6.17 Using Slice Checksums

As described in Section 4.21, the Slice compilers can optionally generate check­sums of Slice definitions. For slice2cpp, the ‑‑checksum option causes the compiler to generate code in each C++ source file that accumulates checksums in a global map. A copy of this map can be obtained by calling a function defined in the header file Ice/SliceChecksums.h:

namespace Ice {
    Ice::SliceChecksumDict sliceChecksums();
}

In order to verify a server’s checksums, a client could simply compare the dictio­naries using the equality operator. However, this is not feasible if it is possible that the server might be linked with more Slice definitions than the client. A more general solution is to iterate over the local checksums as demonstrated below:

Ice::SliceChecksumDict serverChecksums = ...
Ice::SliceChecksumDict localChecksums = Ice::sliceChecksums();

for (Ice::SliceChecksumDict::const_iterator
     p = localChecksums.begin();
     p != localChecksums.end(); ++p) {

    Ice::SliceChecksumDict::const_iterator q
        = serverChecksums.find(p‑>first);
    if (q == serverChecksums.end()) {
        // No match found for type id!
    } else if (p‑>second != q‑>second) {
        // 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.