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Data Sharing

How is the data shared between different nodes?​

In a distributed system, every node has a copy of the database, which can lead to discrepancies when new data is updated on one node. To ensure that every node has the most up-to-date information, a data-sharing interface is needed. This interface periodically checks for new data and shares it with all nodes in the network. This will usually be in a separate module and be called in the setup() function of the task in the index.js module.

For the Linktree task, we will create a dbSharing.js module that serves as the data-sharing interface and is imported into the index.js file. The share() function from dbSharing.js is called every 20 seconds to enable data replication among the nodes. By using the dbSharing module, the system can improve consistency and reliability, which is essential in a blockchain system where data integrity is critical.

Here is a high-level overview of how the module works​

  • It retrieves a list of nodes in the network by requesting a task’s URL.
  • For each node in the list, it retrieves a list of Linktrees associated with the node by requesting the node's URL.
  • For each Linktree retrieved from a node, it verifies the signature associated with the data
  • If the signature is verified, it checks if a local copy of the Linktree already exists in the database.
  • If a local copy exists and the remote copy is newer, it updates the local copy with the remote data. If a local copy does not exist, it creates a new entry in the database with the remote data.

Step 1: Retrieve the list of node URLs associated with a specific task ID.

const nodesUrl = `${SERVICE_URL}/nodes/${TASK_ID}`;
const res = await axios.get(nodesUrl);

let nodeUrlList = res.data.map((e) => {
     return e.data.url;
       };

	// ... check the repo for the full code

Step 2: Retrieve the list of all Linktrees from the database.

let allLinktrees = await db.getAllLinktrees();
allLinktrees = allLinktrees || "[]";

// ...

Step 3: Retrieve the list of Linktrees associated with each node.

for (let url of nodeUrlList) {
  const res = await axios.get(`${url}/task/${TASK_ID}/linktree/all`);

  // ...
}

Step 4: Verify the signature

if (!payload || payload.length == 0) continue;
for (let i = 0; i < payload.length; i++) {
    const value = payload[i].value;
    const isVerified = nacl.sign.detached.verify(
        new TextEncoder().encode(JSON.stringify(value.data)),
        bs58.decode(value.signature),
        bs58.decode(value.publicKey)
    );
    if (!isVerified) {
        console.warn(`${url} is not able to verify the signature`);
        continue;
    } // ...

Step 5: Update the local copy with new data if needed

let localExistingLinktree = allLinktrees.find((e) => {
  e.uuid == linktreePayload.data.uuid;
});
if (localExistingLinktree) {
  if (localExistingLinktree.data.timestamp < linktreePayload.data.timestamp) {
    allLinktrees.push(linktreePayload);
  }
} else {
  allLinktrees.push(linktreePayload);
}