fix: validate payment and invoice amounts client-side

[ajaysehwal]

Summary

Problem

The SDK had almost no client-side amount validation. Methods such as makeInvoice, makeHoldInvoice, and payment flows only checked whether an amount was present:

if (!request.amount) {
  throw new Error("No amount specified");
}

This meant invalid values could be accepted and only fail later at the wallet, including:

• 0, negative numbers, NaN, non-integers, and Infinity
• Very large values without range or overflow checks
• Unsafe sats → msats conversion using * 1000 in LNClient and resolveAmount

Apps could therefore accidentally create or attempt payments with invalid amounts. While wallets would usually reject them, the failures happened late and could produce unclear errors.

Fix

Added shared validation utilities in utils.ts:

• assertPositiveIntegerAmount — rejects missing, non-finite, non-integer, zero/negative, and unsafe integer values
• satoshiToMillisat — validates satoshi amounts before converting them to millisats and protects against overflow

Applied validation to:

• NWCClient

  • makeInvoice
  • makeHoldInvoice
  • payKeysend
  • multiPayKeysend
  • Optional amount in payInvoice
  • Optional amount in multiPayInvoice

• LNClient

  • SATS()
  • resolveAmount()

Invalid amounts now fail immediately with clear errors before any NWC request is sent.

Notes

• payInvoice and multiPayInvoice still allow an omitted amount for normal and zero-amount invoices. Validation only runs when amount is explicitly provided.
• When paying a zero-amount invoice, callers must provide a positive amount representing the amount they intend to pay, not 0.
• Wallet-side balance and budget enforcement remain unchanged. This PR only adds client-side format and range validation.

Test Plan

yarn test src/utils.test.ts src/lnclient/Amount.test.ts src/nwc/NWCClient.test.ts

yarn typecheck

Summary by CodeRabbit

• Bug Fixes
  • Added validation to ensure payment and invoice amounts are positive whole numbers.
  • Invalid amounts—including zero, negative, fractional, non-finite, and overly large values—are now rejected before requests are sent.
  • Improved satoshi-to-millisatoshi conversion safeguards to prevent overflow.
  • Zero-amount invoices can still be paid when no amount is provided.
• Tests
  • Expanded coverage for valid amounts, invalid inputs, payment flows, and conversion boundaries.

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Review configuration:

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: a94f8c79-77c4-4836-a626-737518f63c09

📥 Commits

Reviewing files that changed from the base of the PR and between a007ae7 and e4c1741.

📒 Files selected for processing (2)

• src/nwc/NWCClient.test.ts
• src/nwc/NWCClient.ts

📝 Walkthrough

Walkthrough

Changes

The PR adds shared validation for positive, safe integer monetary amounts and safe satoshi-to-millisatoshi conversion. SATS, resolveAmount, and NWC payment and invoice methods now use these helpers. Tests cover valid values, invalid values, overflow, and optional invoice amounts.

Amount validation

Layer / File(s)	Summary
Validation and conversion helpers src/utils.ts, src/utils.test.ts	Adds assertPositiveIntegerAmount and satoshiToMillisat. Tests cover invalid values, safe-integer limits, conversion, and overflow.
Lightning amount conversion src/lnclient/Amount.ts, src/lnclient/Amount.test.ts	SATS and resolveAmount validate satoshi values and use shared millisatoshi conversion. Tests cover large valid values and invalid amounts.
NWC operation validation src/nwc/NWCClient.ts, src/nwc/NWCClient.test.ts	Invoice, keysend, and multi-payment methods validate amounts before requests. Tests cover invalid amounts and omitted payInvoice amounts.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Merge Risk: 🔵 Low · up to a007a

Optional payment amounts set to null can bypass validation and be sent to the wallet as an invalid amount, causing avoidable payment failures. The PR is otherwise mergeable with owner follow-up to reject explicit null values.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 4 functions across 6 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: client-side validation for payment and invoice amounts.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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Actionable comments posted: 1

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Inline comments:
In `@src/nwc/NWCClient.ts`:
- Around line 516-518: Update the amount validation guards in NWCClient at
src/nwc/NWCClient.ts lines 516-518 and 587-590 to check for !== undefined
instead of != null, so explicit null values are validated and rejected while
omitted undefined amounts remain allowed. Apply this to both request.amount and
invoiceRequest.amount.

🪄 Autofix

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 3f2815c7-1ea3-4b8e-bc3e-e0f4b7a2bead

📥 Commits

Reviewing files that changed from the base of the PR and between 5696f97 and a007ae7.

📒 Files selected for processing (6)

• src/lnclient/Amount.test.ts
• src/lnclient/Amount.ts
• src/nwc/NWCClient.test.ts
• src/nwc/NWCClient.ts
• src/utils.test.ts
• src/utils.ts

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