fix: decoding dynamic bytes w/ zero data

.changeset/shy-moles-ring.md

@@ -0,0 +1,5 @@
+---
+"viem": patch
+---
+
+Fixed decoding zero data bytes

src/utils/abi/decodeAbiParameters.test.ts

@@ -1,5 +1,7 @@
 import { Address } from 'abitype'
+import { AbiCoder } from 'ethers/lib/utils'
 import { assertType, describe, expect, test } from 'vitest'
+import { multicall3Abi } from '../../constants'
 import { Hex } from '../../types'
 import { address } from '../../_test'
 import { seaportContractConfig } from '../../_test/abis'
@@ -1852,6 +1854,48 @@ describe('seaport', () => {
   })
 })
 
+describe('multicall3', () => {
+  test('zero data', () => {
+    expect(
+      decodeAbiParameters(
+        multicall3Abi[0].outputs,
+        '0x000000000000000000000000000000000000000000000000000000000000002000000000000000000000000000000000000000000000000000000000000000010000000000000000000000000000000000000000000000000000000000000020000000000000000000000000000000000000000000000000000000000000000100000000000000000000000000000000000000000000000000000000000000400000000000000000000000000000000000000000000000000000000000000000',
+      ),
+    ).toMatchInlineSnapshot(`
+      [
+        [
+          {
+            "returnData": "0x",
+            "success": true,
+          },
+        ],
+      ]
+    `)
+  })
+
+  test('zero data + non-zero data', () => {
+    expect(
+      decodeAbiParameters(
+        multicall3Abi[0].outputs,
+        '0x00000000000000000000000000000000000000000000000000000000000000200000000000000000000000000000000000000000000000000000000000000002000000000000000000000000000000000000000000000000000000000000004000000000000000000000000000000000000000000000000000000000000000a000000000000000000000000000000000000000000000000000000000000000010000000000000000000000000000000000000000000000000000000000000040000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000010000000000000000000000000000000000000000000000000000000000000040000000000000000000000000000000000000000000000000000000000000006000000000000000000000000000000000000000000000000d752bd588f61926e40000000000000000000000000000000000000000000000002e0e220d3d6cf5630000000000000000000000000000000000000000000000000000000063fa0b5f',
+      ),
+    ).toMatchInlineSnapshot(`
+      [
+        [
+          {
+            "returnData": "0x",
+            "success": true,
+          },
+          {
+            "returnData": "0x00000000000000000000000000000000000000000000000d752bd588f61926e40000000000000000000000000000000000000000000000002e0e220d3d6cf5630000000000000000000000000000000000000000000000000000000063fa0b5f",
+            "success": true,
+          },
+        ],
+      ]
+    `)
+  })
+})
+
 test('invalid size', () => {
   expect(() =>
     decodeAbiParameters(

src/utils/abi/decodeAbiParameters.ts

@@ -195,7 +195,9 @@ function decodeBytes<TParam extends AbiParameter>(
     // so we need to read the offset of the data part first.
     const offset = hexToNumber(slice(data, position, position + 32))
     const length = hexToNumber(slice(data, offset, offset + 32))
-    const value = slice(data, offset + 32, offset + 32 + length)
+    const value =
+      // If there is no length, we have zero data.
+      length === 0 ? '0x' : slice(data, offset + 32, offset + 32 + length)
     return { consumed: 32, value }
   }