File drop needs a local filesystem to deliver into and a receiver it can bind,
so wasm supports neither and never sets a manager. The code still linked in,
because the Engine reached filedrop through an untagged field, and with it the
net/http server and client. That put the wasm binary 0.97MiB over the 60MB
budget, on a main that had 0.34MiB of headroom left.
Split the feature on the js tag: the logic file and the OS dialer become !js,
a js no-op carries the start, stop and rebind entry points the engine calls on
its lifecycle paths, and a build-tagged alias types the manager so engine.go
and connect.go stay untagged and lose the import. iOS keeps the full feature:
the logic file is !js and the iOS dialer stays behind the ios tag.
Drops the wasm binary to 59.89MiB, with no filedrop symbol left in it.
The receiver's host listener is a socket of the Network Extension, so the
SYN-ACK of an accepted connection followed the extension's own-traffic
bypass onto the physical interface and the sender never got an answer.
Bind the listeners to the tunnel interface index the same way the dial
already is; accepted sockets inherit the scope. Other platforms pass a
nil control and keep the current behavior.
A Network Extension's own unscoped sockets bypass its tunnel and leave on
the physical interface, so the file drop dial to a peer address died on
the local network. Bind the socket to the overlay address and the tunnel
interface index, the same way the iOS DNS upstream client dials. Other
platforms keep the plain dialer: Android and the desktops route the
client's own traffic into the tunnel already.
Zoltán Papp