# -*- text -*-

=head1 NAME

edit_db.pl - A CGI/HTTP based editor for the Release Manager data tables


edit_db.pl is invoked as a CGI script only


I got really tired really quickly of making all the changes to the mirror
database tables using SQL*Net. This tool is the result. It also contains
a lot of Perl programming tricks that I've picked up over the years from
various Perl personalities I've had the fortune (good and bad) to meet.

When the tool is invoked, it forks and becomes a daemon process. This
process in turn starts up a mini-HTTP listener on a random port. It also
devises a session identifier using several random elements. This session
ID and the URL to the new HTTP listener are sent back to the browser as a
HTTP redirect request. Then things get interesting.

The listener opens a DBI connection to the database that holds the tables
for the mirror specifications and mirror host-lists. It fills internal
tables with the current state of the DBMS tables, and keeps the DBI
connection active throughout the lifespan of the process. A main page is
then presented, with all the data laid out in a series of forms, with a
range of submit-style buttons for enacting changes or switching to different
screens. All form actions are directed back at the currently-running server.
As such, all the Perl code to handle the requests is already in memory
(though not all of the code is compiled initially; delayed-loading is used
to reduce overhead and startup time).

=head2 The Main Page

At present, the main page is one large sequence of mirror-blocks (a
mirror-block is defined at that grouping from one horizontal ruling line
to the next line, and encompasses the table of specification values, the
list of hosts that comprise the pool, several buttons, and a link back to
the top of the page). It is a good candidate for implementation as a 
frameset, with a main bar that provides the global buttons (exit, add new,
etc.) and links to bring up a specific mirror pool in the other frame. But
I didn't get that far.

The page starts with a title (so that you know you're running the right
application) and a list of all the mirror groups currently in the database.
Each of this is expressed as a hyperlink. Clicking on one takes the browser
to the top of that mirror-block. Following this list of links, are two buttons.
The first takes the user to the screen for adding a new specification. The
second exits the editor (hereafter referred to as "MDE").

From this point, there is a sequence of mirror-blocks (as defined above), one
for each host in the current database. The basic structure of these blocks
is as follows:

    A line with the mirror name, and (currently unused) details
    A delete button affecting the entire set of mirror data
    A button to exit MDE
    A table of specification data:
        Each line shows the field name, and the value.
        Because the release manager uses variables and does
        variable expansion, the expanded value is shown below
        the entry field (but only if it differs from the real
    A line with two buttons:
        The leftmost enacts any changes to fields made in the table
        The rightmost deletes the mirror specification completely
    A second table, this one listing hosts in the mirror pool:
        Each table line shows the hostname, port (if not 80) and
        has a delete button.
        At the bottom of the table is a button to add more hosts
        to the pool. Even those "mirror groups" that consist of
        only one host have the one host entered here.
    Lastly, a link back to the top of the page.

At the end of the main page is a simple page-footer with the current date
and time, and the revision of the tool that is executing.       

=head2 Adding a New Mirror Group

Selecting the "Create a New Mirror Pool" button takes the user to a simple
screen with one entry field and a button to enact the addition of data.
The name of the new mirror pool is entered into the blank provided. When
the button is pressed, the mirror specification is created with most of
the fields filled in with default values. The browser is taken back to the
main screen, positioned at the top of the mirror-block for the newly-added
group. At this point, the user can edit any of the fields that stray from
the defaults (such as the HTTP_AUTH_PASSWD, which is not meant to have a
usable default value).

If no new mirror group is to be added after all, there is a link just under
the page title that will return the browser to the main page without making
any DBMS calls.

=head2 Adding Hosts for the New Group

When a new mirror group is created, there are no hosts automatically added
to the host list. This is because the hosts may have numbers in their
names, to distinguish different members of the same mirror pool. Clicking
on the "add hosts" button takes the user to a screen on which up to four
hosts may be added at a time. There are four rows of entry fields. The
fields are for the hostname, port (if different than the default of 80),
and optionally for the physical hostname (example: dmowebdb.corp.hp.com
has a physical hostname of hpcc518.corp.hp.com).

When the data is all entered, clicking on the "Add These Hosts" button
causes the data to be committed to the DBMS. The user is then taken back
to the main page, with the browser positioned at that mirror-block. As with
the other add-data page, there is an escape link at the top of the page to
return to the main page without affecting the database.

=head2 Editing an Existing Mirror Specification

The editing of existing data is done in-place on the main page. Each of the
mirror-blocks displays the current data for a given specification in editable
entry fields. Changes may be made to as many fields as desired, for a single
mirror-block. When editing is complete, clicking on the "Make changes to
I<host>" (where I<host> is the particular mirror pool) button will commit the
changes. The browser will return to the main page automatically, positioned
at the top of the mirror-block that was just edited.

It is not possible to make changes to more than one mirror-block at a time.
The button clicked is used by the editor to determine which set of entries
should be examined for changes. There is no confirmation screen for simple
edits; if an error is made, it is simple to go back and correct it.

=head2 Editing/Changing Hosts in a Mirror Pool

There is not currently any means by which to edit or change mirror pool host
data. The only approach is to delete the host specification (using the
"Delete" button beside it) in question, then go to the "Adding Hosts" page
for that mirror group and re-entering the newer information.

=head2 Deleting Information

Deleting information, whether an individual host from the list of mirrors
in the pool or an entire mirror specification, is the only truly destructive
operation that MDE provides. Because of this, each of these operations
has a confirmation screen before actually making the changes to the DBMS.

Each of the hosts that comprise the mirror pool has a button on the extreme
right labeled "Delete this mirror". Clicking on it will lead to the removal
of that one host from the mirror pool host list for that mirror group.

At the end of the table of mirror spec values there is a button labeled
"Delete specs for I<hostname>" (where I<hostname> is the mirror group in
question). Clicking on this button will lead to the deletion of the
specifications, but not the host list.

At the top of each mirror-block is a button labeled "Completely delete
I<hostname>". Clicking this button will lead to the entire mirror entry
being removed, specification and host lists alike.

=head2 Exiting

Because the default timeout period is five minutes, the person running this
tool may not want to simply leave the server running until the timeout
triggers. To this end, there is a button labeled "Exit MDE" at the top of
each mirror-block. Clicking this button causes the listener to send one final
page to the browser, then immediately exit.

Note that if the timeout is reached, the browser does not reflect this. The
only indication is that clicking on a link or button returns a "server not
found" error.

=head1 CAVEATS

Tons. But I'm almost certain that this tool will not accidentally destroy
any data. If the person running it hits the wrong button, that's different.
But all the destructive operations have confirmation screens, so the
danger of that should be minimal.

There should also be a better way of tuning certain hard-coded parameters,
such as what DBMS is being connected to, what the timeout between requests
should be, etc.

Lastly, B<and very importantly>, most errors result in the immediate exit
of the WWW server. This is not accidental, this is intentional. The functions
being performed by this tool are fairly sensitive, and anything suspect
needs to be treated as a potential crack attempt. From a browser, it is fairly
trivial to re-start an edit session if a simple mistake causes the termination
of an existing session.

=head1 SEE ALSO

L<HTTP::Daemon>, L<CGI>, L<DBI>

=head1 AUTHOR

Randy J. Ray <randyr@nafohq.hp.com>