Always add the payment address when probing an invoice

[ziggie1984]

Fixes: #10438

[gemini-code-assist]

Summary of Changes

Hello @ziggie1984, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a subtle but critical bug in the invoice probing mechanism. Previously, the payment address might not have been correctly included in probe requests due to an uninitialized slice, leading to potential issues in payment path finding. The change ensures that the payment address slice is always properly sized before data is copied, thereby guaranteeing that the payment address is consistently added when an invoice is probed, improving the reliability of the routing process.

Highlights

• Payment Address Copy Fix: Resolved an issue where the payment address was not being correctly copied when probing an invoice. This occurred because the destination slice (probeRequest.PaymentAddr) was not initialized with a sufficient size, causing the copy operation to be ineffective.
• Slice Initialization: Ensured that the probeRequest.PaymentAddr slice is explicitly initialized with lntypes.HashSize before the payment address data is copied into it, guaranteeing that the address is always properly included in the probe request.

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[gemini-code-assist]

Code Review

This pull request fixes a bug where probing an invoice with a payment address would not work correctly because the destination slice for the copy operation was not initialized. The change correctly initializes the slice before copying.

My review includes a comment pointing out a similar bug in the same function for LSP route probing, which should also be fixed to ensure the feature works as intended in all cases.

[hieblmi]

Thanks for the fix, LGTM!

[github-actions]

Git push to origin failed for v0.20.x-branch with exitcode 1

[github-actions]

Created backport PR for v0.20.x-branch:

• [v0.20.x-branch] Backport #10439: Always add the payment address when probing an invoice #10445 with remaining conflicts!

Please cherry-pick the changes locally and resolve any conflicts.

git fetch origin backport-10439-to-v0.20.x-branch
git worktree add --checkout .worktree/backport-10439-to-v0.20.x-branch backport-10439-to-v0.20.x-branch
cd .worktree/backport-10439-to-v0.20.x-branch
git reset --hard HEAD^
git cherry-pick -x 1c4bcc3b7dba14ed52c69f4b7041bd431d528c49 ac30443cc19b0213912bc704462ddf5af7feae50
git push --force-with-lease