Markus Fritsche
250f3d38f0
The design note says the probe is lmcp-only because checking ssh "is expensive (3-6s per
offline host) and the hub exists specifically to absorb lots of offline hosts". That holds
for an ssh SESSION. A bare TCP connect to port 22 answers the only question a host card
asks — is the box there — with no handshake and no auth.
Measured on the room host: a dead target costs 1.05s, a live one milliseconds, and riding
the existing parallel fan-out keeps wall clock at one budget window — 3.07s for 14 lmcp
plus 9 ssh probes together, against 3.10s for the 14 lmcp probes alone. The cost objection
is answered rather than ignored.
Eight reachable hosts had been reported as "no probe result": dcw2, deus, escher, hermes,
nash, noether, orca, pipi. They now report UP via=ssh, and a host whose port 22 refuses
gets a real reason ("ssh port unreachable") instead of silence.
Deliberately unchanged: a backend with BOTH paths whose lmcp is down still reads DOWN, per
the existing note that remote_* falls through to ssh regardless. Only ssh-ONLY backends
get the new probe. Without nc the probe reports nothing rather than guessing DOWN — an
unprobed host is honest, a wrongly-asserted one is not.
Two detours worth recording, since both were self-inflicted and cost a restart each:
* The first attempt edited /opt/lmcp/hub.lua and restarted the service, which loads
/usr/share/lua/5.4/hub.lua — a separate copy. Nothing keeps the two in step; the log
line still showed the old format string, which is the only reason it was noticed.
* The second attempt compared this repository against the deployed file and concluded
that 120 lines of MCP tool annotations had never been committed. They had. The working
copy was 17 commits stale, so the "drift" was entirely an artefact of the comparison.
Against the current tree the real change is 36 lines, and the patched file now hashes
identical to the running one.
lmcp — Lua MCP server
Lightweight Model Context Protocol (MCP) server in pure Lua.
Runtime dependencies
- Lua 5.1+
- luasocket — needed for the TCP
listener. Packaged as
lua-socketon Arch/ALARM,lua-socketon Debian.
Files
| File | Role |
|---|---|
lmcp.lua |
library: protocol handling, tool registration |
server.lua |
HTTP server loop |
json.lua |
vendored JSON encoder/decoder |
example_server.lua |
sample server with a couple of tools |
Install
Packaged as lmcp in the marfrit overlay repo:
# Arch / ALARM
sudo pacman -S lmcp
# Debian
sudo apt install lmcp
Files land under /usr/share/lua/5.4/ (Lua LUA_PATH).
The example server installs as /usr/bin/lmcp-example.