Propose multiple winning solutions in the driver by fafk · Pull Request #4267 · cowprotocol/services

fafk · 2026-03-17T14:11:04Z

Description

The driver currently proposes only the single highest-scoring solution to the autopilot. With EIP-7702 parallel submission in place, the autopilot's combinatorial auction can now benefit from receiving all valid solutions from a driver to find the optimal set of winners.

Changes

[x] Driver's solve() now returns Vec instead of Option with all valid solutions sorted best-first
[x] Block re-simulation loop now monitors all proposed solutions individually, voiding only those that revert
[x] New per-solver config flag propose-all-solutions (default: false) keeps existing behavior until EIP-7702 infrastructure is ready

How to test

cargo nextest run -p driver --test-threads 1 --run-ignored ignored-only -E 'test(multiple_solutions)'

To enable in production, add to the solver config: propose-all-solutions = true (requires submission-accounts to also be configured along with the forwarder contract).

gemini-code-assist

Code Review

This pull request introduces support for multiple solution proposals from the driver, which is a key feature for enabling EIP-7702 parallel submissions. The changes to Competition::solve to handle multiple solutions, including sorting, caching, and re-simulation, are well-implemented. The new configuration flag propose-all-solutions and associated validation are also correctly added. I've found one issue related to configuration validation for EIP-7702 setup that should be addressed to prevent runtime failures from misconfigurations.

crates/driver/src/infra/solver/eip7702.rs

github-actions · 2026-03-25T00:15:13Z

This pull request has been marked as stale because it has been inactive a while. Please update this pull request or it will be automatically closed.

jmg-duarte · 2026-03-25T13:26:21Z

crates/driver/src/domain/competition/mod.rs

+        // When multi-solution proposals are disabled keep only the best one.
+        if !self.solver.propose_all_solutions() {
+            scored.truncate(1);
+        }


alternatively: you could .take(1) above and drop the whole thing, avoiding processing more solutions

jmg-duarte · 2026-03-25T13:29:28Z

crates/driver/src/domain/competition/mod.rs

+            for (_, settlement) in &scored {
+                lock.push_front(settlement.clone());
+            }


i wonder if the following would be faster:

keeping scored as a vecdeque from the start

extending scored with settlements

replacing settlements with scored

jmg-duarte · 2026-03-25T13:33:02Z

crates/driver/src/domain/competition/mod.rs

+                        if let Err(infra::simulator::Error::Revert(err)) =
+                            self.simulate_settlement(settlement).await
+                        {


nit: this helps reduce the indentation and make this a bit more readable

Suggested change

if let Err(infra::simulator::Error::Revert(err)) =

self.simulate_settlement(settlement).await

{

let err = match self.simulate_settlement(settlement).await {

Err(infra::simulator::Error::Revert(err)) => err,

_ => continue

};

...

jmg-duarte · 2026-03-25T13:34:36Z

crates/driver/src/infra/config/file/mod.rs

    /// delegation. Required when `submission_accounts` is non-empty.
    forwarder_contract: Option<eth::Address>,
+
+    /// If enabled the driver proposes all valid solutions to the autopilot


nit:

Suggested change

/// If enabled the driver proposes all valid solutions to the autopilot

/// If enabled, the driver proposes all valid solutions to the autopilot

jmg-duarte · 2026-03-25T13:36:44Z

crates/driver/src/tests/setup/mod.rs

+    /// Extracts the first solution from the response. Asserts that exactly one
+    /// solution was returned (i.e. `propose-all-solutions` is disabled).


Suggested change

/// Extracts the first solution from the response. Asserts that exactly one

/// solution was returned (i.e. `propose-all-solutions` is disabled).

/// Extracts the first solution from the response. Panics if more than one

/// solution was returned (i.e. `propose-all-solutions` is disabled).

squadgazzz · 2026-03-27T11:54:26Z

crates/driver/src/domain/competition/mod.rs

+            for (_, settlement) in &scored {
+                lock.push_front(settlement.clone());
+            }
            const MAX_SOLUTION_STORAGE: usize = 5;


But scored can hold more than 5 items, right? Should we truncate scored to MAX_SOLUTION_STORAGE before caching, so what is stored and what is returned are always in sync.

squadgazzz · 2026-03-27T11:55:20Z

crates/driver/src/domain/competition/mod.rs

                        }
-                        return;
+                        if let Err(infra::simulator::Error::Revert(err)) =
+                            self.simulate_settlement(settlement).await


All simulations are running sequentially. Any reason for that? Should we run them in parallel?

squadgazzz · 2026-03-27T11:59:08Z

crates/driver/src/domain/competition/mod.rs

+        // Sort all scored settlements descending by score (best first).
+        let mut scored: Vec<(Option<Solved>, Settlement)> = scores
            .into_iter()
-            .max_by_key(|(score, _)| score.to_owned())
+            .sorted_by(|(a, _), (b, _)| b.cmp(a))
            .map(|(score, settlement)| {
-                (
-                    Solved {
-                        id: settlement.solution().clone(),
-                        score,
-                        trades: settlement.orders(),
-                        prices: settlement.prices(),
-                        gas: Some(settlement.gas.estimate),
-                    },
-                    settlement,
-                )
+                let solved = Solved {
+                    id: settlement.solution().clone(),
+                    score,
+                    trades: settlement.orders(),
+                    prices: settlement.prices(),
+                    gas: Some(settlement.gas.estimate),
+                };
+                (Some(solved), settlement)


Why not something like the following?

// proposed let scored: Vec<(Solved, Settlement)> = scores .into_iter() .sorted_by(|(a, _), (b, _)| b.cmp(a)) .map(|(score, settlement)| { let solved = Solved { ... }; (solved, settlement) }) .collect(); // ... let mut voided_ids: HashSet<_> = HashSet::new(); // In the re-simulation loop: if let Err(infra::simulator::Error::Revert(err)) = ... { voided_ids.insert(settlement.solution().get()); // retain / notify as before... } // Return: Ok(scored .into_iter() .filter_map(|(solved, _)| { if voided_ids.contains(&solved.id.get()) { None } else { Some(solved) } }) .collect())

squadgazzz · 2026-03-27T12:01:39Z

crates/driver/src/infra/observe/mod.rs

                .solutions
-                .with_label_values(&[solver, "SolutionNotFound"])
+                .with_label_values(&[solver, "Success"])
                .inc();


Should it be now incremented by the number of solved solutions?

squadgazzz · 2026-03-27T12:02:23Z

crates/driver/src/tests/cases/multiple_solutions.rs

+
+    let solve = test.solve().await.ok();
+    let solutions = solve.solutions();
+    assert_eq!(solutions.len(), 2);


The test should also validate the sorting logic.

squadgazzz · 2026-03-27T12:02:56Z

crates/driver/src/tests/cases/multiple_solutions.rs


+/// Test that when `propose-all-solutions` is enabled, all valid solutions are
+/// returned (sorted best-first) and each can be revealed.
+#[tokio::test]


Another test is missing: voided solution removed from multi-solution response.

squadgazzz · 2026-03-27T12:03:13Z

crates/driver/src/tests/setup/driver.rs

+                .map(|a| format!("\"{a}\""))
+                .collect::<Vec<_>>()
+                .join(", ");
+            writeln!(file, "               submission-accounts = [{accounts}]").unwrap();


Why so many spaces?

github-actions · 2026-04-04T00:15:36Z

This pull request has been marked as stale because it has been inactive a while. Please update this pull request or it will be automatically closed.

fafk added 2 commits March 17, 2026 07:37

Propose all valid solutions

3fdb455

Add a test

7e93ab0

fafk requested a review from a team as a code owner March 17, 2026 14:11

fafk changed the title ~~Many winners driver~~ Propose multiple winning solutions in the driver Mar 17, 2026

gemini-code-assist bot reviewed Mar 17, 2026

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crates/driver/src/infra/solver/eip7702.rs Show resolved Hide resolved

fafk requested a review from MartinquaXD March 17, 2026 14:28

github-actions bot added the stale label Mar 25, 2026

jmg-duarte reviewed Mar 25, 2026

View reviewed changes

github-actions bot removed the stale label Mar 26, 2026

squadgazzz reviewed Mar 27, 2026

View reviewed changes

github-actions bot added the stale label Apr 4, 2026

-                        if let Err(infra::simulator::Error::Revert(err)) =
-                            self.simulate_settlement(settlement).await
-                        {
+                        let err = match self.simulate_settlement(settlement).await {
+                        	Err(infra::simulator::Error::Revert(err)) => err,
+                        	_ => continue
+                        };
+                        ...

	/// If enabled the driver proposes all valid solutions to the autopilot
	/// If enabled, the driver proposes all valid solutions to the autopilot

		/// Extracts the first solution from the response. Asserts that exactly one
		/// solution was returned (i.e. `propose-all-solutions` is disabled).

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fafk commented Mar 17, 2026

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