Add peer id suffix to make sub networks

3 files changed, 31 insertions, 1 deletions

diff --git a/config/config.exs b/config/config.exs
index 3139220..f970078 100644
--- a/config/config.exs
+++ b/config/config.exs
@@ -21,6 +21,18 @@ use Mix.Config
 #     config :logger, level: :info
 #
 
+
+# Peer id suffix
+# ==============
+# This Shard instance will only connect to other instances that use
+# the same suffix.
+#
+# On first run, the instance will try to generate a peer id that
+# has this suffix. This is done by brute-force testing, therefore
+# it is not recommended to use long suffixes.
+config :shard, peer_id_suffix: "S"
+
+
 # It is also possible to import configuration files, relative to this
 # directory. For example, you can emulate configuration per environment
 # by uncommenting the line below and defining dev.exs, test.exs and such.
diff --git a/lib/identity.ex b/lib/identity.ex
index 229d6c7..f1899df 100644
--- a/lib/identity.ex
+++ b/lib/identity.ex
@@ -1,13 +1,15 @@
 defmodule Shard.Identity do
   use Agent
   require Salty.Sign.Ed25519, as: Sign
+  require Logger
 
   def start_link(_) do
     Agent.start_link(__MODULE__, :init, [], name: __MODULE__)
   end
 
   def init() do
-    {:ok, pk, sk} = Sign.keypair
+    Logger.info "Generating keypair..."
+    {pk, sk} = gen_keypair(Application.get_env(:shard, :peer_id_suffix))
     nick_suffix = pk
                   |> binary_part(0, 3)
                   |> Base.encode16
@@ -18,6 +20,18 @@ defmodule Shard.Identity do
     }
   end
 
+  defp gen_keypair(suffix, n \\ 0) do
+    {:ok, pk, sk} = Sign.keypair
+    if rem(n, 10000) == 0 do
+      Logger.info "#{n}... expected #{:math.pow(256, byte_size(suffix))}"
+    end
+    if :binary.longest_common_suffix([pk, suffix]) == byte_size(suffix) do
+      {pk, sk}
+    else
+      gen_keypair(suffix, n+1)
+    end
+  end
+
   def get_keypair() do
     Agent.get(__MODULE__, &(&1.keypair))
   end
diff --git a/lib/net/tcpconn.ex b/lib/net/tcpconn.ex
index 6fc4b1a..44669bb 100644
--- a/lib/net/tcpconn.ex
+++ b/lib/net/tcpconn.ex
@@ -39,6 +39,10 @@ defmodule SNet.TCPConn do
     challenge_sign = decode_pkt(pkt, cli_sess_pkey, sess_skey)
     :ok = Sign.verify_detached(challenge_sign, challenge, cli_pkey)
 
+    expected_suffix = Application.get_env(:shard, :peer_id_suffix)
+    len = byte_size(expected_suffix)
+    ^len = :binary.longest_common_suffix([cli_pkey, expected_suffix])
+
     # Connected
     :inet.setopts(socket, [active: true])