[Token Detection V2] 1 of 7 - Throw on failure for fetchTokenMetadata in token service (#812)

* Add type to fetchTokenMetadata and throw on failure.

* Define fetch token metadata error with const

Author: Cal-L

src/apis/token-service.test.ts

@@ -1,6 +1,10 @@
 import nock from 'nock';
 import { NetworksChainId } from '../network/NetworkController';
-import { fetchTokenList, fetchTokenMetadata } from './token-service';
+import {
+  fetchTokenList,
+  fetchTokenMetadata,
+  FETCH_TOKEN_METADATA_ERROR,
+} from './token-service';
 
 const TOKEN_END_POINT_API = 'https://token-api.metaswap.codefi.network';
 
@@ -233,7 +237,7 @@ describe('Token service', () => {
       expect(token).toStrictEqual(sampleToken);
     });
 
-    it('should return undefined if the fetch is aborted', async () => {
+    it('should throw error if the fetch is aborted', async () => {
       const abortController = new AbortController();
       nock(TOKEN_END_POINT_API)
         .get(`/tokens/${NetworksChainId.mainnet}`)
@@ -242,49 +246,49 @@ describe('Token service', () => {
         .reply(200, sampleTokenList)
         .persist();
 
-      const fetchPromise = fetchTokenMetadata(
-        NetworksChainId.mainnet,
-        '0x514910771af9ca656af840dff83e8264ecf986ca',
-        abortController.signal,
-      );
-      abortController.abort();
-
-      expect(await fetchPromise).toBeUndefined();
+      await expect(async () => {
+        await fetchTokenMetadata(
+          NetworksChainId.mainnet,
+          '0x514910771af9ca656af840dff83e8264ecf986ca',
+          abortController.signal,
+        );
+        abortController.abort();
+      }).rejects.toThrow(FETCH_TOKEN_METADATA_ERROR);
     });
 
-    it('should return undefined if the fetch fails with a network error', async () => {
+    it('should throw error if the fetch fails with a network error', async () => {
       const { signal } = new AbortController();
       nock(TOKEN_END_POINT_API)
         .get(`/tokens/${NetworksChainId.mainnet}`)
         .replyWithError('Example network error')
         .persist();
 
-      const result = await fetchTokenMetadata(
-        NetworksChainId.mainnet,
-        '0x514910771af9ca656af840dff83e8264ecf986ca',
-        signal,
-      );
-
-      expect(result).toBeUndefined();
+      await expect(async () => {
+        await fetchTokenMetadata(
+          NetworksChainId.mainnet,
+          '0x514910771af9ca656af840dff83e8264ecf986ca',
+          signal,
+        );
+      }).rejects.toThrow(FETCH_TOKEN_METADATA_ERROR);
     });
 
-    it('should return undefined if the fetch fails with an unsuccessful status code', async () => {
+    it('should throw error if the fetch fails with an unsuccessful status code', async () => {
       const { signal } = new AbortController();
       nock(TOKEN_END_POINT_API)
         .get(`/tokens/${NetworksChainId.mainnet}`)
         .reply(500)
         .persist();
 
-      const result = await fetchTokenMetadata(
-        NetworksChainId.mainnet,
-        '0x514910771af9ca656af840dff83e8264ecf986ca',
-        signal,
-      );
-
-      expect(result).toBeUndefined();
+      await expect(async () => {
+        await fetchTokenMetadata(
+          NetworksChainId.mainnet,
+          '0x514910771af9ca656af840dff83e8264ecf986ca',
+          signal,
+        );
+      }).rejects.toThrow(FETCH_TOKEN_METADATA_ERROR);
     });
 
-    it('should return undefined if the fetch fails with a timeout', async () => {
+    it('should throw error if the fetch fails with a timeout', async () => {
       const { signal } = new AbortController();
       nock(TOKEN_END_POINT_API)
         .get(`/tokens/${NetworksChainId.mainnet}`)
@@ -293,14 +297,26 @@ describe('Token service', () => {
         .reply(200, sampleTokenList)
         .persist();
 
-      const result = await fetchTokenMetadata(
-        NetworksChainId.mainnet,
-        '0x514910771af9ca656af840dff83e8264ecf986ca',
-        signal,
-        { timeout: ONE_MILLISECOND },
-      );
-
-      expect(result).toBeUndefined();
+      await expect(async () => {
+        await fetchTokenMetadata(
+          NetworksChainId.mainnet,
+          '0x514910771af9ca656af840dff83e8264ecf986ca',
+          signal,
+          { timeout: ONE_MILLISECOND },
+        );
+      }).rejects.toThrow(FETCH_TOKEN_METADATA_ERROR);
     });
   });
+
+  it('should call the tokens api and return undefined', async () => {
+    const { signal } = new AbortController();
+    nock(TOKEN_END_POINT_API)
+      .get(`/tokens/${NetworksChainId.mainnet}`)
+      .reply(404, undefined)
+      .persist();
+
+    const tokens = await fetchTokenList(NetworksChainId.mainnet, signal);
+
+    expect(tokens).toBeUndefined();
+  });
 });

src/apis/token-service.ts

@@ -1,6 +1,8 @@
 import { timeoutFetch } from '../util';
 
 const END_POINT = 'https://token-api.metaswap.codefi.network';
+export const FETCH_TOKEN_METADATA_ERROR =
+  'TokenService Error: No response from fetchTokenMetadata';
 
 /**
  * Get the tokens URL for a specific network.
@@ -63,18 +65,18 @@ export async function fetchTokenList(
  * @param options.timeout - The fetch timeout.
  * @returns The token metadata, or `undefined` if the request was cancelled.
  */
-export async function fetchTokenMetadata(
+export async function fetchTokenMetadata<T>(
   chainId: string,
   tokenAddress: string,
   abortSignal: AbortSignal,
   { timeout = defaultTimeout } = {},
-): Promise<unknown> {
+): Promise<T> {
   const tokenMetadataURL = getTokenMetadataURL(chainId, tokenAddress);
   const response = await queryApi(tokenMetadataURL, abortSignal, timeout);
   if (response) {
-    return parseJsonResponse(response);
+    return parseJsonResponse(response) as Promise<T>;
   }
-  return undefined;
+  throw new Error(FETCH_TOKEN_METADATA_ERROR);
 }
 
 /**