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\r\nAccept: */*\r\n\Accept-Language: zh-cn\r\n\Accept-Encoding: gzip, deflate\r\n\Host: %s:%d\r\n\Connection: Close\r\n\r\n";   /* 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(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:%s\a\n", 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] == '\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);   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-cnHost: 127.0.0.1:80Connection: Close//请求失败HTTP/1.1 400 Bad RequestServer: Apache-Coyote/1.1Date: Tue, 20 Oct 2015 05:23:24 GMTConnection: close//请求成功HTTP/1.1 200 OKServer: Apache-Coyote/1.1Content-Type: text/html;charset=UTF-8Content-Length: 1297Date: Tue, 20 Oct 2015 05:22:36 GMTConnection: 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