Bus gateway

The Bus gateway tool in the sidebar forwards frames received on one connection onto another, with per-rule filtering, identifier rewriting and rate limiting. It turns CANExplorer into a configurable CAN gateway between two interfaces — useful on a bench or in a HIL setup to bridge two buses, inject a subset of one bus's traffic into another, translate identifiers between two address layouts, or protect a slower bus by rate-limiting what reaches it. Any pair of open connections works, including a real interface and the simulated one.

How it works

Each rule forwards frames received on a source connection to a destination connection. Only received bus traffic is forwarded — never frames CANExplorer itself transmits — so frames the gateway injects are not forwarded again, and two mirror rules between the same pair of buses cannot form a loop. (A short echo guard also ignores a forwarded frame that a bus with receive own messages reflects back.)

Turn the gateway On once the rules are set. It keeps running in the background while you use the rest of the application; the per-rule counters update live.

Adding a rule

Field	Meaning
From / →	The source connection (frames come from its bus) and the destination (they are sent on its bus). The destination must be able to transmit. They must differ.
Name	An optional label; defaults to source → destination.
Filter	Which received frames to forward, in the filter syntax: identifiers and ranges in hex (100-1FF), ! to exclude, std/ext/fd. Empty forwards every frame.
New ID	Rewrite the identifier to this value. Most useful with a single-identifier filter, since every forwarded frame gets this identifier.
ID offset	Add this signed hex value to the identifier instead of rewriting it — e.g. +100 to shift a block of identifiers between two address layouts. Ignored when New ID is set.
Rate limit	The minimum milliseconds between forwarded frames of the same identifier; faster frames are dropped. 0 forwards everything.

The payload, length, extended/FD flags and bitrate-switch bit are forwarded unchanged.

The rule list

Each rule shows a status dot — green when it is actively forwarding, amber when enabled but its connections are not both open, grey when switched off — its route, filter, rewrite, rate limit, and the number of frames forwarded and dropped. The On switch enables or disables a single rule; ✕ removes it. Reset counters zeroes the tallies and Clear rules removes them all.

A rule whose source or destination connection has been closed or removed is marked (connection missing) and forwards nothing until the connection is back; frames that cannot be sent (the destination is closed) count as dropped.

In scripts

can_explorer.core.gateway runs the same forwarding over BusSession objects, so a script can set up a gateway on virtual buses without the GUI:

from can_explorer.core.filters import MessageFilter
from can_explorer.core.gateway import Gateway, GatewayRule

sessions = {'A': session_a, 'B': session_b}
gateway = Gateway(sessions.get)
gateway.set_rules([
    GatewayRule('powertrain', 'A', 'B', MessageFilter.parse('100-2FF')),
    GatewayRule('obd', 'A', 'B', MessageFilter.parse('7DF'), new_id=0x600, min_interval=0.1),
])
gateway.start()
...
print(gateway.rules[0].forwarded, gateway.rules[0].dropped)
gateway.stop()