yang-form-foundry

Turn a YANG model into an ng-form-foundry schema your Angular app can render, then revert the edited form value back to RFC 7951 instance data for write-back to a NETCONF/RESTCONF datastore.

Framework-agnostic Node + TypeScript — no framework imports. NestJS is the likely host, but the library assumes only Node; wire it into Express, a worker, or a CLI just as easily.

import { YangFormAdapter, SubprocessEngine } from 'yang-form-foundry';

const adapter = new YangFormAdapter(new SubprocessEngine());

// resolve a device model once (cached by modelId)
await adapter.compile({
  modelId: 'acme-router@2026-01-01',
  entryModule: 'ietf-interfaces',
  source: { kind: 'dir', path: './yang' },
});

// forward: hand the Angular app a NodeGroup it renders with buildFormFromSchema
const schema = await adapter.getFormSchema('acme-router@2026-01-01');

// load the device's current config into a plain form value
const value = await adapter.toFormValue(deviceGetResponse, 'acme-router@2026-01-01');

// reverse: the edited form value → RFC 7951 JSON, ready for a RESTCONF PUT
const rfc7951 = await adapter.toYangData(editedValue, 'acme-router@2026-01-01');

What it does

• Forward — maps a resolved YANG tree to an ng-form-foundry NodeGroup (container → nodeGroup, list → nodeGroupList, leaf/leaf-list → leaf/leafList).
• Reverse — reconstructs RFC 7951 JSON from a plain form value, restoring module-namespaced member names, list keys, and — critically — int64/uint64/decimal64 as strings so precision survives. config false state is shown for context but dropped from write-back.
• Binding stays server-side — the frontend only ever sees the NodeGroup schema and returns a plain value; the resolved YANG model (the "binding") never leaves the adapter.

Architecture

The only part that touches YANG semantics or the environment is the injected YangEngine:

• SubprocessEngine (recommended) shells out to the bundled Python helper, which wraps pyang (and yangson, later) to resolve uses/augment/typedef and emit a normalized effective tree. Requires Python + pip install pyang on the host.
• FakeEngine serves pre-resolved models — used in tests and local dev, no Python required.

Caching is pluggable too (ArtifactCache; an InMemoryCache ships by default).

Using it from NestJS

The core is a plain class, so a NestJS provider is a thin wrapper — see examples/nestjs-provider.ts. A dedicated /nestjs entry point is planned.

Status

0.1.0, early. Structure: container / list (+keys) / leaf / leaf-list. Leaf types now covered:

| YANG type | Form control | Notes | | --- | --- | --- | | string, boolean, int/uint 8–32 | text / checkbox / number | direct | | int64, uint64, decimal64 | text | kept as strings (precision-safe) | | enumeration, identityref | enum (dropdown) | identityref re-qualified across modules | | empty | checkbox | [null] when set, omitted when not | | bits | group of checkboxes | reverts to the space-separated set | | binary, instance-identifier, leafref, union | text | member types / leafref path kept in the binding |

Structural types: plain container → nodeGroup; presence container → nodeGroup flagged presence: true, rendered as an on/off toggle in ng-form-foundry (present-but-empty round-trips as {}, absent is omitted). choice/case → a Choice node: in the form value the selection is { __case, ...fields }, and the adapter flattens it to the inline YANG encoding on write-back (the selected case's fields serialize with no wrapper).

ng-form-foundry renders a choice as a case selector plus the selected case's fields. Remaining: must/when cross-field validity, left to server-side validation — see the adapter plan.

Develop

npm install
npm run build   # tsc -> dist/
npm test        # node:test on the compiled output (no Python needed)

License

Apache-2.0 © Mathias Santos de Brito