node-opcua-alias-name-common

Shared types and VersionTime helpers for OPC UA AliasNames (OPC 10000-17), plus a re-export of the OPC 10000-4 Like matcher.

These packages let a Server publish its own AliasNames and let a Client resolve them. They do not aggregate AliasNames collected from other Servers: Annex B (aggregating Server) and Annex C (GDS) of OPC 10000-17, and the Annex D PubSub change notification, are out of scope. Anything that requires knowing about more than one Server is not implemented here.

This package holds the framework-agnostic pieces used by both node-opcua-alias-name-server and node-opcua-alias-name-client. It deliberately depends on nothing heavier than node-opcua-nodeid and the dependency-free node-opcua-like-matcher.

see http://node-opcua.github.io/

Installation

npm install node-opcua-alias-name-common

What's in the box

The Like matcher (OPC 10000-4, Table 120)

FindAlias takes an AliasNameSearchPattern, which is a Like pattern. The matcher itself lives in node-opcua-like-matcher — Like is a Part 4 primitive that QueryApplications (OPC 10000-12) and event filter ContentFilters also need, and none of them should have to depend on the AliasName package to get a dependency-free string matcher.

It is re-exported here so Part 17 consumers have a single import:

import { like, isValidLikePattern, LikePattern, InvalidLikePatternError } from "node-opcua-alias-name-common";

like("TI101", "TI%");          // true
like("abc4", "abc[13-68]");    // true
like("axb", "a.b");            // false - metacharacters are literal

See that package's README for the wildcard table, the case-sensitivity rules, the reading of \ inside a character list, and the cost bounds and 2048-character pattern limit that keep a wire-supplied pattern from exhausting memory.

VersionTime (OPC 10000-4 clause 7.43)

The LastChange Property of an AliasNameCategoryType is a VersionTime: a UInt32 count of seconds since 2000-01-01T00:00:00Z. It is not a DateTime, which is the easiest thing to get wrong here.

import { toVersionTime, fromVersionTime, maxVersionTime } from "node-opcua-alias-name-common";

toVersionTime(new Date("2000-01-01T00:00:00Z")); // 0
fromVersionTime(86400);                          // 2000-01-02T00:00:00.000Z

Two consequences worth designing around:

• Resolution is one second. Two changes inside the same second are indistinguishable. A Client that sees a LastChange equal to its cached value should re-browse rather than assume nothing changed; only a value older than the cached one means "drop the cache" (clause 6.3.1).
• It wraps in 2136 (VERSION_TIME_WRAP_DATE, 2136-02-07T06:28:16Z). There is nothing in the specification to do about this; it is documented, not handled. Instants before the epoch clamp to 0 rather than wrapping to a far-future value.

maxVersionTime is the rollup used by clause 6.3.1, where a nested category's LastChange is the latest of all its descendants.

IAliasStore

Experimental. The shape of IAliasStore is expected to move before it is considered stable. It is exported so a Server can back its aliases with something other than the address space — a database, a configuration file, an existing tag dictionary — but treat it as provisional.

AliasEntry carries the string part of the alias name as its identity, because clause 6.2 requires the namespace to be ignored when comparing AliasNames — but aliasNameNamespaceUri still reports the namespace it was published in, so a Server does not have to invent one. Omit it and the binding falls back to the Server's own namespace, never to namespace 0, which is reserved for the OPC Foundation.

Three arrays are parallel to referencedNodes, same length and same order:

| Field | Meaning | |---|---| | serverUris | null for a Node on the local Server (clause 7.3) | | referenceTypeIds | AliasFor or the subtype reaching that target (clause 8.2) |

The order of referencedNodes is the store's responsibility and is never reordered: an AliasComparator orders entries relative to one another, and merging by name appends rather than re-sorts.

add and delete return one StatusCode per entry, parallel to the entries passed in, because clauses 6.3.4 and 6.3.5 report per item rather than per call — a single target on another Server yields Uncertain_ReferenceOutOfServer while its siblings succeed.

License

MIT — see LICENSE.