22.16 Using Slice Checksums

As described in Section 4.21, the Slice compilers can optionally generate checksums of Slice definitions. For slice2py, the ‑‑checksum option causes the compiler to generate code that adds checksums to the dictionary Ice.sliceChecksums. The checksums are installed automatically when the Python code is first imported; no action is required by the application.

In order to verify a server’s checksums, a client could simply compare the dictionaries using the 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:

serverChecksums = ...
for i in Ice.sliceChecksums:
    if not serverChecksums.has_key(i):
        # No match found for type id!
    elif Ice.sliceChecksums[i] != serverChecksums[i]:
        # 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.