ethrpc

JavaScript RPC communication with the Ethereum network.

Usage

ethrpc can be installed using npm:

npm install ethrpc

After installing, to use it with Node, require it and call connect:

var rpc = require("ethrpc");
var connectionConfiguration = {
  httpAddresses: ["http://localhost:8545"], // optional, default empty array
  wsAddresses: [], // optional, default empty array
  ipcAddresses: [], // optional, default empty array
  networkID: 3, // optional, used to verify connection to the intended network (blockchain)
  connectionTimeout: 3000, // optional, default 3000
  errorHandler: function (err) { /* out-of-band error */ }, // optional, used for errors that can't be correlated back to a request
};
rpc.connect(connectionConfiguration, function (err) {
  if (err) {
    console.error("Failed to connect to Ethereum node.");
  } else {
    console.log("Connected to Ethereum node!");
  }
});

A minified, browserified file dist/ethrpc.min.js is included for use in the browser. Including this file simply attaches an ethrpc object to window:

<script src="dist/ethrpc.min.js" type="text/javascript"></script>

Basic RPC

The raw method allows you to send in commands that won't be parsed/mangled by ethrpc. (Similar to sending RPC requests with cURL.)

rpc.raw("net_peerCount");
"0x10"

Almost all commands listed in the Ethereum JSON RPC wiki page have named wrappers:

rpc.net.peerCount();
"0x10"

rpc.eth.blockNumber();
"0x35041"

Block and Log Notifications

If you want to subscribe to new blocks or new logs you can get access to a block and log streamer via:

var blockStream = rpc.getBlockStream();

With that, you can then subscribe to new blocks, subscribe to new logs, add log filters (by default you will receive no logs) and subscribe to be notified when blocks/logs are removed as well.

var onBlock = function (block) { /* block party! */ };
var onLog = function (log) { /* log party... */ };
var onBlockAddedSubscriptionToken = blockStream.subscribeToOnBlockAdded(onBlock);
var onLogAddedSubscriptionToken = blockStream.subscribeToOnLogAdded(onLog);
var onBlockRemovedSubscriptionToken = blockStream.subscribeToOnBlockRemoved(onBlock);
var onLogRemovedSubscriptionToken = blockStream.subscribeToOnLogRemoved(onLog);
var logFilterToken = blockStream.addLogFilter({
  address: "0xdeadbeefdeadbeefdeadbeefdeadbeefdeadbeef",
  topics: ["0xbadf00dbadf00dbadf00dbadf00dbadf00dbadf00dbadf00dbadf00dbaadf00d"]
});
blockStream.unsubscribeFromOnBlockAdded(onBlockAddedSubscriptionToken);
blockStream.unsubscribeFromOnBlockRemoved(onBlockRemovedSubscriptionToken);
blockStream.unsubscribeFromOnLogAdded(onLogAddedSubscriptionToken);
blockStream.unsubscribeFromOnLogRemoved(onLogRemovedSubscriptionToken);
blockStream.removeLogFilter(logFilterToken);

Contract upload and download

publish broadcasts (uploads) a compiled contract to the network:

var txHash = rpc.publish("0x603980600b6000396044567c01000000000000000000000000000000000000000000000000000000006000350463643ceff9811415603757600a60405260206040f35b505b6000f3");
// txHash:
"0x6a532c807eb49d78bf0fb7962743c7f155a4b2fc1258b749df85c88b66fc3316"

// To get the contract's address, after the transaction is sealed (mined), get its receipt:
var address = rpc.eth.getTransactionReceipt(txHash).contractAddress;
// address:
"0x86fb6d1f1bd78cc13c6354b6436b6ea0c144de2e"

getCode downloads code from a contract already on the Ethereum network:

var contractCode = rpc.eth.getCode("0x86fb6d1f1bd78cc13c6354b6436b6ea0c144de2e");
// contractCode:
"0x7c010000000000000000000000000000000000000000000000000000000060003504636ffa1caa81141560415760043560405260026040510260605260206060f35b50"

Contract methods: call and sendTransaction

The callOrSendTransaction method executes a method in a contract already on the network. It can broadcast transactions to the network and/or capture return values by calling the contract method(s) locally.

// The method called here doubles its input argument.
var payload = {
  to: "0x5204f18c652d1c31c6a5968cb65e011915285a50",
  name: "double",
  signature: ["int256"],
  params: ["0x5669"], // parameter value(s)
  send: false,
  returns: "int"
};
rpc.callOrSendTransaction(payload);
// returns:
44242

The transaction payload is structured as follows:

Required:

• to: <contract address> (hexstring)
• name: <function name> (string)
• signature: <function signature, e.g. ["int256", "bytes", "int256[]"]> (array)
• params: <parameters passed to the function>

Optional:

• send: <true to sendTransaction, false to call (default)>
• from: <sender's address> (hexstring; defaults to the coinbase account)
• returns: <"int256" (default), "int", "number", "int256[]", "number[]", or "string">

The params and signature fields are required if your function accepts parameters; otherwise, these fields can be excluded. The returns field is used only to format the output, and does not affect the actual RPC request.

Tests

Unit tests are included in test/ethrpc.js, and can be run using npm:

npm test

Alternatively, you can run the tests inside of a docker container. Docker layer caching is leveraged to make it so the build is very fast after the first time (unless you change dependencies):

docker build -t ethrpc . && docker run --rm ethrpc

Internal Architecture

Upon calling connect, a Transporter will be instantiated with the supplied addresses to connect to. A Transport will be created for each of the supplied addresses plus one for web3. Once they have all either successfully connected or failed to connect, Transporter will choose the first address for each transport type (HTTP, WS, IPC, Web3) that connected successfully and use that as the Transport for that transport type. The transport will be chosen automatically based on a preference of Web3 > IPC > WS > HTTP. If no transports are available, the request will fail. The Transports each have their own internal queue of work and if they lose a connection they will queue up incoming requests until a connection can be re-established. Once it is, the queue will be pumped until empty.