Oev 771 flashbots batch by dimriou · Pull Request #346 · smartcontractkit/chainlink-evm

dimriou · 2026-02-04T13:09:47Z

This PR enables Flashbots bundles. Every time a transaction is broadcasted, it will fetch all the past in-flight transactions and create a bundle. The bundle will use the last attempt of each transaction. The bundle broadcasting is a fire and forget process that helps nonce unblocking, so it is not tracked.

github-actions · 2026-02-04T13:11:35Z

⚠️ API Diff Results - Breaking changes detected

📦 Module: `github-com-smartcontractkit-chainlink-evm`

🔴 Breaking Changes (5)

`pkg/config.TransactionManagerV2` (1)

Bundles — ➕ Added

`pkg/txm.TxStore` (2)

FetchUnconfirmedTransactions — ➕ Added
UpdateSignedAttempt — ➕ Added

`pkg/txm/clientwrappers/dualbroadcast` (2)

NewFlashbotsClient — Type changed:

func(
  - github.com/smartcontractkit/chainlink-evm/pkg/client.Client, 
  + github.com/smartcontractkit/chainlink-common/pkg/logger.Logger, 
  + FlashbotsClientRPC, 
  github.com/smartcontractkit/chainlink-evm/pkg/keys.MessageSigner, 
  - *net/url.URL
  + *net/url.URL, 
  + FlashbotsTxStore, 
  + *bool
)
*FlashbotsClient

SelectClient — Type changed:

func(
  github.com/smartcontractkit/chainlink-common/pkg/logger.Logger, 
  github.com/smartcontractkit/chainlink-evm/pkg/client.Client, 
  github.com/smartcontractkit/chainlink-evm/pkg/keys.ChainStore, 
  *net/url.URL, 
  *math/big.Int, 
  - MetaClientTxStore
  + github.com/smartcontractkit/chainlink-evm/pkg/txm.TxStore, 
  + *bool
)
(github.com/smartcontractkit/chainlink-evm/pkg/txm.Client, github.com/smartcontractkit/chainlink-evm/pkg/txm.ErrorHandler, error)

📄 View full apidiff report

pszal

Nice! Some feedback below. Please consider adding more tests.

pszal · 2026-02-19T10:00:35Z

+	if err != nil {
+		return fmt.Errorf("failed to get current block height: %w", err)
+	}
+	targetBlock := currentBlock.NumberU64() + 24


would maxBlock be a more accurate var name?

pszal · 2026-02-19T10:03:30Z

+
+		bodyItems = append(bodyItems, map[string]any{
+			"tx":         hexutil.Encode(txData),
+			"revertMode": "allow", // we always want to allow reverts so bundles are valid even if a single transaction within the bundle goes through


I don't see revertMode, only canRevert:
https://docs.flashbots.net/flashbots-mev-share/searchers/understanding-bundles#bundle-definition

Indeed, but I followed the spec they gave me in our conversation.

Does it make sense to document this spec somewhere (e.g., doc.go)?

Added a link to the docs.

Copilot

Pull request overview

This PR adds optional Flashbots bundle broadcasting to the TXM dual-broadcast client path, gated by a new Bundles config flag. When enabled, after successfully sending a transaction to the Flashbots endpoint, the client builds and submits a bundle composed of in-flight (unconfirmed) transactions.

Changes:

Add Bundles configuration for TransactionManagerV2 (TOML + docs + config interfaces).
Extend txm.TxStore with APIs needed for bundle building (fetch unconfirmed txs; update signed attempts).
Implement Flashbots bundle creation + submission and add unit tests for URL param parsing / bundle request construction.

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
pkg/txmgr/builder.go	Passes `Bundles` config into dual-broadcast client selection.
pkg/txm/txm.go	Extends `TxStore` interface with `FetchUnconfirmedTransactions` and `UpdateSignedAttempt`.
pkg/txm/storage/inmemory_store_manager.go	Adds store-manager forwarding method for fetching all unconfirmed txs.
pkg/txm/storage/inmemory_store.go	Adds `FetchUnconfirmedTransactions()` (deep-copy + nonce sort).
pkg/txm/mock_tx_store_test.go	Updates mock store to satisfy new `TxStore` interface methods.
pkg/txm/clientwrappers/dualbroadcast/selector.go	Threads bundles flag and tx store into Flashbots client constructor.
pkg/txm/clientwrappers/dualbroadcast/flashbots_client.go	Implements bundle send flow, request signing/posting changes, URL param parsing.
pkg/txm/clientwrappers/dualbroadcast/flashbots_client_test.go	Adds tests for URL param parsing and bundle request composition.
pkg/config/toml/testdata/config-full.toml	Adds `Bundles` to the full TOML test config.
pkg/config/toml/docs.toml	Documents `Bundles` TOML setting.
pkg/config/toml/config_test.go	Updates config tests to include `Bundles` defaults/docs handling.
pkg/config/toml/config.go	Adds `Bundles` field to `TransactionManagerV2Config` and merges it in `setFrom`.
pkg/config/config.go	Extends `TransactionManagerV2` interface with `Bundles()`.
pkg/config/chain_scoped_transactions.go	Implements `Bundles()` accessor for chain-scoped config wrapper.
CONFIG.md	Adds `Bundles` to user-facing configuration documentation.

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Copilot · 2026-02-27T10:34:07Z

+		// After successfully sending the transaction, send a bundle with all unconfirmed transactions
+		// Don't act on a bundle error - this is a fire and forget operation but we do want to log the error.
+		if d.bundles {
+			if err := d.SendBundle(ctx, tx.FromAddress, params); err != nil {
+				d.lggr.Error("error sending bundle: ", err)


The PR description says bundle broadcasting is “fire and forget”, but this call is synchronous: SendTransaction will block until SendBundle completes (including an extra BlockByNumber RPC + HTTP request). Consider running SendBundle asynchronously (e.g., in a goroutine with its own bounded context) so transaction broadcasting latency isn’t increased and bundle failures can’t delay TXM.

Copilot · 2026-02-27T10:34:08Z

+	// Sort by nonce in ascending order
+	sort.Slice(transactions, func(i, j int) bool {
+		return *transactions[i].Nonce < *transactions[j].Nonce
+	})


FetchUnconfirmedTransactions adds nonce-sorting and returns an error on nil nonces, but there are no unit tests covering this new behavior. Add tests to validate sorted order and the nil-nonce error so the bundle logic can rely on it safely.

pszal

lgtm

pszal · 2026-02-27T16:05:56Z

-	nonce, err := hexutil.DecodeUint64(response)
+	var resultStr string
+	if err := json.Unmarshal(raw, &resultStr); err != nil {
+		return 0, fmt.Errorf("failed to unmarshal response into string: %w", err)


I see that you log arg when it fails in other places, any reason to not log raw here?

No reason, I added raw as well.

pszal · 2026-02-27T16:15:27Z

+	for _, unconfirmedTx := range unconfirmedTxs {
+		if len(unconfirmedTx.Attempts) > 0 {
+			attempts = append(attempts, unconfirmedTx.Attempts[len(unconfirmedTx.Attempts)-1])
+			if unconfirmedTx.Nonce != nil {


if you check for that here, then it makes sense to check or guarantee in the if above that attempts and nonces are consistent (i.e., you append to both or neither).

pszal · 2026-02-27T16:19:52Z

+	refundRaw := values.Get("refund")
+	if refundRaw != "" {
+		parts := strings.Split(refundRaw, ":")
+		if len(parts) == 2 {


is it ok if its not 2? shouldn't we err?

Yeah, agree

pszal · 2026-02-27T16:23:42Z

+	if err := json.Unmarshal(raw, &bundleResult); err != nil {
+		return fmt.Errorf("failed to decode response %v into bundle result: %w", raw, err)
+	}
+	d.lggr.Infow("Broadcasted transaction bundle", "nonces", nonces, "bundleHash", bundleResult.BundleHash)


is it intentional to log only nonces and not the actual bundle (or at least IDs of its txs)?

Yes. Logs can be very noisy in Core, so the idea here is avoid replicating information that can be recovered by past logs. Similar to how we confirm transactions, we use nonce as an identifier to retrieve information if needed, as the individual transaction details should be available a few lines before this message. I'll add the IDs though to make it cleaner.

+		// Don't act on a bundle error - this is a fire and forget operation but we do want to log the error.
+		if d.bundles {
+			if err := d.SendBundle(ctx, tx.FromAddress, params); err != nil {
+				d.lggr.Errorw("error sending bundle", "err", err)


In general, to fix “log entries created from user input,” any user-influenced string that is written to logs should be sanitized/encoded so it cannot inject new log entries or markup. For plain-text logs, that usually means removing or replacing \n and \r. For HTML-rendered logs, it also means HTML-escaping. In this codebase, the flagged sink is a structured logger call that logs an error value; we can mitigate the issue by converting the error to a string and stripping line breaks (and optionally carriage returns) before logging.

The best minimal fix without changing existing functionality is to sanitize the err value only at the point where CodeQL flags the problem, by converting err to a string, removing \n and \r, and logging that sanitized string instead of the raw error. This keeps the log message content almost identical (minus dangerous control characters) while eliminating the risk of log forging via embedded line breaks. We can use the already-imported strings package, so no new imports are required.

Concretely, in pkg/txm/clientwrappers/dualbroadcast/flashbots_client.go, around line 111–114:

if d.bundles { if err := d.SendBundle(ctx, tx.FromAddress, params); err != nil { d.lggr.Errorw("error sending bundle", "err", err) } }

we will introduce a small sanitization step:

if d.bundles { if err := d.SendBundle(ctx, tx.FromAddress, params); err != nil { sanitizedErr := strings.ReplaceAll(err.Error(), "\n", "") sanitizedErr = strings.ReplaceAll(sanitizedErr, "\r", "") d.lggr.Errorw("error sending bundle", "err", sanitizedErr) } }

This uses strings.ReplaceAll (already imported) and keeps all other logic intact.

dimriou added 3 commits January 22, 2026 15:23

First draft

194ff8e

Merge branch 'develop' into oev-771_flashbots_batch

3b2366e

Pass txStore in constructor

b8d8882

dimriou added 2 commits February 12, 2026 16:10

Update Flashbots client for bundles

2bf7ec7

Update bundle body

6fe2367

dimriou force-pushed the oev-771_flashbots_batch branch from 7f1a37b to 6fe2367 Compare February 17, 2026 11:32

Add bundle config

a1d5fa8

dimriou force-pushed the oev-771_flashbots_batch branch from 60f915c to a1d5fa8 Compare February 18, 2026 10:12

dimriou added 3 commits February 18, 2026 12:36

Merge branch 'develop' into oev-771_flashbots_batch

89311c6

Merge branch 'develop' into oev-771_flashbots_batch

f86fbeb

Fix failed request error message format

b017969

github-advanced-security AI found potential problems Feb 18, 2026

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Comment thread pkg/txm/clientwrappers/dualbroadcast/flashbots_client.go Fixed

pszal reviewed Feb 19, 2026

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dimriou added 4 commits February 19, 2026 14:20

Add parsing tests

7111a3e

Add doc link

1947854

Add test for latest attempt

d478554

Merge branch 'develop' into oev-771_flashbots_batch

87a67e4

dimriou marked this pull request as ready for review February 27, 2026 10:26

dimriou requested a review from a team as a code owner February 27, 2026 10:26

Copilot AI review requested due to automatic review settings February 27, 2026 10:26

dimriou requested review from a team as code owners February 27, 2026 10:26

product-security-plaid-production Bot requested a review from ilija42 February 27, 2026 10:26

Copilot started reviewing on behalf of dimriou February 27, 2026 10:27 View session

Copilot AI reviewed Feb 27, 2026

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pszal reviewed Feb 27, 2026

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Address feedback

c452ad7

dimriou enabled auto-merge (squash) March 2, 2026 16:10

dimriou disabled auto-merge March 2, 2026 16:10

dhaidashenko previously approved these changes Mar 2, 2026

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amit-momin reviewed Mar 2, 2026

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Comment thread pkg/txm/clientwrappers/dualbroadcast/flashbots_client.go Outdated

amit-momin reviewed Mar 2, 2026

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Comment thread pkg/txm/clientwrappers/dualbroadcast/flashbots_client.go

amit-momin reviewed Mar 2, 2026

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Comment thread pkg/txm/clientwrappers/dualbroadcast/flashbots_client.go Outdated

amit-momin reviewed Mar 2, 2026

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Comment thread pkg/txm/clientwrappers/dualbroadcast/flashbots_client.go Outdated

Add nonce gap validation

ca5fe90

dimriou dismissed dhaidashenko’s stale review via ca5fe90 March 2, 2026 17:04

github-advanced-security AI found potential problems Mar 2, 2026

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amit-momin approved these changes Mar 2, 2026

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dhaidashenko approved these changes Mar 2, 2026

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ilija42 approved these changes Mar 2, 2026

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dimriou merged commit 1e75633 into develop Mar 2, 2026
36 of 41 checks passed

dimriou deleted the oev-771_flashbots_batch branch March 2, 2026 18:02

@@ -110,7 +110,9 @@
             		// Don't act on a bundle error - this is a fire and forget operation but we do want to log the error.
             		if d.bundles {
             			if err := d.SendBundle(ctx, tx.FromAddress, params); err != nil {
-            				d.lggr.Errorw("error sending bundle", "err", err)
+            				sanitizedErr := strings.ReplaceAll(err.Error(), "\n", "")
+            				sanitizedErr = strings.ReplaceAll(sanitizedErr, "\r", "")
+            				d.lggr.Errorw("error sending bundle", "err", sanitizedErr)
             			}
             		}
             		return nil

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⚠️ API Diff Results - Breaking changes detected

📦 Module: github-com-smartcontractkit-chainlink-evm

🔴 Breaking Changes (5)

pkg/config.TransactionManagerV2 (1)

pkg/txm.TxStore (2)

pkg/txm/clientwrappers/dualbroadcast (2)

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Pull request overview

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dimriou commented Feb 4, 2026 •

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📦 Module: `github-com-smartcontractkit-chainlink-evm`

`pkg/config.TransactionManagerV2` (1)

`pkg/txm.TxStore` (2)

`pkg/txm/clientwrappers/dualbroadcast` (2)

dimriou Mar 2, 2026 •

edited

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