docs/lib/hydro.js

import crypto from 'crypto'
import got from 'got'
import statsd from '../lib/statsd.js'
import FailBot from '../lib/failbot.js'

const TIME_OUT_TEXT = 'ms has passed since batch creation'

// If the request to Hydro took an age, it could be either our
// network or that Hydro is just slow to respond. (Event possibly
// too slow to respond with a 422 code)
// If this happens, we'd rather kill it now rather than let it
// linger within the thread.
const POST_TIMEOUT_MS = 3000

export default class Hydro {
  constructor({ secret, endpoint } = {}) {
    this.secret = secret || process.env.HYDRO_SECRET
    this.endpoint = endpoint || process.env.HYDRO_ENDPOINT
  }

  /**
   * Can check if it can actually send to Hydro
   */
  maySend() {
    return Boolean(this.secret && this.endpoint && process.env.NODE_ENV !== 'test')
  }

  /**
   * Generate a SHA256 hash of the payload using the secret
   * to authenticate with Hydro
   * @param {string} body
   */
  generatePayloadHmac(body) {
    return crypto.createHmac('sha256', this.secret).update(body).digest('hex')
  }

  /**
   * Publish a single event to Hydro
   * @param {string} schema
   * @param {any} value
   */
  async publish(schema, value) {
    const body = JSON.stringify({
      events: [
        {
          schema,
          value: JSON.stringify(value), // We must double-encode the value property
          cluster: 'potomac', // We only have ability to publish externally to potomac cluster
        },
      ],
    })
    const token = this.generatePayloadHmac(body)

    const doPost = () =>
      got(this.endpoint, {
        method: 'POST',
        body,
        headers: {
          Authorization: `Hydro ${token}`,
          'Content-Type': 'application/json',
          'X-Hydro-App': 'docs-production',
        },
        // Because we prefer to handle the status code manually below
        throwHttpErrors: false,
        // The default is no timeout.
        timeout: POST_TIMEOUT_MS,
      })

    const res = await statsd.asyncTimer(doPost, 'hydro.response_time')()

    const statTags = [`response_code:${res.statusCode}`]
    statsd.increment(`hydro.response_code.${res.statusCode}`, 1, statTags)
    statsd.increment('hydro.response_code.all', 1, statTags)

    // Track hydro exceptions in Sentry,
    // but don't track 5xx because we can't do anything about service availability
    if (res.statusCode !== 200 && res.statusCode < 500) {
      const hydroText = await res.text()
      const err = new Error(
        `Hydro request failed: (${res.statusCode}) ${res.statusMessage} - ${hydroText}`
      )
      err.status = res.statusCode

      // If the Hydro request failed as an "Unprocessable Entity":
      //  - If it was a timeout, don't log it to Sentry
      //  - If not, log it to Sentry for diagnostics
      const hydroFailures = []
      if (res.statusCode === 422) {
        let failureResponse
        try {
          failureResponse = JSON.parse(hydroText)
        } catch (error) {
          // Not JSON... ignore it
        }

        if (failureResponse) {
          const { failures } = failureResponse
          if (Array.isArray(failures) && failures.length > 0) {
            // IMPORTANT: Although these timeouts typically contain a `retriable: true` property,
            // our discussions with the Hydro team left us deciding we did NOT want to retry
            // sending them. The timeout response does NOT guarantee that the original message
            // failed to make it through. As such, if we resend, we may create duplicate events;
            // if we don't, we may drop events.

            // Find the timeouts, if any
            const timeoutFailures = failures.filter(({ error }) => error.includes(TIME_OUT_TEXT))

            // If there were ONLY timeouts, throw the error to avoid logging to Sentry
            if (timeoutFailures.length === failures.length) {
              err.message = `Hydro timed out: ${failures}`
              err.status = 503 // Give it a more accurate error code
              throw err
            }

            // Compile list of the other failures for logging
            hydroFailures.push(...failures.filter(({ error }) => !error.includes(TIME_OUT_TEXT)))
          }
        }

        console.error(
          `Hydro schema validation failed:\n - Request: ${body}\n - Failure: (${res.statusCode}) ${hydroText}`
        )
      }

      FailBot.report(err, {
        hydroStatus: res.statusCode,
        hydroText,
        hydroFailures,
      })

      throw err
    }

    return res
  }
}