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Hack 98 Queue API Calls

How to work around eBay's API
call limit.

Developers working under the Individual
license, explained at the beginning of this chapter, have a strict
limit as to the number of eBay calls they are allowed to make each
day.

Provided that your application uses the API efficiently, as described
in [Hack #99], this
shouldn't pose a problem. And as the theory goes,
anyone needing more than 50 API calls per day is probably running a
business on eBay and can justify one of the higher developer tiers.

Consider the following scenario. As a seller, you might have 55
separate auctions ending on a single day. If you use the script in
[Hack #87], you can retrieve sufficient
data for all your recently closed auctions with only a single
GetSellerList call. But if you use the script in
[Hack #90], you'll
need a minimum of 56 calls: one to retrieve the list of auctions, and
55 more to retrieve the individual auction descriptions. All you need
is to run this single script just once to exceed your API quota for
the day.

If you feel that exceeding your quota is a possibility, you can take
some extra steps to ensure both that your software understands this
limit, and that if your software reaches the limit, it can queue
additional API calls and complete its work the next day.

The first step is to begin recording your
API
call usage. Probably the best way to do this is by adding a counter
to the call_api subroutine in the
ebay.pl script listed at the beginning of this
chapter. The counter code might look something like this:

open (INFILE,"$localdir/apiquota.txt");
my %count = map { split(/,/, $_) } <INFILE>;     [1]
close (INFILE);
chomp %count;
my ($today, $dummy) = split(/ /, &formatdate(time));
$count{$today}++;     [2]
open (OUTFILE,">$localdir/apiquota.txt");
while (($date,$count) = each %count) {
print OUTFILE "$date,$count\n";     [3]
}
close (OUTFILE);
if ( $count{$today} > 50 ) {     [4]
. . . 
# queue this API call for later processing
. . . 
return undef;
exit;
}

Here's how it works. The script retrieves the counts
(line [1]) for all recorded days from the
apiquota.txt file (located in the directory
specified by $localdir in your
config.pl script). It then adds
1 to today's count (line [2]) and writes the updated data back to the file
(line [3]).

Finally, if today's count is above
50 (line [4]), it runs
some code you provide (sorry, I'm not going to do
all the work for you!) to queue the next API
call. You could, for example, set up a temporary cron job, as
described in [Hack #17], to run another
script that resubmits queued API calls.

If nothing else, this nifty snippet of code records accounting data
for your API usage. After a few days of using the API, your
apiquota.txt file will look something like this:

2005-07-11,3
2005-07-12,11
2005-07-13,0
2005-07-14,60
2005-07-15,4

This shows that on July 14, 2005, 60 calls were made, while only 4
calls were made the next day. (Note that since the data is
manipulated as a hash by this script, the records
won't necessarily be recorded in order in the
file.)