Using Slice Checksums in PHP
The Slice compilers can optionally generate checksums of Slice definitions. For slice2php
, the --checksum
option causes the compiler to generate code that adds checksums to the global array Ice_sliceChecksums
. The checksums are installed automatically when the PHP code is first parsed; no action is required by the application.
In order to verify a server's checksums, a client could simply compare the two array objects using a comparison operator. However, this is not feasible if it is possible that the server might return a superset of the client's checksums. A more general solution is to iterate over the local checksums as demonstrated below:
global $Ice_sliceChecksums; $serverChecksums = ... foreach($Ice_sliceChecksums as $key => $value) { if(!isset($serverChecksums[$key])) // No match found for type id! elseif($Ice_sliceChecksums[$key] != $serverChecksums[$key]) // Checksum mismatch! }
In this example, the client first verifies that the server's dictionary contains an entry for each Slice type ID, and then it proceeds to compare the checksums.