[Jmap] Integrity checking of blobs

[Eliza Velasquez <[e-mail]>]

Hello jmap,

While implementing a JMAP client which is designed to download and
maintain a cache of every message file on the server, I was somewhat
surprised to discover that there appears to be nothing built into the
specification to determine a checksum for a given blob ID. I assume JMAP
mail servers or reverse proxies they sit behind might implement the HTTP
Digest header for a blob GET request, but that would necessitate that a
client perform a large number of GET requests for every message in its
cache, and the design of JMAP seems built around avoiding this sort of
thing.

I was expecting something along the lines of a `Blob/get' method which
can return a sha256 sum of a given blob ID. Is this something that I
missed while reading the spec, or is this something that would have to
be added to a new RFC? Also, is there any interest in the community for
such a feature?

-- 
Eliza