From ea23a9308082b5a785305f6e2ef592fe48d6914e Mon Sep 17 00:00:00 2001
From: Floris Bruynooghe <flub@n0.computer>
Date: Thu, 27 Feb 2025 15:27:36 +0100
Subject: [PATCH] Add cid len check to enable multipath

---
 quinn-proto/src/connection/mod.rs | 4 ++--
 quinn-proto/src/shared.rs         | 4 ++++
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/quinn-proto/src/connection/mod.rs b/quinn-proto/src/connection/mod.rs
index 05e8d3bcb..3f7564b77 100644
--- a/quinn-proto/src/connection/mod.rs
+++ b/quinn-proto/src/connection/mod.rs
@@ -1437,9 +1437,9 @@ impl Connection {
     /// Multipath is only enabled after the handshake is completed and if it was negotiated
     /// by both peers.
     pub fn is_multipath_enabled(&self) -> bool {
-        // TODO(flub): Multipath can only be enabled if both sides use non-zero length CIDs.
-        //    Also check that.
         !self.is_handshaking()
+            && self.handshake_cid.len() > 0
+            && self.rem_handshake_cid.len() > 0
             && self.config.initial_max_path_id.is_some()
             && self.peer_params.initial_max_path_id.is_some()
     }
diff --git a/quinn-proto/src/shared.rs b/quinn-proto/src/shared.rs
index aefa1a00e..97d0f797f 100644
--- a/quinn-proto/src/shared.rs
+++ b/quinn-proto/src/shared.rs
@@ -98,6 +98,10 @@ impl ConnectionId {
         res
     }
 
+    pub(crate) fn len(&self) -> usize {
+        self.len as usize
+    }
+
     /// Decode from long header format
     pub(crate) fn decode_long(buf: &mut impl Buf) -> Option<Self> {
         let len = buf.get::<u8>().ok()? as usize;