op-batcher: prevent SpanChannelOut RLP bytes overflowing MaxRLPBytesPerChannel

op-node/rollup/derive/channel_out_test.go

@@ -491,3 +491,29 @@ func testSpanChannelOut_MaxBlocksPerSpanBatch(t *testing.T, tt maxBlocksTest) {
 		require.Equalf(t, batch0, batch, "iteration %d", i)
 	}
 }
+
+func TestSpanChannelOut_ExceedMaxRLPBytesPerChannel(t *testing.T) {
+	for _, algo := range CompressionAlgos {
+		t.Run("testSpanChannelOut_ExceedMaxRLPBytesPerChannel_"+algo.String(), func(t *testing.T) {
+			testSpanChannelOut_ExceedMaxRLPBytesPerChannel(t, algo)
+		})
+	}
+}
+
+func testSpanChannelOut_ExceedMaxRLPBytesPerChannel(t *testing.T, algo CompressionAlgo) {
+
+	largeBatchSize := int(rollup.NewChainSpec(&rollupCfg).MaxRLPBytesPerChannel(0))
+	cout, singularBatches := SpanChannelAndBatches(t, 100, 1, algo)
+
+	cout.rlp[0] = bytes.NewBuffer(make([]byte, largeBatchSize))
+	cout.rlp[1] = bytes.NewBuffer(make([]byte, largeBatchSize))
+	cout.sealedRLPBytes = largeBatchSize
+
+	for _, batch := range singularBatches {
+		err := cout.addSingularBatch(batch, 1)
+		require.ErrorIs(t, err, ErrTooManyRLPBytes)
+	}
+
+	require.Equal(t, cout.activeRLP().Len(), largeBatchSize)
+	require.Greater(t, cout.inactiveRLP().Len(), largeBatchSize)
+}

op-node/rollup/derive/span_channel_out.go

@@ -178,6 +178,7 @@ func (co *SpanChannelOut) addSingularBatch(batch *SingularBatch, seqNum uint64)
 	// the Fjord activation.
 	maxRLPBytesPerChannel := co.chainSpec.MaxRLPBytesPerChannel(batch.Timestamp)
 	if active.Len() > int(maxRLPBytesPerChannel) {
+		co.swapRLP()
 		return fmt.Errorf("could not take %d bytes as replacement of channel of %d bytes, max is %d. err: %w",
 			active.Len(), co.inactiveRLP().Len(), maxRLPBytesPerChannel, ErrTooManyRLPBytes)
 	}