http协议

1. 举例

#include<netinet/in.h>
#include <errno.h>
#include <stdlib.h>
#include <string.h>

int main()
{
   int sockfd;
   char buffer[1024];
   struct sockaddr_in server_addr;
   int portnumber, nbytes;
   FILE *fp;
   char request[1024];
   int i;
   char *host = "127.0.0.1";
   char *http_req = "GET /%s HTTP/1.1
Accept: */*

Accept-Language: zh-cn

Accept-Encoding: gzip, deflate

Host: %s:%d

Connection: Close

";

   /* 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:%sa
", 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(80);
   inet_pton(PF_INET, host, &server_addr.sin_addr);

   /*连接网站*/
   if(connect(sockfd, (struct sockaddr *)(&server_addr), sizeof(struct sockaddr)) == -1) 
   {
      fprintf(stderr, "Connect Error:%sa
", strerror(errno));
      exit(1);
   }

   /*准备request，将要发送给主机*/
   nbytes = sprintf(request, http_req, "maintlogin.jsp", host, 80);
   printf("%s", request);

   /*发送http请求request*/
   if(write(sockfd, request, nbytes) < 0)
   {
      perror("write");
   }

   fp = fopen("index.html", "a");

   while((nbytes = read(sockfd, buffer, 1)))
   {
      if(i < 4)
      {
         if(buffer[0] == '
' || buffer[0] == '
')
         {
            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);
   close(sockfd);
   return 0;
}

2. http_req解释

//http请求
GET /maintlogin.jsp HTTP/1.1    //文件要指定/
Accept: */*     //开头不要有空格
Accept-Language: zh-cn
Host: 127.0.0.1:80
Connection: Close

//请求失败
HTTP/1.1 400 Bad Request
Server: Apache-Coyote/1.1
Date: Tue, 20 Oct 2015 05:23:24 GMT
Connection: close

//请求成功
HTTP/1.1 200 OK
Server: Apache-Coyote/1.1
Content-Type: text/html;charset=UTF-8
Content-Length: 1297
Date: Tue, 20 Oct 2015 05:22:36 GMT
Connection: close

Server 响应头包含处理请求的原始服务器的软件信息
Connection:keep-alive TCP连接仍然保持打开状态
Pragma 页面缓存（1.0）
cache-control 页面缓存（1.1）
如果指定压缩，Accept-Encoding: gzip, deflate，主机头会返回压缩提示，Content-Encoding: gzip。相应的Content-Length也会减小

错误码：见百科

3. 在tcp/ip协议中的位置
http协议通常承载于tcp协议之上，有时也承载于TLS或SSL协议层之上，就成了我们常说的https。http端口是80，https端口是443

4. http消息格式