Limiting announce Application Data

[faragher]

The maximum Application Data field in an announce is 317 bytes. This is a practical MDU limit, not a specification limit.

When working with limited memory, this leads to one of two options, in my opinion.

First is a fully compliant system where the packet is contained monolithically in 512 bytes. It has the advantage of being able to fit any packet and wasting only 12 bytes (which could likely be useful for metadata for processing). The disadvantage is needing to work with the data in-situ and increased programming complexity.

Second is limiting the App_Data field to 256 bytes, making the block easy to store as its own variable. The disadvantage is this doesn't scale across all variables as many of the hashes are 10 bytes or other arbitrary sizes.

Now, none of this really means that much if you're not interested in keeping memory allocations to powers of two, but I had the thought while documenting and implementing the format, and wanted feedback.