Add metrics to redirect service

bskylink/src/metrics.ts

@@ -0,0 +1,136 @@
+import crypto from 'node:crypto'
+
+import {httpLogger} from './logger.js'
+
+/**
+ * New metrics events should be added here
+ */
+type Events = {
+  redirect: {
+    link: string
+    whitelisted: 'unknown' | 'yes'
+    blocked: boolean
+    warned: boolean
+  }
+  invalid_redirect: {
+    link: string
+  }
+}
+
+type Event<M extends Record<string, any>> = {
+  time: number
+  event: keyof M
+  payload: M[keyof M]
+  metadata: Record<string, any>
+}
+
+export type Config = {
+  trackingEndpoint?: string
+}
+
+/**
+ * This MetricsClient is duplicated from both `social-app` and `atproto`
+ * codebases.
+ */
+export class MetricsClient<M extends Record<string, any> = Events> {
+  maxBatchSize = 100
+
+  private disabled: boolean = false
+  private started: boolean = false
+  private queue: Event<M>[] = []
+  private flushInterval: NodeJS.Timeout | null = null
+  constructor(private config: Config) {
+    this.disabled = !config.trackingEndpoint
+  }
+
+  start() {
+    if (this.disabled) return
+    if (this.started) return
+    this.started = true
+    this.flushInterval = setInterval(() => {
+      this.flush()
+    }, 10_000)
+  }
+
+  stop() {
+    if (this.flushInterval) {
+      clearInterval(this.flushInterval)
+      this.flushInterval = null
+    }
+    this.flush()
+  }
+
+  track<E extends keyof M>(event: E, payload: M[E]) {
+    if (this.disabled) return
+
+    this.start()
+
+    /**
+     * deviceId is required for sharding events in Middleman. To avoid a hot
+     * shard, we generate a random anonymous IDs for this client.
+     *
+     * @see https://github.com/bluesky-social/tango/blob/d5819cde419d13e0d2cf837f4b30d48529d64060/middleman/handlers_tracking.go#L195
+     */
+    const anonId = `anon-${crypto.randomUUID()}`
+
+    /**
+     * Event structure is like this to ensure compat with Middleman, which
+     * receives events like this from other codebases, including `social-app`.
+     */
+    const e = {
+      source: 'blink',
+      time: Date.now(),
+      event,
+      payload,
+      metadata: {
+        base: {
+          deviceId: anonId,
+          sessionId: anonId,
+        },
+        session: {
+          did: undefined,
+        },
+      },
+    }
+    this.queue.push(e)
+
+    if (this.queue.length > this.maxBatchSize) {
+      this.flush()
+    }
+  }
+
+  flush() {
+    if (this.disabled) return
+    if (!this.queue.length) return
+    const events = this.queue.splice(0, this.queue.length)
+    this.sendBatch(events)
+  }
+
+  private async sendBatch(events: Event<M>[]) {
+    if (this.disabled || !this.config.trackingEndpoint) return
+
+    try {
+      const res = await fetch(this.config.trackingEndpoint, {
+        method: 'POST',
+        headers: {
+          'Content-Type': 'application/json',
+        },
+        body: JSON.stringify({events}),
+        keepalive: true,
+      })
+
+      if (!res.ok) {
+        const errorText = await res.text().catch(() => 'Unknown error')
+        httpLogger.error(
+          {err: new Error(`${res.status} Failed to fetch - ${errorText}`)},
+          'Failed to send metrics',
+        )
+      } else {
+        // Drain response body to allow connection reuse.
+        await res.text().catch(() => {})
+      }
+    } catch (err) {
+      httpLogger.error({err}, 'Failed to send metrics')
+    }
+  }
+}