Add gasless backend

backend/gasless/.env.example

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+NODE_URL=wss://rpc.vara-network.io
+VOUCHER_ACCOUNT=0x...

backend/gasless/.eslintrc.json

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+{
+  "root": true,
+  "env": {
+    "browser": true,
+    "es2021": true,
+    "node": true
+  },
+  "extends": ["airbnb-typescript/base", "plugin:@typescript-eslint/recommended"],
+  "parser": "@typescript-eslint/parser",
+  "parserOptions": {
+    "ecmaVersion": "latest",
+    "sourceType": "module"
+  },
+  "plugins": ["@typescript-eslint"],
+  "rules": {
+    "semi": ["error", "always"],
+    "object-curly-spacing": ["error", "always"],
+    "indent": [
+      "warn",
+      2,
+      {
+        "SwitchCase": 1,
+        "flatTernaryExpressions": false,
+        "offsetTernaryExpressions": true
+      }
+    ],
+    "linebreak-style": ["error", "unix"],
+    "quotes": ["warn", "single", { "avoidEscape": true }],
+    "@typescript-eslint/no-empty-function": 0,
+    "@typescript-eslint/no-explicit-any": "off",
+    "no-case-declarations": 0,
+    "eol-last": "error",
+    "max-len": ["error", { "code": 120, "tabWidth": 2, "ignoreStrings": true, "ignoreComments": true }],
+    "array-bracket-spacing": ["error", "always"],
+    "computed-property-spacing": ["error", "never"],
+    "no-multi-spaces": "error",
+    "space-before-function-paren": ["error", "never"]
+  }
+}

backend/gasless/.gitignore

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+.DS_Store
+.vscode/
+.binpath
+.metahash
+
+# Rust
+target/
+
+# Npm
+node_modules/
+.env
+dist/

backend/gasless/Dockerfile

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+FROM node:20-alpine
+
+ARG REACT_APP_SIGNALING_SERVER \
+    REACT_APP_NODE_ADDRESS \
+    PATH_TO_META \
+    WS_ADDRESS \
+    PROGRAM_ID
+ENV REACT_APP_SIGNALING_SERVER=${REACT_APP_SIGNALING_SERVER} \
+    REACT_APP_NODE_ADDRESS=${REACT_APP_NODE_ADDRESS} \
+    PATH_TO_META=${PATH_TO_META} \
+    WS_ADDRESS=${WS_ADDRESS} \
+    PROGRAM_ID=${PROGRAM_ID}
+
+WORKDIR /apps
+COPY ./backend/w3bstreaming /apps
+
+RUN yarn install
+RUN yarn build
+
+CMD ["yarn", "start"]

backend/gasless/README.md

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+<p align="center">
+  <a href="https://gear-tech.io">
+    <img src="https://github.com/gear-tech/gear/blob/master/images/logo-grey.png" width="400" alt="GEAR">
+  </a>
+</p>
+<p align=center>
+    <a href="https://github.com/gear-tech/gear-js/blob/master/LICENSE"><img src="https://img.shields.io/badge/License-GPL%203.0-success"></a>
+</p>
+<hr>
+
+# Gasless
+
+## Description
+
+Example of backend for issuing and revoking vouchers (gasless).
+
+Example contains three functions for issuing and revoking vouchers:
+
+1. `issue(account: HexString, programId: HexString, amount: number, durationInSec: number): Promise<string>`
+   - Issues a voucher for the given account, programId, amount, and duration.
+   - Parameters:
+     - `account`: The account to issue the voucher for.
+     - `programId`: The programId to issue the voucher for.
+     - `amount`: The amount to issue the voucher for.
+     - `durationInSec`: The duration to issue the voucher for in seconds.
+   - Returns: A Promise that resolves to the voucherId as a string.
+
+2. `prolong(voucherId: HexString, account: string, balance: number, prolongDurationInSec: number): Promise<void>`
+   - Prolongs the voucher with the given voucherId, account, balance, and prolongDuration.
+   - Parameters:
+     - `voucherId`: The voucherId to prolong.
+     - `account`: The account to prolong the voucher for.
+     - `balance`: The required balance to top up the voucher.
+     - `prolongDurationInSec`: The duration to prolong the voucher for in seconds.
+   - Returns: A Promise that resolves when the operation is complete.
+
+3. `revoke(voucherId: HexString, account: string): Promise<void>`
+   - Revokes the voucher with the given voucherId and account.
+   - Parameters:
+     - `voucherId`: The voucherId to revoke.
+     - `account`: The account to revoke the voucher for.
+   - Returns: A Promise that resolves when the operation is complete.
+
+These functions are part of the `GaslessService` class, which interacts with the Gear API to manage vouchers.
+
+
+## Getting started
+
+### Install packages:
+
+```sh
+yarn install
+```
+
+### Declare environment variables:
+
+Create `.env` file, `.env.example` will let you know what variables are expected.
+
+
+### Build the app:
+
+```sh
+yarn build
+```
+
+### Run the app:
+
+```sh
+yarn start
+```

backend/gasless/package.json

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+{
+  "name": "gasless",
+  "version": "1.0.0",
+  "description": "",
+  "main": "index.js",
+  "scripts": {
+    "build": "rm -rf dist && tsc",
+    "start": "node dist/main.js",
+    "watch": "ts-node-dev src/main.ts"
+  },
+  "keywords": [],
+  "author": "",
+  "license": "ISC",
+  "dependencies": {
+    "@gear-js/api": "^0.36.3",
+    "@polkadot/api": "^10.11.2",
+    "@polkadot/types": "10.10.1",
+    "@polkadot/wasm-crypto": "^7.3.2",
+    "@polkadot/util": "^7.3.2",
+    "dotenv": "^16.0.3",
+    "express": "^4.18.2",
+    "socket.io": "^4.6.1"
+  },
+  "devDependencies": {
+    "@types/express": "^4.17.17",
+    "@types/node": "^20.10.0",
+    "ts-node-dev": "^2.0.0",
+    "types": "*",
+    "typescript": "^5.0.4"
+  }
+}

backend/gasless/src/main.ts

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+import { GearApi, HexString, VoucherIssuedData, IUpdateVoucherParams } from '@gear-js/api';
+import { waitReady } from '@polkadot/wasm-crypto';
+import { hexToU8a, } from '@polkadot/util';
+
+import { Keyring } from '@polkadot/api';
+
+const secondsToBlock = 3;
+
+export class GaslessService  {
+  private api: GearApi;
+
+  constructor() {
+    this.api = new GearApi({ providerAddress: process.env.NODE_URL });
+  }
+
+  /**
+   * Issues a voucher for the given account, programId, amount, and duration.
+   * 
+   * @param account - The account to issue the voucher for.
+   * @param programId - The programId to issue the voucher for.
+   * @param amount - The amount to issue the voucher for.
+   * @param durationInSec - The duration to issue the voucher for.
+   * @returns The voucherId.
+   */
+  async issue(account: HexString, programId: HexString, amount: number, durationInSec: number): Promise<string> {
+    await Promise.all([this.api.isReadyOrError, waitReady()])
+    const voucherAccount = this.getVoucherAccount();
+
+    const durationInBlocks = Math.round(durationInSec / secondsToBlock);
+
+    const { extrinsic } = await this.api.voucher.issue(account, amount * 1e12, durationInBlocks, [programId]);
+
+    const [voucherId] = await new Promise<[HexString, HexString]>((resolve, reject) => {
+      extrinsic.signAndSend(voucherAccount, ({
+        events,
+        status,
+      }) => {
+        if (status.isInBlock) {
+          const viEvent = events.find(({ event }) => event.method === 'VoucherIssued');
+          if (viEvent) {
+            const data = viEvent.event.data as VoucherIssuedData;
+            resolve([data.voucherId.toHex(), status.asInBlock.toHex()]);
+          } else {
+            const efEvent = events.find(({ event }) => event.method === 'ExtrinsicFailed');
+
+            reject(efEvent ? this.api.getExtrinsicFailedError(efEvent?.event) : 'VoucherIssued event not found');
+          }
+        }
+      });
+    });
+
+    return voucherId;
+  }
+
+  /**
+   * Prolongs the voucher with the given voucherId, account, balance, and prolongDurationInSec.
+   * 
+   * @param voucherId - The voucherId to prolong
+   * @param account - The account to prolong the voucher for
+   * @param balance - The required balance to top up the voucher
+   * @param prolongDurationInSec - The duration to prolong the voucher for
+   */
+  async prolong(voucherId: HexString, account: string, balance: number, prolongDurationInSec: number) {
+    const voucherBalance = (await this.api.balance.findOut(voucherId)).toBigInt() / BigInt(1e12);
+    const durationInBlocks = Math.round(prolongDurationInSec / secondsToBlock);
+    const voucherAccount = this.getVoucherAccount();
+
+    const topUp = BigInt(balance) - voucherBalance;
+
+    const params: IUpdateVoucherParams = {};
+
+    if (prolongDurationInSec) {
+      params.prolongDuration = durationInBlocks;
+    }
+
+    if (topUp > 0) {
+      params.balanceTopUp = topUp * BigInt(1e12);
+    }
+
+    const tx = this.api.voucher.update(account, voucherId, params);
+
+    const blockHash = await new Promise<HexString>((resolve, reject) => {
+      tx.signAndSend(voucherAccount, ({
+        events,
+        status,
+      }) => {
+        if (status.isInBlock) {
+          const vuEvent = events.find(({ event }) => event.method === 'VoucherUpdated');
+          if (vuEvent) {
+            resolve(status.asInBlock.toHex());
+          } else {
+            const efEvent = events.find(({ event }) => event.method === 'ExtrinsicFailed');
+            if (efEvent) {
+              reject(JSON.stringify(this.api.getExtrinsicFailedError(efEvent?.event)));
+            } else {
+              reject(new Error('VoucherUpdated event not found'));
+            }
+          }
+        }
+      });
+    });
+  }
+
+  /**
+   * Revokes the voucher with the given voucherId and account.
+   * 
+   * @param voucherId - The voucherId to revoke
+   * @param account - The account to revoke the voucher for
+   */
+  async revoke(voucherId: HexString, account: string) {
+    const voucherAccount = this.getVoucherAccount();
+    const tx = this.api.voucher.revoke(account, voucherId);
+    await new Promise<HexString>((resolve, reject) => {
+      tx.signAndSend(voucherAccount, ({
+        events,
+        status,
+      }) => {
+        if (status.isInBlock) {
+          const vuEvent = events.find(({ event }) => event.method === 'VoucherRevoked');
+          if (vuEvent) {
+            resolve(status.asInBlock.toHex());
+          } else {
+            const efEvent = events.find(({ event }) => event.method === 'ExtrinsicFailed');
+            if (efEvent) {
+              reject(JSON.stringify(this.api.getExtrinsicFailedError(efEvent?.event)));
+            } else {
+              reject(new Error('VoucherRevoked event not found'));
+            }
+          }
+        }
+      });
+    });
+  }
+
+  private getVoucherAccount() {
+    const seed = process.env.VOUCHER_ACCOUNT;
+    const keyring = new Keyring({
+      type: 'sr25519',
+      ss58Format: 137,
+    });
+    const voucherAccount = keyring.addFromSeed(hexToU8a(seed));
+    return voucherAccount;
+  }
+}