routerrpc: add validation to MPP params #9603

NishantBansal2003 · 2025-03-13T17:20:22Z

Change Description

Fixes: #8916
Adds validation to ensure that MPP parameters are compatible with the payment amount before attempting the payment. This prevents payments from entering a path finding loop that would eventually timeout.

Steps to Test

Added itest to validate that a payment with multipath parameters exceeding the allowed maximum amount fails with the expected error.

Pull Request Checklist

Testing

Your PR passes all CI checks.
Tests covering the positive and negative (error paths) are included.
Bug fixes contain tests triggering the bug to prevent regressions.

Code Style and Documentation

The change is not insubstantial. Typo fixes are not accepted to fight bot spam.
The change obeys the Code Documentation and Commenting guidelines, and lines wrap at 80.
Commits follow the Ideal Git Commit Structure.
Any new logging statements use an appropriate subsystem and logging level.
Any new lncli commands have appropriate tags in the comments for the rpc in the proto file.
There is a change description in the release notes, or [skip ci] in the commit message for small changes.

📝 Please see our Contribution Guidelines for further guidance.

coderabbitai · 2025-03-13T17:20:31Z

Important

Review skipped

Auto reviews are limited to specific labels.

🏷️ Labels to auto review (1)

llm-review

Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

🪧 Tips

Chat

There are 3 ways to chat with CodeRabbit:

Review comments: Directly reply to a review comment made by CodeRabbit. Example:
- I pushed a fix in commit <commit_id>, please review it.
- Generate unit testing code for this file.
- Open a follow-up GitHub issue for this discussion.
Files and specific lines of code (under the "Files changed" tab): Tag @coderabbitai in a new review comment at the desired location with your query. Examples:
- @coderabbitai generate unit testing code for this file.
- @coderabbitai modularize this function.
PR comments: Tag @coderabbitai in a new PR comment to ask questions about the PR branch. For the best results, please provide a very specific query, as very limited context is provided in this mode. Examples:
- @coderabbitai gather interesting stats about this repository and render them as a table. Additionally, render a pie chart showing the language distribution in the codebase.
- @coderabbitai read src/utils.ts and generate unit testing code.
- @coderabbitai read the files in the src/scheduler package and generate a class diagram using mermaid and a README in the markdown format.
- @coderabbitai help me debug CodeRabbit configuration file.

Note: Be mindful of the bot's finite context window. It's strongly recommended to break down tasks such as reading entire modules into smaller chunks. For a focused discussion, use review comments to chat about specific files and their changes, instead of using the PR comments.

CodeRabbit Commands (Invoked using PR comments)

@coderabbitai pause to pause the reviews on a PR.
@coderabbitai resume to resume the paused reviews.
@coderabbitai review to trigger an incremental review. This is useful when automatic reviews are disabled for the repository.
@coderabbitai full review to do a full review from scratch and review all the files again.
@coderabbitai summary to regenerate the summary of the PR.
@coderabbitai generate docstrings to generate docstrings for this PR.
@coderabbitai resolve resolve all the CodeRabbit review comments.
@coderabbitai plan to trigger planning for file edits and PR creation.
@coderabbitai configuration to show the current CodeRabbit configuration for the repository.
@coderabbitai help to get help.

Other keywords and placeholders

Add @coderabbitai ignore anywhere in the PR description to prevent this PR from being reviewed.
Add @coderabbitai summary to generate the high-level summary at a specific location in the PR description.
Add @coderabbitai anywhere in the PR title to generate the title automatically.

CodeRabbit Configuration File (`.coderabbit.yaml`)

You can programmatically configure CodeRabbit by adding a .coderabbit.yaml file to the root of your repository.
Please see the configuration documentation for more information.
If your editor has YAML language server enabled, you can add the path at the top of this file to enable auto-completion and validation: # yaml-language-server: $schema=https://coderabbit.ai/integrations/schema.v2.json

Documentation and Community

Visit our Documentation for detailed information on how to use CodeRabbit.
Join our Discord Community to get help, request features, and share feedback.
Follow us on X/Twitter for updates and announcements.

yyforyongyu

Thanks for the PR! Left a few comments re the format and test.

yyforyongyu · 2025-03-17T12:00:10Z

itest/lnd_mpp_test.go

-		FeeLimitMsat:   noFeeLimitMsat,
+		PaymentRequest:   payReq,
+		MaxParts:         10,
+		MaxShardSizeMsat: 30_000_000,


why do we need to set MaxShardSizeMsat here?

To validate that when the mpp params permit sending the full payment amount, the payment is successfully settled. I'll add a comment in the test to make this clear.

Instead of just adding here the MaxShardSizeMsat please create a separate test which tests exactly the validation. This separates the test cases nicely and can be build integrating your test above testValidateMPPParams. First trying a lower shard amount and then increasing it and succeeding.

yyforyongyu · 2025-03-17T12:00:41Z

itest/lnd_mpp_test.go

+// testValidateMPPParams validates that a payment with multipath parameters
+// exceeding the allowed maximum amount fails with the expected error.
+func testValidateMPPParams(
+	ht *lntest.HarnessTest, mts *mppTestScenario, paymentAmt btcutil.Amount,


the format is not quite right, see https://github.com/lightningnetwork/lnd/blob/master/docs/code_formatting_rules.md#wrapping-long-function-definitions

yyforyongyu · 2025-03-17T12:07:38Z

itest/lnd_mpp_test.go

@@ -53,6 +85,9 @@ func testSendMultiPathPayment(ht *lntest.HarnessTest) {
 		mts.alice, mts.dave, expectedPolicy, chanPointAliceDave, false,
 	)

+	// Validate that multipath payment parameters are enforced correctly.
+	testValidateMPPParams(ht, mts, paymentAmt)


Also check this in testSendToRouteMultiPath?

yyforyongyu

LGTM🌹

ziggie1984

Thanks for the fix, left some comments.

lnrpc/routerrpc/router_backend.go

ziggie1984 · 2025-03-19T17:14:56Z

itest/lnd_mpp_test.go

+// exceeding the allowed maximum amount fails with the expected error.
+func testValidateMPPParams(ht *lntest.HarnessTest, mts *mppTestScenario,
+	paymentAmt btcutil.Amount) {
+	// Create an invoice from Bob for the payment.


Nit: New line above

ziggie1984 · 2025-03-19T17:28:40Z

itest/lnd_mpp_test.go

-		FeeLimitMsat:   noFeeLimitMsat,
+		PaymentRequest:   payReq,
+		MaxParts:         10,
+		MaxShardSizeMsat: 30_000_000,


Instead of just adding here the MaxShardSizeMsat please create a separate test which tests exactly the validation. This separates the test cases nicely and can be build integrating your test above testValidateMPPParams. First trying a lower shard amount and then increasing it and succeeding.

yyforyongyu · 2025-03-20T14:34:20Z

lnrpc/routerrpc/router_backend.go

+	// payment amount. In other words, the parameters are invalid if
+	// they do not permit sending the full payment amount.
+	if rpcPayReq.MaxShardSizeMsat > 0 {
+		if payIntent.MaxParts > MaxPartsUpperLimit {


this check should be moved to where we assign payIntent.MaxParts at L863 so we can exit early.

Let's put it at L873, since the MPP will only be used when MaxShardSizeMsat > 0. So, if MaxShardSizeMsat is not being set, then there is no issue with the value of MaxParts?

yyforyongyu · 2025-03-20T14:43:18Z

lnrpc/routerrpc/router_backend.go

+	// Validate that the MPP parameters are compatible with the
+	// payment amount. In other words, the parameters are invalid if
+	// they do not permit sending the full payment amount.
+	if rpcPayReq.MaxShardSizeMsat > 0 {


think we should check payIntent.MaxShardAmt for clarity.

lnrpc/routerrpc/router_backend.go

yyforyongyu · 2025-03-20T14:51:03Z

itest/lnd_mpp_test.go

+	//      \              /
+	//       \__ Dave ____/
+	//
+	paymentAmt := mts.setupSendPaymentCase()


For a simple test like this, I'd say we use ht.CreateSimpleNetwork instead as we are not testing the routing behavior here.

yyforyongyu · 2025-03-20T14:51:17Z

itest/lnd_mpp_test.go

+	//
+	paymentAmt := mts.setupSendPaymentCase()
+
+	// First, test that Alice's payment to Bob fails when the multipath


The comment needs to be updated.

yyforyongyu · 2025-03-20T14:52:37Z

itest/lnd_mpp_test.go

+
+		success := ht.Run(test.name, func(t *testing.T) {
+			// Bob creates an invoice for the payment.
+			payReqs, _, _ := ht.CreatePayReqs(mts.bob, paymentAmt,


I think we can instead create a single invoice for the whole test case as we know only the last send payment will succeed.

yyforyongyu · 2025-03-20T14:54:03Z

itest/lnd_mpp_test.go

+	require.Equal(ht, hex.EncodeToString(invoices[0].RPreimage),
+		payment.PaymentPreimage, "preimage doesn't match")
+
+	// Verify that Bob records the invoice as settled for the full amount.


Can use ht.AssertInvoiceSettled instead.

ziggie1984

I think we should just add a unit-test instead of adding a itest.

Moreover let's remove the minRequired parts check yy has a valid point.

lnrpc/routerrpc/router_backend.go

ziggie1984 · 2025-03-20T17:46:43Z

lnrpc/routerrpc/router_backend.go

@@ -36,6 +36,10 @@ const (
 	// TODO(roasbeef): make this value dynamic based on expected number of
 	// attempts for given amount.
 	DefaultMaxParts = 16
+
+	// MaxPartsUpperLimit defines the maximum allowable number of splits
+	// for MPP when the user is attempting to send a payment.


it's MPP/AMP

ziggie1984 · 2025-03-20T17:57:07Z

itest/lnd_mpp_test.go

+// fails with the expected error when the payment amount exceeds the allowed
+// maximum, and that when the multipath parameters permit the full payment
+// amount, the payment is successfully settled.
+func testValidateMPPParams(ht *lntest.HarnessTest) {


Personally I think a itest for this change might be a bit overkill, can we not just test the extractIntentFromSendRequest via a unit-test in router_backend_test.go ?

ziggie1984

Nice, left some comments.

lnrpc/routerrpc/router_backend.go

ziggie1984 · 2025-03-21T16:24:37Z

lnrpc/routerrpc/router_backend_test.go

+	maxPartsInput    uint32
+	shardAmountMsat  uint64


Nit: Why not keep the naming here from the above code ?

maxShardAmt, maxParts ?

ziggie1984 · 2025-03-21T16:35:27Z

lnrpc/routerrpc/router_backend_test.go

+	valid            bool
+	expectedErrorMsg string
+}
+


Missing godoc, would be great if you could properly test the whole extract func. otherwise create a comment which specifies that you are in specific only testing the shard multipart payment logic.

I have added tests for the entire extract function.

ziggie1984 · 2025-03-21T16:36:46Z

lnrpc/routerrpc/router_backend_test.go

+	}
+
+	for _, testCase := range testCases {
+		testCase := testCase


I think this iis not necessary anymore with the go compiler option loopvar

ziggie1984 · 2025-03-21T16:40:12Z

lnrpc/routerrpc/router_backend_test.go

+	for _, testCase := range testCases {
+		testCase := testCase
+		t.Run(testCase.name, func(t *testing.T) {
+			runExtractIntentTest(t, backend, testCase)


add t.Parallel() to speed up testing.

yyforyongyu

Nice test!

lnrpc/routerrpc/router_backend_test.go

MPins

Well done 👍

Left some comments that might help make the test a bit cleaner.

MPins · 2025-03-28T11:32:47Z

lnrpc/routerrpc/router_backend_test.go

@@ -475,3 +476,348 @@ func testUnmarshalAMP(t *testing.T, test unmarshalAMPTest) {
 		t.Fatalf("test case has non-standard outcome")
 	}
 }
+
+type ExtractIntentTestCase struct {


nit: this struct doesn't need to be exported, so it can start with a lowercase letter.

MPins · 2025-03-28T11:36:37Z

lnrpc/routerrpc/router_backend_test.go

+			backend: &RouterBackend{
+				MaxTotalTimelock: 1000,
+			},


nit: Setting MaxTotalTimelock is not needed.

MPins · 2025-03-28T11:38:42Z

lnrpc/routerrpc/router_backend_test.go

+			backend: &RouterBackend{
+				MaxTotalTimelock: 1000,
+			},


nit: Setting MaxTotalTimelock is not needed.

MPins · 2025-03-28T11:38:49Z

lnrpc/routerrpc/router_backend_test.go

+			backend: &RouterBackend{
+				MaxTotalTimelock: 1000,
+			},


nit: Setting MaxTotalTimelock is not needed.

MPins · 2025-03-28T11:39:11Z

lnrpc/routerrpc/router_backend_test.go

+			backend: &RouterBackend{
+				MaxTotalTimelock: 1000,
+			},


nit: Setting MaxTotalTimelock is not needed.

MPins

Looking closer, I found some missing tests and suggest a few naming changes to make it clearer what each test is actually doing.

Besides the suggested additions I made, we could also add a test for the case where the invoice has an amount specified and the payer is not allowed to override it. However, to test that properly, we would need a non-expired invoice. I don't think it's strictly necessary, though.

MPins · 2025-03-28T17:51:24Z

lnrpc/routerrpc/router_backend_test.go

+				"outgoing_chan_ids are mutually exclusive",
+		},
+		{
+			name:    "Invalid last hop pubkey",


nit: I would change the name of the test to "Invalid last hop pubkey length".

MPins · 2025-03-28T17:56:36Z

lnrpc/routerrpc/router_backend_test.go

+			name:    "Invalid last hop pubkey",
+			backend: &RouterBackend{},
+			sendReq: &SendPaymentRequest{
+				OutgoingChanId: 38484,


nit: Setting OutgoingChanId is not needed.

MPins · 2025-03-28T18:48:33Z

lnrpc/routerrpc/router_backend_test.go

+				"mutually exclusive",
+		},
+		{
+			name:    "Dest custom records with type below minimum",


nit: I would change the name of the test to "Dest custom records with type below minimum range"

MPins · 2025-03-28T18:51:35Z

lnrpc/routerrpc/router_backend_test.go

+			name: "Custom record entry with TLV type below " +
+				"minimum",


nit: I would change the name of the test to "Custom record entry with TLV type below minimum range"

MPins · 2025-03-28T18:56:07Z

lnrpc/routerrpc/router_backend_test.go

+				"payment_request cannot appear together",
+		},
+		{
+			name: "Invalid payment request",


nit: I would change the name of the test to "Invalid payment request length"

MPins · 2025-03-28T19:08:43Z

lnrpc/routerrpc/router_backend_test.go

+				"support AMP payments",
+		},
+		{
+			name: "Invalid payment hash",


nit: I would change the name of the test to "Invalid payment hash length"

MPins · 2025-03-28T20:41:29Z

lnrpc/routerrpc/router_backend_test.go

+			},
+			valid:            false,
+			expectedErrorMsg: "invalid vertex length",
+		},


You can add the test below to increase the code coverage:

{ name: "total time lock exceeds max allowed", backend: &RouterBackend{ MaxTotalTimelock: 1000, }, sendReq: &SendPaymentRequest{ CltvLimit: 1001, }, valid: false, expectedErrorMsg: "total time lock of 1001 exceeds "+ "max allowed 1000", },

MPins · 2025-03-28T20:44:17Z

lnrpc/routerrpc/router_backend_test.go

+			valid: false,
+			expectedErrorMsg: "sat and msat arguments are " +
+				"mutually exclusive",
+		},


You can add the test below to increase the code coverage:

{ name: "Fee limit cannot be negative", backend: &RouterBackend{}, sendReq: &SendPaymentRequest{ FeeLimitSat: -1, }, valid: false, expectedErrorMsg: "amount cannot be negative", },

NishantBansal2003 · 2025-03-29T04:16:21Z

we could also add a test for the case where the invoice has an amount specified and the payer is not allowed to override it. However, to test that properly, we would need a non-expired invoice.

Yes, we require a non-expired invoice, which is why I was unable to add a test for it. Perhaps, in such cases, "itest" would suffice?

MPins

LGTM

MPins · 2025-03-30T10:55:02Z

suffice
Maybe creating an iTest is too much just to cover this use case.

ziggie1984 · 2025-03-31T16:02:36Z

you can use: make unit-cover case=TestExtractIntentFromSendRequest and check the result coverage file for extractIntentFromSendRequest function to check if everything is covered using: go tool cover -html=coverage.txt, thats a pretty nice check on your tests.

Adds validation to ensure that MPP parameters are compatible with the payment amount before attempting the payment. This prevents payments from entering a path finding loop that would eventually timeout. Signed-off-by: Nishant Bansal <[email protected]>

Signed-off-by: Nishant Bansal <[email protected]>

NishantBansal2003 · 2025-04-02T11:22:18Z

you can use: make unit-cover case=TestExtractIntentFromSendRequest and check the result coverage file for extractIntentFromSendRequest function to check if everything is covered using: go tool cover -html=coverage.txt, thats a pretty nice check on your tests.

Thanks, this helped! I have also updated the tests for the latest changes.

lightninglabs-deploy · 2025-04-09T11:47:27Z

@ziggie1984: review reminder

saubyk assigned NishantBansal2003 Mar 14, 2025

NishantBansal2003 force-pushed the validate-mpp branch from 91c0f3d to f4513f2 Compare March 14, 2025 08:20

yyforyongyu reviewed Mar 17, 2025

View reviewed changes

NishantBansal2003 force-pushed the validate-mpp branch from f4513f2 to 480c880 Compare March 19, 2025 02:50

NishantBansal2003 requested a review from yyforyongyu March 19, 2025 02:50

yyforyongyu approved these changes Mar 19, 2025

View reviewed changes

saubyk requested a review from ziggie1984 March 19, 2025 16:22

ziggie1984 requested changes Mar 19, 2025

View reviewed changes

NishantBansal2003 force-pushed the validate-mpp branch 3 times, most recently from ae6dfb4 to 791dd97 Compare March 20, 2025 06:43

NishantBansal2003 requested a review from ziggie1984 March 20, 2025 07:09

yyforyongyu reviewed Mar 20, 2025

View reviewed changes

ziggie1984 requested changes Mar 20, 2025

View reviewed changes

NishantBansal2003 force-pushed the validate-mpp branch from 791dd97 to 7ae2f39 Compare March 21, 2025 05:16

NishantBansal2003 changed the title ~~routerrpc+itest: add validation to MPP params~~ routerrpc: add validation to MPP params Mar 21, 2025

NishantBansal2003 force-pushed the validate-mpp branch from 7ae2f39 to 314b7b1 Compare March 21, 2025 05:49

NishantBansal2003 requested review from ziggie1984 and yyforyongyu March 21, 2025 05:49

ziggie1984 requested changes Mar 21, 2025

View reviewed changes

NishantBansal2003 force-pushed the validate-mpp branch from 314b7b1 to 49cd630 Compare March 22, 2025 06:39

NishantBansal2003 requested a review from ziggie1984 March 22, 2025 09:11

yyforyongyu approved these changes Mar 28, 2025

View reviewed changes

lnrpc/routerrpc/router_backend_test.go Show resolved Hide resolved

MPins reviewed Mar 28, 2025

View reviewed changes

saubyk added this to the v0.19.0 milestone Mar 28, 2025

NishantBansal2003 force-pushed the validate-mpp branch 2 times, most recently from 1adc9fd to e92ae2a Compare March 28, 2025 16:22

MPins reviewed Mar 28, 2025

View reviewed changes

NishantBansal2003 force-pushed the validate-mpp branch from e92ae2a to f659db7 Compare March 29, 2025 04:20

MPins approved these changes Mar 30, 2025

View reviewed changes

MPins mentioned this pull request Mar 31, 2025

cmd/commands: add validation for MPP parameters #9238

Closed

NishantBansal2003 added 2 commits April 2, 2025 16:45

docs: add release notes.

8bd91d5

Signed-off-by: Nishant Bansal <[email protected]>

NishantBansal2003 force-pushed the validate-mpp branch from f659db7 to 8bd91d5 Compare April 2, 2025 11:15

		name: "Custom record entry with TLV type below " +
		"minimum",

routerrpc: add validation to MPP params #9603

Are you sure you want to change the base?

routerrpc: add validation to MPP params #9603

Conversation

NishantBansal2003 commented Mar 13, 2025

Change Description

Steps to Test

Pull Request Checklist

Testing

Code Style and Documentation

coderabbitai bot commented Mar 13, 2025 • edited Loading

Review skipped

Chat

CodeRabbit Commands (Invoked using PR comments)

Other keywords and placeholders

CodeRabbit Configuration File (.coderabbit.yaml)

Documentation and Community

yyforyongyu left a comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

ziggie1984 Mar 19, 2025 • edited Loading

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

yyforyongyu left a comment

Choose a reason for hiding this comment

ziggie1984 left a comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

ziggie1984 Mar 19, 2025 • edited Loading

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

ziggie1984 left a comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

ziggie1984 left a comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

yyforyongyu left a comment

Choose a reason for hiding this comment

MPins left a comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

MPins left a comment • edited Loading

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

NishantBansal2003 commented Mar 29, 2025

MPins left a comment

Choose a reason for hiding this comment

MPins commented Mar 30, 2025

ziggie1984 commented Mar 31, 2025

NishantBansal2003 commented Apr 2, 2025

lightninglabs-deploy commented Apr 9, 2025

coderabbitai bot commented Mar 13, 2025 •

edited

Loading

CodeRabbit Configuration File (`.coderabbit.yaml`)

ziggie1984 Mar 19, 2025 •

edited

Loading

ziggie1984 Mar 19, 2025 •

edited

Loading

MPins left a comment •

edited

Loading