My perl application currently has basic logging. I am using Mod_perl and CGI
When an error occurs in the script the user gets an internal server error page. I know that CPAN CGI has an error reporting feature, but this feature seems to be for a individual script. What I wanted was to capture a stack trace globally and then report it to the user on a webpage. so that when this happens the user gets a nice 'something went wrong' page rather than a clueless Internal Server Error page.
I handled this nicely by creating bootstrap.pl script. I redirected with mod_rewrite all scripts to bootstrap.pl and posted actual url as parameter. In bootstrap I am handling sessions, logging, etc and in the end I am calling eval('script from url'). The most interesting for you is error handling:
use ex::override GLOBAL_die => sub {
my $stackTrace = Devel::StackTrace->new(no_refs => 1)->as_string;
if ($stackTrace =~ /eval \{/) {
CORE::die #_;
} else {
local *__ANON__ = "Exception";
select STDOUT;
print getError500( sprintf(
join("\n",<DATA>),
#_,
$stackTrace,
Dumper(\%ENV)
));
CORE::exit 1;
}
};
This is overwriting die and printing nice error 500 page with full stack on exception. I tried many things and this looks like the best approach for me.
Related
Hello Ladies and Gentleman! I am currently writing a minimalistic chat server that will somewhat resemble IRC. I am writing it in perl using the Mojolicious, but unfortunately have run into an issue. I have the following code:
#!/usr/bin/perl
use warnings;
use strict;
use Mojo::IOLoop::Server;
my $server = Mojo::IOLoop::Server->new;
$server->on(accept => sub {
my ($server, $handle) = #_;
my $data;
print $handle "Connected!\n";
while(1) {
$handle->recv($data, 4096);
if($data) {
print $server "$data";
}
}
});
$server->listen(port => $ARGV[0]);
$server->start;
$server->reactor->start unless $server->reactor->is_running;
Unfortunately, the print $server "$data"; line does not actually work. It gives off the error:
Mojo::Reactor::Poll: I/O watcher failed: Not a GLOB reference at ./server.pl line 20.
I have looked through the documentation for Mojolicious, but cannot find how to send the line I get from client A to the rest of the clients connected.
While $handle is something like a stream you can write on, $server is a Mojo::IOloop::Server object, so it's not a surprise you can't write on it like you're trying to do.
Even if I use Mojolicious quite often, I'm not familiar with every possibilities (there are a lot), but here what I would suggest : you need to store a list of all connected clients (in a hash or an array for instance), and when you receive a message, you iterate through that client list, to send the message to all of them.
You also need a way (not hard to do) to delete clients from your clients list when they disconnect.
Also I'm not quite sure about your infinite loop : I wouldn't be surprised if it was blocking the server on the 1st connected client.
It's better to use Mojolicious functions to do so :
$serv->on(message => sub { send the message to all clients });
And that function would be called every time a message is received.
Here is a good example, using Mojolicious::Light, pretty easy to understand I think : https://github.com/kraih/mojo/wiki/Writing-websocket-chat-using-Mojolicious-Lite
I'm pretty new to Perl. While I just created a simple scripts to retrieve a file with
getstore($url, $file);
But how do I know whether the task is done correctly or the connection interrupted in the middle, or authentication failed, or whatever response. I searched all the web and I found some, like a response list, and some talking about useragent stuff, which I totally can't understand, especially the operator $ua->.
What I wish is to an explanation about that operator stuff (I don't even know what -> used for), and the RC code meaning, and finally, how to use it.
Its a lot of stuff so I appreciate any answer given, even just partially. And, thanks first for whoever will to help. =)
The LWP::Simple module is just that: quite simplistic. The documentation states that the getstore function returns the HTTP status code which we can save into a variable. There are also the is_success and is_error functions that tell us whether a certain return value is ok or not.
my $url = "http://www.example.com/";
my $filename = "some-file.html";
my $rc = getstore($url, $filename)
if (is_error($rc)) {
die "getstore of <$url> failed with $rc";
}
Of course, this doesn't catch errors with the file system.
The die throws a fatal exception that terminates the execution of your script and displays itself on the terminal. If you don't want to abort execution use warn.
The LWP::Simple functions provide high-level controls for common tasks. If you need more control over the requests, you have to manually create an LWP::UserAgent. An user agent (abbreviated ua) is a browser-like object that can make requests to servers. We have very detailed control over these requests, and can even modify the exact header fields.
The -> operator is a general dereference operator, which you'll use a lot when you need complex data structures. It is also used for method calls in object-oriented programming:
$object->method(#args);
would call the method on $object with the #args. We can also call methods on class names. To create a new object, usually the new method is used on the class name:
my $object = The::Class->new();
Methods are just like functions, except that you leave it to the class of the object to figure out which function exactly will be called.
The normal workflow with LWP::UserAgent looks like this:
use LWP::UserAgent; # load the class
my $ua = LWP::UserAgent->new();
We can also provide named arguments to the new method. Because these UA objects are robots, it is considered good manners to tell everybody who sent this Bot. We can do so with the from field:
my $ua = LWP::UserAgent->new(
from => 'ss-tangerine#example.com',
);
We could also change the timeout from the default three minutes. These options can also be set after we constructed a new $ua, so we can do
$ua->timeout(30); # half a minute
The $ua has methods for all the HTTP requests like get and post. To duplicate the behaviour of getstore, we first have to get the URL we are interested in:
my $url = "http://www.example.com/";
my $response = $ua->get($url);
The $response is an object too, and we can ask it whether it is_success:
$response->is_success or die $response->status_line;
So if execution flows past this statement, everything went fine. We can now access the content of the request. NB: use the decoded_content method, as this manages transfer encodings for us:
my $content = $response->decoded_content;
We can now print that to a file:
use autodie; # automatic error handling
open my $fh, ">", "some-file.html";
print {$fh} $content;
(when handling binary files on Windows: binmode $fh after opening the file, or use the ">:raw" open mode)
Done!
To learn about LWP::UserAgent, read the documentation. To learn about objects, read perlootut. You can also visit the perl tag on SO for some book suggestions.
I am getting error as "Internal Server Error.The server encountered an internal error or misconfiguration and was unable to complete your request."
I am submitting a form in html and get its values.
HTML Code (index.cgi)
#!c:/perl/bin/perl.exe
print "Content-type: text/html; charset=iso-8859-1\n\n";
print "<html>";
print "<body>";
print "<form name = 'login' method = 'get' action = '/cgi-bin/login.pl'> <input type = 'text' name = 'uid'><br /><input type = 'text' name = 'pass'><br /><input type = 'submit'>";
print "</body>";
print "</html>";
Perl Code to fetch data (login.pl)
#!c:/perl/bin/perl.exe
use CGI::Carp qw(fatalsToBrowser);
my(%frmfields);
getdata(\%frmfields);
sub getdata {
my ($buffer) = "";
if (($ENV{'REQUEST_METHOD'} eq 'GET')) {
my (%hashref) = shift;
$buffer = $ENV{'QUERY_STRING'};
foreach (split(/&/,$buffer)) {
my ($key, $value) = split(/=/, $_);
$key = decodeURL($key);
$value= decodeURL($value);
$hashref{$key} = $value;
}
}
else{
read(STDIN,$buffer,$ENV{'CONTENT_LENGTH'})
}
}
sub decodeURL{
$_=shift;
tr/+/ /;
s/%(..)/pack('c', hex($1))/eg;
return($_);
}
The HTML page opens correctly but when i submit the form, i get internal server error.
Please help.
What does the web server's error log say?
Independent of what it says, you must stop parsing the form data yourself. There are modules for that, specifically CGI.pm. Using that, you can do this instead:
use CGI;
my $CGI = CGI->new();
my $uid = $CGI->param( 'uid' );
my $pass = $CGI->param( 'pass' );
# rest of your script
Much cleaner and much safer.
I agree with Tore that you must not parse this yourself. Your code has multiple errors. You don't allow multiple parameter values, you don't allow the ; alternate separator, you don't handle POST with a query string in the URL, and so on.
I don't know how long it will be online for free, but chapter 15 of my new "Beginning Perl" book covers Web programming. That should get you started on some decent basics. Note that the online version is an early, rough draft. The actual book also includes Chapter 19 which has a complete Web app example.
could it be this line that's the problem?
my (%hashref) = shift;
You're initialising a proper hash, but shift will give you a hash reference, since you did getdata(\%frmfields);. You probably want this, instead:
my $hashref = shift;
"500 Internal Server Error" just means that something didn't work the way the web server expected. Maybe you don't have CGI enabled. Maybe the script isn't executable. Maybe it's in a directory the web server isn't allowed to access. It's even possible that maybe the web server ran the script successfully and it worked perfectly, but didn't start its output with a valid set of HTTP headers. You need to look in the web server's error log to find out what it didn't like, which may or may not be a Perl issue.
Like everyone else has said, though, don't try to parse query strings and grovel though %ENV yourself. Use one of the many fine modules or frameworks which are available and already known to work correctly. CGI.pm is the granddaddy of them all and works well for smaller projects, but I'd recommend looking into a proper web application framework such as Dancer, Mojolicious, or Catalyst (there are many others, but those are the big three) if you're planning to build anything with more than a handful of relatively simple pages and forms.
I am using WWW::Mechanize to crawl sites, and it works great except for sometimes it will hit a page that returns error code 404 or 500 (not found or internal server error), and then my script will just exit and stop running. This is really messing with my data collection, so is there anyway that WWW::Mechanize will let me catch these errors and see what kind of error code was returned (i.e. 404,500, etc.). Thanks for the help!
You need to disable autocheck:
my $mech = WWW::Mechanize->new( autocheck => 0 );
$mech->get("http://somedomain.com");
if ( $mech->success() ) {
...
}
else {
print "status is: " . $mech->status;
}
Also, as an aside, have a look at WWW::Mechanize::Cached::GZip and WWW::Mechanize::Cached to speed up your development when testing your mech scripts.
Turn off autocheck and manually check status(), which returns the HTTP status code of the response.
This is a 3-digit number like 200 for OK, 404 for Not Found, and so on.
use strict;
use warnings;
use WWW::Mechanize;
my $url = 'http://...';
my $mech = WWW::Mechanize->new(autocheck => 0);
$mech->get($url);
print $mech->status();
See http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html for Status Code Definitions.
If the status code is 400 or above, then you got error...
We store a large amount of files on Amazon S3 that we want website visitors to be able to access via AJAX but we don't want the actual file locations disclosed to visitors.
To accomplish this what I'm hoping to do is to make an AJAX request to a very simple perl script that would simply act as a proxy and return the file to the browser. I already have the script setup to authenticate that the user is logged in and do a database query to figure out the correct url to access the file on S3 but I'm not sure the best way to return the file to the vistor's browser in the most efficient manner.
Any suggestions on the best way to accomplish this would be greatly appreciated. Thanks!
The best way is to use the sendfile system call. If you're opening and reading the file from disk manually and then again write it blockwise to the "sink" end of your Web framework, then you're very wasteful because the data have to travel through the RAM, possibly including buffering.
What you describe in your question is a very common pattern, therefore many solutions already exist around the idea of just setting a special HTTP header, then letting the Web stack below your application deal with it efficiently.
mod_xsendfile for Apache httpd
in lighttpd
X-Accel-Redirect for nginx
Employ the XSendfile middleware in Plack to set the appropriate header. The following minimal program will DTRT and take advantage of the system call where possible.
use IO::File::WithPath qw();
use Plack::Builder qw(builder enable);
builder {
enable 'Plack::Middleware::XSendfile';
sub {
return [200, [], IO::File::WithPath->new('/usr/src/linux/COPYING')];
}
};
Ok. There's example how to implement this using Mojolicious framework.
I suppose you run this script as daemon. Script catches all requests to /json_dir/.*, this request to Stackoverflow API and returns response.
You may run this script as ./example.pl daemon and then try http://127.0.0.1:3000/json_dir/perl
In response you should be able to find your own question titled 'Simple Perl Proxy'.
This code could be used as standalone daemon that listen on certain port and as CGI script (first preferred).
#!/usr/bin/env perl
use Mojolicious::Lite;
get '/json_dir/(.filename)' => sub {
my $self = shift;
my $filename = $self->stash('filename');
my $url = "http://api.stackoverflow.com/1.1/questions?tagged=" . $filename;
$self->ua->get(
$url => sub {
my ($client, $tx) = #_;
json_response($self, $tx);
}
);
$self->render_later;
};
sub json_response {
my ($self, $tx) = #_;
if (my $res = $tx->success) {
$self->tx->res($res);
}
else {
$self->render_not_found;
}
$self->rendered;
}
app->start;
__DATA__
## not_found.html.ep
<!doctype html><html>
<head><title>Not Found</title></head>
<body>File not found</body>
</html>