Remember each sender's secret beside the node's key: no X25519 at restart

A listener lets a quiet sender's secret go with its active state, so a
node started again made one X25519 for every sender that came back (169
us on this Pi, most of a wake's CPU): asymmetric work in proportion to the
links, which design 011 counts as a reason to design again. The secret is
now remembered in a file beside the key (KEY.links, 0600, begun again for
another node's key): a place of 64 bytes a sender in the order allowed,
mapped, so a sender at rest takes no memory for it. A place is the first
28 bytes of the sender's key, a check (FNV-1a of the key and the secret)
and the secret, written secret first and key last; a place whose check
fails is made again. The UDP link checks see a receiver started again
make no X25519.

1 files changed, 7 insertions, 2 deletions

diff --git a/tests/check.py b/tests/check.py
index e46622b..7be32d7 100644
--- a/tests/check.py
+++ b/tests/check.py
@@ -784,7 +784,9 @@ def server_links_udp(aup, pure, work, netem=None):
     delays, loses and reorders packets meanwhile. The receiver takes its
     senders from a file (--senders, the sender among a thousand others) and
     lets a sender's keys and streams go after 400 ms of quiet
-    (--link-idle-ms): the order after a longer pause arrives all the same."""
+    (--link-idle-ms): the order after a longer pause arrives all the same.
+    Started again, it makes no X25519: the secret is remembered beside its
+    key (KEY.links)."""
     import select
     import signal
     import socket
@@ -903,11 +905,14 @@ def server_links_udp(aup, pure, work, netem=None):
             _, error = process.communicate(timeout=30)
             assert process.returncode == 0, error[-1000:]
             stats[name] = [json.loads(line) for line in error.decode().splitlines() if line.startswith('{"active"')][-1]
+    # The receiver, started again, remembered the sender's secret: no X25519 for it.
     assert stats['b']['listener_swept'] >= 1 and stats['b']['listener_woken'] >= 2, stats['b']
+    assert stats['b']['listener_remembered'] == stats['b']['listener_woken'], stats['b']
     return {'orders': sent, 'acknowledged_total': sum(acknowledged),
             'packets_after_restart': stats['a']['link_packets'], 'resent_after_restart': stats['a']['link_resent'],
             'lost_after_restart': stats['a']['link_lost'], 'received_after_restart': stats['b']['listener_received'],
-            'woken_after_restart': stats['b']['listener_woken'], 'swept_after_restart': stats['b']['listener_swept']}
+            'woken_after_restart': stats['b']['listener_woken'], 'swept_after_restart': stats['b']['listener_swept'],
+            'remembered_after_restart': stats['b']['listener_remembered']}
 
 
 def server_links_udp_lossy(aup, pure, work):