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lplex

CAN bus HTTP bridge for NMEA 2000. lplex reads raw CAN frames from a SocketCAN interface, reassembles fast-packets, tracks device discovery, and streams frames to clients over SSE. It supports journaling, cloud replication, and PGN decoding.

What lplex does​

lplex sits between your boat's NMEA 2000 bus and your applications. It handles all the low-level CAN bus complexity (fast-packet reassembly, address claiming, device discovery) and exposes a clean HTTP/SSE interface that any language can consume.

  NMEA 2000 Bus
       |
   SocketCAN (can0)
       |
     lplex                          lplex-cloud
       |                                |
   HTTP/SSE (:8089)    ---- gRPC ----> HTTP/SSE (:8080)
       |                (mTLS)          |
  Local clients                    Remote clients
  (lplexdump, apps)               (dashboards, APIs)

Key features​

  • SSE streaming with two modes: ephemeral (fire-and-forget) and buffered (cursor-based with replay and acknowledgment)
  • Device discovery via PGN 60928 address claims and PGN 126996 product info, with automatic ISO Request probing
  • Journaling to .lpj files with zstd compression, block indexing, and configurable rotation
  • Cloud replication over gRPC with mTLS for remote access to boat data
  • PGN decoding via a custom DSL that generates Go structs, decoders, and protobuf definitions
  • Filtering by PGN, manufacturer, device instance, or CAN NAME
  • Client libraries for Go and TypeScript
  • Embeddable: use the broker as a Go library in your own applications

Components​

BinaryDescriptionPlatforms
lplexBoat server (CAN reader, broker, HTTP, journaling, replication)Linux (SocketCAN)
lplex-cloudCloud server (gRPC receiver, per-instance brokers, HTTP API)Linux
lplexdumpCLI client (SSE consumer, PGN decoder, journal replay)Linux, macOS

Architecture​

lplex uses a single-goroutine broker design with no locks in the hot path:

CANReader goroutine
  |  reads CAN frames, reassembles fast-packets
  v
rxFrames channel
  |
Broker goroutine (single writer, owns all state)
  |  assigns monotonic sequence numbers
  |  appends pre-serialized JSON to ring buffer (64k entries)
  |  updates device registry
  |  fans out to subscribers and consumers
  |  feeds journal channel (if enabled)
  |
  +---> Ring buffer (pre-serialized JSON, RLock for reads)
  +---> DeviceRegistry (source -> device info)
  +---> ValueStore (last frame per source+PGN)
  +---> Consumers (pull-based, cursor + filter + notify)
  +---> Subscribers (push-based, ephemeral channels)
  +---> JournalWriter (optional, zstd-compressed blocks)
  +---> ReplicationClient (optional, gRPC to cloud)

Next steps​