AWS ALB access log file to CSV

alb-log-to-csv.js

const fs       = require('fs')
const path     = require('path')
const util     = require('util')
const { exec } = require('child_process')

const fsPromises  = fs.promises
const execPromise = util.promisify(exec)

const columnHeaders = ["type", "time", "elb", "client:port", "target:port", "request_processing_time", "target_processing_time", "response_processing_time", "elb_status_code", "target_status_code", "received_bytes", "sent_bytes", "request", "user_agent", "ssl_cipher", "ssl_protocol", "target_group_arn", "trace_id", "domain_name", "chosen_cert_arn", "matched_rule_priority", "request_creation_time", "actions_executed", "redirect_url", "error_reason", "target:port_list", "target_status_code_list", "classification", "classification_reason"]

;(async () => {
  const fileName = process.argv[2]
  if (!fileName) {
    printUsage()
    return
  }

  const originalFilePath = path.resolve(fileName)

  if (!(await fileExists(originalFilePath))) {
    console.log(`Provided file doesn't exist!`)
    console.log(`Provided: ${fileName}`)
    console.log(`Resolved: ${originalFilePath}`)
    console.log()
    printUsage()
    return
  }

  let filePath = originalFilePath
  if (fileName.endsWith('.gz')) {
    console.log("Determined that file is gzipped. Unzipping first.")
    filePath = await ungzipFile(originalFilePath)
  }

  const contentRaw = await fsPromises.readFile(filePath)
  const content = contentRaw.toString('utf8')
    .replace(/ /g, ',')

  const colHeaderRow = columnHeaders.join(',')
  const newContent = colHeaderRow + '\n' + content

  const newFilePath = filePath + '.csv'

  await fsPromises.writeFile(newFilePath, newContent)
  console.log(`Wrote new CSV file to:\n${newFilePath}`)
})();

function printUsage() {
  console.log('node alb-log-to-csv <log-file>')
}

async function ungzipFile(filePath) {
  try {
    //The new file that gzip command will output (same file name without the .gz attached)
    const unzipedFileName = filePath.slice(0, -".gz".length)

    //Args:
    // -d: unzip the provided file
    // -k: keep the original file
    await execPromise(`rm -f ${unzipedFileName}`)
    await execPromise(`gzip -dk ${filePath}`)

    return unzipedFileName
  }
  catch (err) {
    console.log("Failed to unzip the gzip file: " + filePath)
    console.log(err)
    process.exit(1)
  }
}

async function fileExists(path) {
  try {
    await fsPromises.stat(path)
    return true
  }
  catch {
    return false
  }
}

Determined that file is gzipped. Unzipping first.
node:buffer:634
    slice: (buf, start, end) => buf.utf8Slice(start, end),
                                    ^

Error: Cannot create a string longer than 0x1fffffe8 characters
    at Object.slice (node:buffer:634:37)
    at Buffer.toString (node:buffer:853:14)
    at /Users/me/Downloads/alb_logs/prod-public/alb-log-to-csv.js:36:30 {
  code: 'ERR_STRING_TOO_LONG'
}

Node.js v20.6.1

I do have a very large ALB file