Added an `additional` field to the return message, so that we can
include any protocol level message to inform the sender about the
cause of the failure. This could for example be a `channel_update` if
the channel has become unusable. The message is no longer fixed size,
as hopefully the failure is a rare event, in which case timing
analysis becomes easy anyway.
Closes#53
If a node is being malicious, we get an error from the next hop either
way. But if we've simply advertised a new cltv-expiry-delta, we
want to send our own error.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
They're not reliable, so we can't count on them. We also don't have a place
for forwarding them in BOLT 2's update_fulfill_htlc.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
FIPS 198 is based on RFC 2104, but further restricts the hashing
functions to the SHA-family, so this is a bit redundant, but my hope
is to avoid confusion about whether there is a difference.
Thanks @rustyrussell for pointing this one out.
