C編程實現http協議

大家都很熟悉HTTP協議的應用，因為每天都在網路上瀏覽著不少東西，也都知道是HTTP協議是相當簡單的。每次用thunder之類的下載軟體下載網頁，當用到那個“用thunder下載全部連結”時總覺得很神奇。

後來想想，其實要實現這些下載功能也並不難，只要按照HTTP協議發送request，然後對接收到的資料進行分析，如果頁面上還有href之類的連結指向標誌就可以進行深一層的下載了。HTTP協議目前用的最多的是1.1版本，要全面透徹地搞懂它就參考RFC2616文檔吧。我是怕rfc文檔了的,要看自己去看吧^_^

原始碼如下：

/******* http用戶端程式 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 開始///////////////////////////////////////////

 

 

/********************************************

功能：搜尋字串右邊起的第一個匹配字元

********************************************/

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：把字串轉換為全小寫

********************************************/

void ToLowerCase(char * s) {

while(s && *s) {*s=tolower(*s);s++;}

}

 

/**************************************************************

功能：從字串src中分析出網站地址和連接埠，並得到使用者要下載的檔案

***************************************************************/

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]);/*將參數轉換為全小寫*/

printf("lowercase parameter.1 is: %s/n", argv[1]);

 

GetHost(argv[1], host_addr, host_file, &portnumber);/*分析網址、連接埠、檔案名稱等*/

printf("webhost:%s/n", host_addr);

printf("hostfile:%s/n", host_file);

printf("portnumber:%d/n/n", portnumber);

 

if((host=gethostbyname(host_addr))==NULL)/*取得主機IP地址*/

{

fprintf(stderr,"Gethostname error, %s/n", strerror(errno));

exit(1);

}

 

/* 客戶程式開始建立 sockfd描述符 */

if((sockfd=socket(AF_INET,SOCK_STREAM,0))==-1)/*建立SOCKET串連*/

{

fprintf(stderr,"Socket Error:%s/a/n",strerror(errno));

exit(1);

}

 

/* 客戶程式填充服務端的資料 */

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);

 

/* 客戶程式發起串連請求 */

if(connect(sockfd,(struct sockaddr *)(&server_addr),sizeof(struct sockaddr))==-1)/*串連網站*/

{

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);/*準備request，將要發送給主機*/

 

/*取得真實的檔案名稱*/

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);

 

/*發送http請求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;

/* 串連成功了，接收http響應，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頭資訊列印在螢幕上*/

}

else {

fwrite(buffer, 1, 1, fp);/*將http主體資訊寫入檔案*/

i++;

if(i%1024 == 0) fflush(fp);/*每1K時存檔一次*/

}

}

fclose(fp);

/* 結束通訊 */

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

不指定檔案名稱字的話,預設就是下載網站預設的首頁了^_^.