fix: added assertion to check for existence of a signature on `topics…

…` for `decodeEventLog` (#205)

* fix: added assertion to check for existence of event signature on topics

* fix: log type

* tests: update snapshots

.changeset/silver-gifts-decide.md

@@ -0,0 +1,5 @@
+---
+"viem": patch
+---
+
+Added an assertion to check for existence of an event signature on `topics` for `decodeEventLog`

src/errors/abi.test.ts

@@ -3,6 +3,7 @@ import {
   AbiDecodingDataSizeInvalidError,
   AbiEncodingArrayLengthMismatchError,
   AbiEncodingLengthMismatchError,
+  AbiEventSignatureEmptyTopicsError,
   DecodeLogTopicsMismatch,
   InvalidAbiDecodingTypeError,
   InvalidAbiEncodingTypeError,
@@ -61,6 +62,17 @@ test('AbiEncodingLengthMismatchError', () => {
   `)
 })
 
+test('AbiEventSignatureEmptyTopicsError', () => {
+  expect(
+    new AbiEventSignatureEmptyTopicsError({ docsPath: '/test' }),
+  ).toMatchInlineSnapshot(`
+    [AbiEventSignatureEmptyTopicsError: Cannot extract event signature from empty topics.
+
+    Docs: https://viem.sh/test.html
+    Version: [email protected]]
+  `)
+})
+
 describe('DecodeLogTopicsMismatch', () => {
   test('default', () => {
     expect(

src/errors/abi.ts

@@ -143,6 +143,15 @@ export class AbiErrorSignatureNotFoundError extends BaseError {
   }
 }
 
+export class AbiEventSignatureEmptyTopicsError extends BaseError {
+  name = 'AbiEventSignatureEmptyTopicsError'
+  constructor({ docsPath }: { docsPath: string }) {
+    super('Cannot extract event signature from empty topics.', {
+      docsPath,
+    })
+  }
+}
+
 export class AbiEventSignatureNotFoundError extends BaseError {
   name = 'AbiEventSignatureNotFoundError'
   constructor(signature: Hex, { docsPath }: { docsPath: string }) {

src/errors/index.ts

@@ -9,6 +9,7 @@ export {
   AbiErrorInputsNotFoundError,
   AbiErrorNotFoundError,
   AbiErrorSignatureNotFoundError,
+  AbiEventSignatureEmptyTopicsError,
   AbiEventSignatureNotFoundError,
   AbiEventNotFoundError,
   AbiFunctionNotFoundError,

src/index.test.ts

@@ -15,6 +15,7 @@ test('exports actions', () => {
       "AbiErrorNotFoundError": [Function],
       "AbiErrorSignatureNotFoundError": [Function],
       "AbiEventNotFoundError": [Function],
+      "AbiEventSignatureEmptyTopicsError": [Function],
       "AbiEventSignatureNotFoundError": [Function],
       "AbiFunctionNotFoundError": [Function],
       "AbiFunctionOutputsNotFoundError": [Function],

src/index.ts

@@ -43,6 +43,7 @@ export {
   AbiErrorNotFoundError,
   AbiErrorSignatureNotFoundError,
   AbiEventNotFoundError,
+  AbiEventSignatureEmptyTopicsError,
   AbiEventSignatureNotFoundError,
   AbiFunctionNotFoundError,
   AbiFunctionOutputsNotFoundError,

src/types/log.ts

@@ -54,7 +54,7 @@ export type Log<
   /** Index of the transaction that created this log or `null` if pending */
   transactionIndex: TIndex | null
   /** List of order-dependent topics */
-  topics: Hex[]
+  topics: [Hex, ...Hex[]] | []
   /** `true` if this filter has been destroyed and is invalid */
   removed: boolean
 } & DecodedAbiEvent<TAbiEvent, TAbi, TEventName>

src/utils/abi/decodeEventLog.test.ts

@@ -522,3 +522,29 @@ test("errors: event doesn't exist", () => {
     Version: [email protected]"
   `)
 })
+
+test('errors: no topics', () => {
+  expect(() =>
+    decodeEventLog({
+      abi: [
+        {
+          inputs: [
+            {
+              indexed: true,
+              name: 'message',
+              type: 'string',
+            },
+          ],
+          name: 'Bar',
+          type: 'event',
+        },
+      ],
+      topics: [],
+    }),
+  ).toThrowErrorMatchingInlineSnapshot(`
+    "Cannot extract event signature from empty topics.
+
+    Docs: https://viem.sh/docs/contract/decodeEventLog.html
+    Version: [email protected]"
+  `)
+})

src/utils/abi/decodeEventLog.ts

@@ -1,5 +1,6 @@
 import { Abi, AbiParameter, Narrow } from 'abitype'
 import {
+  AbiEventSignatureEmptyTopicsError,
   AbiEventSignatureNotFoundError,
   DecodeLogTopicsMismatch,
 } from '../../errors'
@@ -22,7 +23,7 @@ export type DecodeEventLogParameters<
   abi: Narrow<TAbi>
   data?: TData
   eventName?: ExtractEventNameFromAbi<TAbi, TEventName>
-  topics: [signature: Hex, ...args: TTopics]
+  topics: [signature: Hex, ...args: TTopics] | []
 }
 
 export type DecodeEventLogReturnType<
@@ -34,6 +35,8 @@ export type DecodeEventLogReturnType<
   eventName: TEventName
 } & ExtractEventArgsFromTopics<TAbi, TEventName, TTopics, TData>
 
+const docsPath = '/docs/contract/decodeEventLog'
+
 export function decodeEventLog<
   TAbi extends Abi | readonly unknown[],
   TEventName extends string,
@@ -50,14 +53,18 @@ export function decodeEventLog<
   TData
 >): DecodeEventLogReturnType<TAbi, TEventName, TTopics, TData> {
   const [signature, ...argTopics] = topics
+  if (!signature)
+    throw new AbiEventSignatureEmptyTopicsError({
+      docsPath,
+    })
   const abiItem = (abi as Abi).find(
     (x) =>
       x.type === 'event' &&
       signature === getEventSelector(formatAbiItem(x) as EventDefinition),
   )
   if (!(abiItem && 'name' in abiItem))
     throw new AbiEventSignatureNotFoundError(signature, {
-      docsPath: '/docs/contract/decodeEventLog',
+      docsPath,
     })
 
   const { name, inputs } = abiItem