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Listen to external event published by Guardian

Introduction

Guardian will publish number of events to NATS server to hook into those events , which extends the function that is suitable to the solution.

Hooks to external event

To hooks into Guardian events, we need to have a client, that is connected to same NATS instance with Guardian and implement the response function for a specific event.
Below is the sample for .NodeJs and in case of other language please refer to Nats.io for complete documentation.

publish/subscribe events

The events with type=publish is publish/subscribe pattern so that the same message can be received by multiple clients. If there are multiple clients make sure it is handled by duplicate message processing.
import { connect, JSONCodec } from "nats";
(async () => {
const nc = await connect({ servers: "localhost:4222" });
const c = JSONCodec();
const sub = nc.subscribe("externals-events.ipfs_added_file");
(async () => {
for await (const m of sub) {
console.log(`[${sub.getProcessed()}]`, c.decode(m.data));
}
console.log("subscription closed");
})();
})();
To get more information please click https://github.com/nats-io/nats.js#publish-and-subscribe

request/reply events

Some event has type=request for which we need to subscribe and respond to the event.

Example:

For the before/after IPFS event, if the listener responds an error then IPFS service will be skipped and upload/response the actual content. This same scenario also happens when we do not have listener to an event. For example we can use this to encrypt/decrypt IPFS content file
const responseToIpfsEvent = (type: string, cb: (data: Buffer) => Buffer) => {
const sub = nc.subscribe(type);
console.log("√ Listening to IPFS event: %s", type);
(async () => {
for await (const m of sub) {
console.log(`[${sub.getProcessed()} - ${m.subject}]`);
try {
const payload = c.decode(m.data) as any;
const body = cb(Buffer.from(payload.content, 'base64'));
const responseMessage = { body: body.toString('base64') }
const archResponse = zlib.deflateSync(JSON.stringify(responseMessage)).toString('binary');
m.respond(StringCodec().encode(archResponse));
} catch (e) {
// It is important that you should handle the content to make sure that is your encrypted/decrypted, skip if that is system ipds file
const archResponse = zlib.deflateSync(JSON.stringify({ error: e.message })).toString('binary');
m.respond(StringCodec().encode(archResponse));
}
}
console.log("Subscription closed");
})();
};

External events list

event
type
payload
notes
externals-events.ipfs_added_file
publish
{cid, url}
Event is published when an IPFS file is added
external-events.token_minted
publish
{ tokenId, tokenValue, memo }
When token is minted successfully
external-events.error_logs
publish
{message, type, attributes}
When an error is sent to logger service
external-events.block_run_action_event
publish
{blockType, blockTag, uuid ,data, result}
After runAction is finished, events are called by these blocks:
  1. 1.
    aggregateDocumentBlock
  2. 2.
    mintDocumentBlock
  3. 3.
    sendToGuardianBlock
  4. 4.
    timerBlock after runAction finish
external-events.ipfs_before_upload_content
request
{content}
The base64 of the content (buffer) to be hooked and modified
external-events.ipfs_after_read_content
request
{content}
The base64 of the content (buffer) to be modified/processed

Example

This example demonstrates implementation of encryption / decryption of simple IPFS content.
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Introduction
Hooks to external event
External events list
Example