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2009年06月11日

Sending DBI trace output to FirePHP with HTTP::Engine

As promised last time, here is a complete example of how to send DBI trace output to FirePHP in an HTTP::Engine demo web application.

First we create a very small example SQLite database. Let's model a company that has two departments with two employees each. Create a file called create.sql and enter the following SQL commands:

CREATE TABLE departments (
    id INTEGER PRIMARY KEY,
    name TEXT
);

CREATE TABLE employees (
    id INTEGER PRIMARY KEY,
    name TEXT,
    department_id INTEGER
);

INSERT INTO departments (id, name) VALUES (1, 'publishing');
INSERT INTO departments (id, name) VALUES (2, 'accounting');

INSERT INTO employees (id, name, department_id)
    VALUES (1, 'Yamamura Masayoshi', 1);

INSERT INTO employees (id, name, department_id)
    VALUES (2, 'Ueda Akira', 1);

INSERT INTO employees (id, name, department_id)
    VALUES (3, 'Matsumoto Daichi', 2);

INSERT INTO employees (id, name, department_id)
    VALUES (4, 'Yasuda Ryota', 2);

Now we create the database itself:

sqlite3 kaisha.db <create.sql

The web application is pretty simple as well. We create an HTTP::Engine object and run it; the handler connects to the database, runs a simple query, creates an HTML table from the results and sends it in a response back to the engine.

#!/usr/bin/env perl

use strict;
use warnings;
use DBI;
use HTTP::Engine;
use HTTP::Engine::FirePHP;

my $engine = HTTP::Engine->new(
    interface => {
        module => 'ServerSimple',
        args   => {
            host => 'localhost',
            port => '1984',
        },
        request_handler => \&handler,
    },
)->run;

sub handler {
    my $req = shift;
    my $dbh = DBI->connect('dbi:SQLite:dbname=kaisha.db', '', '');
    my $res = HTTP::Engine::Response->new;

    $dbh->trace(2, $res->get_fire_php_fh);

    my $r = $dbh->selectall_arrayref('
        SELECT E.name, D.name
        FROM employees E, departments D
        WHERE D.id = E.department_id
    ');

    $dbh->disconnect;

    my $body = "<table>\n" . 
        (join "\n" =>
             map { sprintf "<tr><td>%s</td><td>%s</td></tr>\n", @$_ } @$r
        )
        . "</table>\n";
    $res->status(200);
    $res->body($body);
    $res;
}

The relevant command to send DBI trace output to FirePHP is:

$dbh->trace(2, $res->get_fire_php_fh);

In version 0.02, HTTP::Engine::FirePHP gives HTTP::Engine::Response the method get_fire_php_fh, which will return a filehandle that has been opened to a PerlIO::via::ToFirePHP layer, so you don't even need to do that manually anymore.

With this one line, DBI knows that it should trace all calls and send the trace output to the filehandle. The trace output will automatically be put into the HTTP response headers so FirePHP can display them. Here is what the Firebug console looks like when we make a request to the server:

Sending DBI trace output to FirePHP

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posted at: 14:54 | path: /dev | permalink | 0 comments | 0 trackbacks

Log to FirePHP via an PerlIO layer

I have released PerlIO::via::ToFirePHP. This PerlIO layer sends everything it receives to FirePHP. When constructing a filehandle using this layer using open(), you need to pass an object of type FirePHP::Dispatcher that has been initialized with a HTTP::Headers object.

use PerlIO::via::ToFirePHP;
my $fire_php = FirePHP::Dispatcher->new(HTTP::Headers->new);
open my $fh, '>:via(ToFirePHP)', $fire_php;

Everything you print on the filehandle will be sent to FirePHP.

A typical use of this PerlIO layer is to send DBI trace output to FirePHP:

use PerlIO::via::ToFirePHP;

my $dbh = DBI->connect(...);

open my $fh, '>:via(ToFirePHP)',
    FirePHP::Dispatcher->new($http_headers_object);
$dbh->trace(2, $fh);

Now the trace output of all calls to that database handle will be sent to FirePHP.

The PerlIO layer is implemented in PerlIO::via::ToFirePHP instead of just PerlIO::via::FirePHP because of a bug in PerlIO::via in perl 5.10.0 and earlier versions. If we used just PerlIO::via::FirePHP, we would not be able to use the shorthand layer notation of open my $fh, ':>via(FirePHP), $fire_php. PerlIO::via would look for a PUSHED method in package FirePHP. There is no such method, but because FirePHP::Dispatcher has been loaded, the namespace FirePHP has been autovivified. So PerlIO::via would stop looking. This bug seems to be fixed in perl 5.10.1.

In the next article I will show a complete example of how to send DBI trace output to FirePHP in an HTTP::Engine demo web application.

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posted at: 12:05 | path: /dev | permalink | 1 comment | 0 trackbacks

2009年06月07日

Logging to Firefox with HTTP::Engine::FirePHP

I have released HTTP::Engine::FirePHP on CPAN; the development version is on Github.

If you are developing a web application and don't want to or can't check the error log, the traditional way is to include debug messages in the HTML page. However, this messes up the layout and mixes content with logging; the two really need to be separate.

FirePHP is a Firebug plugin which enables you to log to your Firebug Console by sending certain HTTP headers in the HTTP response. FirePHP is not just useful for PHP, though; any server-side application that can manipulate HTTP headers can log to Firebug.

The FirePHP response headers use the Wildfire protocol. The CPAN module FirePHP::Dispatcher can generate these headers.

This module then integrates FirePHP::Dispatcher with HTTP::Engine. By simply using this module, HTTP::Engine::Response gets a fire_php() accessor through which you can log to FirePHP.

Here is an example:

#!/usr/bin/env perl
use strict;
use warnings;
use Data::Dumper;
use HTTP::Engine;
use HTTP::Engine::Response;
use HTTP::Engine::FirePHP;

HTTP::Engine->new(
    interface => {
        module => 'ServerSimple',
        args   => {
            host => 'localhost',
            port => '10012',
        },
        request_handler => sub {
            my $req = shift;
            my $res = HTTP::Engine::Response->new(body => 'Hello');
            $res->fire_php->info('Hello from HTTP::Engine');
            $res->fire_php->warn(sprintf 'path was %s', $req->uri->path);
            $res->fire_php->log(Dumper $req);
            $res;
        },
    },
)->run;

When you load the response into Firefox, open the Firebug Console and you will find the logged messages there.

Logging to Firefox with HTTP::Engine::FirePHP

When you restart the HTTP::Engine-based server, be sure to do a shift-reload of the relevant page in Firefox; this ensures that headers aren't cached. If you don't do this, you might see remnant headers from previous responses.

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posted at: 14:54 | path: /dev | permalink | 0 comments | 0 trackbacks

2009年05月02日

Perlbal article

As spotted by Korean Perl hacker @saillinux, there is an article called "The Juggler: Scaling your website with the Perlbal web server" about the reverse proxy load balancer and web server Perlbal in PDF format; it was published by Linux Magazine in November 2007.

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posted at: 17:21 | path: /misc | permalink | 0 comments | 0 trackbacks