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Saturday, 26 February 2022

Tiny.c server

 /*
 * tiny.c - a minimal HTTP server that serves static and
 *          dynamic content with the GET method. Neither
 *          robust, secure, nor modular. Use for instructional
 *          purposes only.
 *          Dave O'Hallaron, Carnegie Mellon
 *
 *          usage: tiny <port>
 */

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <netdb.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <sys/wait.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#define BUFSIZE 1024
#define MAXERRS 16

extern char **environ; /* the environment */

/*
 * error - wrapper for perror used for bad syscalls
 */
void error(char *msg) {
  perror(msg);
  exit(1);
}

/*
 * cerror - returns an error message to the client
 */
void cerror(FILE *stream, char *cause, char *errno,
        char *shortmsg, char *longmsg) {
  fprintf(stream, "HTTP/1.1 %s %s\n", errno, shortmsg);
  fprintf(stream, "Content-type: text/html\n");
  fprintf(stream, "\n");
  fprintf(stream, "<html><title>Tiny Error</title>");
  fprintf(stream, "<body bgcolor=""ffffff"">\n");
  fprintf(stream, "%s: %s\n", errno, shortmsg);
  fprintf(stream, "<p>%s: %s\n", longmsg, cause);
  fprintf(stream, "<hr><em>The Tiny Web server</em>\n");
}

int main(int argc, char **argv) {

  /* variables for connection management */
  int parentfd;          /* parent socket */
unsigned  int childfd;           /* child socket */
  int portno;            /* port to listen on */
  int clientlen;         /* byte size of client's address */
  struct hostent *hostp; /* client host info */
  char *hostaddrp;       /* dotted decimal host addr string */
  int optval;            /* flag value for setsockopt */
  struct sockaddr_in serveraddr; /* server's addr */
  struct sockaddr_in clientaddr; /* client addr */

  /* variables for connection I/O */
  FILE *stream;          /* stream version of childfd */
  char buf[BUFSIZE];     /* message buffer */
  char method[BUFSIZE];  /* request method */
  char uri[BUFSIZE];     /* request uri */
  char version[BUFSIZE]; /* request method */
  char filename[BUFSIZE];/* path derived from uri */
  char filetype[BUFSIZE];/* path derived from uri */
  char cgiargs[BUFSIZE]; /* cgi argument list */
  char *p;               /* temporary pointer */
  int is_static;         /* static request? */
  struct stat sbuf;      /* file status */
  int fd;                /* static content filedes */
  int pid;               /* process id from fork */
  int wait_status;       /* status from wait */

  /* check command line args */
  if (argc != 2) {
    fprintf(stderr, "usage: %s <port>\n", argv[0]);
    exit(1);
  }
  portno = atoi(argv[1]);

  /* open socket descriptor */
  parentfd = socket(AF_INET, SOCK_STREAM, 0);
  if (parentfd < 0)
    error("ERROR opening socket");

  /* allows us to restart server immediately */
  optval = 1;
  setsockopt(parentfd, SOL_SOCKET, SO_REUSEADDR,
         (const void *)&optval , sizeof(int));

  /* bind port to socket */
  bzero((char *) &serveraddr, sizeof(serveraddr));
  serveraddr.sin_family = AF_INET;
serveraddr.sin_addr.s_addr = inet_addr("127.0.0.2");
 
    /*  serveraddr.sin_addr.s_addr = htonl(INADDR_ANY);*/
  serveraddr.sin_port = htons((unsigned short)portno);
  if (bind(parentfd, (struct sockaddr *) &serveraddr,
       sizeof(serveraddr)) < 0)
    error("ERROR on binding");

  /* get us ready to accept connection requests */
  if (listen(parentfd, 5) < 0) /* allow 5 requests to queue up */
    error("ERROR on listen");

  /*
   * main loop: wait for a connection request, parse HTTP,
   * serve requested content, close connection.
   */
  clientlen = sizeof(clientaddr);
  while (1) {

    /* wait for a connection request */
 childfd=   accept(parentfd, (struct sockaddr *) &clientaddr,(unsigned int*) &clientlen);
    if (childfd < 0)
      error("ERROR on accept");
    
    /* determine who sent the message */
    hostp = gethostbyaddr((const char *)&clientaddr.sin_addr.s_addr,
              sizeof(clientaddr.sin_addr.s_addr), AF_INET);
    if (hostp == NULL)
      error("ERROR on gethostbyaddr");
    hostaddrp = inet_ntoa(clientaddr.sin_addr);
    if (hostaddrp == NULL)
      error("ERROR on inet_ntoa\n");
    
    /* open the child socket descriptor as a stream */
    if ((stream = fdopen(childfd, "r+")) == NULL)
      error("ERROR on fdopen");

    /* get the HTTP request line */
    fgets(buf, BUFSIZE, stream);
    printf("%s", buf);
    sscanf(buf, "%s %s %s\n", method, uri, version);

    /* tiny only supports the GET method */
    if (strcasecmp(method, "GET")) {
      cerror(stream, method, "501", "Not Implemented",
         "Tiny does not implement this method");
      fclose(stream);
      close(childfd);
      continue;
    }

    /* read (and ignore) the HTTP headers */
    fgets(buf, BUFSIZE, stream);
    printf("%s", buf);
    while(strcmp(buf, "\r\n")) {
      fgets(buf, BUFSIZE, stream);
      printf("%s", buf);
    }

    /* parse the uri [crufty] */
    if (!strstr(uri, "cgi-bin")) { /* static content */
      is_static = 1;
      strcpy(cgiargs, "");
      strcpy(filename, ".");
      strcat(filename, uri);
      if (uri[strlen(uri)-1] == '/')
    strcat(filename, "index.html");
    }
/*    else {
    is_static = 0;
      p = index(uri, '?');
      if (p) {
    strcpy(cgiargs, p+1);
    *p = '\0';
      }*/
      else {
    strcpy(cgiargs, "");
      }
      strcpy(filename, ".");
      strcat(filename, uri);
    }

    /* make sure the file exists */
    if (stat(filename, &sbuf) < 0) {
      cerror(stream, filename, "404", "Not found",    "Tiny couldn't find this file");
      fclose(stream);
      close(childfd);
 //     continue;
    }

    /* serve static content */
    if (is_static) {
      if (strstr(filename, ".html"))
    strcpy(filetype, "text/html");
      else if (strstr(filename, ".gif"))
    strcpy(filetype, "image/gif");
      else if (strstr(filename, ".jpg"))
    strcpy(filetype, "image/jpg");
      else
    strcpy(filetype, "text/plain");

      /* print response header */
      fprintf(stream, "HTTP/1.1 200 OK\n");
      fprintf(stream, "Server: Tiny Web Server\n");
      fprintf(stream, "Content-length: %d\n", (int)sbuf.st_size);
      fprintf(stream, "Content-type: %s\n", filetype);
      fprintf(stream, "\r\n");
      fflush(stream);

      /* Use mmap to return arbitrary-sized response body */
      fd = open(filename, O_RDONLY);
void *  p = mmap(0, sbuf.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
      fwrite(p, 1, sbuf.st_size, stream);
      munmap(p, sbuf.st_size);
    }

    /* serve dynamic content */
    else {
      /* make sure file is a regular executable file */
      if (!(S_IFREG & sbuf.st_mode) || !(S_IXUSR & sbuf.st_mode)) {
    cerror(stream, filename, "403", "Forbidden",
           "You are not allow to access this item");
    fclose(stream);
    close(childfd);
//    continue;
      }

      /* a real server would set other CGI environ vars as well*/
      setenv("QUERY_STRING", cgiargs, 1);

      /* print first part of response header */
      sprintf(buf, "HTTP/1.1 200 OK\n");
      write(childfd, buf, strlen(buf));
      sprintf(buf, "Server: Tiny Web Server\n");
      write(childfd, buf, strlen(buf));

      /* create and run the child CGI process so that all child
         output to stdout and stderr goes back to the client via the
         childfd socket descriptor */
      pid = fork();
      if (pid < 0) {
    perror("ERROR in fork");
    exit(1);
      }
      else if (pid > 0) { /* parent process */
    wait(&wait_status);
      }
      else { /* child  process*/
    close(0); /* close stdin */
    dup2(childfd, 1); /* map socket to stdout */
    dup2(childfd, 2); /* map socket to stderr */
    if (execve(filename, NULL, environ) < 0) {
      perror("ERROR in execve");
    }
      }
    }

    /* clean up */
    fclose(stream);
    close(childfd);

  }
}

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