Maypole::Manual::Flox(User Contributed Perl DocumentatMaypole::Manual::Flox(3)NAMEMaypole::Manual::Flox - Flox: A Free Social Networking Site
DESCRIPTION
Friendster, Tribe, and now Google's Orkut - it seems like in early
2004, everyone wanted to be a social networking site. At the time, I
was too busy to be a social networking site, as I was working on my own
project at the time - Maypole. However, I realised that if I could
implement a social networking system using Maypole, then Maypole could
probably do anything.
I'd already decided there was room for a free, open-source networking
site, and then Peter Sergeant came up with the hook - localizing it to
universities and societies, and tying in meet-ups with restaurant
bookings. I called it Flox, partially because it flocks people together
and partially because it's localised for my home town of Oxford and its
university student population.
Flox is still in, uh, flux, but it does the essentials. We're going to
see how it was put together, and how the techniques shown in the
Request Cookbook can help to create a sophisticated web application. Of
course, I didn't have this manual available at the time, so it took a
bit longer than it should have done...
Mapping the concepts
Any Maypole application should start with two things: a database
schema, and some idea of what the pages involved are going to look
like. Usually, these pages will be displaying or editing some element
of the database, so these two concepts should come hand in hand.
When I started looking at social networking sites, I began by
identifying the concepts which were going to make up the tables of the
application. At its most basic, a site like Orkut or Flox has two
distinct concepts: a user, and a connection between two users.
Additionally, there's the idea of an invitation to a new user, which
can be extended, accepted, declined or ignored. These three will make
up the key tables; there are an extra two tables in Flox, but they're
essentially enumerations that are a bit easier to edit: each user has
an affiliation to a particular college or department, and a status in
the university. (Undergraduate, graduate, and so on.)
For this first run-through, we're going to ignore the ideas of
societies and communities, and end up with a schema like so:
CREATE TABLE user (
id int not null auto_increment primary key,
first_name varchar(50),
last_name varchar(50),
email varchar(255),
profile text,
password varchar(255),
affiliation int,
unistatus int,
status ENUM("real", "invitee"),
photo blob,
photo_type varchar(30)
);
CREATE TABLE connection (
id int not null auto_increment primary key,
from_user int,
to_user int,
status ENUM("offered", "confirmed")
);
CREATE TABLE invitation (
id char(32) not null primary key,
issuer int,
recipient int,
expires date
);
Plus the definition of our two auxiliary tables:
CREATE TABLE affiliation (
id int not null auto_increment primary key,
name varchar(255)
);
CREATE TABLE unistatus (
id int not null auto_increment primary key,
name varchar(255)
);
Notice that, for simplicity, invitations and friendship connections are
quite similar: they are extended from one user to another. This means
that people who haven't accepted an invite yet still have a place in
the user table, with a different "status". Similarly, a connection
between users can be offered, and when it is accepted, its status is
changed to "confirmed" and a reciprocal relationship put in place.
We also have some idea, based on what we want to happen, of what pages
and actions we're going to define. Leaving the user aside for the
moment, we want an action which extends an invitation from the current
user to a new user. We want a page the new user can go to in order to
accept that invitation. Similarly, we want an action which offers a
friendship connection to an existing user, and a page the user can go
to to accept or reject it. This gives us five pages so far:
invitation/issue
invitation/accept
user/befriend
connection/accept
connection/reject
Notice that the "befriend" action is performed on a user, not a
connection. This is distinct from "invitation/issue" because when
befriending, we have a real user on the system that we want to do
something to. This makes sense if you think of it in terms of object
oriented programming - we could say
Flox::Connection->create(to => $user)
but it's clearer to say
$user->befriend
Similarly, we could say
Flox::User->create({ ... })->issue_invitation_to
but it's clearer to say
Flox::Invitation->issue( to => Flox::User->create({ ... }) )
because it more accurately reflects the principal subject and object of
these actions.
Returning to look at the user class, we want to be able to view a
user's profile, edit one's own profile, set up the profile for the
first time, upload pictures and display pictures. We also need to
handle the concepts of logging in and logging out.
As usual, though, we'll start with a handler class which sets up the
database:
package Flox;
use Maypole::Application;
Flox->setup("dbi:mysql:flox");
Flox->config->display_tables([qw[user invitation connection]]);
1;
Very simple, as these things are meant to be. Now let's build on it.
Users and Authentication
The concept of a current user is absolutely critical in a site like
Flox; it represents "me", the viewer of the page, as the site explores
the connections in my world. We've described the authentication hacks
briefly in the Request Cookbook, but now it's time to go into a little
more detail about how user handling is done.
We also want to be able to refer to the current user from the
templates, so we use the overridable "additional_data" method in the
driver class to give us a "my" template variable:
sub additional_data {
my $r = shift; $r->template_args->{my} = $r->user;
}
I've called it "my" rather than "me" because we it lets us check "[%
my.name %]", and so on.
Viewing a user
The first page that a user will see after logging in will be their own
profile, so in order to speed development, we'll start by getting a
"user/view" page up.
The only difference from a programming point of view between this
action and the default "view" action is that, if no user ID is given,
then we want to view "me", the current user. Remembering that the
default view action does nothing, our "Flox::User::view" action only
needs to do nothing plus ensure it has a user in the "objects" slot,
putting "$r->{user}" in there if not:
sub view :Exported {
my ($class, $r) = @_;
$r->objects([ $r->user ]) unless @{ $r->objects || [] };
}
Maypole, unfortunately, is very good at making programming boring. The
downside of having to write very little code at all is that we now have
to spend most of our time writing nice HTML for the templates.
Pictures of Users
The next stage is viewing the user's photo. Assuming we've got the
photo stored in the database already (which is a reasonable assumption
for the moment since we don't have a way to upload a photo quite yet)
then we can use a variation of the "Displaying pictures" hack from the
Request Cookbook:
sub view_picture :Exported {
my ($self, $r) = @_;
my $user = $r->objects->[0] || $r->user;
if ($r->content_type($user->photo_type)) {
$r->output($user->photo);
} else {
# Read no-photo photo
$r->content_type("image/png");
$r->output(slurp_file("images/no-photo.png"));
}
}
We begin by getting a user object, just like in the "view" action:
either the user whose ID was passed in on the URL, or the current user.
Then we check if a "photo_type" has been set in this user's record. If
so, then we'll use that as the content type for this request, and the
data in the "photo" attribute as the data to send out. The trick here
is that setting "$r->{output}" overrides the whole view class
processing and allows us to write the content out directly.
In our template, we can now say
<IMG SRC="[%base%]/user/view_picture/[% user.id %]">
and the appropriate user's mugshot will appear.
However, if we're throwing big chunks of data around like "photo", it's
now worth optimizing the "User" class to ensure that only pertitent
data is fetched by default, and "photo" and friends are only fetched on
demand. The "lazy population" section of Class::DBI's man page explains
how to group the columns by usage so that we can optimize fetches:
Flox::User->columns(Primary => qw/id/);
Flox::User->columns(Essential => qw/status/);
Flox::User->columns(Helpful => qw/ first_name last_name email password/)
Flox::User->columns(Display => qw/ profile affiliation unistatus /);
Flox::User->columns(Photo => qw/ photo photo_type /);
This means that the status and ID columns will always be retrieved when
we deal with a user; next, any one of the name, email or password
columns will cause that group of data to be retrieved; if we go on to
display more information about a user, we also load up the profile,
affiliation and university status; finally, if we're throwing around
photos, then we load in the photo type and photo data.
These groupings are somewhat arbitrary, and there needs to be a lot of
profiling to determine the most efficient groupings of columns to load,
but they demonstrate one principle about working in Maypole: this is
the first time in dealing with Maypole that we've had to explicitly
list the columns of a table, but Maypole has so far Just Worked.
There's a difference, though, between Maypole just working and Maypole
working well, and if you want to optimize your application, then you
need to start putting in the code to do that. The beauty of Maypole is
that you can do as much or as little of such optimization as you want
or need.
So now we can view users and their photos. It's time to allow the users
to edit their profiles and upload a new photo.
Editing user profiles
I introduced Flox to a bunch of friends and told them to be as ruthless
as possible in finding bugs and trying to break it. And break it they
did; within an hour the screens were thoroughly messed up as users had
nasty HTML tags in their profiles, names, email addresses and so on.
This spawned another hack in the request cookbook: "Limiting data for
display". I changed the untaint columns to use "html" untainting, and
all was better:
Flox::User->untaint_columns(
html => [qw/first_name last_name profile/],
printable => [qw/password/],
integer => [qw/affiliation unistatus /],
email => [qw/email/]
);
The next stage was the ability to upload a photo. We unleash the
"Uploading files" recipe, with an additional check to make sure the
photo is of a sensible size:
use constant MAX_IMAGE_SIZE => 512 * 1024;
sub do_upload :Exported {
my ($class, $r) = @_;
my $user = $r->user;
my $upload = $r->ar->upload("picture");
if ($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> };
use Image::Size;
my ($x, $y) = imgsize(\$image);
return $r->error("Image too big! ($x, $y) Maximum size is 350x350")
if $y > 350 or $x > 350;
$r->user->photo_type($ct);
$r->user->photo($image);
}
$r->objects([ $user ]);
$r->template("view");
}
Now we've gone as far as we want to go about user editing at the
moment. Let's have a look at the real meat of a social networking
site: getting other people involved, and registering connections
between users.
Invitations
We need to do two things to make invitations work: first provide a way
to issue an invitation, and then provide a way to accept it. Since what
we're doing in issuing an invitation is essentially creating a new one,
we'll use our usual practice of having a page to display the form to
offer an invitation, and then use a "do_edit" method to actually do the
work. So our "issue" method is just an empty action:
sub issue :Exported {}
and the template proceeds as normal:
[% PROCESS header %]
<h2> Invite a friend </h2>
<FORM ACTION="[%base%]/invitation/do_edit/" METHOD="post">
<TABLE>
Now we use the "Catching errors in a form" recipe from the Request
Cookbook and write our form template:
<TR><TD>
First name: <INPUT TYPE="text" NAME="forename"
VALUE="[%request.params.forename%]">
</TD>
<TD>
Last name: <INPUT TYPE="text" NAME="surname"
VALUE="[%request.params.surname%]">
</TD></TR>
[% IF errors.forename OR errors.surname %]
<TR>
<TD><SPAN class="error">[% errors.forename %]</SPAN> </TD>
<TD><SPAN class="error">[% errors.surname %]</SPAN> </TD>
</TR>
[% END %]
<TR>
...
Now we need to work on the "do_edit" action. This has to validate the
form parameters, create the invited user, create the row in the
"invitation" table, and send an email to the new user asking them to
join.
We'd normally use "create_from_cgi" to do the first two stages, but
this time we handle the untainting manually, because there are a
surprising number of things we need to check before we actually do the
create. So here's the untainting of the parameters:
sub do_edit :Exported {
my ($self, $r) = @_;
my $h = CGI::Untaint->new(%{$r->params});
my (%errors, %ex);
for (qw( email forename surname )) {
$ex{$_} = $h->extract(
"-as_".($_ eq "email" ? "email" : "printable") => $_
) or $errors{$_} = $h->error;
}
Next, we do the usual dance of throwing the user back at the form in
case of errors:
if (keys %errors) {
$r->template_args->{message} =
"There was something wrong with that...";
$r->template_args->{errors} = \%errors;
$r->template("issue");
return;
}
We've introduced a new template variable here, "message", which we'll
use to display any important messages to the user.
The first check we need to do is whether or not we already have a user
with that email address. If we have, and they're a real user, then we
abort the invite progress and instead redirect them to viewing that
user's profile.
my ($user) = Flox::User->search({ email => $ex{email} });
if ($user) {
if ($user->status eq "real") {
$r->template_args->{message} =
"That user already seems to exist on Flox. ".
"Is this the one you meant?";
$self->redirect_to_user($r, $user);
}
Where "redirect_to_user" looks like this:
sub redirect_to_user {
my ($self, $r, $user) = @_;
$r->objects([ $user ]);
$r->template("view");
$r->model_class("Flox::User"); # Naughty.
}
This is, as the comment quite rightly points out, naughty. We're
currently doing a "/invitation/do_edit/" and we want to turn this into
a "/user/view/xxx", changing the table, template and arguments all at
once. To do this, we have to change the Maypole request object's idea
of the model class, since this determines where to look for the
template: if we didn't, we'd end up with "invitation/view" instead of
"user/view".
Ideally, we'd do this with a Apache redirect, but we want to get that
"message" in there as well, so this will have to do. This isn't good
practice; we put it into a subroutine so that we can fix it up if we
find a better way to do it.
Anyway back in the "do_edit" action, this is what we should do if a
user already exists on the system and has accepted an invite already.
What if we're trying to invite a user but someone else has invited them
first and they haven't replied yet?
} else {
# Put it back to the form
$r->template_args->{message} =
"That user has already been invited; " .
"please wait for them to accept";
$r->template("issue");
}
return;
}
Race conditions suck.
Okay. Now we know that the user doesn't exist, and so can create the
new one:
my $new_user = Flox::User->create({
email => $ex{email},
first_name => $ex{forename},
last_name => $ex{surname},
status => "invitee"
});
We want to give the invitee a URL that they can go to in order to
accept the invite. Now we don't just want the IDs of our invites to be
sequential, since someone could get one invite, and then guess the rest
of the invite codes. We provide a relatively secure MD5 hash as the
invite ID:
my $random = md5_hex(time.(0+{}).$$.rand);
For additional security, we're going to have the URL in the form
"/invitation/accept/id/from_id/to_id", encoding the user ids of the two
users. Now we can send email to the invitee to ask them to visit that
URL:
my $newid = $new_user->id;
my $myid = $r->user->id;
_send_mail(to => $ex{email},
url => "$random/$myid/$newid",
user => $r->user);
I'm not going to show the "_send_mail" routine, since it's boring. We
haven't actually created the "Invitation" object yet, so let's do that
now.
Flox::Invitation->create({
id => $random,
issuer => $r->user,
recipient => $new_user,
expires => Time::Piece->new(time + LIFETIME)->datetime
});
You can also imagine a daily cron job that cleans up the "Invitation"
table looking for invitations that ever got replied to within their
lifetime:
($_->expires > localtime && $_->delete)
for Flox::Invitation->retrieve_all;
Notice that we don't check whether the ID is already used. We could,
but, you know, if MD5 sums start colliding, we have much bigger
problems on our hands.
Anyway, now we've got the invitation created, we can go back to whence
we came: viewing the original user:
$self->redirect_to_user($r, $r->user);
Now our invitee has an email, and goes click on the URL. What happens?
XXX
Friendship Connections
XXX
Links
The source for Flox is available at
http://cvs.simon-cozens.org/viewcvs.cgi/flox <http://cvs.simon-
cozens.org/viewcvs.cgi/flox>.
Contents, Next The Maypole iBuySpy Portal, Previous Maypole Request
Hacking Cookbook
perl v5.14.1 2007-08-03 Maypole::Manual::Flox(3)
