Cloudflare Tail Workers logging

export default {
  async tail(events, env, ctx) {
    const logs = []

    for (const event of events) {
      const context = {
        worker: event.scriptName,
        outcome: event.outcome,
        request: event.event?.request && {
          method: event.event.request.method,
          url: event.event.request.url,
        },
      }

      for (const log of event.logs) {
        const message = log.message
          .map((part) => (typeof part === "string" ? part : JSON.stringify(part)))
          .join(" ")
        logs.push({ ...context, dt: log.timestamp, level: log.level, message })
      }

      for (const exception of event.exceptions) {
        logs.push({ ...context, dt: exception.timestamp, level: "error", message: `${exception.name}: ${exception.message}` })
      }

      // Record failed invocations without an exception, e.g. exceeded CPU or memory limits
      if (!["ok", "canceled"].includes(event.outcome) && event.exceptions.length === 0) {
        logs.push({ ...context, dt: event.eventTimestamp, level: "error", message: `Worker invocation ended with outcome ${event.outcome}` })
      }
    }

    if (logs.length === 0) return

    ctx.waitUntil(
      fetch("https://$INGESTING_HOST", {
        method: "POST",
        headers: {
          "Authorization": "Bearer $SOURCE_TOKEN",
          "Content-Type": "application/json",
        },
        body: JSON.stringify(logs),
      })
    )
  },
}