p2p

Author: pavel-kirienko

libudpard/udpard.c

@@ -1188,7 +1188,7 @@ static void tx_send_ack(udpard_rx_t* const    rx,
 
 bool udpard_tx_new(udpard_tx_t* const              self,
                    const uint64_t                  local_uid,
-                   const uint64_t                  p2p_transfer_id_base_seed,
+                   const uint64_t                  p2p_transfer_id_seed,
                    const size_t                    enqueued_frames_limit,
                    const udpard_tx_mem_resources_t memory,
                    const udpard_tx_vtable_t* const vtable)
@@ -1199,7 +1199,7 @@ bool udpard_tx_new(udpard_tx_t* const              self,
         mem_zero(sizeof(*self), self);
         self->vtable                = vtable;
         self->local_uid             = local_uid;
-        self->p2p_transfer_id_base  = hash_pair_u64(p2p_transfer_id_base_seed, local_uid);
+        self->p2p_transfer_id       = hash_pair_u64(p2p_transfer_id_seed, local_uid);
         self->ack_baseline_timeout  = UDPARD_TX_ACK_BASELINE_TIMEOUT_DEFAULT_us;
         self->enqueued_frames_limit = enqueued_frames_limit;
         self->enqueued_frames_count = 0;
@@ -1264,7 +1264,7 @@ bool udpard_tx_push_p2p(udpard_tx_t* const             self,
             .priority              = priority,
             .kind                  = (feedback != NULL) ? frame_msg_reliable : frame_msg_best,
             .transfer_payload_size = (uint32_t)bytes_scattered_size(payload),
-            .transfer_id           = remote.uid + self->p2p_transfer_id_base++, // Preserve monotonicity.
+            .transfer_id           = self->p2p_transfer_id++, // Shared for all remotes, hence no ack ambiguity.
             .sender_uid            = self->local_uid,
         };
         if (out_transfer_id != NULL) {

libudpard/udpard.h

@@ -398,7 +398,8 @@ struct udpard_tx_t
     uint64_t local_uid;
 
     /// A random-initialized counter for outgoing P2P transfers. Must not be changed by the application.
-    uint64_t p2p_transfer_id_base;
+    /// The shared counter for all P2P transfers ensures uniqueness of the transfer-ID per remote node.
+    uint64_t p2p_transfer_id;
 
     /// The maximum number of Cyphal transfer payload bytes per UDP datagram. See UDPARD_MTU_*.
     /// The Cyphal/UDP header is added to this value to obtain the total UDP datagram payload size.
@@ -474,7 +475,7 @@ struct udpard_tx_t
 /// True on success, false if any of the arguments are invalid.
 bool udpard_tx_new(udpard_tx_t* const              self,
                    const uint64_t                  local_uid,
-                   const uint64_t                  p2p_transfer_id_base_seed,
+                   const uint64_t                  p2p_transfer_id_seed,
                    const size_t                    enqueued_frames_limit,
                    const udpard_tx_mem_resources_t memory,
                    const udpard_tx_vtable_t* const vtable);
@@ -488,6 +489,7 @@ bool udpard_tx_new(udpard_tx_t* const              self,
 /// such that it is likely to be distinct per application startup (embedded systems can use noinit memory sections,
 /// hash uninitialized SRAM, use timers or ADC noise, etc). It is essential to provide a monotonic contiguous
 /// counter per topic to allow remotes to recover the original publication order and detect lost messages.
+/// The random starting point will ensure global uniqueness across topics.
 /// Related thread on random transfer-ID init: https://forum.opencyphal.org/t/improve-the-transfer-id-timeout/2375
 ///
 /// The user context value is carried through to the callbacks. It must contain enough context to allow subject-ID