use nonce in handshake

To prevent stale hello replies to cause joins and thus stale sessions,
each run gets a random ID, which used as nonce in the handshake.

1 files changed, 8 insertions, 0 deletions

diff --git a/src/transport/mod.rs b/src/transport/mod.rs
index 83c4e8d..e8d654d 100644
--- a/src/transport/mod.rs
+++ b/src/transport/mod.rs
@@ -12,6 +12,9 @@ pub use crate::document::replica::Epoch;
 pub mod firewall;
 pub mod mycelium;
 
+/// Random identifier of one run of a node (from start to exit).
+pub type RunId = [u8; 16];
+
 /// Most heads listed in a keepalive; more are sent as a digest. A head takes 34 bytes on
 /// the wire, so 32 of them keep a keepalive within one Mycelium chunk (1300 bytes; see
 /// the size test in `mycelium`). There are rarely more heads than nodes that wrote
@@ -120,6 +123,8 @@ pub struct HelloRequest {
     pub auth: Vec<u8>,
     /// The sender is ready (same meaning as `SyncEnvelope::ready`).
     pub ready: bool,
+    /// Random per run of the sender; the reply echoes it.
+    pub run_id: RunId,
 }
 
 #[derive(Debug, Clone)]
@@ -131,6 +136,9 @@ pub struct HelloReply {
     pub auth: Vec<u8>,
     /// The sender is ready.
     pub ready: bool,
+    /// The `run_id` of the HELLO answered. A reply to a HELLO from an earlier run of the
+    /// recipient (delivered late, or queued while it was down) is ignored.
+    pub run_id: RunId,
 }
 
 #[derive(Debug, Clone)]