Module @agoric/casting

Agoric Casting

This Agoric Casting package follows ocap broadcasts in a flexible, future-proof way.

TL;DR: You can run yarn demo, or to follow a mailbox castingSpec do:

npx agoric follow -Bhttp://devnet.agoric.net/network-config :mailbox.agoric1foobarbaz -otext

An example of following an on-chain mailbox in code (using this package) is:

// First, obtain a Hardened JS environment via Endo.
import '@endo/init/pre-remoting.js'; // needed only for the next line
import '@endo/init';

import {
  iterateLatest,
  makeFollower,
  makeLeader,
  makeCastingSpec,
} from '@agoric/casting';

// Iterate over a mailbox follower on the devnet.
const leader = makeLeader('https://devnet.agoric.net/network-config');
const castingSpec = makeCastingSpec(':mailbox.agoric1foobarbaz');
const follower = makeFollower(castingSpec, leader);
for await (const { value } of iterateLatest(follower)) {
  console.log(`here's a mailbox value`, value);
}

Follower options

The followerOpts argument in makeFollower(leader, key, followerOpts) provides an optional bag of options:

  • the proof option, which has three possibilities:
    • 'strict' - release data only after proving it was validated (may incur waits for one block's data to be validated in the next block),
    • 'optimistic' (default) - release data immediately, but may crash the follower in the future if an already-released value could not be proven,
    • 'none' - release data immediately without validation
  • the decode option is a function to translate buf: Uint8Array into data: string
    • (default) - interpret buf as a utf-8 string, then JSON.parse it
  • the unserializer option can be
    • (default) - release unserialized objects using @endo/marshal's makeMarshal()
    • null - don't additionally unserialize data before releasing it
    • any unserializer object supporting E(unserializer).fromCapData(data)
  • the crasher option can be
    • null (default) follower failures only propagate an exception/rejection
    • any crasher object supporting E(crasher).crash(reason)

Behind the scenes

  • the network config contains enough information to obtain Tendermint RPC nodes for a given Agoric network. You can use makeLeaderFromRpcAddresses directly if you want to avoid fetching a network-config.
  • each follower uses periodic CosmJS state polling (every X milliseconds) which can be refreshed more expediently via a Tendermint subscription to the corresponding state_change event
  • published (string) values are automatically unmarshalled, but without object references. a custom marshaller for your application.
  • the iterateRecent adapter transforms a follower into a local async iterator that produces only the last queried value (with no history reconstruction)

Status

This package currently depends on:

Short-term goals:

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Agoric Casting