BM-1652: [V-BND-VUL-005] add partial payment

contracts/snapshots/BoundlessMarketBasicTest.json

@@ -1,6 +1,6 @@
 {
   "ERC20 approve: required for depositCollateral": "45966",
-  "bytecode size implementation": "24312",
+  "bytecode size implementation": "24383",
   "bytecode size proxy": "89",
   "deposit: first ever deposit": "50942",
   "deposit: second deposit": "33842",

contracts/src/BoundlessMarket.sol

@@ -562,10 +562,17 @@ contract BoundlessMarket is
         // If the price is higher, we charge the client the difference.
         // If the price is lower, we refund the client the difference.
         uint96 lockPrice = lock.price;
+        bool partialPayment = false;
+        uint96 finalPrice = price;
+
         if (price > lockPrice) {
             uint96 clientOwes = price - lockPrice;
             if (clientAccount.balance < clientOwes) {
-                return abi.encodeWithSelector(InsufficientBalance.selector, client);
+                // If the client does not have enough balance to cover the full amount owed,
+                // we will only charge them what they have available.
+                clientOwes = clientAccount.balance;
+                finalPrice = lockPrice + clientOwes;
+                partialPayment = true;
             }
             unchecked {
                 clientAccount.balance -= clientOwes;
@@ -577,9 +584,12 @@ contract BoundlessMarket is
 
         requestLocks[id].setProverPaidAfterLockDeadline(assessorProver);
         if (MARKET_FEE_BPS > 0) {
-            price = _applyMarketFee(price);
+            finalPrice = _applyMarketFee(finalPrice);
+        }
+        accounts[assessorProver].balance += finalPrice;
+        if (partialPayment) {
+            return abi.encodeWithSelector(PartialPayment.selector, price, finalPrice);
         }
-        accounts[assessorProver].balance += price;
     }
 
     /// @notice For a request that has never been locked. Marks the request as fulfilled, and transfers payment if eligible.

contracts/src/IBoundlessMarket.sol

@@ -148,6 +148,12 @@ interface IBoundlessMarket {
     /// @dev selector 0x897f6c58
     error InsufficientBalance(address account);
 
+    /// @notice Error when a payment is partially settled due to insufficient funds.
+    /// @param fullAmount The full amount that was required.
+    /// @param paidAmount The amount that was actually paid.
+    /// @dev selector 0x6008fdcb
+    error PartialPayment(uint256 fullAmount, uint256 paidAmount);
+
     /// @notice Error when a signature did not pass verification checks.
     /// @dev selector 0x8baa579f
     error InvalidSignature();

contracts/test/BoundlessMarket.t.sol

@@ -3920,6 +3920,11 @@ contract BoundlessMarketBasicTest is BoundlessMarketTest {
         client.snapshotBalance();
         testProver.snapshotBalance();
 
+        // Withdraw some funds so we only have funds to cover for the first offer
+        // and we have a deficit for the second offer to test the partial payment path
+        vm.prank(client.addr());
+        boundlessMarket.withdraw(DEFAULT_BALANCE - 2 ether);
+
         // Lock request A
         vm.prank(testProverAddress);
         boundlessMarket.lockRequest(requestA, clientSignatureA);
@@ -3944,16 +3949,27 @@ contract BoundlessMarketBasicTest is BoundlessMarketTest {
         vm.expectEmit(true, true, true, true);
         bytes32 imageId = bytesToBytes32(requestB.requirements.predicate.data);
         emit MockCallback.MockCallbackCalled(imageId, APP_JOURNAL, fill.seal);
-        boundlessMarket.priceAndFulfill(requests, clientSignatures, fills, assessorReceipt);
+        bytes[] memory errors = boundlessMarket.priceAndFulfill(requests, clientSignatures, fills, assessorReceipt);
+        // Verify that the second request was partially payed
+        assertEq(errors.length, 1, "Expected one error");
+        assertEq(
+            errors[0],
+            abi.encodeWithSelector(IBoundlessMarket.PartialPayment.selector, 3 ether, 2 ether),
+            "Unexpected error"
+        );
 
         // Verify only the second request's callback was called
         assertEq(mockCallback.getCallCount(), 0, "First request's callback should not be called");
         assertEq(mockHighGasCallback.getCallCount(), 1, "Second request's callback should be called once");
 
+        // Deposit back original funds so that the Market original balance is restored
+        vm.prank(client.addr());
+        boundlessMarket.deposit{value: DEFAULT_BALANCE - 2 ether}();
+
         // Verify request state and balances
         expectRequestFulfilled(fill.id);
-        client.expectBalanceChange(-3 ether);
-        testProver.expectBalanceChange(3 ether);
+        client.expectBalanceChange(-2 ether);
+        testProver.expectBalanceChange(2 ether);
         testProver.expectCollateralBalanceChange(-1 ether); // Lost stake from lock
         expectMarketBalanceUnchanged();
     }

crates/boundless-market/src/contracts/artifacts/IBoundlessMarket.sol

@@ -148,6 +148,12 @@ interface IBoundlessMarket {
     /// @dev selector 0x897f6c58
     error InsufficientBalance(address account);
 
+    /// @notice Error when a payment is partially settled due to insufficient funds.
+    /// @param fullAmount The full amount that was required.
+    /// @param paidAmount The amount that was actually paid.
+    /// @dev selector 0x6008fdcb
+    error PartialPayment(uint256 fullAmount, uint256 paidAmount);
+
     /// @notice Error when a signature did not pass verification checks.
     /// @dev selector 0x8baa579f
     error InvalidSignature();