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ci: add preview
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‎.github/workflows/preview.yaml‎

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name: Preview
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on:
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pull_request:
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branches:
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- '**'
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# Lets a preview be built for a pull request that predates this workflow,
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# or rebuilt without pushing to it: run this workflow and pass the number.
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workflow_dispatch:
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inputs:
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pr:
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description: 'Pull request number to build a preview for'
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required: true
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type: string
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permissions:
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contents: read
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pull-requests: write
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concurrency:
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group: preview-${{ github.event.pull_request.number || inputs.pr }}
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cancel-in-progress: true
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jobs:
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preview:
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runs-on: ubuntu-latest
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steps:
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- uses: actions/checkout@v4
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with:
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ref: ${{ github.event_name == 'workflow_dispatch' && format('refs/pull/{0}/head', inputs.pr) || github.ref }}
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- name: Set up Node.js
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uses: actions/setup-node@v4
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with:
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node-version: '20'
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- name: Install dependencies
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run: npm ci
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- name: Build
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run: npm run build
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- name: Upload to Swarm
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id: upload
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run: node scripts/upload-to-swarm.mjs build
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- name: Write summary
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run: |
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{
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echo "### Preview"
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echo
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echo "${{ steps.upload.outputs.url }}"
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echo
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echo "Swarm reference: \`${{ steps.upload.outputs.reference }}\`"
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} >> "$GITHUB_STEP_SUMMARY"
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# Fails on pull requests from forks, where GITHUB_TOKEN is read-only.
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# The preview URL is in the job summary either way.
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- name: Comment the preview link
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continue-on-error: true
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uses: actions/github-script@v7
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env:
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PR_NUMBER: ${{ github.event.pull_request.number || inputs.pr }}
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PREVIEW_URL: ${{ steps.upload.outputs.url }}
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PREVIEW_REFERENCE: ${{ steps.upload.outputs.reference }}
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with:
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script: |
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const marker = '<!-- swarm-preview -->'
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const issue_number = Number(process.env.PR_NUMBER)
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const body = [
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marker,
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`**Preview:** ${process.env.PREVIEW_URL}`,
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'',
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`Built from ${context.sha.slice(0, 7)} and uploaded to Swarm as \`${process.env.PREVIEW_REFERENCE}\`.`,
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'Previews are unpaid uploads to a public gateway, so they are not guaranteed to stay retrievable.',
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].join('\n')
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const comments = await github.paginate(github.rest.issues.listComments, {
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...context.repo,
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issue_number,
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})
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const existing = comments.find(comment => comment.body.includes(marker))
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if (existing) {
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await github.rest.issues.updateComment({ ...context.repo, comment_id: existing.id, body })
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} else {
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await github.rest.issues.createComment({ ...context.repo, issue_number, body })
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}

‎scripts/upload-to-swarm.mjs‎

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// Upload a built site to Swarm through a public gateway and print the URL it
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// can be previewed at. Used by .github/workflows/preview.yaml, but it works
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// the same way when run by hand:
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//
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// node scripts/upload-to-swarm.mjs build
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// node scripts/upload-to-swarm.mjs build --gateway https://bzz.limo
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//
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// The directory is packed into a tar and posted to the gateway's /bzz endpoint
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// as a collection. https://bzz.limo pays for uploads itself, so any 32-byte
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// postage batch id is accepted and we do not need a funded batch of our own.
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//
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// The gateway serves a collection both at /bzz/<reference>/ and — with the
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// reference re-encoded as a CIDv1, which fits in a 63 character DNS label —
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// at https://<cid>.bzz.limo/. Only the second one serves the site from the
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// root, so it is the URL we report: a Docusaurus build with baseUrl "/" works
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// there unchanged.
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import { readFileSync, appendFileSync, existsSync, statSync, rmSync } from 'node:fs';
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import { execFileSync } from 'node:child_process';
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import { tmpdir } from 'node:os';
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import { join } from 'node:path';
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const DEFAULT_GATEWAY = 'https://bzz.limo';
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// The gateway ignores which batch is named, but the header has to be a 32-byte hex id.
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const FAKE_BATCH_ID = '00'.repeat(32);
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const UPLOAD_TIMEOUT_MS = 10 * 60 * 1000;
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const UPLOAD_ATTEMPTS = 3;
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const args = process.argv.slice(2);
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const dir = args.find(arg => !arg.startsWith('--'));
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const gateway = (readOption('--gateway') ?? DEFAULT_GATEWAY).replace(/\/+$/, '');
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const indexDocument = readOption('--index') ?? 'index.html';
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const errorDocument = readOption('--error') ?? '404.html';
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function readOption(name) {
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const index = args.indexOf(name);
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return index === -1 ? undefined : args[index + 1];
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}
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if (!dir) {
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console.error('usage: node scripts/upload-to-swarm.mjs <directory> [--gateway url]');
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process.exit(1);
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}
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if (!existsSync(dir) || !statSync(dir).isDirectory()) {
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console.error(`not a directory: ${dir}`);
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process.exit(1);
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}
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/** Encode a Swarm reference as a CIDv1 (swarm-manifest codec, keccak-256 multihash). */
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function toCid(reference) {
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const bytes = Buffer.concat([Buffer.from([0x01, 0xfa, 0x1b, 0x20]), Buffer.from(reference, 'hex')]);
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const alphabet = 'abcdefghijklmnopqrstuvwxyz234567';
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let bits = 0;
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let value = 0;
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let out = '';
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for (const byte of bytes) {
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value = (value << 8) | byte;
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bits += 8;
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while (bits >= 5) {
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out += alphabet[(value >>> (bits - 5)) & 31];
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bits -= 5;
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}
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}
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if (bits > 0) {
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out += alphabet[(value << (5 - bits)) & 31];
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}
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return `b${out}`;
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}
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async function upload(tar) {
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for (let attempt = 1; attempt <= UPLOAD_ATTEMPTS; attempt++) {
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try {
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const response = await fetch(`${gateway}/bzz`, {
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method: 'POST',
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headers: {
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'content-type': 'application/x-tar',
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'swarm-postage-batch-id': FAKE_BATCH_ID,
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'swarm-collection': 'true',
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'swarm-index-document': indexDocument,
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'swarm-error-document': errorDocument,
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},
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body: tar,
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signal: AbortSignal.timeout(UPLOAD_TIMEOUT_MS),
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});
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const body = await response.text();
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if (!response.ok) {
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throw new Error(`gateway responded ${response.status}: ${body.trim()}`);
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}
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const { reference } = JSON.parse(body);
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if (!/^[0-9a-f]{64}$/.test(reference ?? '')) {
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throw new Error(`gateway returned an unexpected reference: ${body.trim()}`);
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}
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return reference;
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} catch (error) {
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console.error(`upload attempt ${attempt}/${UPLOAD_ATTEMPTS} failed: ${error.message}`);
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if (attempt === UPLOAD_ATTEMPTS) {
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process.exit(1);
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}
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}
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}
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}
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const tarPath = join(tmpdir(), `swarm-upload-${process.pid}.tar`);
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execFileSync('tar', ['-C', dir, '-cf', tarPath, '.']);
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const tar = readFileSync(tarPath);
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rmSync(tarPath, { force: true });
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console.log(`uploading ${dir} (${(tar.length / 1024 / 1024).toFixed(1)} MB) to ${gateway}`);
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const reference = await upload(tar);
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const cid = toCid(reference);
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const url = `https://${cid}.bzz.limo/`;
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console.log(`reference: ${reference}`);
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console.log(`cid: ${cid}`);
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console.log(`url: ${url}`);
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if (process.env.GITHUB_OUTPUT) {
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appendFileSync(process.env.GITHUB_OUTPUT, `reference=${reference}\ncid=${cid}\nurl=${url}\n`);
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}

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