feat: Add BankCapabilities to expose bank feature flags by Copilot · Pull Request #36 · larsdecker/fints

Copilot · 2026-03-07T00:44:03Z

Banks vary in which FinTS business transactions they support. There was no way to discover this without probing each endpoint individually.

Changes

New `BankCapabilities` interface (`types.ts`)

Nine flags derived from parameter segments in the sync response:

Flag	FinTS source
`supportsAccounts`	always `true` (universally supported)
`supportsBalance`	HISALS present
`supportsTransactions`	HIKAZS present
`supportsHoldings`	HIWPDS present
`supportsStandingOrders`	HICDBS present
`supportsCreditTransfer`	HICCSS present
`supportsDirectDebit`	HIDSES present
`requiresTanForTransactions`	HIKAZS `minSignatures > 0`
`requiresTanForBalance`	HISALS `minSignatures > 0`

`Dialog` (`dialog.ts`)

Adds supportsCreditTransfer, supportsDirectDebit, hikazsMinSignatures, hisalsMinSignatures fields, populated during sync()
Adds capabilities getter that assembles BankCapabilities from current dialog state

`Client` (`client.ts`)

Adds capabilities(): Promise<BankCapabilities> — runs a sync dialog and returns dialog.capabilities

const client = new PinTanClient({ blz, name, pin, url });
const caps = await client.capabilities();

if (!caps.supportsTransactions) {
  console.log("This bank does not support statement fetching");
}
if (caps.requiresTanForBalance) {
  console.log("A TAN is needed to query balances");
}

BankCapabilities is exported from the package's public index.

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Co-authored-by: larsdecker <1968186+larsdecker@users.noreply.github.com>

- Add BankCapabilities interface to types.ts with 9 capability flags derived from FinTS parameter segments (HIKAZS, HISALS, HIWPDS, HICCSS, HIDSES, HICDBS) - Add supportsCreditTransfer, supportsDirectDebit, hikazsMinSignatures and hisalsMinSignatures fields to Dialog, populated during sync() - Add Dialog.capabilities getter assembling BankCapabilities from state - Add Client.capabilities() async method (sync + return capabilities) - Add tests in test-client.ts and test-dialog.ts Co-authored-by: larsdecker <1968186+larsdecker@users.noreply.github.com>

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chatgpt-codex-connector · 2026-03-07T01:19:49Z

packages/fints/src/dialog.ts

+        const hikazs = response.findSegment(HIKAZS);
+        this.hikazsMinSignatures = hikazs?.minSignatures ?? 0;
+        const hisals = response.findSegment(HISALS);
+        this.hisalsMinSignatures = hisals?.minSignatures ?? 0;


Derive TAN requirements from negotiated segment version

sync() determines supported HIKAZS/HISALS versions via segmentMaxVersion(...), but requiresTanForTransactions/requiresTanForBalance are populated from response.findSegment(...), which returns the first segment instance, not necessarily the version that will actually be used by requests. When a bank advertises multiple versions of these parameter segments and minSignatures differs between versions, dialog.capabilities can report incorrect TAN requirements; read minSignatures from the selected max version (or aggregate safely across all advertised versions).

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Copilot

Pull request overview

Adds a first-class way to discover which FinTS business transactions a bank advertises during the initial sync dialog, so callers can avoid probing endpoints individually.

Changes:

Introduce a new BankCapabilities interface to represent bank feature flags derived from sync parameter segments.
Extend Dialog.sync() to record additional capability-related fields and add a dialog.capabilities getter.
Add Client.capabilities() plus unit tests covering both Dialog and Client capability derivation.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
packages/fints/src/types.ts	Adds `BankCapabilities` interface and documentation.
packages/fints/src/dialog.ts	Captures additional sync-derived fields and exposes them via a `capabilities` getter.
packages/fints/src/client.ts	Adds `capabilities(): Promise<BankCapabilities>` convenience API.
packages/fints/src/tests/test-dialog.ts	Tests `Dialog.capabilities` mapping from dialog state.
packages/fints/src/tests/test-client.ts	Tests `Client.capabilities()` behavior using mocked sync/end responses.
IMPLEMENTATION_SUMMARY.md	Removed from repository in this PR.

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Copilot · 2026-03-07T01:21:31Z

packages/fints/src/dialog.ts

@@ -153,12 +174,18 @@ export class Dialog extends DialogConfig {
        this.hicdbVersion = response.segmentMaxVersion(HICDBS);


sync() sets hisalsVersion/hikazsVersion/hicdbVersion directly to segmentMaxVersion(...), which can be 0 when the parameter segment is absent. These version fields are later used to construct request segments (e.g. HKSAL/HKKAZ) that throw on unsupported versions, so this can cause a local "Unsupported ... version 0" error instead of a clear "feature not supported" result. Consider keeping the request version at a valid default (e.g. latest supported) and tracking support separately, or add explicit capability checks before constructing versioned request segments.

@copilot apply changes based on this feedback

Fixed in 3c89d4c. The approach:

Added dedicated supportsBalance, supportsTransactions, and supportsStandingOrders boolean fields (defaulting to false) alongside the existing supportsCreditTransfer/supportsDirectDebit pattern.

sync() now sets each boolean flag from segmentMaxVersion > 0 and only updates the request-version field when the bank actually advertises support — so hisalsVersion, hikazsVersion, and hicdbVersion keep their safe defaults (6, 6, 1) when the segment is absent, preventing any "Unsupported version 0" error in HKSAL/HKKAZ.

The capabilities getter now reads from the boolean fields rather than > 0 version checks, which also fixes incorrect pre-sync() values (the old defaults of 6/6/1 would have produced true before sync ran).

Also merged the two separate ./types import statements into one.

Copilot · 2026-03-07T01:21:31Z

packages/fints/src/dialog.ts

    HICCSS,
    Segment,
 } from "./segments";
+import { BankCapabilities } from "./types";


There are now two separate imports from ./types (Connection above and BankCapabilities here). Consider merging them into a single import to avoid duplication and keep import blocks consistent.

Copilot · 2026-03-07T01:21:32Z

packages/fints/src/dialog.ts

+    public get capabilities(): BankCapabilities {
+        return {
+            supportsAccounts: true,
+            supportsBalance: this.hisalsVersion > 0,
+            supportsTransactions: this.hikazsVersion > 0,


capabilities can return incorrect supports* values if accessed before sync() runs, because several *Version fields have non-zero defaults (e.g. hisalsVersion = 6, hikazsVersion = 6, hicdbVersion = 1). Consider adding a guard (e.g. track hasSynced and throw) or deriving support from fields that are only set during sync so consumers can’t accidentally get a misleading capabilities object.

Copilot · 2026-03-07T01:21:32Z

packages/fints/src/client.ts

+    public async capabilities(): Promise<BankCapabilities> {
+        const dialog = this.createDialog();
+        await dialog.sync();
+        return dialog.capabilities;
+    }


The PR description focuses on adding BankCapabilities, but the diff also removes IMPLEMENTATION_SUMMARY.md entirely. If that removal is intentional cleanup, please mention it in the PR description or move it to a separate PR to keep this change focused.

larsdecker · 2026-03-17T23:46:38Z

@copilot apply changes based on the comments in this thread

- Add supportsBalance, supportsTransactions, supportsStandingOrders boolean fields (default false) to Dialog, populated during sync() - Keep hisalsVersion, hikazsVersion, hicdbVersion at their safe defaults when the bank does not advertise the feature, preventing 'Unsupported version 0' errors in HKSAL/HKKAZ constructors - Update capabilities getter to use the new boolean fields instead of version > 0 checks, fixing misleading results before sync() runs - Merge the two separate import blocks from ./types into one - Add pre-sync capabilities test to test-dialog.ts Co-authored-by: larsdecker <1968186+larsdecker@users.noreply.github.com>

This file pre-existed and was unintentionally removed in the feature commit. Restoring it to keep this PR focused on the BankCapabilities feature only. Co-authored-by: larsdecker <1968186+larsdecker@users.noreply.github.com>

Copilot · 2026-03-17T23:54:31Z

@copilot apply changes based on the comments in this thread

All four review comments are now addressed:

dialog.ts:172-174 (3c89d4c) — sync() now keeps hisalsVersion/hikazsVersion/hicdbVersion at their safe defaults when the segment is absent and tracks support via dedicated supportsBalance/supportsTransactions/supportsStandingOrders booleans instead.
dialog.ts:18 (3c89d4c) — Duplicate ./types imports merged into one.
dialog.ts:364-368 (3c89d4c) — capabilities getter now reads from the boolean fields (all default false), so it returns correct values both before and after sync().
client.ts:70-74 (318cfba) — IMPLEMENTATION_SUMMARY.md was a pre-existing file accidentally deleted in the feature commit; it has been restored.

Initial plan

9c9db11

Copilot AI assigned Copilot and larsdecker Mar 7, 2026

Copilot started work on behalf of larsdecker March 7, 2026 00:44 View session

Copilot AI and others added 2 commits March 7, 2026 00:53

chore: initial plan setup

d2a0397

Co-authored-by: larsdecker <1968186+larsdecker@users.noreply.github.com>

Copilot AI changed the title ~~[WIP] Add feature flags for bank capabilities~~ feat: Add BankCapabilities to expose bank feature flags Mar 7, 2026

Copilot finished work on behalf of larsdecker March 7, 2026 01:00

larsdecker marked this pull request as ready for review March 7, 2026 01:16

Copilot AI review requested due to automatic review settings March 7, 2026 01:16

Copilot started reviewing on behalf of larsdecker March 7, 2026 01:17 View session

chatgpt-codex-connector bot reviewed Mar 7, 2026

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Copilot AI reviewed Mar 7, 2026

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Copilot started work on behalf of larsdecker March 17, 2026 23:46 View session

Copilot AI requested a review from larsdecker March 17, 2026 23:51

Copilot finished work on behalf of larsdecker March 17, 2026 23:51

Copilot started work on behalf of larsdecker March 17, 2026 23:51 View session

Copilot finished work on behalf of larsdecker March 17, 2026 23:54

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		@@ -153,12 +174,18 @@ export class Dialog extends DialogConfig {
		this.hicdbVersion = response.segmentMaxVersion(HICDBS);

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Changes

New BankCapabilities interface (types.ts)

Dialog (dialog.ts)

Client (client.ts)

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New `BankCapabilities` interface (`types.ts`)

`Dialog` (`dialog.ts`)

`Client` (`client.ts`)