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import { JSONRPCRequestPayload } from '@0xproject/types';
import { promisify } from '@0xproject/utils';
import * as _ from 'lodash';
import RpcSubprovider = require('web3-provider-engine/subproviders/rpc');
import { Callback } from '../types';
import { Subprovider } from './subprovider';
/**
* This class implements the [web3-provider-engine](https://github.com/MetaMask/provider-engine) subprovider interface.
* It attempts to handle each JSON RPC request by sequentially attempting to receive a valid response from one of a
* set of JSON RPC endpoints.
*/
export class RedundantRPCSubprovider extends Subprovider {
private _rpcs: RpcSubprovider[];
private static async _firstSuccessAsync(
rpcs: RpcSubprovider[],
payload: JSONRPCRequestPayload,
next: Callback,
): Promise<any> {
let lastErr: Error | undefined;
for (const rpc of rpcs) {
try {
const data = await promisify(rpc.handleRequest.bind(rpc))(payload, next);
return data;
} catch (err) {
lastErr = err;
continue;
}
}
if (!_.isUndefined(lastErr)) {
throw lastErr;
}
}
/**
* Instantiates a new RedundantRPCSubprovider
* @param endpoints JSON RPC endpoints to attempt. Attempts are made in the order of the endpoints.
*/
constructor(endpoints: string[]) {
super();
this._rpcs = _.map(endpoints, endpoint => {
return new RpcSubprovider({
rpcUrl: endpoint,
});
});
}
/**
* 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:async-suffix
public async handleRequest(
payload: JSONRPCRequestPayload,
next: Callback,
end: (err: Error | null, data?: any) => void,
): Promise<void> {
const rpcsCopy = this._rpcs.slice();
try {
const data = await RedundantRPCSubprovider._firstSuccessAsync(rpcsCopy, payload, next);
end(null, data);
} catch (err) {
end(err);
}
}
}
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