CouchCocoa attempts to provide progress information about replications, so the
app can display a progress bar or similar UI, or at least indicate when
replication has completed. This is surprisingly difficult. I got it working
well with regular CouchDB, but now I’m re-opening the can of worms because
BigCouch doesn’t use integral sequence numbers and so the status messages
provided by the replicator contain binary goop, for example:
“status”: "Processed
<<\"3264-g1AAAADzeJzLYWBgYMlgTmFQSElKzi9KdUhJMtLLTS3KLElMT9VLzskvTUnMK9HLSy3JAapkSmRIsv___39WEgMDsyGqNhM82pIcgGRSPUynDvEW5rEASYYGIAXUvB-s24F4eyG6D0B0Q-xWzgIA8ZZODg\">>
/
<<\"3264-g1AAAADzeJzLYWBgYMlgTmFQSElKzi9KdUhJMtLLTS3KLElMT9VLzskvTUnMK9HLSy3JAapkSmRIsv___39WEgMDsyGqNkM82pIcgGRSPUynDvEW5rEASYYGIAXUvB-s2wFVtwlB3QcguiF2K2cBAO-bTgs\">>
changes”
I’ve updated my parser to be able to tweeze out the two binary blobs, and I
figured I could at least compare them for string equality to detect when the
last change is processed. Unfortunately this doesn’t appear to work. The
example above is the last status message I got in a pull from Cloudant;
apparently it’s completed, because nothing else has been copied over in the 15
minutes since, but the two blobs are not exactly equal. (They are _almost_
equal, up to the last 25 or so characters.)
The unfortunate result is that in the iOS GrocerySync app, the replication
progress bar gets stuck and never goes away.
I realize that these blobs are probably deliberately opaque and their format
Subject To Change Without Notice, but it would be helpful if I had some kind of
heuristic about their current format that would at least let me detect when a
replication has ended. Any suggestions?
—Jens
