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/src/config.ts

@@ -0,0 +1,82 @@
+import {envInt, envList, envStr} from '@atproto/common'
+
+export type Config = {
+  service: ServiceConfig
+  db: DbConfig
+}
+
+export type ServiceConfig = {
+  port: number
+  version?: string
+  hostnames: string[]
+  appHostname: string
+}
+
+export type DbConfig = {
+  url: string
+  migrationUrl?: string
+  pool: DbPoolConfig
+  schema?: string
+}
+
+export type DbPoolConfig = {
+  size: number
+  maxUses: number
+  idleTimeoutMs: number
+}
+
+export type Environment = {
+  port?: number
+  version?: string
+  hostnames: string[]
+  appHostname?: string
+  dbPostgresUrl?: string
+  dbPostgresMigrationUrl?: string
+  dbPostgresSchema?: string
+  dbPostgresPoolSize?: number
+  dbPostgresPoolMaxUses?: number
+  dbPostgresPoolIdleTimeoutMs?: number
+}
+
+export const readEnv = (): Environment => {
+  return {
+    port: envInt('LINK_PORT'),
+    version: envStr('LINK_VERSION'),
+    hostnames: envList('LINK_HOSTNAMES'),
+    appHostname: envStr('LINK_APP_HOSTNAME'),
+    dbPostgresUrl: envStr('LINK_DB_POSTGRES_URL'),
+    dbPostgresMigrationUrl: envStr('LINK_DB_POSTGRES_MIGRATION_URL'),
+    dbPostgresSchema: envStr('LINK_DB_POSTGRES_SCHEMA'),
+    dbPostgresPoolSize: envInt('LINK_DB_POSTGRES_POOL_SIZE'),
+    dbPostgresPoolMaxUses: envInt('LINK_DB_POSTGRES_POOL_MAX_USES'),
+    dbPostgresPoolIdleTimeoutMs: envInt(
+      'LINK_DB_POSTGRES_POOL_IDLE_TIMEOUT_MS',
+    ),
+  }
+}
+
+export const envToCfg = (env: Environment): Config => {
+  const serviceCfg: ServiceConfig = {
+    port: env.port ?? 3000,
+    version: env.version,
+    hostnames: env.hostnames,
+    appHostname: env.appHostname || 'bsky.app',
+  }
+  if (!env.dbPostgresUrl) {
+    throw new Error('Must configure postgres url (LINK_DB_POSTGRES_URL)')
+  }
+  const dbCfg: DbConfig = {
+    url: env.dbPostgresUrl,
+    migrationUrl: env.dbPostgresMigrationUrl,
+    schema: env.dbPostgresSchema,
+    pool: {
+      idleTimeoutMs: env.dbPostgresPoolIdleTimeoutMs ?? 10000,
+      maxUses: env.dbPostgresPoolMaxUses ?? Infinity,
+      size: env.dbPostgresPoolSize ?? 10,
+    },
+  }
+  return {
+    service: serviceCfg,
+    db: dbCfg,
+  }
+}