ciplink-tagserver

One server per site that owns all the PLC connections and serves tag values to React (or any) apps over a WebSocket. Apps never talk to the PLCs: each PLC gets one connection, one thread and one poll loop, however many screens are open.

It is built on ciplink, a fork of pycomm3 that reads by instance ID and reloads its tag table by itself after online edits. 0.3 needs ciplink 0.2.

Structure (tags, types, UDTs) always comes from the controller. Intent (what may be written, limits, units, deadband, bit names, poll rates) comes from rules in the config. Nothing is declared twice: the TypeScript tag tree is generated from the running server.

Install

pip install ciplink-tagserver

or from a checkout with uv: uv sync, then uv run ciplink-tagserver ....

Run

ciplink-tagserver run --config tagserver.toml          # real PLCs
ciplink-tagserver run --config tagserver.toml --mock   # simulated values, no PLC needed
ciplink-tagserver dump-tags --config tagserver.toml --plc PLC1 --out PLC1_tags.json
ciplink-tagserver types --url http://127.0.0.1:8765 --token T --out src/plc.ts

Add --log-file tagserver.log to run to log to a file (rotated at 10 MB, 5 kept) instead of the console.

Upgrading from 0.2 (breaking)

• Writes need a writable rule. A token write pattern alone no longer allows a write: the tag's rule must also say writable = true (see Rules). Add rules for your setpoints before upgrading, or every write is rejected with kind: "not_writable".
• Write patterns no longer use fnmatch. [ and ] are literal now, so PLC1/Tank[*].Level matches PLC1/Tank[3].Level, and the old Arr[[]3] trick no longer matches anything.
• types writes a typed tag tree by default; --format names gives the 0.2 name union.
• Value entries gain a 4th element (the error), acks gain kind and value. 0.2 clients ignore both.

All changes: CHANGELOG.md.

Run at Windows startup

From an administrator terminal (right-click Terminal, "Run as administrator"):

ciplink-tagserver service install --config C:\TagServer\tagserver.toml
ciplink-tagserver service status
ciplink-tagserver service remove

install registers a Task Scheduler task that starts at every boot as SYSTEM, without anyone logging in, and starts it now. The task runs ciplink-tagserver service run, which starts the server again 5 s after it stops for any reason; Task Scheduler also restarts the task itself if it fails. Logs go to tagserver.log next to the config (--log-file to change it). Use full paths in the config, or paths relative to it; the task runs in the config's folder. --name sets the task name (default ciplink-tagserver), so several servers can run on one PC with different configs and ports.

Config

[server]
host = "127.0.0.1"      # localhost only by default
port = 8765
cycle_ms = 250          # poll period per PLC
audit_log = "audit.log" # JSON lines of every write attempt ("" for none)
tier2_period_s = 3      # each tier-2 tag is read about this often
grace_s = 10            # a tag leaving tier 1 stays at tier 2 this long
pages_file = "pages.json" # what each page showed, learned from the clients ("" to keep it in memory)
planner = true          # read structs whole when that saves reads (false to troubleshoot)
whole_max_bytes = 1500  # largest struct the planner reads whole
momentary_timeout_ms = 1000 # a pressed momentary tag with no hold this long is released

[plc.PLC1]
path = "192.168.1.10"                # a ciplink/pycomm3 path, e.g. "10.0.0.5/1/3"
tag_cache_file = "cache/PLC1.json"   # optional: fast restarts
mock_tags = "PLC1_tags.json"         # optional: used only with --mock

[[plc.PLC1.rule]]                    # see Rules
match = "Line1.*.SpeedSP"
writable = true

[token.viewer]
secret = "change-me-too"             # no write patterns: read-only

[token.hmi1]
secret = "change-me"
write = ["PLC1/Line1.*.SpeedSP", "PLC1/Program:Station1.Door*"]

Relative file paths are relative to the config file. A complete example is examples/bench/tagserver.toml.

Tag names are qualified as <plc>/<tag>, e.g. PLC1/Program:Main.Speed (a slash cannot appear in a Logix tag name). With exactly one PLC configured, unqualified names mean that PLC.

Patterns (rules, poll groups, token write patterns) ignore case; * matches any run of characters (dots and brackets too), ? one character, everything else is literal: Tank[*].Level matches Tank[3].Level. Rule and group patterns match the tag inside its PLC (Tank[3].Level); token write patterns match the qualified name (PLC1/Tank[3].Level). match may be one pattern or a list.

Rules

[[plc.PLC1.rule]]
match    = "Bench.SpeedSP"
writable = true        # a setpoint: writes also need a token write pattern
min      = 0
max      = 1800
units    = "rpm"
description = "Spindle speed setpoint"   # else the controller's description, when ciplink can read it

[[plc.PLC1.rule]]
match    = "Bench.Speed"
deadband = 0.5         # changes smaller than this (vs the last value sent) are not sent

[[plc.PLC1.rule]]
match    = "Bench.StatusWord"
always   = true        # read at tier 1 even with no subscribers (alarms, logging); literal names only
bits     = { EStop = 0, DoorOpen = 1, Fault = 2 }   # Bench.StatusWord.EStop is Bench.StatusWord.0

[[plc.PLC1.rule]]
match    = "Bench.Recipe"
together = true        # members of this struct are always read in one read: no torn values across scans

• Several rules can match a tag. For each field, the first rule in the file that sets it wins, so put specific rules first.
• A bit X.<n> takes only writable from X's rules; min, max, units, deadband, bits never apply to a bit.
• Bit names (X.EStop) work wherever a tag name does (sub, write, momentary). Values and acks are keyed by the name exactly as the client sent it. An unknown name reads as missing.
• Unknown keys are ignored.

Poll groups

[[plc.PLC1.group]]
name    = "fast"
rate_ms = 50
match   = ["Bench.Axis.Position", "Bench.Axis.Velocity"]

[[plc.PLC1.group]]
name    = "slow"
rate_ms = 2000
match   = ["Tank[*].Temp"]

A group sets the poll rate of a tag only while it is at tier 1 (on a loaded page, or always): polling a tag nobody looks at faster is wasted. At tier 2 or 3 the group is ignored. The first matching group wins; tags in no group are read every cycle_ms. The loop ticks at the smallest rate among cycle_ms and the groups that have tier-1 tags, and each tick plans what is due together (a group tag due with the cycle's tags shares their packets). /stats shows groups: {name: {rate_ms, tags, last_period_ms}} per PLC: tags is 0 while no page shows them.

Writes

Checked in this order, before anything is sent to the PLC; a rejected write's ack carries kind:

The PLC thread runs queued writes between the packets of a cycle (a write waits about one packet, not a whole cycle), then reads the written tag back (a bit: its word) and publishes it. The ack is {"op":"ack","id":N,"ok":true,"error":null,"kind":null,"value":<read-back>}. A write while the PLC is not connected fails at once with refused; a connection lost during the write gives comm. Writes are never retried. Every attempt, allowed or not, is one JSON line in audit_log (time, token, tag, old, value, ok, error, kind, and momentary for buttons), written by a background thread.

Momentary buttons

{"op":"momentary","id":N,"tag":"Bench.StartPB","action":"press"|"hold"|"release"}, for BOOL tags and bits, with the same checks as a write. press writes true and release false, each acked like a write. While the button is held the client sends hold every 300 ms (no ack). With no press or hold for momentary_timeout_ms, the server writes false itself (/stats momentary_timeouts), and a closed connection releases everything it held, also when the server shuts down. A release that fails because the PLC is not reachable is written again when the PLC connects, and one refused while it stays connected (a tag table reload, a busy controller) is written again every half second until it goes through. So a lost tab, a crashed browser or a cut cable never leaves a jog button pressed.

Tag info

The first time a connection subscribes a name, the server sends its info before the values:

{"op":"info","d":{"Bench.SpeedSP":{"type":"REAL","writable":true,"rate_ms":250,"group":null,
 "min":0,"max":1800,"units":"rpm","description":"Spindle speed setpoint"}}}

type comes from the controller (null until the PLC is connected), writable is true only when the rule says so and this connection's token may write it, dims is set for a whole array, bits on a word with bit names. Bits and bit names are BOOL. Info is sent again after a tag table reload and when a PLC connects.

Codegen: the typed tag tree

ciplink-tagserver types --url http://127.0.0.1:8765 --token T --out src/plc.ts

reads GET /tags from a running server (real or --mock) and writes a TypeScript module: one interface per UDT, a PLC1Tags interface of the controller and Program: scopes, and export const PLC1 = tagTree<PLC1Tags>(...).

import { PLC1 } from "./plc";
<TagValue name={PLC1.Tank[2].Level} />          // "Tank[2].Level"
<NumericInput name={PLC1.Bench.SpeedSP} />       // compiles only if the rule makes it writable
<TagLamp name={PLC1.Bench.StatusWord.EStop} />   // bit names from the rules; .bit(3) for any bit

Leaves are TagRef<number|boolean|string, W>, with W true where a rule makes the path writable, so useWriteTag, NumericInput and MomentaryButton reject read-only tags at compile time. Arrays are TagArray<T, N> with a literal length, not refs: a bare array name reads and writes only its first element, so use Trend[0]. The header gives the tag table version: run it again after a download and let tsc show what changed. With one --plc (or none) names are unqualified; with several, one tree per PLC with qualified names. --format names writes the 0.2 union type TagName = "..." | ....

Protocol (v1)

JSON messages over ws://host:port/ws. Every 0.3 addition is optional, so 0.2 clients keep working.

• A bad token, a first message that is not hello, or another protocol version: closed with code 4401.
• quality: good; missing (no such tag, or not readable from outside: value null); bad (the read failed: the last value is kept); stale (PLC disconnected: last value kept). error is null when good, else {"kind": "...", "message": "..."} with ciplink's kinds (not_found, access, comm, ...).
• Values: structs are objects, arrays lists, bytes hex strings, NaN and infinities the strings "NaN", "Infinity", "-Infinity". t is ms since the epoch. A numeric change below the rule's deadband is not sent.
• Writes and reconnects: see Writes. Reconnects back off 1, 2, 5, then every 10 s.

tests/conformance/ checks a server against this table over a real WebSocket (an in-process --mock Test Bench by default): pytest tests/conformance --url http://host:8765 --token T --viewer-token V runs it against any server serving the Test Bench tags and rules.

Tiers and pages

A poll costs about 12 ms per packet plus 1.35 ms per read, so the server reads only what is on screen every cycle:

A tag's tier is the lowest among its subscriptions. A tag new at tier 2 is read at the next tick, then in its slice. When its last tier-1 subscription ends it is read at tier 2 for grace_s more, so going back to a page finds fresh values, then it drops out (or to tier 3).

Pages. A tier-1 sub carrying "page": "/line1" (the client's current route) teaches the server that page's tags; it keeps the union per page in pages_file (saved a moment after a change, by an atomic rename, and loaded at startup). A sub with a page and no tags subscribes the tags learned for that page, at its tier (2 for a link to it); it is empty until the page has been visited, and follows what the page learns. Its values are keyed by the plain tag names with one PLC, else by qualified names.

Known limits: a page's learned list only grows (a tag removed from a page, or deleted from the PLC, stays listed until you edit or delete pages_file), and a tier-1 subscription re-sent after the route changed (say, a component that stays mounted across pages) teaches the new page its tags too.

Read planner. Members of one struct can be read through one read of that struct and sliced out: for Line1.Motor.Speed and Line1.Motor.Current, Line1.Motor is read once. Two or more elements of a 1-D atomic array (Trend[3], Trend[4], Trend[7]) can become one ranged read Trend[3]{5}. An extra packet costs far more than a few reads, so the planner estimates each read's request and reply bytes and takes groups best first, each only if it adds at most 450 reply bytes per read saved and the cycle's estimated packet count stays what plain reads would take. A together rule forces its struct whole whatever the cost (if it fits a packet). Never grouped: bit access, element counts, whole arrays, strings, BOOL arrays, and AOIs that cannot be read whole. If a struct read fails, its members are read one by one in the same cycle, and the struct is tried whole again after 60 s or a reload (group_fallbacks). planner = false turns it off.

HTTP

• GET /health: per PLC state, last_cycle_ms, last_ok_ts, reconnects, reloads.
• GET /stats: sessions, writes, write_rejects, momentary_timeouts, and per PLC reads_per_cycle, tags_per_cycle, last_cycle_ms, cycle_ms, overruns, subscriptions, tier1, tier2, tier3, group_fallbacks and groups.
• GET /tags?plc=NAME with Authorization: Bearer <secret>: {plc, state, version, tags: [{name, type, dims?, aoi_readable?}], types: {UDT: {members: {m: {type, dims?}}}}, rules, groups}. Strings show as type STRING. plc may be left out with one PLC. CORS allows GET from any origin (the TagBrowser fetches it).

React

@ciplink/react is the React side: one provider that owns the WebSocket, and hooks and components that subscribe while mounted. See client/README.md for the full API.

import { TagServerProvider, TagValue, TagLamp, NumericInput, MomentaryButton, derive } from "@ciplink/react";
import { PLC1 } from "./plc"; // generated

const avgLevel = derive((get) => [0, 1, 2, 3].reduce((s, i) => s + (get(PLC1.Tank[i].Level) ?? 0), 0) / 4);

<TagServerProvider url="ws://127.0.0.1:8765/ws" token="change-me" page={route}>
  <TagValue name={PLC1.Bench.Speed} decimals={1} />          {/* units from the rule */}
  <TagLamp name={PLC1.Bench.StatusWord.EStop} />
  <NumericInput name={PLC1.Bench.SpeedSP} />                  {/* min/max from the rule, inline confirm */}
  <MomentaryButton name={PLC1.Bench.StartPB}>Start</MomentaryButton>
  <TagValue name={avgLevel} decimals={1} unit="%" />
</TagServerProvider>

• useTag, useTags, useTagInfo, useWriteTag (resolves with the ack), useMomentary, useTagServer.
• Every component is fixed size: nothing moves when values, quality, info or pending state change.
• Bits (X.3, .bit(3)) are computed from the word in the client; derive computes values from other tags with the worst input quality. <TagLink> prefetches a page's learned tags at tier 2; <TagBrowser> is a tree of /tags where only expanded rows subscribe.

The Test Bench example

examples/bench/ is a small mock-driven bench that exercises every signal: momentary Start/Stop with the watchdog, a writable setpoint with limits, a deadbanded speed that follows it, a 50 ms axis group only on the Motion page, an always status word with bit names, a together recipe, an array of UDTs with a slow group and a derived average, a ranged-read trend, a program-scope tag, a missing tag, the tag browser and a status bar. Its src/plc.ts is generated against the mock server. npm run e2e drives it in Chrome and checks values, groups, writes, buttons, the watchdog and that no control ever moves.

Mock mode

--mock replaces every PLC driver with a simulation of the tags in that PLC's mock_tags file, either the 0.2 flat {"Line1.Speed": "REAL"} or structured:

{"types": {"TankData": {"Level": "REAL", "Temp": "REAL", "Valve": "BOOL"}},
 "tags":  {"Tank": "TankData[4]", "Trend": "REAL[16]", "Bench": "BenchData", "Program:Bench.Mode": "DINT"}}

Types are NAME or NAME[n]. Reads support members, elements, ranges, bits and whole structs, so the planner runs as on a PLC. Values are shaped by the name: temp 20-90, level 0-100, position ramps, count counts, words carry a few toggling bits, speed follows its SpeedSP while a sibling Running is true, StartPB/StopPB set Running, and written values hold. Writes are type-checked like ciplink's. Unknown names are missing. dump-tags writes a flat file from a real PLC's tag list.

Safety

• Writes are off unless a token has write patterns and a rule makes the tag writable.
• Every write attempt, allowed or not, is appended to the audit log.
• Momentary buttons are released by the server when the client stops holding them.
• The server binds to 127.0.0.1 by default. Put it behind a TLS proxy before opening it to a network: tokens travel in clear text over plain ws:// and http://.
• Change the example secrets.