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tailscale/cmd
Josh Bleecher Snyder 6f23087175 wgengine/magicsock: unify initial bind and rebind
We had two separate code paths for the initial UDP listener bind
and any subsequent rebinds.

IPv6 got left out of the rebind code.
Rather than duplicate it there, unify the two code paths.
Then improve the resulting code:

* Rebind had nested listen attempts to try the user-specified port first,
  and then fall back to :0 if that failed. Convert that into a loop.
* Initial bind tried only the user-specified port.
  Rebind tried the user-specified port and 0.
  But there are actually three ports of interest:
  The one the user specified, the most recent port in use, and 0.
  We now try all three in order, as appropriate.
* In the extremely rare case in which binding to port 0 fails,
  use a dummy net.PacketConn whose reads block until close.
  This will keep the wireguard-go receive func goroutine alive.

As a pleasant side-effect of this, if we decide that
we need to resuscitate #1796, it will now be much easier.

Fixes #1799

Co-authored-by: David Anderson <danderson@tailscale.com>
Signed-off-by: Josh Bleecher Snyder <josharian@gmail.com>
4 years ago
..
cloner all: adjust Unix permissions for those without umasks 4 years ago
derper cmd/derper: add /bootstrap-dns handler 4 years ago
hello client/tailscale/apitype: move local API types to new apitype package 4 years ago
microproxy cmd/microproxy: add -insecure flag 4 years ago
mkpkg cmd/mkpkg: support adding empty directories. 5 years ago
tailscale cmd/tailscale: fix typo in error message (#1807) 4 years ago
tailscaled wgengine/magicsock: unify initial bind and rebind 4 years ago
tsshd net/interfaces: remove IsTailscaleIP, make callers use tsaddr. 4 years ago