Listens on MX_RELAY_LISTEN (default 127.0.0.1:8088) and forwards to
MX_RELAY_UPSTREAM (default 127.0.0.1:808 — AVEVA's NetTcpPortSharing
SMSvcHost listener). Hex-dumps every byte both directions to stderr
with C->S / S->C tags + per-direction offset prefixes.
Usage:
$env:MX_RELAY_LISTEN = '0.0.0.0:8088'
.\rust\target\debug\examples\asb-relay.exe 2> relay.log
# then in another shell:
dotnet run --project src\MxAsbClient.Probe -c Release -- `
'--endpoint=net.tcp://desktop-6jl3kko:8088/ASBService/Default_ZB_MxDataProvider/IDataV2'
Tested against the live AVEVA install on this box — captured a
620-byte client→server exchange including the full .NET probe's
preamble, SizedEnvelope, and End record. The capture surfaced one
critical missing piece in our wire format:
**WCF binary message framing prepends Action + To strings out-of-band**
before the actual NBFX SOAP envelope. The .NET probe's envelope
payload begins:
74 27 [39 bytes "http://asb.contracts/20111111:connectIn"] ← Action
4b [75 bytes "net.tcp://desktop-6jl3kko:8088/.../IDataV2"] ← To
56 02 ... ← <s:Envelope>
The 0x74 / 0x4b prefix bytes appear to be WCF-internal framing that
stores Action and To headers OUT of the SOAP envelope as a binary
optimization. Our F25 envelope encoder doesn't emit this — it goes
straight to `<s:Envelope>` (which the probe captured as `56 02 ...`
PrefixDictionaryElement_s + dict id 2). This is likely why the
server fault'd at AddressFilter mismatch in the previous iteration.
Note: when going through the relay, the .NET probe's `:8088` port
appears in the To URL inside the binary header, which doesn't match
the registered service URL on SMSvcHost — so this exact relay setup
returns the AddressFilterMismatch fault. The capture is still
valuable (we see what bytes WCF emits for our action/header
structure). For a fault-free dispatch, we'd need to:
* rewrite the binary header's port (0x4b length / URL bytes) at
the relay, OR
* listen on port 808 directly (requires stopping SMSvcHost), OR
* run an admin-elevated Wireshark/Npcap loopback capture.
Cleanup: dotnet probe must use `--endpoint=URL` (single arg with `=`),
not space-separated; the probe's GetArg helper splits on `=`.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Joseph Doherty
d4ee5f3a18