1Maypole::Manual::CookboUoske(r3)Contributed Perl DocumenMtaaytpioolne::Manual::Cookbook(3)
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6 Maypole::Manual::Cookbook - Maypole Cookbook
7
9 Hacks; design patterns; recipes: call it what you like, this chapter is
10 a developing collection of techniques which can be slotted in to
11 Maypole applications to solve common problems or make the development
12 process easier.
13 As Maypole developers, we don't necessarily know the "best practice"
15 for developing Maypole applications ourselves, in the same way that
16 Larry Wall didn't know all about the best Perl programming style as
17 soon as he wrote Perl. These techniques are what we're using at the
18 moment, but they may be refined, modularized, or rendered irrelevant
19 over time. But they've certainly saved us a bunch of hours work.
20 Frontend hacks
22 These hacks deal with changing the way Maypole relates to the outside
23 world; alternate front-ends to the Apache and CGI interfaces, or
24 subclassing chunks of the front-end modules to alter Maypole's
25 behaviour in particular ways.
26 Separate model class modules
28 You want to put all the "BeerDB::Beer" routines in a separate module,
30 so you say:
31 package BeerDB::Beer;
33 BeerDB::Beer->has_a(brewery => "BeerDB::Brewery");
34 sub foo :Exported {}
35 And in BeerDB.pm, you put:
37 use BeerDB::Beer;
39 It doesn't work.
41 Solution: It doesn't work because of the timing of the module loading.
43 "use BeerDB::Beer" will try to set up the "has_a" relationships at
44 compile time, when the database tables haven't even been set up, since
45 they're set up by
46 BeerDB->setup("...")
48 which does its stuff at runtime. There are two ways around this; you
50 can either move the "setup" call to compile time, like so:
51 BEGIN { BeerDB->setup("...") }
53 or move the module loading to run-time (my preferred solution):
55 BeerDB->setup("...");
57 BeerDB::Beer->require;
58 Redirecting to SSL for sensitive information
60 You have a website with forms that people will be entering sensitive
62 information into, such as credit cards or login details. You want to
63 make sure that they aren't sent in plain text but over SSL instead.
64 Solution
66 The solution is a bit tricky for 2 reasons :
68 Firstly -- Many browsers and web clients will change a redirected POST
70 request into a GET request (which displays all that sensitive
71 information in the browser, or access logs and possibly elsewhere)
72 and/or drops the values on the floor.
73 Secondly -- If somebody has sent that sensitive information in plain
75 text already, then sending it again over SSL won't solve the problem.
76 Redirecting a request is actually rather simple :
78 $r->redirect_request('https://www.example.com/path'); # perldoc Maypole
80 for API
81 .. as is checking the protocol :
83 $r->get_protocol(); # returns 'http' or 'https'
85 You should check that the action that generates the form that people
87 will enter the sensitive information into is https and redirect if not.
88 You should also check that no information is lost when redirecting,
90 possibly by storing it in a session and retrieving it later - see
91 Maypole::Plugin::Session
92 Debugging with the command line
94 You're seeing bizarre problems with Maypole output, and you want to
96 test it in some place outside of the whole
97 Apache/mod_perl/HTTP/Internet/browser circus.
98 Solution: Use the Maypole::CLI module to go directly from a URL to
100 standard output, bypassing Apache and the network altogether.
101 Maypole::CLI is not a standalone front-end, but to allow you to debug
103 your applications without having to change the front-end they use, it
104 temporarily "borgs" an application. If you run it from the command
105 line, you're expected to use it like so:
106 perl -MMaypole::CLI=Application -e1 'http://your.server/path/table/action'
108 For example:
110 perl -MMaypole::CLI=BeerDB -e1 'http://localhost/beerdb/beer/view/1?o2=desc'
112 You can also use the "Maypole::CLI" module programatically to create
114 test suites for your application. See the Maypole tests themselves or
115 the documentation to "Maypole::CLI" for examples of this.
116 Don't forget also to turn on debugging output in your application:
118 package BeerDB;
120 use strict;
121 use warnings;
122 use Maypole::Application qw(-Debug);
123 Changing how URLs are parsed
125 You don't like the way Maypole URLs look, and want something that
127 either fits in with the rest of your site or hides the internal
128 workings of the system.
129 Solution: So far we've been using the "/table/action/id/args" form of a
131 URL as though it was "the Maypole way"; well, there is no Maypole way.
132 Maypole is just a framework and absolutely everything about it is
133 overridable.
134 If we want to provide our own URL handling, the method to override in
136 the driver class is "parse_path". This is responsible for taking
137 "$r->path" and filling the "table", "action" and "args" slots of the
138 request object. Normally it does this just by splitting the path on
139 '"/"' characters, but you can do it any way you want, including getting
140 the information from "POST" form parameters or session variables.
141 For instance, suppose we want our URLs to be of the form
143 "ProductDisplay.html?id=123", we could provide a "parse_path" method
144 like so:
145 sub parse_path {
147 my $r = shift;
148 $r->path("ProductList.html") unless $r->path;
149 ($r->path =~ /^(.*?)([A-Z]\w+)\.html/);
150 $r->table(lc $1);
151 $r->action(lc $2);
152 my %query = $r->ar->args;
153 $self->args([ $query{id} ]);
154 }
155 This takes the path, which already has the query parameters stripped
157 off and parsed, and finds the table and action portions of the
158 filename, lower-cases them, and then grabs the "id" from the query.
159 Later methods will confirm whether or not these tables and actions
160 exist.
161 See the iBuySpy Portal for another example of custom URL processing.
163 Maypole for mobile devices
165 You want Maypole to use different templates to display on particular
167 browsers.
168 Solution: There are several ways to do this, but here's the neatest
170 we've found. Maypole chooses where to get its templates either by
171 looking at the "template_root" config parameter or, if this is not
172 given, calling the "get_template_root" method to ask the front-end to
173 try to work it out. We can give the front-end a little bit of help, by
174 putting this method in our driver class:
175 sub get_template_root {
177 my $r = shift;
178 my $browser = $r->headers_in->get('User-Agent');
179 if ($browser =~ /mobile|palm|nokia/i) {
180 "/home/myapp/templates/mobile";
181 } else {
182 "/home/myapp/templates/desktop";
183 }
184 }
185 (Maybe there's a better way to detect a mobile browser, but you get the
187 idea.)
188 Content display hacks
190 These hacks deal primarily with the presentation of data to the user,
191 modifying the view template or changing the way that the results of
192 particular actions are displayed.
193 Null Action
195 You need an "action" which doesn't really do anything, but just formats
197 up a template.
198 Solution: There are two ways to do this, depending on what precisely
200 you need. If you just need to display a template, "Apache::Template"
201 style, with no Maypole objects in it, then you don't need to write any
202 code; just create your template, and it will be available in the usual
203 way.
204 If, on the other hand, you want to display some data, and what you're
206 essentially doing is a variant of the "view" action, then you need to
207 ensure that you have an exported action, as described in the templates
208 and actions chapter:
209 sub my_view :Exported { }
211 Template Switcheroo
213 An action doesn't have any data of its own to display, but needs to
215 display something.
216 Solution: This is an extremely common hack. You've just issued an
218 action like "beer/do_edit", which updates the database. You don't want
219 to display a page that says "Record updated" or similar. Lesser
220 application servers would issue a redirect to have the browser request
221 "/beer/view/id" instead, but we can actually modify the Maypole request
222 on the fly and, after doing the update, pretend that we were going to
223 "/beer/view/id" all along. We do this by setting the objects in the
224 "objects" slot and changing the "template" to the one we wanted to go
225 to.
226 In this example from Flox, we've just performed an "accept" method on a
228 "Flox::Invitation" object and we want to go back to viewing a user's
229 page.
230 sub accept :Exported {
232 my ($self, $r) = @_;
233 my $invitation = $r->objects->[0];
234 # [... do stuff to $invitation ...]
235 $r->objects([$r->user]);
236 $r->model_class("Flox::User");
237 $r->template("view");
238 }
239 This hack is so common that it's expected that there'll be a neater way
241 of doing this in the future.
242 XSLT
244 Here's a hack I've used a number of times. You want to store structured
246 data in a database and to abstract out its display.
247 Solution: You have your data as XML, because handling big chunks of XML
249 is a solved problem. Build your database schema as usual around the
250 important elements that you want to be able to search and browse on.
251 For instance, I have an XML format for songs which has a header section
252 of the key, title and so on, plus another section for the lyrics and
253 chords:
254 <song>
256 <header>
257 <title>Layla</title>
258 <artist>Derek and the Dominos</artist>
259 <key>Dm</key>
260 </header>
261 <lyrics>
262 <verse>...</verse>
263 <chorus>
264 <line> <sup>A</sup>Lay<sup>Dm</sup>la <sup>Bb</sup> </line>
265 <line> <sup>C</sup>Got me on my <sup>Dm</sup>knees </line>
266 ...
267 I store the title, artist and key in the database, as well as an "xml"
269 field which contains the whole song as XML.
270 To load the songs into the database, I can "use" the driver class for
272 my application, since that's a handy way of setting up the database
273 classes we're going to need to use. Then the handy XML::TreeBuilder
274 will handle the XML parsing for us:
275 use Songbook;
277 use XML::TreeBuilder;
278 my $t = XML::TreeBuilder->new;
279 $t->parse_file("songs.xml");
280 for my $song ($t->find("song")) {
282 my ($key) = $song->find("key"); $key &&= $key->as_text;
283 my ($title) = $song->find("title"); $title = $title->as_text;
284 my ($artist) = $song->find("artist"); $artist = $artist->as_text;
285 my ($first_line) = $song->find("line");
286 $first_line = join "", grep { !ref } $first_line->content_list;
287 $first_line =~ s/[,\.\?!]\s*$//;
288 Songbook::Song->find_or_create({
289 title => $title,
290 first_line => $first_line,
291 song_key => Songbook::SongKey->find_or_create({name => $key}),
292 artist => Songbook::Artist->find_or_create({name => $artist}),
293 xml => $song->as_XML
294 });
295 }
296 Now we need to set up the custom display for each song; thankfully,
298 with the Template::Plugin::XSLT module, this is as simple as putting
299 the following into templates/song/view:
300 [%
302 USE transform = XSLT("song.xsl");
303 song.xml | $transform
304 %]
305 We essentially pipe the XML for the selected song through to an XSL
307 transformation, and this will fill out all the HTML we need. Job done.
308 Displaying pictures
310 You want to serve a picture, a Word document, or something else which
312 doesn't have a content type of "text/html", out of your database.
313 Solution: Fill the content and content-type yourself.
315 Here's a subroutine which displays the "photo" for either a specified
317 user or the currently logged in user. We set the "output" slot of the
318 Maypole request object: if this is done then the view class is not
319 called upon to process a template, since we already have some output to
320 display. We also set the "content_type" using one from the database.
321 sub view_picture :Exported {
323 my ($self, $r) = @_;
324 my $user = $r->objects->[0];
325 $r->content_type($user->photo_type);
326 $r->output($user->photo);
327 }
328 Of course, the file doesn't necessarily need to be in the database
330 itself; if your file is stored in the filesystem, but you have a file
331 name or some other pointer in the database, you can still arrange for
332 the data to be fetched and inserted into "$r->output".
333 REST
335 You want to provide a programmatic interface to your Maypole site.
337 Solution: The best way to do this is with "REST", which uses a
339 descriptive URL to encode the request. For instance, in Flox we
340 describe a social networking system. One neat thing you can do with
341 social networks is to use them for reputation tracking, and we can use
342 that information for spam detection. So if a message arrives from
343 "person@someco.com", we want to know if they're in our network of
344 friends or not and mark the message appropriately. We'll do this by
345 having a web agent (say, WWW::Mechanize or LWP::UserAgent) request a
346 URL of the form
347 "http://flox.simon-cozens.org/user/relationship_by_email/person%40someco.com".
348 Naturally, they'll need to present the appropriate cookie just like a
349 normal browser, but that's a solved problem. We're just interested in
350 the REST request.
351 The request will return a single integer status code: 0 if they're not
353 in the system at all, 1 if they're in the system, and 2 if they're our
354 friend.
355 All we need to do to implement this is provide the
357 "relationship_by_email" action, and use it to fill in the output in the
358 same way as we did when displaying a picture. Since
359 "person%40someco.com" is not the ID of a row in the user table, it will
360 appear in the "args" array:
361 use URI::Escape;
363 sub relationship_by_email :Exported {
364 my ($self, $r) = @_;
365 my $email = uri_unescape($r->args->[0]);
366 $r->content_type("text/plain");
367 my $user;
368 unless (($user) = Flox::User->search(email => $email)) {
369 $r->content("0\n"); return;
370 }
371 if ($r->user->is_friend($user)) { $r->contenti("2\n"); return; };
373 $r->content("1\n"); return;
374 }
375 Component-based Pages
377 You're designing something like a portal site which has a number of
379 components, all displaying different bits of information about
380 different objects. You want to include the output of one Maypole
381 request call while building up another.
382 Solution: Use Maypole::Plugin::Component. By inheriting like this:
384 package BeerDB;
386 use Maypole::Application qw(Component);
387 you can call the "component" method on the Maypole request object to
389 make a "sub-request". For instance, if you have a template
390 <DIV class="latestnews">
392 [% request.component("/news/latest_comp") %]
393 </DIV>
394 <DIV class="links">
396 [% request.component("/links/list_comp") %]
397 </DIV>
398 then the results of calling the "/news/latest_comp" action and template
400 will be inserted in the "latestnews" DIV, and the results of calling
401 "/links/list_comp" will be placed in the "links" DIV. Naturally, you're
402 responsible for exporting actions and creating templates which return
403 fragments of HTML suitable for inserting into the appropriate
404 locations.
405 Alternatively, if you've already got all the objects you need, you can
407 probably just "[% PROCESS %]" the templates directly.
408 Bailing out with an error
410 Maypole's error handling sucks. Something really bad has happened to
412 the current request, and you want to stop processing now and tell the
413 user about it.
414 Solution: Maypole's error handling sucks because you haven't written it
416 yet. Maypole doesn't know what you want to do with an error, so it
417 doesn't guess. One common thing to do is to display a template with an
418 error message in it somewhere.
419 Put this in your driver class:
421 sub error {
423 my ($r, $message) = @_;
424 $r->template("error");
425 $r->template_args->{error} = $message;
426 return OK;
427 }
428 And then have a custom/error template like so:
430 [% PROCESS header %]
432 <H2> There was some kind of error... </H2>
433 <P>
434 I'm sorry, something went so badly wrong, we couldn't recover. This
435 may help:
436 </P>
437 <DIV CLASS="messages"> [% error %] </DIV>
438 Now in your actions you can say things like this:
440 if (1 == 0) { return $r->error("Sky fell!") }
442 This essentially uses the template switcheroo hack to always display
444 the error template, while populating the template with an "error"
445 parameter. Since you "return $r->error", this will terminate the
446 processing of the current action.
447 The really, really neat thing about this hack is that since "error"
449 returns "OK", you can even use it in your "authenticate" routine:
450 sub authenticate {
452 my ($self, $r) = @_;
453 $r->get_user;
454 return $r->error("You do not exist. Go away.")
455 if $r->user and $r->user->status ne "real";
456 ...
457 }
458 This will bail out processing the authentication, the model class, and
460 everything, and just skip to displaying the error message.
461 Non-showstopper errors or other notifications are best handled by
463 tacking a "messages" template variable onto the request:
464 if ((localtime)[6] == 1) {
466 push @{$r->template_args->{messages}}, "Warning: Today is Monday";
467 }
468 Now custom/messages can contain:
470 [% IF messages %]
472 <DIV class="messages">
473 <UL>
474 [% FOR message = messages %]
475 <LI> [% message %] </LI>
476 [% END %]
477 </UL>
478 </DIV>
479 [% END %]
480 And you can display messages to your user by adding "PROCESS messages"
482 at an appropriate point in your template; you may also want to use a
483 template switcheroo to ensure that you're displaying a page that has
484 the messages box in it.
485 Authentication and Authorization hacks
487 The next series of hacks deals with providing the concept of a "user"
488 for a site, and what you do with one when you've got one.
489 Logging In
491 You need the concept of a "current user".
493 Solution: Use something like
495 Maypole::Plugin::Authentication::UserSessionCookie to authenticate a
496 user against a user class and store a current user object in the
497 request object.
498 "UserSessionCookie" provides the "get_user" method which tries to get a
500 user object, either based on the cookie for an already authenticated
501 session, or by comparing "user" and "password" form parameters against
502 a "user" table in the database. Its behaviour is highly customizable
503 and described in its documentation.
504 Pass-through login
506 You want to intercept a request from a non-logged-in user and have them
508 log in before sending them on their way to wherever they were
509 originally going. Override "Maypole::authenticate" in your driver
510 class, something like this:
511 Solution:
513 use Maypole::Constants; # Otherwise it will silently fail!
515 sub authenticate {
517 my ($self, $r) = @_;
518 $r->get_user;
519 return OK if $r->user;
520 # Force them to the login page.
521 $r->template("login");
522 return OK;
523 }
524 This will display the "login" template, which should look something
526 like this:
527 [% INCLUDE header %]
529 <h2> You need to log in </h2>
531 <DIV class="login">
533 [% IF login_error %]
534 <FONT COLOR="#FF0000"> [% login_error %] </FONT>
535 [% END %]
536 <FORM ACTION="[% base ; '/' ; request.path %]" METHOD="post">
537 Username:
538 <INPUT TYPE="text" NAME="[% config.auth.user_field || "user" %]"><BR>
539 Password: <INPUT TYPE="password" NAME="password"> <BR>
540 <INPUT TYPE="submit">
541 </FORM>
542 </DIV>
543 [% INCLUDE footer %]
544 Notice that this request gets "POST"ed back to wherever it came from,
546 using "request.path". This is because if the user submits correct
547 credentials, "get_user" will now return a valid user object, and the
548 request will pass through unhindered to the original URL.
549 Logging Out
551 Now your users are logged in, you want a way of having them log out
553 again and taking the authentication cookie away from them, sending them
554 back to the front page as an unprivileged user.
555 Solution: Just call the "logout" method of
557 "Maypole::Plugin::Authentication::UserSessionCookie". You may also want
558 to use the template switcheroo hack to send them back to the frontpage.
559 Multi-level Authorization
561 You have both a global site access policy (for instance, requiring a
563 user to be logged in except for certain pages) and a policy for
564 particular tables. (Only allowing an admin to delete records in some
565 tables, say, or not wanting people to get at the default set of methods
566 provided by the model class.)
567 You don't know whether to override the global "authenticate" method or
569 provide one for each class.
570 Solution: Do both. Maypole checks whether there is an "authenticate"
572 method for the model class (e.g. BeerDB::Beer) and if so calls that. If
573 there's no such method, it calls the default global "authenticate"
574 method in "Maypole", which always succeeds. You can override the global
575 method as we saw above, and you can provide methods in the model
576 classes.
577 To use per-table access control you can just add methods to your model
579 subclasses that specify individual policies, perhaps like this:
580 sub authenticate { # Ensure we can only create, reject or accept
582 my ($self, $r) = @_;
583 return OK if $r->action =~ /^(issue|accept|reject|do_edit)$/;
584 return; # fail if any other action
585 }
586 If you define a method like this, the global "authenticate" method will
588 not be called, so if you want it to be called you need to do so
589 explicitly:
590 sub authenticate { # Ensure we can only create, reject or accept
592 my ($self, $r) = @_;
593 return unless $r->authenticate($r) == OK; # fail if not logged in
594 # now it's safe to use $r->user
595 return OK if $r->action =~ /^(accept|reject)$/
596 or ($r->user eq 'fred' and $r->action =~ /^(issue|do_edit)$/);
597 return; # fail if any other action
598 }
599 Creating and editing hacks
601 These hacks particularly deal with issues related to the "do_edit"
602 built-in action.
603 Limiting data for display
605 You want the user to be able to type in some text that you're later
607 going to display on the site, but you don't want them to stick images
608 in it, launch cross-site scripting attacks or otherwise insert messy
609 HTML.
610 Solution: Use the CGI::Untaint::html module to sanitize the HTML on
612 input. "CGI::Untaint::html" uses HTML::Sanitizer to ensure that tags
613 are properly closed and can restrict the use of certain tags and
614 attributes to a pre-defined list.
615 Simply replace:
617 App::Table->untaint_columns(
619 text => [qw/name description/]
620 );
621 with:
623 App::Table->untaint_columns(
625 html => [qw/name description/]
626 );
627 And incoming HTML will be checked and cleaned before it is written to
629 the database.
630 Getting data from external sources
632 You want to supplement the data received from a form with additional
634 data from another source.
635 Solution: Munge the contents of " $r->params " before jumping to the
637 original "do_edit" routine. For instance, in this method, we use a
638 Net::Amazon object to fill in some fields of a database row based on an
639 ISBN:
640 use Net::Amazon;
642 my $amazon = Net::Amazon->new(token => 'YOUR_AMZN_TOKEN');
643 ...
645 sub create_from_isbn :Exported {
647 my ($self, $r) = @_;
648 my $book_info = $amazon->search(asin => $r->params->{isbn})->properties;
649 # Rewrite the CGI parameters with the ones from Amazon
651 $r->params->{title} = $book_info->title;
652 $r->params->{publisher} = $book_info->publisher;
653 $r->params->{year} = $book_info->year;
654 $r->params->{author} = join('and', $book_info->authors());
655 # And jump to the usual edit/create routine
657 $self->do_edit($r);
658 }
659 The request will carry on as though it were a normal "do_edit" POST,
661 but with the additional fields we have provided. You might also want
662 to add a template switcheroo so the user can verify the details you
663 imported.
664 Catching errors in a form
666 A user has submitted erroneous input to an edit/create form. You want
668 to send him back to the form with errors displayed against the
669 erroneous fields, but have the other fields maintain the values that
670 the user submitted.
671 Solution: This is basically what the default "edit" template and
673 "do_edit" method conspire to do, but it's worth highlighting again how
674 they work.
675 If there are any errors, these are placed in a hash, with each error
677 keyed to the erroneous field. The hash is put into the template as
678 "errors", and we process the same edit template again:
679 $r->template_args->{errors} = \%errors;
681 $r->template("edit");
682 This throws us back to the form, and so the form's template should take
684 note of the errors, like so:
685 FOR col = classmetadata.columns;
687 NEXT IF col == "id";
688 "<P>";
689 "<B>"; classmetadata.colnames.$col; "</B>";
690 ": ";
691 item.to_field(col).as_HTML;
692 "</P>";
693 IF errors.$col;
694 "<FONT COLOR=\"#ff0000\">"; errors.$col; "</FONT>";
695 END;
696 END;
697 If we're designing our own templates, instead of using generic ones, we
699 can make this process a lot simpler. For instance:
700 <TR><TD>
702 First name: <INPUT TYPE="text" NAME="forename">
703 </TD>
704 <TD>
705 Last name: <INPUT TYPE="text" NAME="surname">
706 </TD></TR>
707 [% IF errors.forename OR errors.surname %]
709 <TR>
710 <TD><SPAN class="error">[% errors.forename %]</SPAN> </TD>
711 <TD><SPAN class="error">[% errors.surname %]</SPAN> </TD>
712 </TR>
713 [% END %]
714 The next thing we want to do is to put the originally-submitted values
716 back into the form. We can do this relatively easily because Maypole
717 passes the Maypole request object to the form, and the POST parameters
718 are going to be stored in a hash as "request.params". Hence:
719 <TR><TD>
721 First name: <INPUT TYPE="text" NAME="forename"
722 VALUE="[%request.params.forename%]">
723 </TD>
724 <TD>
725 Last name: <INPUT TYPE="text" NAME="surname"
726 VALUE="[%request.params.surname%]">
727 </TD></TR>
728 Finally, we might want to only re-fill a field if it is not erroneous,
730 so that we don't get the same bad input resubmitted. This is easy
731 enough:
732 <TR><TD>
734 First name: <INPUT TYPE="text" NAME="forename"
735 VALUE="[%request.params.forename UNLESS errors.forename%]">
736 </TD>
737 <TD>
738 Last name: <INPUT TYPE="text" NAME="surname"
739 VALUE="[%request.params.surname UNLESS errors.surname%]">
740 </TD></TR>
741 Uploading files and other data
743 You want the user to be able to upload files to store in the database.
745 Solution: It's messy.
747 First, we set up an upload form, in an ordinary dummy action. Here's
749 the action:
750 sub upload_picture : Exported {}
752 And here's the custom/upload_picture template:
754 <FORM action="/user/do_upload" enctype="multipart/form-data" method="POST">
756 <P> Please provide a picture in JPEG, PNG or GIF format:
758 </P>
759 <INPUT TYPE="file" NAME="picture">
760 <BR>
761 <INPUT TYPE="submit">
762 </FORM>
763 (Although you'll probably want a bit more HTML around it than that.)
765 Now we need to write the "do_upload" action. At this point we have to
767 get a little friendly with the front-end system. If we're using
768 Apache::Request, then the "upload" method of the "Apache::Request"
769 object (which Apache::MVC helpfully stores in "$r->{ar}") will work for
770 us:
771 sub do_upload :Exported {
773 my ($class, $r) = @_;
774 my $user = $r->user;
775 my $upload = $r->ar->upload("picture");
776 This returns a Apache::Upload object, which we can query for its
778 content type and a file handle from which we can read the data. It's
779 also worth checking the image isn't going to be too massive before we
780 try reading it and running out of memory, and that the content type is
781 something we're prepared to deal with.
782 if ($upload) {
784 my $ct = $upload->info("Content-type");
785 return $r->error("Unknown image file type $ct")
786 if $ct !~ m{image/(jpeg|gif|png)};
787 return $r->error("File too big! Maximum size is ".MAX_IMAGE_SIZE)
788 if $upload->size > MAX_IMAGE_SIZE;
789 my $fh = $upload->fh;
791 my $image = do { local $/; <$fh> };
792 Don't forget "binmode()" in there if you're on a platform that needs
794 it. Now we can store the content type and data into our database,
795 store it into a file, or whatever:
796 $r->user->photo_type($ct);
798 $r->user->photo($image);
799 }
800 And finally, we use our familiar template switcheroo hack to get back
802 to a useful page:
803 $r->objects([ $user ]);
805 $r->template("view");
806 }
807 Now, as we've mentioned, this only works because we're getting familiar
809 with "Apache::Request" and its "Apache::Upload" objects. If we're using
810 CGI::Maypole instead, we can write the action in a similar style:
811 sub do_upload :Exported {
813 my ($class, $r) = @_;
814 my $user = $r->user;
815 my $cgi = $r->cgi;
816 if ($cgi->upload == 1) { # if there was one file uploaded
817 my $filename = $cgi->param('picture');
818 my $ct = $cgi->upload_info($filename, 'mime');
819 return $r->error("Unknown image file type $ct")
820 if $ct !~ m{image/(jpeg|gif|png)};
821 return $r->error("File too big! Maximum size is ".MAX_IMAGE_SIZE)
822 if $cgi->upload_info($filename, 'size') > MAX_IMAGE_SIZE;
823 my $fh = $cgi->upload($filename);
824 my $image = do { local $/; <$fh> };
825 $r->user->photo_type($ct);
826 $r->user->photo($image);
827 }
828 $r->objects([ $user ]);
830 $r->template("view");
831 }
832 It's easy to adapt this to upload multiple files if desired. You will
834 also need to enable uploads in your driver initialization, with the
835 slightly confusing statement:
836 $CGI::Simple::DISABLE_UPLOADS = 0; # enable uploads
838 Combine with the "Displaying pictures" hack above for a happy time.
840 Links
842 Contents, Next Flox, Previous The Beer Database, Twice
843perl v5.32.0 2020-07-28 Maypole::Manual::Cookbook(3)