Bsky short link service (#4542)

* bskylink: scaffold service w/ initial config and schema

* bskylink: implement link creation and redirects

* bskylink: tidy

* bskylink: tests

* bskylink: tidy, add error handler

* bskylink: add dockerfile

* bskylink: add build

* bskylink: fix some express plumbing

* bskyweb: proxy fallthrough routes to link service redirects

* bskyweb: build w/ link proxy

* Add AASA to bskylink (#4588)

---------

Co-authored-by: Hailey <me@haileyok.com>

bskylink/tests/index.ts

@@ -0,0 +1,84 @@
+import assert from 'node:assert'
+import {AddressInfo} from 'node:net'
+import {after, before, describe, it} from 'node:test'
+
+import {Database, envToCfg, LinkService, readEnv} from '../src/index.js'
+
+describe('link service', async () => {
+  let linkService: LinkService
+  let baseUrl: string
+  before(async () => {
+    const env = readEnv()
+    const cfg = envToCfg({
+      ...env,
+      hostnames: ['test.bsky.link'],
+      appHostname: 'test.bsky.app',
+      dbPostgresSchema: 'link_test',
+      dbPostgresUrl: process.env.DB_POSTGRES_URL,
+    })
+    const migrateDb = Database.postgres({
+      url: cfg.db.url,
+      schema: cfg.db.schema,
+    })
+    await migrateDb.migrateToLatestOrThrow()
+    await migrateDb.close()
+    linkService = await LinkService.create(cfg)
+    await linkService.start()
+    const {port} = linkService.server?.address() as AddressInfo
+    baseUrl = `http://localhost:${port}`
+  })
+
+  after(async () => {
+    await linkService?.destroy()
+  })
+
+  it('creates a starter pack link', async () => {
+    const link = await getLink('/start/did:example:alice/xxx')
+    const url = new URL(link)
+    assert.strictEqual(url.origin, 'https://test.bsky.link')
+    assert.match(url.pathname, /^\/[a-z0-9]+$/i)
+  })
+
+  it('normalizes input paths and provides same link each time.', async () => {
+    const link1 = await getLink('/start/did%3Aexample%3Abob/yyy')
+    const link2 = await getLink('/start/did:example:bob/yyy/')
+    assert.strictEqual(link1, link2)
+  })
+
+  it('serves permanent redirect, preserving query params.', async () => {
+    const link = await getLink('/start/did:example:carol/zzz/')
+    const [status, location] = await getRedirect(`${link}?a=b`)
+    assert.strictEqual(status, 301)
+    const locationUrl = new URL(location)
+    assert.strictEqual(
+      locationUrl.pathname + locationUrl.search,
+      '/start/did:example:carol/zzz?a=b',
+    )
+  })
+
+  async function getRedirect(link: string): Promise<[number, string]> {
+    const url = new URL(link)
+    const base = new URL(baseUrl)
+    url.protocol = base.protocol
+    url.host = base.host
+    const res = await fetch(url, {redirect: 'manual'})
+    await res.arrayBuffer() // drain
+    assert(
+      res.status === 301 || res.status === 303,
+      'response was not a redirect',
+    )
+    return [res.status, res.headers.get('location') ?? '']
+  }
+
+  async function getLink(path: string): Promise<string> {
+    const res = await fetch(new URL('/link', baseUrl), {
+      method: 'post',
+      headers: {'content-type': 'application/json'},
+      body: JSON.stringify({path}),
+    })
+    assert.strictEqual(res.status, 200)
+    const payload = await res.json()
+    assert(typeof payload.url === 'string')
+    return payload.url
+  }
+})