X-Git-Url: https://git.decadent.org.uk/gitweb/?a=blobdiff_plain;f=doc%2FRequest.pod;h=1782cd5df5b23c5b1c5600aade6e0e0e8d8fabfb;hb=b90c6e146c423746001d304953b6b136acc666db;hp=6af82784ba5263dc2e78a07a681251bf63e1bbd2;hpb=d6437cf11ffb95f80143ea9af87e3bc972b0807e;p=maypole.git

diff --git a/doc/Request.pod b/doc/Request.pod
index 6af8278..1782cd5 100644
--- a/doc/Request.pod
+++ b/doc/Request.pod
@@ -1,44 +1,197 @@
 =head1 Maypole Request Hacking Cookbook
 
+Hacks; design patterns; recipes: call it what you like, this chapter is a
+developing collection of techniques which can be slotted in to Maypole
+applications to solve common problems or make the development process easier.
+
+As Maypole developers, we don't necessarily know the "best practice" for
+developing Maypole applications ourselves, in the same way that Larry Wall
+didn't know all about the best Perl programming style as soon as he wrote
+Perl. These techniques are what we're using at the moment, but they may
+be refined, modularized, or rendered irrelevant over time. But they've
+certainly saved us a bunch of hours work.
+
 =head2 Frontend hacks
 
-=head3 Changing how params are parsed
+These hacks deal with changing the way Maypole relates to the outside world;
+alternate front-ends to the Apache and CGI interfaces, or subclassing chunks
+of the front-end modules to alter Maypole's behaviour in particular ways.
 
-=head3 REST
+=head3 Separate model class modules
 
-=head2 Authentication hacks
+You want to put all the C<BeerDB::Beer> routines in a separate module,
+so you say:
 
-=head2 Creating and editing hacks
+    package BeerDB::Beer;
+    BeerDB::Beer->has_a(brewery => "BeerDB::Brewery");
+    sub foo :Exported {}
 
-=head3 Getting data from external sources
+And in F<BeerDB.pm>, you put:
 
-You want to supplement the data received from a form with additional
-data from another source.
+    use BeerDB::Beer;
 
-B<Solution>: Munge the contents of C< $r-E<gt>params > before jumping
-to the original C<do_edit> routine. For instance, in this method,
-we use a C<Net::Amazon> object to fill in some fields of a database row based
-on an ISBN:
+It doesn't work.
 
-    sub create_from_isbn :Exported {
-       my ($self, $r) = @_;
-       my $response = $ua->search(asin => $r->{params}{isbn});
-       my ($prop) = $response->properties;
-       # Rewrite the CGI parameters with the ones from Amazon
-       @{$r->{params}{qw(title publisher author year)} =            
-           ($prop->title,
-           $prop->publisher,
-           (join "/", $prop->authors()),
-           $prop->year());
-       # And jump to the usual edit/create routine
-       $self->do_edit($r);
+B<Solution>: It doesn't work because of the timing of the module
+loading. C<use Beer::Beer> will try to set up the C<has_a> relationships
+at compile time, when the database tables haven't even been set up,
+since they're set up by
+
+    BeerDB->setup("...")
+
+which does its stuff at runtime. There are two ways around this; you can
+either move the C<setup> call to compile time, like so:
+
+    BEGIN { BeerDB->setup("...") }
+
+or move the module loading to run-time (my preferred solution):
+
+    BeerDB->setup("...");
+    BeerDB::Beer->require;
+
+=head3 Debugging with the command line
+
+You're seeing bizarre problems with Maypole output, and you want to test it in
+some place outside of the whole Apache/mod_perl/HTTP/Internet/browser circus.
+
+B<Solution>: Use the C<Maypole::CLI> module to go directly from a URL to
+standard output, bypassing Apache and the network altogether.
+
+C<Maypole::CLI> is not a standalone front-end, but to allow you to debug your
+applications without having to change the front-end they use, it temporarily
+"borgs" an application. If you run it from the command line, you're expected
+to use it like so:
+
+    perl -MMaypole::CLI=Application -e1 'http://your.server/path/table/action'
+
+For example:
+
+    perl -MMaypole::CLI=BeerDB -e1 'http://localhost/beerdb/beer/view/1?o2=desc'
+
+You can also use the C<Maypole::CLI> module programatically to create
+test suites for your application. See the Maypole tests themselves or
+the documentation to C<Maypole::CLI> for examples of this.
+
+=head3 Changing how URLs are parsed
+
+You don't like the way Maypole URLs look, and want something that either
+fits in with the rest of your site or hides the internal workings of the
+system.
+
+C<Solution>: So far we've been using the C</table/action/id/args> form
+of a URL as though it was "the Maypole way"; well, there is no Maypole
+way. Maypole is just a framework and absolutely everything about it is 
+overridable. 
+
+If we want to provide our own URL handling, the method to override in
+the driver class is C<parse_path>. This is responsible for taking
+C<$r-E<gt>{path}> and filling the C<table>, C<action> and C<args> slots
+of the request object. Normally it does this just by splitting the path
+on C</>s, but you can do it any way you want, including getting the
+information from C<POST> form parameters or session variables. 
+
+For instance, suppose we want our URLs to be of the form
+C<ProductDisplay.html?id=123>, we could provide a C<parse_path> method
+like so:
+
+    sub parse_path {
+        my $r = shift;
+        $r->{path} ||= "ProductList.html";
+        ($r->{table}, $r->{action}) = 
+            ($r->{path} =~ /^(.*?)([A-Z]\w+)\.html/);
+        $r->{table}  = lc $r->{table};
+        $r->{action} = lc $r->{action};
+        my %query = $r->{ar}->args;
+        $self->{args} = [ $query{id} ];
     }
 
-The request will carry on as though it were a normal C<do_edit> POST, but
-with the additional fields we have provided.
+This takes the path, which already has the query parameters stripped off
+and parsed, and finds the table and action portions of the filename,
+lower-cases them, and then grabs the C<id> from the query. Later methods
+will confirm whether or not these tables and actions exist.
+
+See L<BuySpy.pod> for another example of custom URL processing.
+
+=head3 Maypole for mobile devices
+
+You want Maypole to use different templates to display on particular
+browsers.
+
+B<Solution>: There are several ways to do this, but here's the neatest
+we've found. Maypole chooses where to get its templates either by
+looking at the C<template_root> config parameter or, if this is not
+given, calling the C<get_template_root> method to ask the front-end to
+try to work it out. We can give the front-end a little bit of help, by
+putting this method in our driver class:
+
+    sub get_template_root {
+        my $r = shift;
+        my $browser = $r->{ar}->headers_in->get('User-Agent');
+        if ($browser =~ /mobile|palm|nokia/i) {
+            "/home/myapp/templates/mobile";
+        } else {
+            "/home/myapp/templates/desktop";
+        }
+    }
+
+(Maybe there's a better way to detect a mobile browser, but you get the
+idea.)
 
 =head2 Content display hacks
 
+These hacks deal primarily with the presentation of data to the user,
+modifying the C<view> template or changing the way that the results of
+particular actions are displayed.
+
+=head3 Null Action
+
+You need an "action" which doesn't really do anything, but just formats
+up a template.
+
+B<Solution>: There are two ways to do this, depending on what precisely
+you need. If you just need to display a template, C<Apache::Template>
+style, with no Maypole objects in it, then you don't need to write any
+code; just create your template, and it will be available in the usual
+way.
+
+If, on the other hand, you want to display some data, and what you're
+essentially doing is a variant of the C<view> action, then you need to
+ensure that you have an exported action, as described in
+L<StandardTemplates.pod>:
+
+    sub my_view :Exported { }
+
+=head3 Template Switcheroo
+
+An action doesn't have any data of its own to display, but needs to display
+B<something>.
+
+B<Solution>: This is an B<extremely> common hack. You've just issued an
+action like C<beer/do_edit>, which updates the database. You don't want
+to display a page that says "Record updated" or similar. Lesser
+application servers would issue a redirect to have the browser request
+C</beer/view/I<id>> instead, but we can actually modify the Maypole
+request on the fly and, after doing the update, pretend that we were
+going to C</beer/view/I<id>> all along. We do this by setting the
+objects in the C<objects> slot and changing the C<template> to the
+one we wanted to go to.
+
+In this example from L<Flox.pod>, we've just performed an C<accept>
+method on a C<Flox::Invitation> object and we want to go back to viewing
+a user's page.
+
+    sub accept :Exported {
+        my ($self, $r) = @_;
+        my $invitation = $r->objects->[0];
+        # [... do stuff to $invitation ...]
+        $r->{objects} = [$r->{user}];
+        $r->{model_class} = "Flox::User";
+        $r->{template} = "view";
+    }
+
+This hack is so common that it's expected that there'll be a neater
+way of doing this in the future.
+
 =head3 XSLT
 
 Here's a hack I've used a number of times. You want to store structured
@@ -107,8 +260,8 @@ transformation, and this will fill out all the HTML we need. Job done.
 
 =head3 Displaying pictures
 
-You want to serve a picture, or something else which doesn't have a
-content type of C<text/html>, out of your database.
+You want to serve a picture, a Word document, or something else which
+doesn't have a content type of C<text/html>, out of your database.
 
 B<Solution>: Fill the content and content-type yourself.
 
@@ -120,8 +273,412 @@ We also set the C<content_type> using one from the database.
 
     sub view_picture :Exported {
         my ($self, $r) = @_;
-        my $user = $r->{objects}->[0] || $r->{user};
-        if ($r->{content_type} = $user->photo_type) {
-           $r->{output} = $user->photo;
+        my $user = $r->{objects}->[0];
+        $r->{content_type} = $user->photo_type;
+        $r->{output} = $user->photo;
+    }
+
+Of course, the file doesn't necessarily need to be in the database
+itself; if your file is stored in the filesystem, but you have a file
+name or some other pointer in the database, you can still arrange for
+the data to be fetched and inserted into C<$r-E<gt>{output}>.
+
+=head3 REST
+
+You want to provide a programmatic interface to your Maypole site.
+
+B<Solution>: The best way to do this is with C<REST>, which uses a
+descriptive URL to encode the request. For instance, in L<Flox.pod> we
+describe a social networking system. One neat thing you can do with
+social networks is to use them for reputation tracking, and we can use
+that information for spam detection. So if a message arrives from
+C<person@someco.com>, we want to know if they're in our network of
+friends or not and mark the message appropriately. We'll do this by
+having a web agent (say, L<WWW::Mechanize> or L<LWP::UserAgent>) request
+a URL of the form
+C<http://flox.simon-cozens.org/user/relationship_by_email/person%40someco.com>.
+Naturally, they'll need to present the appropriate cookie just like a
+normal browser, but that's a solved problem. We're just interested in
+the REST request.
+
+The request will return a single integer status code: 0 if they're not
+in the system at all, 1 if they're in the system, and 2 if they're our
+friend.
+
+All we need to do to implement this is provide the C<relationship_by_email>
+action, and use it to fill in the output in the same way as we did when
+displaying a picture. Since C<person%40someco.com> is not the ID of a
+row in the user table, it will appear in the C<args> array:
+
+    use URI::Escape;
+    sub relationship_by_email :Exported {
+        my ($self, $r) = @_;
+        my $email = uri_unescape($r->{args}[0]);
+        $r->{content_type} = "text/plain";
+        my $user;
+        unless (($user) = Flox::User->search(email => $email)) {
+            $r->{content} = "0\n"; return;
         }
+
+        if ($r->{user}->is_friend($user)) { $r->{content} = "2\n"; return; };
+        $r->{content} = "1\n"; return;
     }
+
+=head3 Component-based Pages
+
+You're designing something like a portal site which has a number of
+components, all displaying different bits of information about different
+objects. You want to include the output of one Maypole request call while
+building up another. 
+
+B<Solution>: Use C<Maypole::Component>. By inheriting from this, you can
+call the C<component> method on the Maypole request object to make a 
+"sub-request". For instance, if you have a template
+
+    <DIV class="latestnews">
+    [% request.component("/news/latest_comp") %]
+    </DIV>
+
+    <DIV class="links">
+    [% request.component("/links/list_comp") %]
+    </DIV>
+
+then the results of calling the C</news/latest_comp> action and template
+will be inserted in the C<latestnews> DIV, and the results of calling
+C</links/list_comp> will be placed in the C<links> DIV. Naturally, you're
+responsible for exporting actions and creating templates which return 
+fragments of HTML suitable for inserting into the appropriate locations.
+
+Alternatively, if you've already got all the objects you need, you can
+probably just C<[% PROCESS %]> the templates directly.
+
+=head3 Bailing out with an error
+
+Maypole's error handling sucks. Something really bad has happened to the
+current request, and you want to stop processing now and tell the user about
+it.
+
+B<Solution>: Maypole's error handling sucks because you haven't written it
+yet. Maypole doesn't know what you want to do with an error, so it doesn't
+guess. One common thing to do is to display a template with an error message
+in it somewhere.
+
+Put this in your driver class:
+
+    sub error { 
+        my ($r, $message) = @_;
+        $r->{template} = "error";
+        $r->{template_args}{error} = $message;
+        return OK;
+    }
+
+And then have a F<custom/error> template like so:
+
+    [% PROCESS header %]
+    <H2> There was some kind of error... </H2>
+    <P>
+    I'm sorry, something went so badly wrong, we couldn't recover. This
+    may help:
+    </P>
+    <DIV CLASS="messages"> [% error %] </DIV>
+
+Now in your actions you can say things like this:
+
+    if (1 == 0) { return $r->error("Sky fell!") }
+
+This essentially uses the template switcheroo hack to always display the
+error template, while populating the template with an C<error> parameter.
+Since you C<return $r-E<gt>error>, this will terminate the processing
+of the current action.
+
+The really, really neat thing about this hack is that since C<error>
+returns C<OK>, you can even use it in your C<authenticate> routine:
+
+    sub authenticate {
+        my ($self, $r) = @_;
+        $r->get_user;
+        return $r->error("You do not exist. Go away.")
+            if $r->{user} and $r->{user}->status ne "real";
+        ...
+    }
+
+This will bail out processing the authentication, the model class, and
+everything, and just skip to displaying the error message. 
+
+Non-showstopper errors or other notifications are best handled by tacking a
+C<messages> template variable onto the request:
+
+    if ((localtime)[6] == 1) {
+        push @{$r->{template_args}{messages}}, "Warning: Today is Monday";
+    }
+
+Now F<custom/messages> can contain:
+
+    [% IF messages %]
+    <DIV class="messages">
+    <UL>
+        [% FOR message = messages %]
+           <LI> [% message %] </LI>
+        [% END %]
+    </UL>
+    </DIV>
+    [% END %]
+
+And you can display messages to your user by adding C<PROCESS messages> at an
+appropriate point in your template; you may also want to use a template
+switcheroo to ensure that you're displaying a page that has the messages box in
+it.
+
+=head2 Authentication hacks
+
+The next series of hacks deals with providing the concept of a "user" for
+a site, and what you do with one when you've got one.
+
+=head3 Logging In
+
+You need the concept of a "current user".
+
+B<Solution>: Use something like
+C<Maypole::Authentication::UserSessionCookie> to authenticate a user
+against a user class and store a current user object in the request
+object.
+
+C<UserSessionCookie> provides the C<get_user> method which tries to get
+a user object, either based on the cookie for an already authenticated
+session, or by comparing C<username> and C<password> form parameters
+against a C<user> table in the database. Its behaviour is highly
+customizable, so see the documentation, or the authentication paper at
+C<http://maypole.simon-cozens.org/docs/authentication.html> for examples.
+
+=head3 Pass-through login
+
+You want to intercept a request from a non-logged-in user and have
+them log in before sending them on their way to wherever they were
+originally going.
+
+B<Solution>:
+
+    sub authenticate {
+        my ($self, $r) = @_;
+        $r->get_user;
+        return OK if $r->{user};
+        # Force them to the login page.
+        $r->{template} = "login";
+        return OK;
+    }
+
+This will display the C<login> template, which should look something
+like this:
+
+    [% INCLUDE header %]
+
+      <h2> You need to log in </h2>
+
+    <DIV class="login">
+    [% IF login_error %]
+       <FONT COLOR="#FF0000"> [% login_error %] </FONT>
+    [% END %]
+      <FORM ACTION="/[% request.path%]" METHOD="post">
+    Username: 
+        <INPUT TYPE="text" NAME="[% config.auth.user_field || "user" %]"> <BR>
+    Password: <INPUT TYPE="password" NAME="password"> <BR>
+    <INPUT TYPE="submit">
+    </FORM>
+    </DIV>
+
+Notice that this request gets C<POST>ed back to wherever it came from, using
+C<request.path>. This is because if the user submits correct credentials,
+C<get_user> will now return a valid user object, and the request will pass
+through unhindered to the original URL.
+
+=head3 Logging Out
+
+Now your users are logged in, you want a way of having them log out
+again and taking the authentication cookie away from them, sending
+them back to the front page as an unprivileged user.
+
+B<Solution>: This action, on the user class, is probably overkill, but
+it does the job:
+
+    sub logout :Exported {
+        my ($class, $r) = @_;
+        # Remove the user from the request object
+        my $user = delete $r->{user};
+        # Destroy the session
+        tied(%{$r->{session}})->delete;
+        # Send a new cookie which expires the previous one
+        my $cookie = Apache::Cookie->new($r->{ar},
+            -name => $r->config->{auth}{cookie_name},
+            -value => undef,
+            -path => "/"
+            -expires => "-10m"
+        );
+        $cookie->bake();
+        # Template switcheroo
+        $r->template("frontpage");
+    }
+
+=head3 Multi-level Authentication
+
+You have both a global site access policy (for instance, requiring a
+user to be logged in except for certain pages) and a policy for
+particular tables. (Only allowing an admin to delete records in some
+tables, say, or not wanting people to get at the default set of methods
+provided by the model class.) 
+
+You don't know whether to override the global C<authenticate> method or
+provide one for each class.
+
+B<Solution>: Do both. Have a global C<authenticate> method which calls 
+a C<sub_authenticate> method based on the class:
+
+    sub authenticate {
+        ...
+        if ($r->{user}) {
+            return $r->model_class->sub_authenticate($r)
+                if $r->model_class->can("sub_authenticate");
+            return OK;
+        }
+        ...
+    }
+
+And now your C<sub_authenticate> methods can specify the policy for
+each table:
+
+    sub sub_authenticate { # Ensure we can only create, reject or accept
+        my ($self, $r) = @_;
+        return OK if $r->{action} =~ /^(issue|accept|reject|do_edit)$/;
+        return;
+    }
+
+=head2 Creating and editing hacks
+
+These hacks particularly deal with issues related to the C<do_edit>
+built-in action.
+
+=head3 Limiting data for display
+
+You want the user to be able to type in some text that you're later
+going to display on the site, but you don't want them to stick images in
+it, launch cross-site scripting attacks or otherwise insert messy HTML.
+
+B<Solution>: Use the C<CGI::Untaint::html> module to sanitize the HTML
+on input. C<CGI::Untaint::html> uses C<HTML::Sanitizer> to ensure that
+tags are properly closed and can restrict the use of certain tags and
+attributes to a pre-defined list.
+
+Simply replace:
+
+    App::Table->untaint_columns(
+        text      => [qw/name description/]
+    );
+
+with:
+
+    App::Table->untaint_columns(
+        html      => [qw/name description/]
+    );
+
+And incoming HTML will be checked and cleaned before it is written to
+the database.
+
+=head3 Getting data from external sources
+
+You want to supplement the data received from a form with additional
+data from another source.
+
+B<Solution>: Munge the contents of C< $r-E<gt>params > before jumping
+to the original C<do_edit> routine. For instance, in this method,
+we use a C<Net::Amazon> object to fill in some fields of a database row based
+on an ISBN:
+
+    sub create_from_isbn :Exported {
+       my ($self, $r) = @_;
+       my $response = $ua->search(asin => $r->{params}{isbn});
+       my ($prop) = $response->properties;
+       # Rewrite the CGI parameters with the ones from Amazon
+       @{$r->{params}{qw(title publisher author year)} =            
+           ($prop->title,
+           $prop->publisher,
+           (join "/", $prop->authors()),
+           $prop->year());
+       # And jump to the usual edit/create routine
+       $self->do_edit($r);
+    }
+
+The request will carry on as though it were a normal C<do_edit> POST, but
+with the additional fields we have provided.
+
+=head3 Uploading files and other data
+
+You want the user to be able to upload files to store in the database.
+
+B<Solution>: It's messy.
+
+First, we set up an upload form, in an ordinary dummy action. Here's
+the action:
+
+    sub upload_picture : Exported {}
+
+And here's the template:
+
+    <FORM action="/user/do_upload" enctype="multipart/form-data" method="POST">
+
+    <P> Please provide a picture in JPEG, PNG or GIF format:
+    </P>
+    <INPUT TYPE="file" NAME="picture">
+    <BR>
+    <INPUT TYPE="submit">
+    </FORM>
+
+(Although you'll probably want a bit more HTML around it than that.)
+
+Now we need to write the C<do_upload> action. At this point we have to get a
+little friendly with the front-end system. If we're using C<Apache::Request>,
+then the C<upload> method of the C<Apache::Request> object (which
+C<Apache::MVC> helpfully stores in C<$r-E<gt>{ar}>) will work for us:
+
+    sub do_upload :Exported {
+        my ($class, $r) = @_;
+        my $user = $r->{user};
+        my $upload = $r->{ar}->upload("picture");
+
+This returns a C<Apache::Upload> object, which we can query for its
+content type and a file handle from which we can read the data. It's
+also worth checking the image isn't going to be too massive before we
+try reading it and running out of memory, and that the content type is
+something we're prepared to deal with. 
+
+    if ($upload) {
+        my $ct = $upload->info("Content-type");
+        return $r->error("Unknown image file type $ct")
+            if $ct !~ m{image/(jpeg|gif|png)};
+        return $r->error("File too big! Maximum size is ".MAX_IMAGE_SIZE)
+            if $upload->size > MAX_IMAGE_SIZE;
+
+        my $fh = $upload->fh;
+        my $image = do { local $/; <$fh> };
+
+Now we can store the content type and data into our database, store it
+into a file, or whatever:
+
+        $r->{user}->photo_type($ct);
+        $r->{user}->photo($image);
+    }
+
+And finally, we use our familiar template switcheroo hack to get back to
+a useful page:
+
+        $r->objects([ $user ]);
+        $r->{template} = "view";
+    }
+
+Now, as we've mentioned, this only works because we're getting familiar with
+C<Apache::Request> and its C<Apache::Upload> objects. If we're planning to use
+C<CGI::Maypole> instead, or want to write our application in a generic way so
+that it'll work regardless of front-end, then we need to replace the C<upload>
+call with an equivalent which uses the C<CGI> module to get the upload data.
+This is convoluted and horrific and we're not going to show it here, but it's
+possible.
+
+Combine with the "Displaying pictures" hack above for a happy time.