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LNbits 1.x sends the payment object as a JSON string inside the webhook body, effectively double-encoding it. The route used Express's default strict JSON parser, which rejected the top-level string with 400. Even with an object body, the strict Zod schema rejected LNbits' extra payment fields.
As a result, paid invoices were only confirmed by the maintenance poll up to a minute later, while the invoice page still showed “waiting for payment”.
Fix
/callbacks/lnbits now uses json({ strict: false }), accepting both object and JSON-string bodies.
The controller parses string bodies and returns 400 Malformed body for invalid JSON.
The body schema is no longer strict; it validates payment_hash and strips LNbits' extra fields.
HMAC verification and invoice lookup from LNbits remain unchanged.
Non-functional change (docs, style, minor refactor)
Bug fix (non-breaking change which fixes an issue)
New feature (non-breaking change which adds functionality)
Breaking change (fix or feature that would cause existing functionality to change)
Checklist:
My code follows the code style of this project.
My change requires a change to the documentation.
I have updated the documentation accordingly.
I have read the CONTRIBUTING document.
I have added tests to cover my code changes.
I added a changeset, or this is docs-only and I added an empty changeset.
All new and existing tests passed.
Summary by CodeRabbit
New Features
LNbits callbacks now accept payment data sent as either a JSON object or a JSON-encoded string. Valid payment requests can include additional fields, which are ignored during validation.
Bug Fixes
Invalid JSON callback bodies return a clear malformed-body response instead of proceeding to invoice lookup.
No actionable comments were generated in the recent review.
Walkthrough
The LNbits callback route now accepts JSON string bodies. The controller parses string bodies before validation, and the schema strips unknown fields while validating the payment data. Malformed JSON strings return 400 Malformed body.
The /lnbits route accepts non-object JSON values. The controller parses string bodies, returns 400 Malformed body when parsing fails, and passes validated data to invoice processing. The schema strips unknown fields. Tests cover string and object bodies, extra fields, and malformed JSON. The changeset records the callback-body update.
Issue 1066 describes LNbits 1.x callback bodies rejected by strict schema validation. This PR adds parsing for string bodies and strips extra fields during validation.
Merge Risk: Minimal · up to 0832f
The callback compatibility change is mergeable after normal checks; no specific remaining risk is established.
Security architecture risk: Low · up to 0832f
The callback accepts additional body formats while preserving HMAC checks, payment-hash validation and provider-side payment verification. No introduced authorization bypass was identified. Existing recovery limitations and unverified production concurrency leave limited residual uncertainty.
Retained concerns
No architecture-level concerns identified.
Security review details
Security Blast Radius
inferred — The sensitive path remains invoice lookup, persistence, confirmation and notification in an application configured for LNbits. Additional body representations do not introduce new payment identities or authority: the same hash could already be submitted in a minimal object body.
Trust Boundaries and Controls
observed — The route rejects requests when payments are disabled or another processor is selected. The controller verifies a secret-derived HMAC and unexpired timestamp before inner-body processing. That HMAC authenticates the expiry, not the payment hash or body; this authority scope existed before the PR and is not widened by accepting another representation of the same hash.
Resilience and Maintainability Implications
observed — Confirmation retains a database-side confirmed_at guard and a serializable transaction, providing an existing control against repeating confirmation-side effects. The PR does not alter this control. Exact concurrent transaction outcomes were not verified against a production database, and notification remains outside the confirmation transaction.
Pre-merge checks: 5
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The title clearly describes the main change: accepting LNbits 1.x callback bodies.
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No eligible functions found in the changed files. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentat…
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No eligible functions found in the changed files. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentation-only edits and deletions within surviving functions are included; unchanged diff context and fully deleted functions are excluded. Analyzed 0 functions across 6 files. (1 skipped: 1 unsupported.)
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Autofix · Keep fixing CodeRabbit findings and required CI, and resolving merge conflicts
A rabbit checks the callback stream JSON strings now join the team Extra fields fall away with care A valid hash goes onward there “Malformed!” gets a four-oh-oh Then off to invoice lookup we go!
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Accepts LNbits callbacks as either plain objects or JSON-encoded strings.
LNbits 1.x callbacks can reach invoice confirmation.
No actionable issues found. Tests were inspected but not run.
Diagram
%%{init: {'theme': 'neutral'}}%%
flowchart TD
A[LNbits callback] --> B[Check active provider]
B --> C[Parse JSON, allowing strings]
C --> D[Verify HMAC]
D --> E{Body is a string?}
E -->|Yes| F[Decode inner JSON]
E -->|No| G[Check payment_hash]
F --> G
G --> H[Read invoice from LNbits]
H --> I[Existing invoice update and confirmation]
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Description
Problem
LNbits 1.x sends the payment object as a JSON string inside the webhook body, effectively double-encoding it. The route used Express's default strict JSON parser, which rejected the top-level string with
400. Even with an object body, the strict Zod schema rejected LNbits' extra payment fields.As a result, paid invoices were only confirmed by the maintenance poll up to a minute later, while the invoice page still showed “waiting for payment”.
Fix
/callbacks/lnbitsnow usesjson({ strict: false }), accepting both object and JSON-string bodies.400 Malformed bodyfor invalid JSON.payment_hashand strips LNbits' extra fields.Related Issue
Closes - #1066
Motivation and Context
How Has This Been Tested?
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Types of changes
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Summary by CodeRabbit