BFGMiner (at least) will also send mining.suggest_target("hex target") upon connection, if the user has a preferred target.
Why would it do this?
There is already mining.suggest_difficulty(difficulty)
No, there isn't.
Nothing implements this, and it isn't documented anywhere.
Using a target fixes the inherent problems with using difficulty as a Number:
- There is no agreement over which difficulty measurement is to be used. The official spec says bdiff; BTCGuild uses pdiff; various scrypt pools use Ldiff
- Some common targets (such as pdiff 1) cannot be accurately conveyed without huge data sizes
- Implementing conversion to/from difficulty accurately requires a bignum library, so often (eg, *gminer) it is just approximated.
Seems like a valid concern to me since it was described over a year ago and yours isn't documented anywhere except as part of your code. Of course you're free to implement whatever you want on top of stratum. Cgminer happily works with any arbitrary diffs and does not have problems with the accuracy of the shares it returns in response, using true diff 1 as the base for all stratum operations. I wasn't aware there was any controversy about the move to true diff1; that old simplification only affected getwork. Since work in stratum is even
defined in terms of difficulty, it makes even less sense to then request a difficulty as a target. I don't see a problem with you using it for your software and your pool but I can't see why it should be seen as part of the stratum spec.