Fiber Dev Log 2026-09-17

[chenyukang]

Updates

Fiber v0.9.1 release was released on September 11, bringing fixes for payment settlement and force-close reconciliation, clearer channel-funding diagnostics, and configurable peer-message limits.

Beyond the release, work continues on Hosted LSP signing and recovery, liquidity swaps, and an updated on-chain settlement format.

Improvements & Fixes

Payment settlement follows the correct attempt and commitment

Concurrent payments to the same invoice can share a payment hash, but each forwarding attempt must follow its own downstream result. A fix in v0.9.1 restricts automatic fulfillment from the node's preimage store to locally terminated TLCs. Forwarded TLCs continue to resolve through their specific downstream channel and TLC, preventing a preimage learned from one attempt from incorrectly fulfilling another.

Force-close reconciliation now checks which TLCs belong to the commitment actually published on-chain. It verifies the historical settlement snapshot against the commitment lock and persists that snapshot for recovery. Offered updates excluded from the confirmed commitment can be failed back to the payer or upstream channel, while included TLCs remain subject to on-chain resolution. This addresses channels waiting for settlement of TLCs that were never included in the published commitment. Reconciliation still waits when a valid historical snapshot is unavailable.

• Scope preimage settlement to local TLCs
• Reconcile force-closed channels against the published commitment

Clearer funding failures and configurable traffic limits

Channel-opening failure records now retain the channel ID, the relevant funding phase, and the local failure cause where available. This gives operators more useful context when funding collaboration or transaction signing fails. Peer-facing abort messages use generic reasons, while detailed local diagnostics remain available for troubleshooting.

The release also makes peer-message admission limits configurable through fiber.peer_message_policy. Operators can adjust per-peer message and byte rates, temporary bans, and global in-flight message budgets. Omitted settings retain the existing defaults.

• Improve diagnostic clarity for funding failures
• Make peer-message rate limits configurable

Developer Experience

Browser configuration and native-node setup

The fiber-js example now shows how to adapt its bundled configuration for browsers: replace TCP bootnodes with secure WebSocket addresses and disable listening-address announcements. This builds on the default-configuration helper introduced in the previous update and addresses the browser's transport requirements explicitly.

Native-node documentation now pins both the installer and release bundle to v0.9.1. The guide covers Linux, macOS, and Windows setup, including key creation or import, reusable startup scripts, network separation, and backup requirements.

• Customize the fiber-js configuration for browsers
• Update native-node installation guidance for v0.9.1

Encrypted-data payments and liquidity labs

A new Testnet tutorial demonstrates a payment that unlocks encrypted data. Two browser-run Fiber nodes act as buyer and seller; after a successful invoice payment, the buyer uses the revealed payment preimage as the AES-GCM decryption key. The example includes a last-hop routing hint and a downloadable standalone application, showing how to connect payment completion to data access without an application backend.

Three interactive concept labs let readers explore directional channel liquidity, route bottlenecks and multi-path payments, and circular rebalancing. An accompanying liquidity guide explains these concepts in more depth. The guide and simulations are now grouped under Concepts → Liquidity.

• Add the encrypted-data payment tutorial
• Add interactive liquidity concept labs
• Add the Fiber liquidity guide

In Pipeline

Hosted LSP signing and recovery

The Hosted LSP draft has expanded channel-signing recovery work, including tests for tenant and signer restarts at several signing checkpoints. It also checks TLC safety deadlines during both channel maintenance and signature submission. A delayed signer response cannot resume the off-chain exchange after that deadline; timeout handling attempts to force-close using the latest stored signed commitment.

The implementation remains a prototype. Production signer delivery, session fencing, and an explicit signer-readiness check before dispatching buffered payments remain unfinished.

• WIP Hosted LSP implementation

Liquidity swap execution and recovery

The Loop In and Loop Out draft has expanded payout validation, transaction recovery, and provider-side Loop In payment and claim orchestration. Loop Out payment requests now carry the quoted UDT asset through to the payment adapter.

New real-process test suites exercise swap flows, provider restart recovery, UDT payout validation, and on-chain refund timing. Coverage remains bounded: the UDT Loop Out suite stops at the provider-payout stage, and automatic progression into the refund state remains unfinished. The work is still in draft.

• Develop liquidity management with Loop In and Loop Out

Full payment hashes in on-chain settlement

Coordinated node and commitment-lock changes are open for a settlement layout that carries the full 32-byte payment hash. The node implementation negotiates and persists the layout per channel and updates transaction construction, fee calculations, and watchtower parsing. The contract changes retain support for the legacy layout and add compatibility tests. Neither change is merged.

• Add node support for full-payment-hash settlement
• Add full-payment-hash support to the commitment lock