Currently we cannot distinguish bi-directional and uni-directional
connectivity between peers. This is what currently happens for a
connection from A to B...
A: remoteUDPAddr=X
B: remoteUDPAddr=nil
A: send fast heartbeats over UDP
B: receive heartbeat; remoteUDPAddr is nil
remoteUDPAddr=Y
send 'established' over TCP
established=true
send slow heartbeats over UDP
A: receive 'established' over TCP
established=true
send slow heartbeats over UDP
If udp packets make it through from A to B but not B to A then both
ends mark the connection as 'established'. Conversely, if udp packets
make it through from B to A but not A to B then the connection is not
marked as 'established' at either end.
In the new scheme, this is what happens...
A: receivedHeartbeat=false, remoteUDPAddr=X
B: receivedHeartbeat=false, remoteUDPAddr=nil
A: send fast heartbeats over UDP
B: receive heartbeat; receivedHeartbeat is false
remoteUDPAddr=Y
receivedHeartbeat=true
send 'established' over TCP
send fast heartbeats over UDP
A: receive 'established' over TCP (*)
established=true
send slow heartbeats over UDP
A: receive heartbeat; receivedHeartbeat is false (*)
receivedHeartbeat=true
send 'established' over TCP
B: receive 'established' over TCP
established=true
send slow heartbeats over UDP
(*) either of these may occur first
Now, if udp packets make it through from A to B not not B to A then A
marks the connection as 'established' but B doesn't. Conversely, if
udp packets make it through from B to A but not A to B then B marks
the connection as 'established' but A doesn't.
I considered a couple of different factorings, that is
* Implementing the fallback as a Lookup
* Having a server struct that held the resolv.conf and methods for
handling queries
but ultimately, this is simple and works.
It's more precise to use dig rather than ping. The stock ubuntu image
doesn't come with dig (in package dnsutils), but luckily Aanand made
an image which is exactly ubuntu+dnsutils.
1) log more lifecycle events
- acceptance
- handshake completion
- added & removed (from our connection map)
The latter is a bit verbose but may help us track down the cause for
going to introduce here, then this would fall in the 'debug' category.
2) better error logging
- log error as part of "shutting down" log event rather than separately
- indicate "blocked UDP connectivity" as a possible cause when
getting a timeout on a not-fully-established connection.
The rationale for the latter is that inbound connections get
marked as established when first receiving a heartbeat frame over
UDP, which are the only frames that get transmitted prior to the
connection being fully established. Note that outbound
connections get marked as established when receiving the
ConnectionEstablished message over TCP, which is sent by the peer
when it first receives a heartbeat. See #342.
Closes#340.
conn.shutdown was only set/accessed in handleShutdown, which in turn
is only called on termination of queryLoop and hence multiple
invocations are impossible.
* Put prefixes (including msg IDs) in front of log messages to
distinguish them
* Failed lookups get logged under Info as per issue #311
* More accurate messages as per issue #311
So as not to pollute command-line flags with test.* options.
It appears that importing "testing" (from stdlib) will add flags. To
avoid this, we need code to not depend on testing. But, since
testing_utils was previously in the same package as the rest of the
code, it dragged testing in.
Renaming testing_util.go to e.g., util_for_test.go might be enough to
avoid it being compiled with the regular code. We may want it to be
available to tests for other packages -- after all it is utilities for
testing -- so it goes in its own package.
NB I removed free variables from the LookupFunc implementations, to
avoid confusion between `s` the receiver and the closed-over `s`.
Also corrected a mistake in the write error log message.
Matthias Radestock