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New example: Dynamic content with 'send_file()'
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‎lib/dancer_bootstrap_fontawesome_template.pm

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@@ -12,6 +12,7 @@ use examples::photo_gallery;
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use examples::markdown;
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use examples::template_plugins;
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use examples::error_handling;
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use examples::dynamic_content;
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our $VERSION = '0.1';
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‎lib/examples/dynamic_content.pm

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package examples::dynamic_content;
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use Dancer ':syntax';
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use strict;
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use warnings;
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use POSIX qw(strftime);
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use Data::Dumper;
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=pod
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This module demonstrates returning dynamic content to the user from a Dancer route handler.
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The data is generated on-line, without having to temporarily store it in a file or in memory.
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=cut
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# Show the main page to the user
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get '/dynamic_content' => sub {
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template 'examples/dynamic_content.tt';
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};
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=pod
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Return dynamic content to the user.
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The content is generated on-line, not from a stored file or a memory buffer.
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Common usage examples:
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Returning the results of a "select * from TABLE" query, without storing the results in a temporary file.
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Couple of technical notes:
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1. send_file() documentation:
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https://metacpan.org/module/Dancer#send_file
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2. send_file was originally designed to send either physical files, or in-memory scalars.
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The streaming option was added later - so some hacks are required.
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3. The "override" callback will take care of all data sent to the user/front-end-HTTP-server,
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and so the first parameter to 'send_file' doesn't matter
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(just needs to be a scalar-ref, otherwise it will be mistaken for a file-name).
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4. The "$respond" parameter is a PSGI-related opaque object. Use it to generate the 'writer' object.
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5. The "$response" parameter is the original Dancer::Response object that Dancer generated.
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Can be safely ignored, as we generate our own response.
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=cut
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get '/dynamic_content_download' => sub {
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send_file(
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\"foo", # anything, as long as it's a scalar-ref
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streaming => 1, # enable streaming
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callbacks => {
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override => sub {
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my ( $respond, $response ) = @_;
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my $http_status_code = 200 ;
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# Tech.note: This is a hash of HTTP header/values, but the
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# function below requires an even-numbered array-ref.
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my @http_headers = ( 'Content-Type' => 'text/plain',
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'Content-Disposition' => 'attachment; filename="foo.txt"',
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# Since this is dynamic content,
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# try hard (with extra HTTP headers) to prevent caching.
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'Last-Modified' => strftime("%a, %d %b %Y %H:%M:%S GMT", gmtime),
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'Expires' => 'Tue, 03 Jul 2001 06:00:00 GMT',
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'Cache-Control' => 'no-store, no-cache, must-revalidate, max-age=0',
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'Pragma' => 'no-cache' );
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# Send the HTTP headers
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# (back to either the user or the upstream HTTP web-server front-end)
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my $writer = $respond->( [ $http_status_code, \@http_headers ] );
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# Generate a lot of text...
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foreach my $line_number ( 1 .. 1000000 ) {
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$writer->write("Hello World (line $line_number)\n");
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}
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},
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},
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);
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};
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true;

‎views/examples/dynamic_content.tt

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<!-- BootStrap NavBar -->
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<div class="navbar">
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<div class="navbar-inner">
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<div class="container">
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<h3><a class="brand" href="[% request.uri_base %]"><img src="images/dancer_man.png"> Perl Dancer</a></h3>
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</div>
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</div>
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</div>
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<!-- HEADER line -->
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<div class="container">
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<div class="page-header">
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<div class="row">
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<div class="span12">
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<h2>Dancer + Bootstrap Examples</h2>
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<h1>Dynamic Content Generation</h1>
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</div>
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</div>
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</div>
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<div class="row">
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<div class="span12">
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This example shows how to return dynamic content (generated by the Perl/Dancer script) to the user.
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<br/>
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Useful if you need to send data to the client, that is not based on a physical file or a variable in memory (or if the data is too big to fit in memory).
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<br/>
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<br/>
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<br/>
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<h3>Code Highlights</h3>
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<ul>
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<li>The Dancer code is in
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<a href="[% request.uri_for("/show_file",file => "dynamic_content.pm", example => "Dynamic Content", url => request.uri_for("/dynamic_content") ) %]">
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<code>./lib/examples/dynamic_content.pm</code> <i class="icon-eye-open"></i> </a>.
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</li>
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<li>This HTML template is in
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<a href="[% request.uri_for("/show_file",file => "dynamic_content.tt", example =>"Dynamic Content", url => request.uri_for("/dynamic_content") ) %]">
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<code>./views/examples/dynamic_content.tt</code> <i class="icon-eye-open"></i> </a>.
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</li>
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<li>This is functionally equivalent to the following 'classic' CGI code:
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<pre>
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#!/usr/bin/perl
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use CGI qw/:standard/;
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print header(-type=>"text/plain", -attachment=>"foo.txt");
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foreach $line ( 1 .. 10000 ) {
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print "Hello World (line $line)\n";
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}
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</pre>
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</li>
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<li>Due the Dancer architecture, we can't simply <code>print</code> the data we want to send to the use (as in classic CGI programs). Instead, we supply a callback <code>sub</code> which will send the data to the user.</li>
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</li>
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<li>Using <code>send_file</code> with the <b>streaming</b> parameter, we create a subroutine that will send the data back to the user.</li>
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<li>See the <b>dynamic_content.pm</b> perl module for a detailed example.</li>
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</ul>
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</div>
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</div>
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<br/>
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<br/>
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<br/>
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<div class="row">
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<div class="span12">
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<h1>Download</h1>
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Clicking this button will send you a 25MB text file.<br/>
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The content is dynamically generated by the Dancer code.<br/>
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<a class="btn btn-primary" href="[% request.uri_for("/dynamic_content_download") %]">Download Dynamic Content</a>
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</div>
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</div>
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<br/>
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<br/>
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<br/>
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<br/>
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<br/>
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<br/>

‎views/index.tt

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<li><a href="[% request.uri_for("/markdown")%]">Markdown Text Rendering</a></li>
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<li><a href="[% request.uri_for("/template_plugins")%]">Template::Toolkit plugins</a></li>
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<li><a href="[% request.uri_for("/error_handling")%]">Dancer's Error Handling</a></li>
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<li><a href="[% request.uri_for("/dynamic_content")%]">Generate Dynamic Content</a></li>
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</ul>
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</div>
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</div>

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