DeDuplication Logic in v4

PhilDay · June 10, 2024, 1:00pm

Hi Folks,

Can someone point me to the message deduplication code in V4 please - I want to look at how the system handles messages from different gateways if some parts of the payload for what appears to be the same valid message (same devId, fCnt) but with different content in the payload.

Thanks
Phil

brocaar · July 2, 2024, 10:42am

Here you go:

github.com

chirpstack/chirpstack/blob/master/chirpstack/src/uplink/mod.rs#L159


      
                  Ok(ufl)
              }
          }
          
          #[derive(Clone)]
          pub struct RoamingMetaData {
              pub base_payload: backend::BasePayload,
              pub ul_meta_data: backend::ULMetaData,
          }
          
          pub async fn deduplicate_uplink(event: gw::UplinkFrame) {
              if let Err(e) = _deduplicate_uplink(event).await {
                  error!(error = %e.full(), "Deduplication error");
              }
          }
          
          async fn _deduplicate_uplink(event: gw::UplinkFrame) -> Result<()> {
              let phy_str = hex::encode(&event.phy_payload);
              let tx_info_str = match &event.tx_info {
                  Some(tx_info) => hex::encode(tx_info.encode_to_vec()),
                  None => "".to_string(),

PhilDay · July 30, 2024, 3:05pm

Thanks. My Rust isn’t brilliant - but from what I can see the tx_info and phy_payload have to match for an event to be considered a duplicate, is that right ?

So if a gateway was able to fake a packet for a device (accepting this means some breach in the keys) with the same fCnt as a valid packet, and both arrived in the dedup window they wouldn’t be considered as duplicates - and one would be delivered and the second dropped as being an invalid framecount ?

(My interest is is how we might detect this from outside Chirpstack)

brocaar · August 12, 2024, 9:38am

Correct, a duplicate means the same PhyPayload + same Tx Info (containing frequency, data-rate etc… which should be te same for all receivers).

system · November 10, 2024, 9:38am

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