Add checksums to detect data corruption

[magro]

After reading this report about S3's outage in 2008 I think it makes sense to add data corruption checks to eventuate. The report says

We've now determined that message corruption was the cause of the server-to-server communication problems. More specifically, we found that there were a handful of messages on Sunday morning that had a single bit corrupted such that the message was still intelligible, but the system state information was incorrect. We use MD5 checksums throughout the system, for example, to prevent, detect, and recover from corruption that can occur during receipt, storage, and retrieval of customers' objects. However, we didn't have the same protection in place to detect whether this particular internal state information had been corrupted. As a result, when the corruption occurred, we didn't detect it and it spread throughout the system causing the symptoms described above. We hadn't encountered server-to-server communication issues of this scale before and, as a result, it took some time during the event to diagnose and recover from it.

eventuate could check if

• stored / replayed events got corrupted by adding a checksum to the stored event or event payload
• replicated events got corrupted by adding a checksum to the serialized / transmitted data