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d6c8702e90
Both tests started flaking after my 910735448 ("tstest/natlab/vnet:
send unsolicited IPv6 Router Advertisements") added background RA
traffic on v6-enabled networks.
TestPacketSideEffects races the periodic unsolicited-RA goroutine
against its synchronous packet-count assertions: when the multicast
RA fires after the test has registered its sinks, both sinks receive
it and "got 1 packet, want N" becomes "got N+2".
TestProtocolQEMU's reader was doing raw Read on the SOCK_STREAM unix
socket and comparing the whole result to the expected length-prefixed
packet. The kernel is free to coalesce the on-register RA frame and
the test packet into one Read, in which case bytes.Equal fails and
the entire chunk (including the test packet's bytes) gets discarded
as "unexpected", leading to a 5s i/o timeout. Parse the QEMU uint32
length-prefix framing with io.ReadFull instead so we read exactly one
frame per iteration regardless of how the kernel buffers them. The
SOCK_DGRAM path (TestProtocolUnixDgram) keeps the original raw Read
since datagram boundaries are preserved.
These where the top two flakes in oss on the flakes dashboards.
Updates #13038
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Change-Id: I32983656b692921a0f43a4a5e9a8a6ab2555ee49