ipcpd: Update DHT for unicast layer

This is a rewrite of the DHT for name-to-address resolution in the
unicast layer. It is now integrated as a proper directory policy. The
dir_wait_running function is removed, instead the a DHT peer is passed
on during IPCP enrolment.

Each DHT request/response gets a random 64-bit ID ('cookie'). DHT
messages to the same peer are deduped, except in the case when the DHT
is low on contacts. In that case, it will contact the per it received
at enrolment for more contacts. To combat packet loss, these messages
are not deduped by means of a 'magic cookie', chosen at random when
the DHT starts.

The DHT parameters (Kademlia) can be set using the configfile or the
IRM command line tools:

if DIRECTORY_POLICY == DHT
        [dht_alpha <search factor> (default: 3)]
        [dht_k <replication factor> (default: 8)]
        [dht_t_expire <expiration (s)> (default: 86400)]
        [dht_t_refresh <contact refresh (s)> (default: 900)]
        [dht_t_replicate <replication (s)> (default: 900)]

This commit also adds support for a protocol debug level (PP).
Protocol debugging for the DHT can be enabled using the
DEBUG_PROTO_DHT build flag.

The DHT has the following message types:

DHT_STORE, sent to k peers. Not acknowledged.

    DHT_STORE --> [2861814146dbf9b5|ed:d9:e2:c4].
      key: bcc236ab6ec69e65 [32 bytes]
      val: 00000000c4e2d9ed [8 bytes]
      exp: 2025-08-03 17:29:44 (UTC).

DHT_FIND_NODE_REQ, sent to 'alpha' peers, with a corresponding
response. This is used to update the peer routing table to iteratively
look for the nodes with IDs closest to the requested key.

    DHT_FIND_NODE_REQ --> [a62f92abffb451c4|ed:d9:e2:c4].
      cookie: 2d4b7acef8308210
      key:    a62f92abffb451c4 [32 bytes]

    DHT_FIND_NODE_RSP <-- [2861814146dbf9b5|ed:d9:e2:c4].
      cookie: 2d4b7acef8308210
      key:    a62f92abffb451c4 [32 bytes]
      contacts: [1]
        [a62f92abffb451c4|9f:0d:c1:fb]

DHT_FIND_VALUE_REQ, sent to 'k' peers, with a corresponding
response. Used to find a value for a key. Will also send its closest
known peers in the response.

    DHT_FIND_VALUE_REQ --> [2861814146dbf9b5|ed:d9:e2:c4].
      cookie: 80a1adcb09a2ff0a
      key:    42dee3b0415b4f69 [32 bytes]

    DHT_FIND_VALUE_RSP <-- [2861814146dbf9b5|ed:d9:e2:c4].
      cookie: 80a1adcb09a2ff0a
      key:    42dee3b0415b4f69 [32 bytes]
        values: [1]
          00000000c4e2d9ed [8 bytes]
        contacts: [1]
          [a62f92abffb451c4|9f:0d:c1:fb]

Also removes ubuntu 20 from appveyor config as it is not supported anymore.

Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks>
Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>

2 files changed, 17 insertions, 3 deletions

diff --git a/src/lib/pb/enroll.proto b/src/lib/pb/enroll.proto
index 7fe612a8..60e964c6 100644
--- a/src/lib/pb/enroll.proto
+++ b/src/lib/pb/enroll.proto
@@ -24,7 +24,6 @@ syntax = "proto2";
 import "ipcp_config.proto";
 
 message enroll_req_msg {
-        /* TODO authentication */
         required bytes id = 1;
 }
 
diff --git a/src/lib/pb/ipcp_config.proto b/src/lib/pb/ipcp_config.proto
index 28528b0c..aaff599e 100644
--- a/src/lib/pb/ipcp_config.proto
+++ b/src/lib/pb/ipcp_config.proto
@@ -31,10 +31,25 @@ message dt_config_msg {
         required uint32 routing_type = 4;
 }
 
+message dir_dht_config_msg {
+        required uint32 alpha       = 1;
+        required uint32 k           = 2;
+        required uint32 t_expire    = 3;
+        required uint32 t_refresh   = 4;
+        required uint32 t_replicate = 5;
+        required uint64 peer        = 6;
+}
+
+message dir_config_msg {
+        required uint32 pol             = 1;
+        optional dir_dht_config_msg dht = 2;
+}
+
 message uni_config_msg {
         required dt_config_msg dt      = 1;
-        required uint32 addr_auth_type = 2;
-        required uint32 cong_avoid     = 3;
+        required dir_config_msg  dir   = 2;
+        required uint32 addr_auth_type = 3;
+        required uint32 cong_avoid     = 4;
 }
 
 message eth_config_msg {