From 6d1abf7bd8565bf0377a42b823a6ad98959c340a Mon Sep 17 00:00:00 2001
From: David <104078303+davidtaikocha@users.noreply.github.com>
Date: Fri, 9 Dec 2022 23:56:49 +0800
Subject: [PATCH] feat(protocol): allow empty L2 blocks  (#406)

* feat(protocol): allow empty blocks by updating `LibTxDecoder`

* test: update test_genesis

* feat: allow txList with zero byte
---
 packages/protocol/contracts/L1/v1/V1Proposing.sol |  2 +-
 packages/protocol/contracts/libs/LibTxDecoder.sol |  4 +++-
 .../test/genesis/generate_genesis.test.ts         |  8 +++++---
 packages/protocol/test/libs/LibTxDecoder.test.ts  | 15 +++++++++++----
 4 files changed, 20 insertions(+), 9 deletions(-)

diff --git a/packages/protocol/contracts/L1/v1/V1Proposing.sol b/packages/protocol/contracts/L1/v1/V1Proposing.sol
index 6add00c3b10..0ef68db1b5d 100644
--- a/packages/protocol/contracts/L1/v1/V1Proposing.sol
+++ b/packages/protocol/contracts/L1/v1/V1Proposing.sol
@@ -77,7 +77,7 @@ library V1Proposing {
             bytes calldata txList = inputs[1];
             // perform validation and populate some fields
             require(
-                txList.length > 0 &&
+                txList.length >= 0 &&
                     txList.length <= LibConstants.K_TXLIST_MAX_BYTES &&
                     meta.txListHash == txList.hashTxList(),
                 "L1:txList"
diff --git a/packages/protocol/contracts/libs/LibTxDecoder.sol b/packages/protocol/contracts/libs/LibTxDecoder.sol
index 9c10316f7d9..9dff797f56a 100644
--- a/packages/protocol/contracts/libs/LibTxDecoder.sol
+++ b/packages/protocol/contracts/libs/LibTxDecoder.sol
@@ -78,8 +78,10 @@ library LibTxDecoder {
     function decodeTxList(
         bytes calldata encoded
     ) public pure returns (TxList memory txList) {
+        if (encoded.length == 0) {
+            return txList;
+        }
         LibRLPReader.RLPItem[] memory txs = LibRLPReader.readList(encoded);
-        require(txs.length > 0, "empty txList");
 
         Tx[] memory _txList = new Tx[](txs.length);
         for (uint256 i = 0; i < txs.length; i++) {
diff --git a/packages/protocol/test/genesis/generate_genesis.test.ts b/packages/protocol/test/genesis/generate_genesis.test.ts
index 4abe3611ab1..05503c8872e 100644
--- a/packages/protocol/test/genesis/generate_genesis.test.ts
+++ b/packages/protocol/test/genesis/generate_genesis.test.ts
@@ -142,9 +142,11 @@ action("Generate Genesis", function () {
                 signer
             )
 
-            await expect(
-                LibTxDecoder.decodeTxList(ethers.utils.RLP.encode([]))
-            ).to.be.revertedWith("empty txList")
+            const decoded = await LibTxDecoder.callStatic.decodeTxList(
+                ethers.utils.RLP.encode([])
+            )
+
+            expect(decoded.items.length).to.be.eql(0)
         })
 
         it("TaikoL2", async function () {
diff --git a/packages/protocol/test/libs/LibTxDecoder.test.ts b/packages/protocol/test/libs/LibTxDecoder.test.ts
index 10ab421264b..6e46b66bd4a 100644
--- a/packages/protocol/test/libs/LibTxDecoder.test.ts
+++ b/packages/protocol/test/libs/LibTxDecoder.test.ts
@@ -30,12 +30,19 @@ describe("LibTxDecoder", function () {
     }
 
     describe("decodeTxList", function () {
-        it("should revert if tx list is empty", async function () {
+        it("should not revert if tx list is empty", async function () {
             const txList: string[] = []
             const txListBytes = await rlpEncodeTxList(txList)
-            await expect(
-                libTxDecoder.callStatic.decodeTxList(txListBytes)
-            ).to.be.revertedWith("empty txList")
+
+            let decoded = await libTxDecoder.callStatic.decodeTxList(
+                txListBytes
+            )
+
+            expect(decoded.items.length).to.be.eql(0)
+
+            decoded = await libTxDecoder.callStatic.decodeTxList([])
+
+            expect(decoded.items.length).to.be.eql(0)
         })
 
         it("should revert with random bytes", async function () {