1 files changed, 93 insertions, 0 deletions
diff --git a/packages/create-astro/src/actions/verify.ts b/packages/create-astro/src/actions/verify.ts
new file mode 100644
index 000000000..73359142b
--- /dev/null
+++ b/packages/create-astro/src/actions/verify.ts
@@ -0,0 +1,93 @@
+import type { Context } from './context';
+
+import { color } from '@astrojs/cli-kit';
+import fetch from 'node-fetch-native';
+import dns from 'node:dns/promises';
+import { bannerAbort, error, info, log } from '../messages.js';
+import { getTemplateTarget } from './template.js';
+
+export async function verify(
+	ctx: Pick<Context, 'version' | 'dryRun' | 'template' | 'ref' | 'exit'>
+) {
+	if (!ctx.dryRun) {
+		const online = await isOnline();
+		if (!online) {
+			bannerAbort();
+			log('');
+			error('error', `Unable to connect to the internet.`);
+			ctx.exit(1);
+		}
+	}
+
+	if (ctx.template) {
+		const ok = await verifyTemplate(ctx.template, ctx.ref);
+		if (!ok) {
+			bannerAbort();
+			log('');
+			error('error', `Template ${color.reset(ctx.template)} ${color.dim('could not be found!')}`);
+			await info('check', 'https://astro.build/examples');
+			ctx.exit(1);
+		}
+	}
+}
+
+function isOnline(): Promise<boolean> {
+	return dns.lookup('github.com').then(
+		() => true,
+		() => false
+	);
+}
+
+async function verifyTemplate(tmpl: string, ref?: string) {
+	const target = getTemplateTarget(tmpl, ref);
+	const { repo, subdir, ref: branch } = parseGitURI(target.replace('github:', ''));
+	const url = new URL(`/repos/${repo}/contents${subdir}?ref=${branch}`, 'https://api.github.com/');
+
+	let res = await fetch(url.toString(), {
+		headers: {
+			Accept: 'application/vnd.github+json',
+			'X-GitHub-Api-Version': '2022-11-28',
+		},
+	});
+
+	// If users hit a ratelimit, fallback to the GitHub website
+	if (res.status === 403) {
+		res = await fetch(`https://github.com/${repo}/tree/${branch}${subdir}`);
+	}
+
+	return res.status === 200;
+}
+
+// Adapted from https://github.com/unjs/giget/blob/main/src/_utils.ts
+// MIT License
+
+// Copyright (c) Pooya Parsa <pooya@pi0.io>
+
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+const GIT_RE = /^(?<repo>[\w.-]+\/[\w.-]+)(?<subdir>[^#]+)?(?<ref>#[\w.-]+)?/;
+
+function parseGitURI(input: string) {
+	const m = input.match(GIT_RE)?.groups;
+	if (!m) throw new Error(`Unable to parse "${input}"`);
+	return {
+		repo: m.repo,
+		subdir: m.subdir || '/',
+		ref: m.ref ? m.ref.slice(1) : 'main',
+	};
+}