@ndn/repo

This package is part of NDNts, Named Data Networking libraries for the modern web.

This package implements a Data repository. The repo is primarily designed to be embedded into Node and web applications, rather than running as a standalone daemon process. Data ingestion is mainly supported through APIs, not command packets. Data retrieval is on par with other repo implementations.

import { makeInMemoryDataStore, RepoProducer, PrefixRegShorter } from "@ndn/repo";

// other imports for examples
import { consume } from "@ndn/endpoint";
import { Name, Interest, Data } from "@ndn/packet";
import { delay } from "@ndn/util";
import assert from "node:assert/strict";

DataStore

DataStore is a Data packet storage, based on an abstract-level compatible key-value database. It implements most of DataStore interfaces defined in @ndn/repo-api package, offering APIs to insert and delete Data packets.

DataStore.create() function creates a DataStore instance, but it's more convenient to use a helper function:

• makeInMemoryDataStore() creates an in-memory DataStore, backed by memory-level.
• makePersistentDataStore(location) creates a persistent DataStore, backed by level.
  • location is a directory path (relative or absolute) in Node.js, or an IDB database name in browser.

The DataStore type implements AsyncDisposable interface. With await using keyword (TypeScript only), the DataStore is closed when the variable goes out of scope. Alternatively, you can invoke await store[Symbol.asyncDispose]() explicitly.

await using store = await makeInMemoryDataStore();

The DataStore type supports Data insertion, Data deletion, and Data lookup. During insertion, you can set an expiration time upon which the packet disappears.

// Insert Data packets.
await store.insert(new Data("/A/0"));
// You can totally insert multiple Data packets in one command.
// This is even preferred, because it bundles them into one LevelDB transaction and runs faster.
await store.insert(new Data("/A/1"), new Data("/A/2"));
// You can also pass the result of fetch() function from @ndn/segmented-object package directly to
// insert() function, because it accepts AsyncIterable<Data> and Iterable<Data> types.

// You can set an expiration time during insertion. Packets disappear upon expiration.
await store.insert({ expireTime: Date.now() + 50 }, new Data("/A/3"));
await delay(50); // Poof, it's gone.
// Inserting new Data packet with same name would overwrite previous packet, even if their implicit
// digests differ. You cannot store two packets with same name.

// Delete Data packets.
await store.delete(new Name("/A/0"), new Name("/A/4"));
// It's harmless to delete non-existent packets, such as /A/4 above.

// Now let's retrieve them.
const rA1 = await store.find(new Interest("/A/1"));
assert.equal(`${rA1?.name}`, "/8=A/8=1");
// Prefix name is supported too.
const rA = await store.find(new Interest("/A", Interest.CanBePrefix));
assert(["/8=A/8=1", "/8=A/8=2"].includes(`${rA?.name}`));
// /A/3 has disappeared because it is expired.
const rA3 = await store.find(new Interest("/A/3"));
assert.equal(rA3, undefined);

RepoProducer

RepoProducer makes packets in a DataStore available for retrieval.

RepoProducer.create() function creates a RepoProducer instance, serving Data from an existing DataStore instance.

The reg option passed to this function controls what name prefixes should be registered:

• PrefixRegStatic(new Name("/A"), new Name("/B")) registers a fixed set of prefixes.
• PrefixRegShorter(1) registers prefixes that are 1-component shorter than each Data name.
• See test cases for more options.

These registrations are effectively within NDNts logical forwarder. Typically you'll combine them with a prefix readvertise module such as @ndn/nfdmgmt to propagate the prefix registration to remote forwarders.

The RepoProducer type implements Disposable interface. With using keyword (TypeScript only), the producer is closed when the variable goes out of scope. Alternatively, you can invoke repoProducer[Symbol.dispose]() explicitly.

// Construct a RepoProducer.
using repoProducer = RepoProducer.create(store, { reg: PrefixRegShorter(1) });
await delay(10); // prefix registration is asynchronous so we delay a little bit

// Try to retrieve Data.
const retrieved = await consume("/A/2");
assert.equal(`${retrieved?.name}`, "/8=A/8=2");