feat: fetch --dry-run previews the price without paying

[reneaaron]

What

Adds fetch --dry-run: sends the request unpaid and reports the 402 challenge instead of settling it. Needs no wallet.

$ alby fetch --dry-run "https://www.l402apps.com/api/apis"
{
  "url": "https://www.l402apps.com/api/apis",
  "status": 402,
  "payment_required": true,
  "amount_in_sats": 10,
  "description": "L402 Apps — Get APIs directory"
}

• Price in sats is extracted from wherever the protocol puts the lightning invoice: WWW-Authenticate (L402 ... invoice= / MPP Payment ... invoice=) or a lightning-native x402's base64 Payment-Required header.
• When no lightning invoice is offered (e.g. a USDC-only x402 hit directly instead of through the l402.space bridge), the raw challenge is surfaced so the terms are still visible.
• A free endpoint reports payment_required: false.
• Payment flags (--max-amount/--currency/--unit/--network/--credentials) are rejected alongside --dry-run since a dry run never pays.

Why

From the review discussion on getAlby/payments-skill#28: prices listed on 402index.io can be missing, stale, or dynamic — the 402 challenge is the authoritative price at request time, but checking it previously meant hand-crafting a curl. Use case: comparing prices between two providers before paying.

Per that discussion this is deliberately not documented in the skill for now — the --max-amount default already guards automated flows.

Test

• yarn test green (111 pass, 2 skipped); 5 new unit tests cover L402, MPP, base64-x402 extraction, no-lightning-challenge fallback, and free endpoints (using a real BOLT-11 so decoding is exercised).
• Verified live against all three challenge shapes without paying: native L402 (10 sats), bridged x402 via l402.space (19 sats), lightning-native x402 (15 sats).

Summary by CodeRabbit

• New Features

  • Added a --dry-run option to preview request pricing without making payments.
  • Reports Lightning invoice amounts, descriptions, payment challenges, and non-payment response statuses.
  • Supports pricing details from multiple payment challenge formats and response bodies.

• Bug Fixes

  • Standardized request handling, including automatic JSON content types for applicable requests.

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Review details

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 9a676cdb-059b-4f5f-a40f-4da91e5236f7

📥 Commits

Reviewing files that changed from the base of the PR and between 46cd43b and ff7e19c.

📒 Files selected for processing (2)

• src/test/fetch-dry-run.test.ts
• src/tools/lightning/fetch.ts

📝 Walkthrough

Walkthrough

The fetch command adds a --dry-run mode that performs requests without a wallet, detects 402 payment challenges, extracts Lightning invoice pricing, and reports non-payment responses. Request option construction is shared with the existing payment flow and covered by new tests.

Changes

Fetch dry-run flow

Layer / File(s)	Summary
Shared request option construction src/tools/lightning/fetch.ts	Centralizes request method, JSON body, and default content-type handling for fetch402.
Dry-run response parsing src/tools/lightning/fetch.ts, src/test/fetch-dry-run.test.ts	Adds dryRun402 and DryRun402Result, supporting Lightning invoice extraction from L402, MPP, x402, and response-body formats, with tests for invoice and non-402 responses.
Fetch CLI dry-run wiring src/commands/fetch.ts	Adds --dry-run, passes request parameters to dryRun402, outputs its result, and skips payment-related processing.

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

Sequence Diagram(s)

sequenceDiagram
  participant CLI
  participant dryRun402
  participant HTTPServer
  participant Invoice
  CLI->>dryRun402: Submit URL, method, body, and headers
  dryRun402->>HTTPServer: Send request without wallet
  HTTPServer-->>dryRun402: Return status and payment challenge
  dryRun402->>Invoice: Parse extracted BOLT11 invoice
  Invoice-->>dryRun402: Return amount and description
  dryRun402-->>CLI: Output dry-run result

Loading

Possibly related PRs

• getAlby/cli#7: Introduced the fetch and fetch402 pipeline extended by this dry-run flow.
• getAlby/cli#46: Previously modified the fetch pipeline and parameter handling used by this change.
• getAlby/cli#59: Also updates fetch402 recovery handling and fetch command payment-path wiring.

Suggested reviewers: rolznz

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main change: adding fetch --dry-run to preview price information without paying.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
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.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/fetch-dry-run

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Actionable comments posted: 3

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@src/commands/fetch.ts`:
- Around line 161-172: Change the dry-run branch in the fetch command to reject,
rather than silently ignore, any payment-related options: max-amount, currency,
unit, network, credentials, or resume. Add the validation before calling
dryRun402, report the invalid combination, and preserve the existing dry-run
behavior when none of those flags are supplied.

In `@src/tools/lightning/fetch.ts`:
- Around line 156-159: Update dryRun402 to enforce a request timeout by
supplying an AbortSignal or equivalent timeout through its fetch options,
matching the timeout behavior used by the paying path via fetch402Lib. Preserve
the existing URL, request construction, and response handling while ensuring
unresponsive targets cannot hang indefinitely.
- Around line 168-178: Update the invoice handling in dryRun402 around
extractLightningInvoice and new Invoice so malformed BOLT11 decoding is caught
with try/catch; only return the payment-required result after successful
decoding, and fall through to the existing raw-challenge fallback when
construction fails.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

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

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 1512f2e0-4d57-470a-ae96-ddf67b399ffb

📥 Commits

Reviewing files that changed from the base of the PR and between 48cbcea and 46cd43b.

📒 Files selected for processing (3)

• src/commands/fetch.ts
• src/test/fetch-dry-run.test.ts
• src/tools/lightning/fetch.ts