4 files changed, 106 insertions, 14 deletions
diff --git a/packages/subproviders/src/index.ts b/packages/subproviders/src/index.ts
index 71d643f14..9d4480e59 100644
--- a/packages/subproviders/src/index.ts
+++ b/packages/subproviders/src/index.ts
@@ -1,5 +1,6 @@
 import Eth from '@ledgerhq/hw-app-eth';
 import TransportU2F from '@ledgerhq/hw-transport-u2f';
+export import Web3ProviderEngine = require('web3-provider-engine');
 export { ECSignature } from '@0xproject/types';
 
 import { LedgerEthereumClient } from './types';
@@ -10,6 +11,7 @@ export { FakeGasEstimateSubprovider } from './subproviders/fake_gas_estimate_sub
 export { SignerSubprovider } from './subproviders/signer';
 export { RedundantSubprovider } from './subproviders/redundant_subprovider';
 export { LedgerSubprovider } from './subproviders/ledger';
+export { RPCSubprovider } from './subproviders/rpc_subprovider';
 export { GanacheSubprovider } from './subproviders/ganache';
 export { Subprovider } from './subproviders/subprovider';
 export { NonceTrackerSubprovider } from './subproviders/nonce_tracker';
diff --git a/packages/subproviders/src/subproviders/rpc_subprovider.ts b/packages/subproviders/src/subproviders/rpc_subprovider.ts
new file mode 100644
index 000000000..3ad0e5325
--- /dev/null
+++ b/packages/subproviders/src/subproviders/rpc_subprovider.ts
@@ -0,0 +1,90 @@
+import { assert } from '@0xproject/assert';
+import { StatusCodes } from '@0xproject/types';
+import { fetchAsync } from '@0xproject/utils';
+import { JSONRPCRequestPayload } from 'ethereum-types';
+import JsonRpcError = require('json-rpc-error');
+
+import { Callback, ErrorCallback } from '../types';
+
+import { Subprovider } from './subprovider';
+
+/**
+ * This class implements the [web3-provider-engine](https://github.com/MetaMask/provider-engine) subprovider interface.
+ * It forwards on JSON RPC requests to the supplied `rpcUrl` endpoint
+ */
+export class RPCSubprovider extends Subprovider {
+    private _rpcUrl: string;
+    private _requestTimeoutMs: number;
+    constructor(rpcUrl: string, requestTimeoutMs: number = 20000) {
+        super();
+        assert.isString('rpcUrl', rpcUrl);
+        assert.isNumber('requestTimeoutMs', requestTimeoutMs);
+        this._rpcUrl = rpcUrl;
+        this._requestTimeoutMs = requestTimeoutMs;
+    }
+    /**
+     * This method conforms to the web3-provider-engine interface.
+     * It is called internally by the ProviderEngine when it is this subproviders
+     * turn to handle a JSON RPC request.
+     * @param payload JSON RPC payload
+     * @param next Callback to call if this subprovider decides not to handle the request
+     * @param end Callback to call if subprovider handled the request and wants to pass back the request.
+     */
+    // tslint:disable-next-line:prefer-function-over-method async-suffix
+    public async handleRequest(payload: JSONRPCRequestPayload, _next: Callback, end: ErrorCallback): Promise<void> {
+        const finalPayload = Subprovider._createFinalPayload(payload);
+        const headers = new Headers({
+            Accept: 'application/json',
+            'Content-Type': 'application/json',
+        });
+
+        let response;
+        try {
+            response = await fetchAsync(
+                this._rpcUrl,
+                {
+                    method: 'POST',
+                    headers,
+                    body: JSON.stringify(finalPayload),
+                },
+                this._requestTimeoutMs,
+            );
+        } catch (err) {
+            end(new JsonRpcError.InternalError(err));
+            return;
+        }
+
+        const text = await response.text();
+        if (!response.ok) {
+            const statusCode = response.status;
+            switch (statusCode) {
+                case StatusCodes.MethodNotAllowed:
+                    end(new JsonRpcError.MethodNotFound());
+                    return;
+                case StatusCodes.GatewayTimeout:
+                    const errMsg =
+                        'Gateway timeout. The request took too long to process. This can happen when querying logs over too wide a block range.';
+                    const err = new Error(errMsg);
+                    end(new JsonRpcError.InternalError(err));
+                    return;
+                default:
+                    end(new JsonRpcError.InternalError(text));
+                    return;
+            }
+        }
+
+        let data;
+        try {
+            data = JSON.parse(text);
+        } catch (err) {
+            end(new JsonRpcError.InternalError(err));
+            return;
+        }
+
+        if (data.error) {
+            end(data.error);
+            return;
+        }
+        end(null, data.result);
+    }
+}
diff --git a/packages/subproviders/src/subproviders/subprovider.ts b/packages/subproviders/src/subproviders/subprovider.ts
index ff8378c4e..5dc273569 100644
--- a/packages/subproviders/src/subproviders/subprovider.ts
+++ b/packages/subproviders/src/subproviders/subprovider.ts
@@ -9,18 +9,7 @@ import { Callback, ErrorCallback, JSONRPCRequestPayloadWithMethod } from '../typ
 export abstract class Subprovider {
     // tslint:disable-next-line:underscore-private-and-protected
     private engine!: Provider;
-    // Ported from: https://github.com/MetaMask/provider-engine/blob/master/util/random-id.js
-    private static _getRandomId(): number {
-        const extraDigits = 3;
-        const baseTen = 10;
-        // 13 time digits
-        const datePart = new Date().getTime() * Math.pow(baseTen, extraDigits);
-        // 3 random digits
-        const extraPart = Math.floor(Math.random() * Math.pow(baseTen, extraDigits));
-        // 16 digits
-        return datePart + extraPart;
-    }
-    private static _createFinalPayload(
+    protected static _createFinalPayload(
         payload: Partial<JSONRPCRequestPayloadWithMethod>,
     ): Partial<JSONRPCRequestPayloadWithMethod> {
         const finalPayload = {
@@ -32,6 +21,17 @@ export abstract class Subprovider {
         };
         return finalPayload;
     }
+    // Ported from: https://github.com/MetaMask/provider-engine/blob/master/util/random-id.js
+    private static _getRandomId(): number {
+        const extraDigits = 3;
+        const baseTen = 10;
+        // 13 time digits
+        const datePart = new Date().getTime() * Math.pow(baseTen, extraDigits);
+        // 3 random digits
+        const extraPart = Math.floor(Math.random() * Math.pow(baseTen, extraDigits));
+        // 16 digits
+        return datePart + extraPart;
+    }
     // tslint:disable-next-line:async-suffix
     public abstract async handleRequest(
         payload: JSONRPCRequestPayload,
diff --git a/packages/subproviders/src/utils/subprovider_utils.ts b/packages/subproviders/src/utils/subprovider_utils.ts
index 24ebedd06..beda408ab 100644
--- a/packages/subproviders/src/utils/subprovider_utils.ts
+++ b/packages/subproviders/src/utils/subprovider_utils.ts
@@ -1,4 +1,4 @@
-import ProviderEngine = require('web3-provider-engine');
+import Web3ProviderEngine = require('web3-provider-engine');
 
 import { Subprovider } from '../subproviders/subprovider';
 
@@ -7,7 +7,7 @@ import { Subprovider } from '../subproviders/subprovider';
  * @param provider    Given provider
  * @param subprovider Subprovider to prepend
  */
-export function prependSubprovider(provider: ProviderEngine, subprovider: Subprovider): void {
+export function prependSubprovider(provider: Web3ProviderEngine, subprovider: Subprovider): void {
     subprovider.setEngine(provider);
     // HACK: We use implementation details of provider engine here
     // https://github.com/MetaMask/provider-engine/blob/master/index.js#L68