Completing an offer and delivering it ran with no lock held across the two,
while a sender could send DELETE at any point and withdraw ran spool.Remove
without looking at the offer's state. A withdrawal landing in that window
deleted the staged bytes out from under the copy: delivery failed with
"open spooled file: no such file or directory", the transfer was recorded as
failed, and the payload was gone although the sender had seen its upload
succeed.
A completed offer is no longer withdrawable, and publishing or discarding one
offer's payloads now serialises on a per-offer lock the two sinks share, so a
removal waits for a delivery in flight instead of racing it. deliver() drops
the spool as its last step and reaches it through removeLocked, since the
lock it would otherwise retake is the one it already holds.
Android cannot address the user's shared storage by path, so a received
file had to land in app-private storage and be copied out afterwards,
needing twice the space of the transfer.
Put the staging area behind a Sink interface the receiver writes every
payload through. The filesystem spool implements it unchanged and stays
the default; a platform that cannot be addressed by path implements the
gomobile-bound half instead and stages payloads wherever it can reach.
The writer reports its own total rather than returning a written count:
gomobile copies a []byte argument into a fresh Java array and carries no
count back out.
A failed delivery now drops the staged payloads. The filesystem spool
swept them up on its next pass, but a sink holding entries the engine
cannot address by path has no such fallback.
Zoltán Papp