Better error for Service.at

packages/gateway/src/index.ts

@@ -271,7 +271,6 @@ class HttpGateway implements OasisGateway {
         address: bytes.toHex(request.address!),
       }
     );
-    // todo: throw cleaner error when code doesn't exist
     return {
       code: bytes.parseHex(response.code),
     };

packages/service/src/error.ts

@@ -1,5 +1,13 @@
+import { bytes } from '@oasislabs/common';
 import { RpcOptions } from './oasis-gateway';
 
+export function NO_CODE_ERROR_MSG(address: Uint8Array): string {
+  return `
+    No code exists for address ${bytes.toHex(address)}.
+    Either your address is incorrect or the deploy failed.
+  `;
+}
+
 export class RpcError extends Error {
   constructor(
     readonly rpcArgs: any[],
@@ -15,3 +23,9 @@ export class DeployError extends Error {
     super(...params);
   }
 }
+
+export class ServiceError extends Error {
+  constructor(readonly address: Uint8Array, ...params: any[]) {
+    super(...params);
+  }
+}

packages/service/src/oasis-gateway.ts

@@ -44,7 +44,7 @@ export type GetCodeRequest = {
 };
 
 export type GetCodeResponse = {
-  code: Uint8Array;
+  code: Uint8Array | null;
 };
 
 export type RpcRequest = {

packages/service/src/rpc.ts

@@ -3,7 +3,7 @@ import camelCase from 'camelcase';
 import { KeyStore } from '@oasislabs/confidential';
 import { bytes } from '@oasislabs/common';
 
-import { RpcError } from './error';
+import { RpcError, ServiceError, NO_CODE_ERROR_MSG } from './error';
 import { Idl, IdlError, RpcFn, RpcInput } from './idl';
 import { ServiceOptions } from './service';
 import { OasisGateway, RpcOptions } from './oasis-gateway';
@@ -183,7 +183,12 @@ export class RpcFactory {
   ): Promise<RpcCoder> {
     // Check the contract's deploy header to see if it's confidential.
     let response = await options.gateway!.getCode({ address });
-    let deployHeader = header.parseFromCode(response.code);
+
+    if (!response.code) {
+      throw new ServiceError(address, NO_CODE_ERROR_MSG(address));
+    }
+
+    let deployHeader = header.parseFromCode(response.code!);
 
     if (!deployHeader || !deployHeader.body.confidential) {
       return OasisCoder.plaintext();

packages/service/src/service.ts

@@ -11,6 +11,7 @@ import {
   SubscribeRequest,
   SubscribeTopic,
 } from './oasis-gateway';
+import { ServiceError, NO_CODE_ERROR_MSG } from './error';
 
 /**
  * Service is the object representation of an Oasis rpc service.
@@ -85,6 +86,11 @@ export default class Service {
 
     options = Service.setupOptions(options);
     let response = await options.gateway!.getCode({ address: _address });
+
+    if (!response.code) {
+      throw new ServiceError(_address, NO_CODE_ERROR_MSG(_address));
+    }
+
     let wasm = DeployHeaderReader.initcode(response.code);
     let idl = await fromWasm(wasm);
     return new Service(idl, address, options);
@@ -157,7 +163,10 @@ export default class Service {
   public removeEventListener(event: string, listener: Listener) {
     let subscription = this._inner.subscriptions.get(event);
     if (subscription === undefined) {
-      throw new Error(`no subscriptions found for ${event}`);
+      throw new ServiceError(
+        this._inner.address,
+        `no subscriptions found for ${event}`
+      );
     }
 
     this._inner.listeners.removeListener(event, listener);

packages/service/test/service.spec.ts

@@ -14,6 +14,7 @@ import {
 } from './utils';
 import { OasisCoder } from '../src/coder/oasis';
 import { makeExpectedBytecode } from './utils';
+import { NO_CODE_ERROR_MSG } from '../src/error';
 
 setGateway(new EmptyOasisGateway());
 
@@ -154,6 +155,33 @@ describe('Service', () => {
 
     expect(bytes.parseHex(address)).toEqual(s._inner.address);
   });
+
+  it('Service.at should give an informative error when an invalid address is used', async () => {
+    const address = bytes.parseHex(
+      '0x288e7e1cc60962f40d4d782950470e3705c5acf4'
+    );
+    const bin = bytes.toHex(
+      new Uint8Array(
+        require('fs').readFileSync('test/wasm/mantle-counter.wasm')
+      )
+    );
+    const gateway = {
+      // Null getCode response means the service doesn't exist at the address.
+      getCode: () => {
+        return { code: null };
+      },
+    };
+
+    try {
+      // @ts-ignore
+      await Service.at(address, {
+        gateway,
+        db: new DummyStorage(),
+      });
+    } catch (e) {
+      expect(e.message).toBe(NO_CODE_ERROR_MSG(address));
+    }
+  });
 });
 
 function confidentialCoder() {

packages/web3/src/gateway.ts

@@ -201,9 +201,10 @@ export default class Web3Gateway implements OasisGateway {
       bytes.toHex(request.address),
       'latest'
     );
-    // todo: throw cleaner error when code doesn't exist
+
+    // Note: the gateway returns '0x' for all addresses without code.
     return {
-      code: bytes.parseHex(response),
+      code: response === '0x' ? null : bytes.parseHex(response),
     };
   }