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).
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 value). 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.
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.
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.
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 host" (where 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.
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.
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 hostname" (where 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 hostname". Clicking this button will lead to the entire mirror entry being removed, specification and host lists alike.
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.
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, 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.
Randy J. Ray <email@example.com>