fix: Throw clearer error when the NPM registry returns 404

packages/snaps-controllers/src/snaps/location/npm.test.ts

@@ -246,6 +246,26 @@ describe('NpmLocation', () => {
     );
   });
 
+  it('throws if NPM returns 404', async () => {
+    const customFetchMock = jest.fn().mockResolvedValue({
+      ok: false,
+      body: null,
+      status: 404,
+    } as any);
+
+    const location = new NpmLocation(
+      new URL('npm:@metamask/jsx-example-snap'),
+      {
+        versionRange: exampleSnapVersion,
+        fetch: customFetchMock as typeof fetch,
+      },
+    );
+
+    await expect(location.manifest()).rejects.toThrow(
+      '"@metamask/jsx-example-snap" was not found in the NPM registry',
+    );
+  });
+
   it('throws if the NPM tarball URL is invalid', async () => {
     const customFetchMock = jest.fn();
 

packages/snaps-controllers/src/snaps/location/npm.ts

@@ -220,11 +220,15 @@ export class NpmLocation extends BaseNpmLocation {
   async fetchNpmTarball(tarballUrl: URL): Promise<Map<string, VirtualFile>> {
     // Perform a raw fetch because we want the Response object itself.
     const tarballResponse = await this.meta.fetch(tarballUrl.toString());
-    if (!tarballResponse.ok || !tarballResponse.body) {
-      throw new Error(
-        `Failed to fetch tarball for package "${this.meta.packageName}".`,
-      );
-    }
+
+    assert(
+      tarballResponse.status !== 404,
+      `"${this.meta.packageName}" was not found in the NPM registry`,
+    );
+    assert(
+      tarballResponse.ok && tarballResponse.body,
+      `Failed to fetch tarball for package "${this.meta.packageName}"`,
+    );
 
     // We assume that NPM is a good actor and provides us with a valid `content-length` header.
     const tarballSizeString = tarballResponse.headers.get('content-length');
@@ -234,6 +238,7 @@ export class NpmLocation extends BaseNpmLocation {
       tarballSize <= TARBALL_SIZE_SAFETY_LIMIT,
       'Snap tarball exceeds size limit',
     );
+
     return new Promise((resolve, reject) => {
       const files = new Map();