Linux_C socket 服务器(cat ,execl功能)

客户端和web服务器交互的基本结构如下：

  （1）客户端发送请求

            GET filename HTTP/version

  　　　可选参数

　　　  空行

　（2）服务器发送应答

             HTTP/version status-code status-message

             附加信息

             空行

              内容

webserv.c

/* webserv.c    a minimal web server (version 0.2)
 * usage : webserv portnumber
 */
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <string.h>
#include <sys/stat.h>
#include <netinet/in.h>
#include <netdb.h>

/**************************************************************
 * 下面I/O的函数一些总结：
 *   1.可以在参数列表中指定并可以格式化输出函数： fprintf();
 *          eg:fprintf(stderr, "usage: webserv portnum");
 *             fprintf((FILE*)fp, "HTTP/1.0 200 OK
");
 *   2.从指定FILE指针中读取一字符串， char* fgets(char* buf, int size, FILE* stream)
 *          buf为保存字符的内存空间，直到出现换行、文件尾、已读了size-1个字符为止，最后加NULL作为字符串结束。返回NULL表示出错。
 *          eg:fgets(request, BUFSIZ, fpin);
 *   3.读一个字符，写一个字符。 eg: while((c=getc(fpfile))!=EOF) putc(c, fpsock);
 *************************************************************/


int make_server_socket(int);

int main(int argc, char* argv[]) {
  int sock, fd;
  FILE * fpin;
  char request[BUFSIZ];
  
  if(argc==1) {
    fprintf(stderr , "usage :webserv portnum.
");
    exit(1);
  }
  sock=make_server_socket(atoi(argv[1]));
  if(sock==-1)
    exit(2);
  while(1) {
    /* take a call and buffer it */
    fd=accept(sock, NULL, NULL);
    fpin=fdopen(fd, "r");
    /* read request */
    fgets(request, BUFSIZ, fpin);
    printf("get a call ; request = %s", request);
    read_til_crnl(fpin);
    /* do what client asks */
    process_rq(request, fd);
    
    fclose(fpin);
  }
  return 0;
}

int make_server_socket(int portnum) {
  int sock;
  struct sockaddr_in saddr;
  struct hostent *hp;
  char hostname[BUFSIZ];
  
  sock=socket(PF_INET, SOCK_STREAM, 0);
  if(sock==-1)
    return -1;
  
  gethostname(hostname, BUFSIZ);
  hp=gethostbyname(hostname);
  bzero(&saddr, sizeof(saddr));
  bcopy((void*)hp->h_addr, (void*)&saddr.sin_addr, hp->h_length);
  saddr.sin_port=htons(portnum);
  saddr.sin_family=AF_INET;
  
  if(bind(sock, (struct sockaddr*)&saddr, sizeof(saddr))!=0)
    return -1;
  if(listen(sock ,1)!=0)
    return -1;
  return sock;
}

/**********************************************************************
 * read_til_crnl(FILE* )
 * skip over all request info until a CRNL is seen
 *********************************************************************/
read_til_crnl(FILE* fp) {
  char buf[BUFSIZ];
  while(fgets(buf, BUFSIZ, fp)!=NULL && strcmp(buf, "
")!=0)
    ;
}

/*********************************************************************
 * process_rq(char* rq, int fd)
 * do what the request asks for and write reply to fd
 * handles request in a new process
 * rq is HTTP command: GET /foo/bar.html HTTP/1.0
 ********************************************************************/
process_rq(char *rq, int fd) {
  char cmd[BUFSIZ], arg[BUFSIZ];
  /*creat a new process and return if not the child*/
  if(fork()!=0) 
    return ;
  strcpy(arg, "./");   /* precede args with .*/
  if(sscanf(rq, "%s %s", cmd, arg+2)!=2)
    return ;
  if(strcmp(cmd, "GET")!=0)
    cannot_do(fd);
  else if(not_exist(arg))
    do_404(arg, fd);
  else if(isadir(arg))
    do_ls(arg, fd);
  else if(ends_in_cgi(arg))
    do_exec(arg, fd);
  else 
    do_cat(arg, fd);
}



/*********************************************************
 * the reply header thing: all functions need one
 * if content_type is NULL then don't send content type
 ********************************************************/
header(FILE* fp, char * content_type) {
  fprintf(fp, "HTTP/1.0 200 OK
");
  if(content_type)
    fprintf(fp, "Content-type: %s
", content_type);
}

/********************************************************* 
 * simple functions first:
 *   cannot_do(fd): unimplemented HTTP command
 * and  do_404*(item ,fd)  no such object
 ********************************************************/

cannot_do(fd) {
  FILE *fp=fdopen(fd, "w");
  
  fprintf(fp, "HTTP/1.0 501 Not Implemented
");
  fprintf(fp, "Content-type: text/plain
");
  fprintf(fp, "
");
  
  fprintf(fp, "That command is not yet implemented
");
  fclose(fp);
}

do_404(char* item, int fd) {
  FILE* fp=fdopen(fd, "w");
  
  fprintf(fp, "HTTP/1.0 404 Not Found
");
  fprintf(fp, "Content-type:text/plain
");
  fprintf(fp, "
" );
  
  fprintf(fp, "The item you requested: %s
is not found
", item);
  fclose(fp);
}

/******************************************************************
 * the directory listing sectoin
 * isadir() uses stat, not_exist() uses stat
 * do_ls runs ls. It should not
 *****************************************************************/

isadir(char *f) {
  struct stat info;
  return (stat(f, &info)!=-1 && S_ISDIR(info.st_mode));
}

not_exist(char *f) {
  struct stat info;
  return (stat(f, &info)==-1);
}

do_ls(char *dir, int fd) {
  FILE* fp;
  fp=fdopen(fd, "w");
  header(fp, "text/plain");
  fprintf(fp, "
");
  fflush(fp);
  
  dup2(fd, 1);   /*注意这里的文件标识符为fd,即是socket单位，而不是fdopen()的返回值，切记切记*/
  dup2(fd, 2);
  close(fd);
  execlp("ls", "ls", "-l",dir, NULL);
  perror(dir);
  exit(1);
}

/*******************************************************
 * the cgi stuff function to check extension and
 * one to run the program.
 ******************************************************/
char * file_type(char* f) {
  /* returns 'extension' of file */
  char *cp;
  if((cp=strrchr(f, '.'))!=NULL)
    return cp+1;
  return "";
}

ends_in_cgi(char* f) {
  return (strcmp(file_type(f) , "cgi")==0);
}

do_exec(char *prog, int fd) {
  FILE *fp;
  
  fp=fdopen(fd, "w");
  header(fp, NULL);
  fflush(fp);
  dup2(fd, 1);
  dup2(fd, 2);
  close(fd);
  execl(prog, prog, NULL);
  perror(prog);
}

/*******************************************************************
 * do_cat(filename, fd)
 * sends back contents after a header
 ******************************************************************/
do_cat(char* f, int fd) {
  char *extension = file_type(f);
  char *content = "text/plain";
  FILE *fpsock, *fpfile;
  int c;
  
  if(strcmp(extension, "html")==0)
    content = "text/html";
  else if(strcmp(extension, "gif")==0)
    content = "image/gif";
  else if(strcmp(extension, "jpg")==0)
    content = "image/jpeg";
  else if(strcmp(extension, "jpeg")==0)
    content = "image/jpeg";

  fpsock = fdopen(fd, "w");
  fpfile = fopen(f, "r");
  if(fpsock != NULL && fpfile!=NULL) {
    header(fpsock, content);
    fprintf(fpsock, "
");
    while((c=getc(fpfile))!=EOF)
      putc(c, fpsock);
    fclose(fpfile);
    fclose(fpsock);
  }
  exit(0);
}

用法说明: gcc webserv.c -o webserv

 ./webserv 12345(端口号)

然后在浏览器中输入主机名加端口号可访问

 注意：在do_ls（）中，dup2(sock_in, 1),dup2(sock_in,2),一定要注意这一点，重定向的应该是sockid而不是fin=fdopen(sockid,"w").