Weavechain

Hello World

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Context on What's Happening

In this exercise, we're going to walk you through the basics of connecting to a Weavechain node, writing data, and reading it.

• In the first step, you'll create a public / private keypair that represents your account. Normally you'd save this to be able to 'login again' with the same account, but for this exercise we don't need to keep it.
• The first step also includes a step to write "Hello World!" to the node, with many fields nulled out to be filled automatically by the server.
• The second step creates a second user, connects to the node, and then reads the last record written by the previous user.
• The third step is purely informational, describing the definition of the remote table.

Javascript

Import the API library

import { WeaveAPI, WeaveHelper } from "@weavechain/weave-js-api"

1. Create a new session, then write a message

(hover the code block and click ⏵ to run it)

// Generate a key pair
const [ pub, pvk ] = WeaveHelper.generateKeys();
console.log("Public key: ", pub);
console.log("Private key: ", pvk);

// Connect to a public node (which was configured to allow writes from anyone)
const node = "https://public.weavechain.com:443/92f30f0b6be2732cb817c19839b0940c";
const organization = "weavedemo";
const encrypted = node.startsWith("http://");

// Create a new session
const cfg = WeaveHelper.getConfig(node, pub, pvk, encrypted)

const nodeApi = new WeaveAPI().create(cfg);
await nodeApi.init();

// Write a new record in a pre-defined table
//   hosted by the public node in an SQLite database
// Note: the table is public for this example, but it could have full RBAC
const scope = "shared";
const table = "hello";

const session = await nodeApi.login(organization, pub, scope || "*");

// The target table can optionally have some special columns that are auto-filled by the backend
const record = [
        null, //id, filled server side
        null, //timestamp, filled server side
        null, //writer public key, filled server side
        null, //signature, filled server side
        null, //writer IP, filled server side. Erasure is applied to obfuscate it on read
        "*",  //row level read access control (could be roles, accounts, blockchain wallets, NFTs etc.)
        "Hello World!"
    ];
const records = new WeaveHelper.Records(table, [ record ]);
await nodeApi.write(session, scope, records, WeaveHelper.Options.WRITE_DEFAULT);

2. Create a new session, read the last inserted record

const [ pub, pvk ] = WeaveHelper.generateKeys();
console.log("Public key: ", pub);
console.log("Private key: ", pvk);

// Connect
const node = "https://public.weavechain.com:443/92f30f0b6be2732cb817c19839b0940c";
const organization = "weavedemo";
const encrypted = node.startsWith("http://");

// Create a new session
const cfg = WeaveHelper.getConfig(node, pub, pvk, encrypted)

const nodeApi = new WeaveAPI().create(cfg);
await nodeApi.init();

const scope = "shared";
const table = "hello";

const session = await nodeApi.login(organization, pub, scope || "*");

// Read the last record
const limit = 1;
const filter = new WeaveHelper.Filter(null, {"id": "DESC"}, limit, null, null, null);
const result = await nodeApi.read(session, scope, table, filter, WeaveHelper.Options.READ_DEFAULT_NO_CHAIN);
console.log(result);

3. Remote table definition

{
    "columns": {
        "id": { "type": "LONG", "isIndexed": True, "isUnique": True, "isNullable": False },
        "ts": { "type": "LONG" },
        "pubkey": { "type": "STRING" },
        "sig": { "type": "STRING" },
        "ip": { "type": "STRING", "readTransform": "ERASURE" },
        "roles": { "type": "STRING" },
        "message": { "type": "STRING" }
    },
    "idColumnIndex": 0,
    "timestampColumnIndex": 1,
    "ownerColumnIndex": 2,
    "signatureColumnIndex": 3,
    "sourceIpColumnIndex": 4,
    "allowedRolesColumnIndex": 5,
    "isLocal": False,
    "applyReadTransformations": True
}

• idColumnIndex: specifies the column to contain an autogenerated ID
• timestampColumnIndex: fills the column automatically with the network time
• ownerColumnIndex: fills the column automatically with the public key of the writer
• signatureColumnIndex: fills the column with details about the record at write time (hash and signature)
• sourceIpColumnIndex: fills the IP column automatically with the source writer
• allowedRolesColumnIndex: Optional feature: row-level read access (controlled by the writer). "*" allows anyone to read it
• isLocal": set to False allows reading by remote clients
• applyReadTransformations: set to True enables data transformations at read