Using Slice Checksums in Java
The Slice compilers can optionally generate checksums of Slice definitions. For slice2java, the --checksum option causes the compiler to generate a new Java class that adds checksums to a static map member. Assuming we supplied the option --checksum Checksums to slice2java, the generated class Checksums.java looks like this:
public class Checksums {
public static java.util.Map<String, String> checksums;
}
The read-only map checksums is initialized automatically prior to first use; no action is required by the application.
In order to verify a server's checksums, a client could simply compare the dictionaries using the equals method. 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:
java.util.Map<String, String> serverChecksums = ...
java.util.Iterator<java.util.Map.Entry<String, String>> i =
Checksums.checksums.entrySet().iterator();
while(i.hasNext()) {
java.util.Map.Entry<String, String> e = i.next();
String id = e.getKey();
String checksum = e.getValue();
String serverChecksum = serverChecksums.get(id);
if (serverChecksum == null) {
// No match found for type id!
} else if (!checksum.equals(serverChecksum)) {
// 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.