Serving CGI Scripts With Nginx On Debian Squeeze/Ubuntu 11.04 - Page 2

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Submitted by falko (Contact Author) (Forums) on Thu, 2011-09-29 17:10. ::

3 Using Simple CGI

Another approach is to use a CGI wrapper script, as described here: http://wiki.nginx.org/NginxSimpleCGI

The advantage over Thttpd is that each vhost can have its own cgi-bin directory. The CGI wrapper should work well for simple CGI scripts, but you might get problems with more complex scripts.

Let's install the requirements for the CGI wrapper script:

apt-get install libfcgi-perl libfcgi-procmanager-perl

Now we create the /usr/local/bin/cgiwrap-fcgi.pl wrapper script (the script is taken from http://wiki.nginx.org/NginxSimpleCGI):

vi /usr/local/bin/cgiwrap-fcgi.pl

#!/usr/bin/perl
use FCGI;
use Socket;
use FCGI::ProcManager;
sub shutdown { FCGI::CloseSocket($socket); exit; }
sub restart  { FCGI::CloseSocket($socket); &main; }
use sigtrap 'handler', \&shutdown, 'normal-signals';
use sigtrap 'handler', \&restart,  'HUP';
require 'syscall.ph';
use POSIX qw(setsid);

END()   { }
BEGIN() { }
{
  no warnings;
  *CORE::GLOBAL::exit = sub { die "fakeexit\nrc=" . shift() . "\n"; };
};

eval q{exit};
if ($@) {
  exit unless $@ =~ /^fakeexit/;
}
&main;

sub daemonize() {
  chdir '/' or die "Can't chdir to /: $!";
  defined( my $pid = fork ) or die "Can't fork: $!";
  exit if $pid;
  setsid() or die "Can't start a new session: $!";
  umask 0;
}

sub main {
  $proc_manager = FCGI::ProcManager->new( {n_processes => 5} );
  $socket = FCGI::OpenSocket( "/var/run/nginx/cgiwrap-dispatch.sock", 10 )
  ; #use UNIX sockets - user running this script must have w access to the 'nginx' folder!!
  $request =
  FCGI::Request( \*STDIN, \*STDOUT, \*STDERR, \%req_params, $socket,
  &FCGI::FAIL_ACCEPT_ON_INTR );
  $proc_manager->pm_manage();
  if ($request) { request_loop() }
  FCGI::CloseSocket($socket);
}

sub request_loop {
  while ( $request->Accept() >= 0 ) {
    $proc_manager->pm_pre_dispatch();

    #processing any STDIN input from WebServer (for CGI-POST actions)
    $stdin_passthrough = '';
    { no warnings; $req_len = 0 + $req_params{'CONTENT_LENGTH'}; };
    if ( ( $req_params{'REQUEST_METHOD'} eq 'POST' ) && ( $req_len != 0 ) ) {
      my $bytes_read = 0;
      while ( $bytes_read < $req_len ) {
        my $data = '';
        my $bytes = read( STDIN, $data, ( $req_len - $bytes_read ) );
        last if ( $bytes == 0 || !defined($bytes) );
        $stdin_passthrough .= $data;
        $bytes_read += $bytes;
      }
    }

    #running the cgi app
    if (
      ( -x $req_params{SCRIPT_FILENAME} ) &&    #can I execute this?
      ( -s $req_params{SCRIPT_FILENAME} ) &&    #Is this file empty?
      ( -r $req_params{SCRIPT_FILENAME} )       #can I read this file?
    ) {
      pipe( CHILD_RD,   PARENT_WR );
      pipe( PARENT_ERR, CHILD_ERR );
      my $pid = open( CHILD_O, "-|" );
      unless ( defined($pid) ) {
        print("Content-type: text/plain\r\n\r\n");
        print "Error: CGI app returned no output - Executing $req_params{SCRIPT_FILENAME} failed !\n";
        next;
      }
      $oldfh = select(PARENT_ERR);
      $|     = 1;
      select(CHILD_O);
      $| = 1;
      select($oldfh);
      if ( $pid > 0 ) {
        close(CHILD_RD);
        close(CHILD_ERR);
        print PARENT_WR $stdin_passthrough;
        close(PARENT_WR);
        $rin = $rout = $ein = $eout = '';
        vec( $rin, fileno(CHILD_O),    1 ) = 1;
        vec( $rin, fileno(PARENT_ERR), 1 ) = 1;
        $ein    = $rin;
        $nfound = 0;

        while ( $nfound = select( $rout = $rin, undef, $ein = $eout, 10 ) ) {
          die "$!" unless $nfound != -1;
          $r1 = vec( $rout, fileno(PARENT_ERR), 1 ) == 1;
          $r2 = vec( $rout, fileno(CHILD_O),    1 ) == 1;
          $e1 = vec( $eout, fileno(PARENT_ERR), 1 ) == 1;
          $e2 = vec( $eout, fileno(CHILD_O),    1 ) == 1;

          if ($r1) {
            while ( $bytes = read( PARENT_ERR, $errbytes, 4096 ) ) {
              print STDERR $errbytes;
            }
            if ($!) {
              $err = $!;
              die $!;
              vec( $rin, fileno(PARENT_ERR), 1 ) = 0
              unless ( $err == EINTR or $err == EAGAIN );
            }
          }
          if ($r2) {
            while ( $bytes = read( CHILD_O, $s, 4096 ) ) {
              print $s;
            }
            if ( !defined($bytes) ) {
              $err = $!;
              die $!;
              vec( $rin, fileno(CHILD_O), 1 ) = 0
              unless ( $err == EINTR or $err == EAGAIN );
            }
          }
          last if ( $e1 || $e2 );
        }
        close CHILD_RD;
        close PARENT_ERR;
        waitpid( $pid, 0 );
      } else {
        foreach $key ( keys %req_params ) {
          $ENV{$key} = $req_params{$key};
        }

        # cd to the script's local directory
        if ( $req_params{SCRIPT_FILENAME} =~ /^(.*)\/[^\/] +$/ ) {
          chdir $1;
        }
        close(PARENT_WR);
        #close(PARENT_ERR);
        close(STDIN);
        close(STDERR);

        #fcntl(CHILD_RD, F_DUPFD, 0);
        syscall( &SYS_dup2, fileno(CHILD_RD),  0 );
        syscall( &SYS_dup2, fileno(CHILD_ERR), 2 );

        #open(STDIN, "<&CHILD_RD");
        exec( $req_params{SCRIPT_FILENAME} );
        die("exec failed");
      }
    } else {
      print("Content-type: text/plain\r\n\r\n");
      print "Error: No such CGI app - $req_params{SCRIPT_FILENAME} may not exist or is not executable by this process.\n";
    }
  }
}

Make the script executable...

chmod 755 /usr/local/bin/cgiwrap-fcgi.pl

... and create the /var/run/nginx/ directory where the script will create its socket (that nginx will connect to):

mkdir /var/run/nginx/

By default, nginx runs as the www-data user; nginx must have read and write access to the /var/run/nginx/ directory, therefore we do a chown:

chown www-data:www-data /var/run/nginx/

Because the socket /var/run/nginx/cgiwrap-dispatch.sock (which will be created by the wrapper) must also be owned by www-data, we start the wrapper as the www-data user:

su www-data

/usr/local/bin/cgiwrap-fcgi.pl &> /dev/null &

The wrapper should now run as a daemon in the background, so we can become root again:

exit

Now open your vhost configuration file...

vi /etc/nginx/sites-enabled/www.example.com.vhost

... and add a location /cgi-bin {} section to the server {} container:

server {
[...]
   location /cgi-bin {
      root /var/www/www.example.com;
      gzip off; #gzip makes scripts feel slower since they have to complete before getting gzipped
      fastcgi_pass  unix:/var/run/nginx/cgiwrap-dispatch.sock;
      include /etc/nginx/fastcgi_params;
      fastcgi_index index.cgi;
      fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
   }
[...]
}

Reload nginx:

/etc/init.d/nginx reload

Next we create our cgi-bin directory - /var/www/www.example.com/cgi-bin because we defined root /var/www/www.example.com; in the location /cgi-bin {} container:

mkdir /var/www/www.example.com/cgi-bin

Now we place our CGI scripts in it and make them executable. For testing purposes I will create a small Hello World Perl script (instead of hello_world.cgi you can also use the extension .pl -> hello_world.pl):

vi /var/www/www.example.com/cgi-bin/hello_world.cgi

#!/usr/bin/perl -w

     # Tell perl to send a html header.
     # So your browser gets the output
     # rather then <stdout>(command line
     # on the server.)
print "Content-type: text/html\n\n";

     # print your basic html tags.
     # and the content of them.
print "<html><head><title>Hello World!! </title></head>\n";
print "<body><h1>Hello world</h1></body></html>\n";

chmod 755 /var/www/www.example.com/cgi-bin/hello_world.cgi

Open a browser and test the script:

http://www.example.com/cgi-bin/hello_world.cgi

If all goes well, you should get the following output:


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