fix: refine stacktrace attribution of errors thrown from middleware (#21470)

* Refine middleware types to include the method signature and to express the nullability of the middleware.

* Make sure that the stacktrace does not involve middleware unless the error originated from the middleware itself.

Co-authored-by: steveluscher <github@steveluscher.com>

web3.js/src/connection.ts

@@ -760,19 +760,24 @@ function createRpcClient(
     agentManager = new AgentManager(useHttps);
   }
 
-  let fetchWithMiddleware: (url: string, options: any) => Promise<Response>;
+  let fetchWithMiddleware:
+    | ((url: string, options: any) => Promise<Response>)
+    | undefined;
 
   if (fetchMiddleware) {
-    fetchWithMiddleware = (url: string, options: any) => {
-      return new Promise<Response>((resolve, reject) => {
-        fetchMiddleware(url, options, async (url: string, options: any) => {
+    fetchWithMiddleware = async (url: string, options: any) => {
+      const modifiedFetchArgs = await new Promise<[string, any]>(
+        (resolve, reject) => {
           try {
-            resolve(await fetch(url, options));
+            fetchMiddleware(url, options, (modifiedUrl, modifiedOptions) =>
+              resolve([modifiedUrl, modifiedOptions]),
+            );
           } catch (error) {
             reject(error);
           }
-        });
-      });
+        },
+      );
+      return await fetch(...modifiedFetchArgs);
     };
   }
 
@@ -1972,7 +1977,7 @@ export type HttpHeaders = {[header: string]: string};
 export type FetchMiddleware = (
   url: string,
   options: any,
-  fetch: Function,
+  fetch: (modifiedUrl: string, modifiedOptions: any) => void,
 ) => void;
 
 /**

web3.js/test/connection.test.ts

@@ -133,6 +133,35 @@ describe('Connection', () => {
     });
   }
 
+  it('should attribute middleware fatals to the middleware', async () => {
+    let connection = new Connection(url, {
+      // eslint-disable-next-line @typescript-eslint/no-unused-vars
+      fetchMiddleware: (_url, _options, _fetch) => {
+        throw new Error('This middleware experienced a fatal error');
+      },
+    });
+    const error = await expect(connection.getVersion()).to.be.rejectedWith(
+      'This middleware experienced a fatal error',
+    );
+    expect(error)
+      .to.be.an.instanceOf(Error)
+      .and.to.have.property('stack')
+      .that.include('fetchMiddleware');
+  });
+
+  it('should not attribute fetch errors to the middleware', async () => {
+    let connection = new Connection(url, {
+      fetchMiddleware: (url, _options, fetch) => {
+        fetch(url, 'An `Object` was expected here; this is a `TypeError`.');
+      },
+    });
+    const error = await expect(connection.getVersion()).to.be.rejected;
+    expect(error)
+      .to.be.an.instanceOf(Error)
+      .and.to.have.property('stack')
+      .that.does.not.include('fetchMiddleware');
+  });
+
   it('get account info - not found', async () => {
     const account = Keypair.generate();