Filer Helper to detect mime via CLI

file-helper.ts

import { exec as defaultExec } from 'child_process'
import fs from 'fs'
import util from 'util'

import safePromise from './safe-promise'
const exec = util.promisify(defaultExec)

const detectFile = async (filePath: string): Promise<string> => {
    // mmmagic avoided due to https://github.com/mscdex/mmmagic/issues/141#issuecomment-570085390
    // file-typ avoided due to https://github.com/sindresorhus/file-type#supported-file-types
    const fileCommand = `file --mime-type ${filePath} | grep -oh  "[a-z]*/[a-z]*$"`
    const { stdout, stderr } = await exec(fileCommand)
    if (stderr) {
        throw stderr
    }
    return stdout.trim()
}

const getMimeFromExt = async (
    fileExtension: string
): Promise<[string] | [null, string]> => {
    // https://github.com/jshttp/mime-types is a good alternate
    const mimeTypesFetchingCommand = `wget -qO- http://svn.apache.org/repos/asf/httpd/httpd/trunk/docs/conf/mime.types | egrep -v ^# | awk '{ for (i=2; i<=NF; i++) {print $i" "$1}}' | sort | grep ${fileExtension} | grep -oh  "[a-z]*/[a-z]*$"`
    // @ToDo cache the above data in redis and return that while asynchronously update the redis
    const { stdout, stderr } = await exec(mimeTypesFetchingCommand)
    if (stderr) {
        return [stderr]
    }
    const mime = String(stdout).trim()
    return [null, mime]
}

export const getFilesizeInBytes = (filePath: string): number =>
    fs.statSync(filePath).size

interface IFileHelper {
    detectedFileMime: string
    fileExtension: string
    fileFormat: string
    fileType: string
    mimeTypeFromExt?: string
}

export default async (filePath: string): Promise<IFileHelper> => {
    const [detectFileError, detectedFileMime] = await safePromise(
        detectFile(filePath)
    )
    if (detectFileError) {
        throw detectFileError
    }
    if (!detectedFileMime) {
        throw new Error('file meme detection failed')
    }
    const mimeParts = String(detectedFileMime).split('/')
    const fileType = mimeParts[0]
    const fileFormat = mimeParts[1]
    const fileExtension = filePath
        .substring(filePath.lastIndexOf('.') + 1)
        .toLowerCase()
    const [mimeTypesFetchingError, mimeTypeFromExt] = await getMimeFromExt(
        fileExtension
    )
    if (mimeTypesFetchingError) {
        throw mimeTypesFetchingError
    }
    return {
        detectedFileMime,
        fileExtension,
        fileFormat,
        fileType,
        mimeTypeFromExt,
    }
}