next.js/packages/next/src/trace/report/to-json.ts

import { traceGlobals, traceId } from '../shared'
import fs from 'fs'
import path from 'path'
import { PHASE_DEVELOPMENT_SERVER } from '../../shared/lib/constants'
import type { TraceEvent } from '../types'

// eslint-disable-next-line @typescript-eslint/no-unused-vars
const localEndpoint = {
  serviceName: 'nextjs',
  ipv4: '127.0.0.1',
  port: 9411,
}

type Event = TraceEvent & {
  localEndpoint?: typeof localEndpoint
}

// Batch events as zipkin allows for multiple events to be sent in one go
export function batcher(reportEvents: (evts: Event[]) => Promise<void>) {
  const events: Event[] = []
  // Promise queue to ensure events are always sent on flushAll
  const queue = new Set()
  return {
    flushAll: async () => {
      await Promise.all(queue)
      if (events.length > 0) {
        await reportEvents(events)
        events.length = 0
      }
    },
    report: (event: Event) => {
      events.push(event)

      if (events.length > 100) {
        const evts = events.slice()
        events.length = 0
        const report = reportEvents(evts)
        queue.add(report)
        report.then(() => queue.delete(report))
      }
    },
  }
}

let writeStream: RotatingWriteStream
let batch: ReturnType<typeof batcher> | undefined

const writeStreamOptions = {
  flags: 'a',
  encoding: 'utf8' as const,
}
class RotatingWriteStream {
  file: string
  writeStream!: fs.WriteStream
  size: number
  sizeLimit: number
  private rotatePromise: Promise<void> | undefined
  private drainPromise: Promise<void> | undefined
  constructor(file: string, sizeLimit: number) {
    this.file = file
    this.size = 0
    this.sizeLimit = sizeLimit
    this.createWriteStream()
  }
  private createWriteStream() {
    this.writeStream = fs.createWriteStream(this.file, writeStreamOptions)
  }
  // Recreate the file
  private async rotate() {
    await this.end()
    try {
      fs.unlinkSync(this.file)
    } catch (err: any) {
      // It's fine if the file does not exist yet
      if (err.code !== 'ENOENT') {
        throw err
      }
    }
    this.size = 0
    this.createWriteStream()
    this.rotatePromise = undefined
  }
  async write(data: string): Promise<void> {
    if (this.rotatePromise) await this.rotatePromise

    this.size += data.length
    if (this.size > this.sizeLimit) {
      await (this.rotatePromise = this.rotate())
    }

    if (!this.writeStream.write(data, 'utf8')) {
      if (this.drainPromise === undefined) {
        this.drainPromise = new Promise<void>((resolve, _reject) => {
          this.writeStream.once('drain', () => {
            this.drainPromise = undefined
            resolve()
          })
        })
      }
      await this.drainPromise
    }
  }

  end(): Promise<void> {
    return new Promise((resolve) => {
      this.writeStream.end(resolve)
    })
  }
}

const reportToLocalHost = (event: TraceEvent) => {
  const distDir = traceGlobals.get('distDir')
  const phase = traceGlobals.get('phase')
  if (!distDir || !phase) {
    return
  }

  if (!batch) {
    batch = batcher(async (events: Event[]) => {
      if (!writeStream) {
        await fs.promises.mkdir(distDir, { recursive: true })
        const file = path.join(distDir, 'trace')
        writeStream = new RotatingWriteStream(
          file,
          // Development is limited to 50MB, production is unlimited
          phase === PHASE_DEVELOPMENT_SERVER ? 52428800 : Infinity
        )
      }
      const eventsJson = JSON.stringify(events)
      try {
        await writeStream.write(eventsJson + '\n')
      } catch (err) {
        console.log(err)
      }
    })
  }

  batch.report({
    ...event,
    traceId,
  })
}

export default {
  flushAll: (opts?: { end: boolean }) =>
    batch
      ? batch.flushAll().then(() => {
          const phase = traceGlobals.get('phase')
          // Only end writeStream when manually flushing in production
          if (opts?.end || phase !== PHASE_DEVELOPMENT_SERVER) {
            return writeStream.end()
          }
        })
      : undefined,
  report: reportToLocalHost,
}