From 01a84848b53858630839a6b6fb02081f9a07794d Mon Sep 17 00:00:00 2001
From: Cristovao Honorato <cristovao.honorato@gmail.com>
Date: Wed, 25 Oct 2023 19:57:13 +0200
Subject: [PATCH] Add test for contract specific signature empty

---
 contracts/test/TestSignature.sol | 10 +++++++
 test/06_SignatureChecker.spec.ts | 51 +++++++++++++++++++++++++++++++-
 2 files changed, 60 insertions(+), 1 deletion(-)

diff --git a/contracts/test/TestSignature.sol b/contracts/test/TestSignature.sol
index 70113528..1614cc26 100644
--- a/contracts/test/TestSignature.sol
+++ b/contracts/test/TestSignature.sol
@@ -33,6 +33,16 @@ contract ContractSignerMaybe is IERC1271 {
     }
 }
 
+contract ContractSignerOnlyEmpty is IERC1271 {
+    function isValidSignature(
+        bytes32,
+        bytes memory contractSpecificSignature
+    ) external pure override returns (bytes4) {
+        bool isValid = contractSpecificSignature.length == 0;
+        return isValid ? bytes4(0x1626ba7e) : bytes4(0x33333333);
+    }
+}
+
 contract ContractSignerFaulty {}
 
 contract ContractSignerReturnSize {
diff --git a/test/06_SignatureChecker.spec.ts b/test/06_SignatureChecker.spec.ts
index 91724a22..6886b27a 100644
--- a/test/06_SignatureChecker.spec.ts
+++ b/test/06_SignatureChecker.spec.ts
@@ -322,6 +322,55 @@ describe("SignatureChecker", async () => {
         .to.emit(testSignature, "Hello")
         .withArgs(AddressZero);
     });
+
+    it("signer returns isValid for empty specific signature only", async () => {
+      const { testSignature, relayer } = await loadFixture(setup);
+
+      const ContractSigner = await hre.ethers.getContractFactory(
+        "ContractSignerOnlyEmpty"
+      );
+      const contractSigner = await ContractSigner.deploy();
+
+      const transaction = await testSignature.populateTransaction.goodbye(
+        0,
+        "0xbadfed"
+      );
+
+      const signatureGood = makeContractSignature(
+        transaction,
+        "0x",
+        keccak256(toUtf8Bytes("some irrelevant salt")),
+        contractSigner.address
+      );
+
+      const signatureBad = makeContractSignature(
+        transaction,
+        "0xffff",
+        keccak256(toUtf8Bytes("some irrelevant salt")),
+        contractSigner.address
+      );
+
+      const transactionWithGoodSig = {
+        ...transaction,
+        data: `${transaction.data}${signatureGood.slice(2)}`,
+      };
+      const transactionWithBadSig = {
+        ...transaction,
+        data: `${transaction.data}${signatureBad.slice(2)}`,
+      };
+
+      await expect(await relayer.sendTransaction(transaction))
+        .to.emit(testSignature, "Goodbye")
+        .withArgs(AddressZero);
+
+      await expect(await relayer.sendTransaction(transactionWithGoodSig))
+        .to.emit(testSignature, "Goodbye")
+        .withArgs(contractSigner.address);
+
+      await expect(await relayer.sendTransaction(transactionWithBadSig))
+        .to.emit(testSignature, "Goodbye")
+        .withArgs(AddressZero);
+    });
     it("signer bad return size", async () => {
       const { testSignature, relayer } = await loadFixture(setup);
 
@@ -427,7 +476,7 @@ function makeContractSignature(
   r: string,
   s?: string
 ) {
-  const dataBytesLength = (transaction.data?.length as number) / 2 - 1;
+  const dataBytesLength = ((transaction.data?.length as number) - 2) / 2;
 
   r = defaultAbiCoder.encode(["address"], [r]);
   s = s || defaultAbiCoder.encode(["uint256"], [dataBytesLength]);