0, 0, 0);
	}
	closesocket(sock);
}

/* END */

测试代码:

#include 
#include "httpdownload.h"
int http_callback(int status, unsigned int total_bytes, unsigned int already_bytes, unsigned int tim)
{
	switch ( status ) {
		case HDL_READYOK:
			printf("ready to download, total.bytes=%u/n", total_bytes);
			break;
		case HDL_DOWNING:
			printf("downloading... (%u/%u) bytes/n", already_bytes, total_bytes);
			break;
		case HDL_FINISH:
			printf("download finish! download total.bytes=%u/n", already_bytes);
			break;
		default:
			printf("status: %#x/n", status);	
	}	
	return 0;
}

int main(int argc, char *argv[])
{
	pq_http_download(argv[1], argv[2], NULL, http_callback);
}

一个http下载程序的c实现
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

#define RECVBUFSIZE    2048
#define READBUFSIZE     2048

/********************************************
功能：搜索字符串右边起的第一个匹配字符
********************************************/
char * Rstrchr(char * s, char x)  {
int i = strlen(s);
if(!(*s))  return 0;
while(s[i-1]) if(strchr(s + (i - 1), x))  return (s + (i - 1));  else i--;
return 0;
}

/********************************************
功能：把字符串转换为全小写
********************************************/
void ToLowerCase(char *s)  {
while(*s)  {
*s=tolower(*s);
s++;
}//while
}

/**************************************************************
功能：从字符串src中分析出网站地址和端口，并得到用户要下载的文件
***************************************************************/
void GetHost(char * src, char * web, char * file, int * port)  {
char * pA;
char * pB;
memset(web, 0, sizeof(web));
memset(file, 0, sizeof(file));
*port = 0;
if(!(*src))  return;
pA = src;
if(!strncmp(pA, "http://", strlen("http://")))  pA = src+strlen("http://");
else if(!strncmp(pA, "https://", strlen("https://")))  pA = src+strlen("https://");
pB = strchr(pA, '/');
if(pB)  {
memcpy(web, pA, strlen(pA) - strlen(pB));
if(pB+1)  {
memcpy(file, pB + 1, strlen(pB) - 1);
file[strlen(pB) - 1] = 0;
}
}
else  memcpy(web, pA, strlen(pA));
if(pB)  web[strlen(pA) - strlen(pB)] = 0;
else  web[strlen(pA)] = 0;
pA = strchr(web, ':');
if(pA)  *port = atoi(pA + 1);
else *port = 80;
}


int find_start(char *buf, int size) 
{
int i;
char *p;
p = strstr(buf, "\r\n\r\n");
if(p) {
i = p - buf + 4;
if(i >= size)
i = -1;
}
else
i = -1;
return i;
}

//唯一的参数就是网址网址
int main(int argc, char **argv) {
int sockfd;
int fd;
struct hostent *host;
int portnumber;
char url[128];
char host_addr[256];
char host_file[1024];
char request[1024];
struct sockaddr_in server_sockaddr;
char recvbuf[RECVBUFSIZE];
int sendbytes, recvbytes, totalsend, totalsended;
int file_start_pos;

sprintf(url, "%s", argv[1]);
ToLowerCase(url);
GetHost(url, host_addr, host_file, &portnumber);
host = gethostbyname(host_addr);

sockfd = socket(PF_INET, SOCK_STREAM, 0);
server_sockaddr.sin_family = PF_INET;
server_sockaddr.sin_port = htons(portnumber);
server_sockaddr.sin_addr = *((struct in_addr *)host->h_addr);
bzero(&(server_sockaddr.sin_zero), 8);
connect(sockfd, (struct sockaddr *)&server_sockaddr, sizeof(struct sockaddr));

sprintf(request, "GET /%s HTTP/1.1\r\nAccept: */*\r\nAccept-Language: zh-cn\r\n\
User-Agent: Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0)\r\n\
Host: %s:%d\r\nConnection: Keep-Alive\r\n\r\n", host_file, host_addr, portnumber);

sendbytes = 0;
totalsended = 0;            //already send
totalsend = strlen(request);        //will send
while(totalsended < totalsend) {    
sendbytes = send(sockfd, request+totalsended, totalsend - totalsended, 0);
totalsended += sendbytes;
}//while

fd = open("download", O_CREAT | O_TRUNC | O_RDWR, 0777);
recvbytes = recv(sockfd, recvbuf, RECVBUFSIZE, 0);    //delete the head
file_start_pos = find_start(recvbuf, recvbytes);
write(fd, recvbuf+file_start_pos, recvbytes-file_start_pos);
while((recvbytes = recv(sockfd, recvbuf, RECVBUFSIZE, 0)) > 0) {
write(fd, recvbuf, recvbytes);
}//while

close(fd);
close(sockfd);
return 0;
}//main()