C编程实现http协议

大家都很熟悉HTTP协议的应用，因为每天都在网络上浏览着不少东西，也都知道是HTTP协议是相当简单的。每次用thunder之类的下载软件下载网页，当用到那个“用thunder下载全部链接”时总觉得很神奇。

后来想想，其实要实现这些下载功能也并不难，只要按照HTTP协议发送request，然后对接收到的数据进行分析，如果页面上还有href之类的链接指向标志就可以进行深一层的下载了。HTTP协议目前用的最多的是1.1版本，要全面透彻地搞懂它就参考RFC2616文档吧。我是怕rfc文档了的,要看自己去看吧^_^

源代码如下：

/******* http客户端程序 httpclient.c ************/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <errno.h>
#include <unistd.h>
#include <netinet/in.h>
#include <limits.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <ctype.h>

//////////////////////////////httpclient.c 开始///////////////////////////////////////////


/********************************************
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) {*s=tolower(*s);s++;}
}

/**************************************************************
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 main(int argc, char *argv[])
{
	int sockfd;
	char buffer[1024];
	struct sockaddr_in server_addr;
	struct hostent *host;
	int portnumber,nbytes;
	char host_addr[256];
	char host_file[1024];
	char local_file[256];
	FILE * fp;
	char request[1024];
	int send, totalsend;
	int i;
	char * pt;

	if(argc!=2)
	{
		fprintf(stderr,"Usage:%s web-address\a\n",argv[0]);
		exit(1);
	}
	printf("parameter.1 is: %s\n", argv[1]);
	ToLowerCase(argv[1]);/*将参数转换为全小写*/
	printf("lowercase parameter.1 is: %s\n", argv[1]);

	GetHost(argv[1], host_addr, host_file, &portnumber);/*分析网址、端口、文件名等*/
	printf("webhost:%s\n", host_addr);
	printf("hostfile:%s\n", host_file);
	printf("portnumber:%d\n\n", portnumber);

	if((host=gethostbyname(host_addr))==NULL)/*取得主机IP地址*/
	{
		fprintf(stderr,"Gethostname error, %s\n", strerror(errno));
		exit(1);
	}

	/* 客户程序开始建立 sockfd描述符 */
	if((sockfd=socket(AF_INET,SOCK_STREAM,0))==-1)/*建立SOCKET连接*/
	{
		fprintf(stderr,"Socket Error:%s\a\n",strerror(errno));
		exit(1);
	}

	/* 客户程序填充服务端的资料 */
	bzero(&server_addr,sizeof(server_addr));
	server_addr.sin_family=AF_INET;
	server_addr.sin_port=htons(portnumber);
	server_addr.sin_addr=*((struct in_addr *)host->h_addr);

	/* 客户程序发起连接请求 */
	if(connect(sockfd,(struct sockaddr *)(&server_addr),sizeof(struct sockaddr))==-1)/*连接网站*/
	{
		fprintf(stderr,"Connect Error:%s\a\n",strerror(errno));
		exit(1);
	}

	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: Close\r\n\r\n", host_file, host_addr, portnumber);
	printf("%s", request);/*准备request，将要发送给主机*/

	/*取得真实的文件名*/
	if(host_file && *host_file) pt = Rstrchr(host_file, '/');
	else pt = 0;

	memset(local_file, 0, sizeof(local_file));
	if(pt && *pt) {
		if((pt + 1) && *(pt+1)) strcpy(local_file, pt + 1);
		else memcpy(local_file, host_file, strlen(host_file) - 1);
	}
	else if(host_file && *host_file) strcpy(local_file, host_file);
	else strcpy(local_file, "index.html");
	printf("local filename to write:%s\n\n", local_file);

	/*发送http请求request*/
	send = 0;totalsend = 0;
	nbytes=strlen(request);
	while(totalsend < nbytes) {
		send = write(sockfd, request + totalsend, nbytes - totalsend);
		if(send==-1) {printf("send error!%s\n", strerror(errno));exit(0);}
		totalsend+=send;
		printf("%d bytes send OK!\n", totalsend);
	}

	fp = fopen(local_file, "a");
	if(!fp) {
		printf("create file error! %s\n", strerror(errno));
		return 0;
	}
	printf("\nThe following is the response header:\n");
	i=0;
	/* 连接成功了，接收http响应，response */
	while((nbytes=read(sockfd,buffer,1))==1)
	{
		if(i < 4) {
			if(buffer[0] == '\r' || buffer[0] == '\n') i++;
			else i = 0;
			printf("%c", buffer[0]);/*把http头信息打印在屏幕上*/
		}
		else {
			fwrite(buffer, 1, 1, fp);/*将http主体信息写入文件*/
			i++;
			if(i%1024 == 0) fflush(fp);/*每1K时存盘一次*/
		}
	}
	fclose(fp);
	/* 结束通讯 */
	close(sockfd);
	exit(0);
}

 

zj@zj:~/C_pram/practice/http_client$ ls

httpclient  httpclient.c

zj@zj:~/C_pram/practice/http_client$ ./httpclient http://www.baidu.com/

parameter.1 is: http://www.baidu.com/

lowercase parameter.1 is: http://www.baidu.com/

webhost:www.baidu.com

hostfile:

portnumber:80

GET / HTTP/1.1

Accept: */*

Accept-Language: zh-cn

User-Agent: Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0)

Host: www.baidu.com:80

Connection: Close

local filename to write:index.html

163 bytes send OK!

The following is the response header:

HTTP/1.1 200 OK

Date: Wed, 29 Oct 2008 10:41:40 GMT

Server: BWS/1.0

Content-Length: 4216

Content-Type: text/html

Cache-Control: private

Expires: Wed, 29 Oct 2008 10:41:40 GMT

Set-Cookie: BAIDUID=A93059C8DDF7F1BC47C10CAF9779030E:FG=1; expires=Wed, 29-Oct-38 10:41:40 GMT; path=/; domain=.baidu.com

P3P: CP=" OTI DSP COR IVA OUR IND COM "

zj@zj:~/C_pram/practice/http_client$ ls

httpclient  httpclient.c  index.html

不指定文件名字的话,默认就是下载网站默认的首页了^_^.