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Web3 Stack

Polkadot

Polkadot - Layer 0

Relay chain - nominated proof of stake chain

limited functionality

no support for smart contract

collect states from parachains

Parachains - layer 1

offers dapp, smart contract, ... and connect to relay chain

parachains block was sent to relay chain for validity

layer 2 can be built upon layer 1 parachain

can also act as bridges to connect with other blockchain ecosystem (Bitcoin, Ethereum)

Parathreads

function the same as parachains but was charged based on each block instead of signing a two year lease with Polkadot

Kusama - standalone independent blockchain

“test protocol”

Substrate - sdk to build blockchain

RPC (Remote procedure calls)

a way for an external program—for example, a browser or front-end application—to communicate with a Substrate node. They are used for checking storage values, submitting transactions, and querying the current consensus authorities. Substrate comes with several

default RPCs⁠

. In many cases, it is useful to add custom RPCs to your node.

API Design Paradigms

⁠

event driven API

is created to solve the above problem where the client needs to send multiple requests before the web API returns a complete status

WebHooks

Client - register with interested events and callback URL

API Provider sends event data whenever updated to the callback URL

Drawbacks

Failures - ensure delivery through retries

Firewalls - apps running behind firewalls can send but receiving can be tricky

Noise - typically, each webhook represents a single even. Many events in a short time can be noisy

Best for trigger the server to send events to predefined client endpoints

WebSockets

Client - Server

Client sends Handshake (HTTP) & Server upgrade to WebSocket which is a bidirectional communication channel

Benefits

bidirectional low latency communication

reduced overhead of http requests

Drawbacks

Clients are responsible for connections

scalability challenges

Best for Bi-directional communication between clients and servers

HTTP Streaming

client sent a request and server response with a new event that runs indefinitly

Benefits

can stream over simple http

native browser support

Drawbacks

bidirectional communication is challenging

buffering in client side can be limiting

Best for One-way communication over HTTP

request-response API

representational state transfer (REST)

center around resources

collection (https://foobar.com/api/v1/users)

entity (https://foobar.com/api/v1/users/user-1)

Benefits

standard method names, arguments, and status codes

utilizes http features

easy to main

Drawbacks

big payloads

multiple http roundtrips (getting an entity and it sub resources took two api calls)

best for Create Read Update Delete (CRUD) Operations

remote procedural call (RPC)

center around actions

endpoint for each action (https://slack.com/api/chat.postMessage)

Benefits

easy to understand

lightweight payloads

high performance

Drawbacks

discovery is difficult

limited standardization (heavy reference to documentation)

leads to function explosion

best for exposing several actions

GraphQL

get, post for most programs

user defined a structure that the response should be and the api returns the payload in that structure

Benefits

saves multiple round trips

avoids versioning

smaller payload size

Drawbacks

added complexity for server

optimizing performance is difficult

too complicated for a simple API

best when need querying flexibility

Polkadot.js

install by

yarn add @polkadot/api

API Interface was dynamically generated base on the connected node

Metadata

api.<type>.<module>.<section>

const - runtime constants

query - chain state

tx - all extrinsics

API Provider & API Instance

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