Cloud Functions for Firebase - Converting PDF to image

Question

Cloud Functions for Firebase has this nice sample where they create a thumbnail for each uploaded image. This is done by making use of ImageMagick.

I tried to convert the sample to convert PDFs to images. This is something ImageMagick can do, but I can't make it work with Cloud Functions for Firebase. I keep getting a code 1 error:

ChildProcessError: `convert /tmp/cd9d0278-16b2-42be-aa3d-45b5adf89332.pdf[0] -density 200 /tmp/cd9d0278-16b2-42be-aa3d-45b5adf89332.pdf` failed with code 1
    at ChildProcess.<anonymous> (/user_code/node_modules/child-process-promise/lib/index.js:132:23)
    at emitTwo (events.js:106:13)
    at ChildProcess.emit (events.js:191:7)
    at maybeClose (internal/child_process.js:877:16)
    at Socket.<anonymous> (internal/child_process.js:334:11)
    at emitOne (events.js:96:13)
    at Socket.emit (events.js:188:7)
    at Pipe._handle.close [as _onclose] (net.js:498:12)

Of course one possibility is that converting PDFs are simply not supported.

const functions = require('firebase-functions');
const gcs = require('@google-cloud/storage')();
const spawn = require('child-process-promise').spawn;
// [END import]

// [START generateThumbnail]
/**
 * When an image is uploaded in the Storage bucket We generate a thumbnail automatically using
 * ImageMagick.
 */
// [START generateThumbnailTrigger]
exports.generateThumbnail = functions.storage.object().onChange(event => {
// [END generateThumbnailTrigger]
    // [START eventAttributes]
    const object = event.data; // The Storage object.

    const fileBucket = object.bucket; // The Storage bucket that contains the file.
    const filePath = object.name; // File path in the bucket.
    const contentType = object.contentType; // File content type.
    const resourceState = object.resourceState; // The resourceState is 'exists' or 'not_exists' (for file/folder deletions).
    // [END eventAttributes]

    // [START stopConditions]
    // Exit if this is triggered on a file that is not an image.
    if (!contentType.startsWith('application/pdf')) {
        console.log('This is not a pdf.');
        return;
    }

    // Get the file name.
    const fileName = filePath.split('/').pop();
    // Exit if the image is already a thumbnail.
    if (fileName.startsWith('thumb_')) {
        console.log('Already a Thumbnail.');
        return;
    }

    // Exit if this is a move or deletion event.
    if (resourceState === 'not_exists') {
        console.log('This is a deletion event.');
        return;
    }
    // [END stopConditions]

    // [START thumbnailGeneration]
    // Download file from bucket.
    const bucket = gcs.bucket(fileBucket);
    const tempFilePath = `/tmp/${fileName}`;
    return bucket.file(filePath).download({
        destination: tempFilePath
    }).then(() => {
        console.log('Pdf downloaded locally to', tempFilePath);
        // Generate a thumbnail of the first page using ImageMagick.
        return spawn('convert', [tempFilePath+'[0]' ,'-density', '200', tempFilePath]).then(() => {
            console.log('Thumbnail created at', tempFilePath);
            // Convert pdf extension to png
            const thumbFilePath = filePath.replace('.pdf', 'png');
            // Uploading the thumbnail.
            return bucket.upload(tempFilePath, {
                destination: thumbFilePath
            });
        });
    });
    // [END thumbnailGeneration]
});

It seems that for converting pdf files, you also need the ghostscript package, which isn't installed by default on Google Cloud Functions. — EJay, Apr 18 '17 at 21:38
Haven't found one yet. At least not using cloud functions for firebase. — EJay, Apr 27 '17 at 15:42
You could use PDF.js (https://github.com/mozilla/pdf.js) library to generate thumbnails — hordern, Aug 16 '17 at 23:03
PDF.js has bugs that will prevent from rendering text for some pdfs on server (and it's there since 2014): https://github.com/mozilla/pdf.js/issues/4244 — vir us, Mar 10 '20 at 09:46

score 9 · Answer 1 · answered Nov 18 '17 at 16:07

Node modules can install native code that is in the same directory as the Cloud Function's source code. I found that some node libraries on github that do this for ghostscript which is a very useful library for PDF processing:

Node library that wraps Ghostscript command line: https://github.com/sina-masnadi/node-gs
Compiled Ghostscript which is used via git submodule: https://github.com/sina-masnadi/lambda-ghostscript

I put lambda-ghostscript into a sub-directory of my functions directory, then add the node-gs as a dependency in my package file like this:

{
  "name": "functions",
  "dependencies": {
    "@google-cloud/storage": "^1.3.1",
    "child-process-promise": "^2.2.1",
    "firebase-admin": "~5.4.0",
    "firebase-functions": "^0.7.2",
    "gs": "https://github.com/sina-masnadi/node-gs/tarball/master"
  }
}

Then in my index.js file I can just require the node library to easily use ghostscript from JavaScript. Here's the complete code for the Cloud Function that uses a Google Cloud Storage trigger:

const functions = require('firebase-functions');
const gcs = require('@google-cloud/storage')();
const spawn = require('child-process-promise').spawn;
const path = require('path');
const os = require('os');
const fs = require('fs');
var   gs = require('gs');

exports.makePNG = functions.storage.object().onChange(event => {

  // ignore delete events
  if (event.data.resourceState == 'not_exists') return false;

  const filePath = event.data.name;
  const fileDir = path.dirname(filePath);
  const fileName = path.basename(filePath);
  const tempFilePath = path.join(os.tmpdir(), fileName);
  if (fileName.endsWith('.png')) return false;
  if (!fileName.endsWith('.pdf')) return false;

  const newName = path.basename(filePath, '.pdf') + '.png';
  const tempNewPath = path.join(os.tmpdir(), newName);


  // // Download file from bucket.
  const bucket = gcs.bucket(event.data.bucket);

  return bucket.file(filePath).download({
    destination: tempFilePath
  }).then(() => {
    console.log('Image downloaded locally to', tempFilePath);

    return new Promise(function (resolve, reject) {
        gs()
          .batch()
          .nopause()
          .option('-r' + 50 * 2)
          .option('-dDownScaleFactor=2')
          .executablePath('lambda-ghostscript/bin/./gs')
          .device('png16m')
          .output(tempNewPath)
          .input(tempFilePath)
          .exec(function (err, stdout, stderr) {
              if (!err) {
                console.log('gs executed w/o error');            
                console.log('stdout',stdout);            
                console.log('stderr',stderr);            
                resolve();
              } else {
                console.log('gs error:', err);
                reject(err);
              }
          });
    });

  }).then(() => {
    console.log('PNG created at', tempNewPath);

    // Uploading the thumbnail.
    return bucket.upload(tempNewPath, {destination: newName});
  // Once the thumbnail has been uploaded delete the local file to free up disk space.
  }).then(() => {
    fs.unlinkSync(tempNewPath);
    fs.unlinkSync(tempFilePath);
  }).catch((err) => {
    console.log('exception:', err);
    return err;
  });

});

Here's the project on github: https://github.com/ultrasaurus/ghostscript-cloud-function

Disclaimer: This is using compiled native code and I verified experimentally that works for this case, so it is probably fine. I didn't look into the specific compile options and validate if they exactly correct for the Cloud Functions environment.

Can you give me an ELI5 regarding what your first paragraph means? — Badrush, Jan 24 '19 at 15:59
NodeJS is for JavaScript apps. JavaScript is an interpreted language, so the same code that runs on my mac will run on a linux server (or wherever). When you install a "package" (npm install) it can include source code from other languages (like C or C++) that is (typically) compiled locally into "object" code. If I compile code for running on my mac and then copy it to a linux server, then it won't work. I need to compile it for the target OS and h/w, if I do that, and put in the same directory as my Cloud Function, then I can upload and it works! — Ultrasaurus, Feb 05 '19 at 07:03
I tried it with firebase cloud function and its not working, I am getting spawn EACSESS error. Any chance you could provide a solution? — Don-Ricardo, Oct 02 '19 at 13:43
@Don-Ricardo I know it's two years late but it's likely because you need to `chmod` your gs — Jia Jian Goi, Jul 22 '21 at 12:40

score 2 · Answer 2 · answered Oct 16 '20 at 09:52

WORKING SOLUTION

Thank you @Ultrasaurus for pointing out this approach! However, for me it did not work and in your Github repo your also stated I haven't tested them. I modified your solution a little bit and got the following code, which is 100% working for me:

{
  "dependencies": {
    "@google-cloud/firestore": "^4.4.0",
    "@google-cloud/storage": "^5.3.0",
    "ghostscript": "https://github.com/musubu/node-ghostscript/tarball/master",
    "pdf-image": "^2.0.0",
    "rimraf": "^3.0.2",
    "uuid": "^8.3.1"
  }
}

The function is triggered by a Firestore event:

const Storage = require('@google-cloud/storage')
const fs = require('fs')
const rimraf = require('rimraf')
const os = require('os')
const gs = require('ghostscript')

const GOOGLE_PROJECT_ID = 'MY_GOOGLE_PROJECT_ID'
const GOOGLE_STORAGE_BUCKET_NAME = 'MY_GOOGLE_STORAGE_BUCKET_NAME'

const storage = new Storage.Storage({
  projectId: GOOGLE_PROJECT_ID
})

exports.createImage = async (event) => {
  let {
    appointment,
    name
  } = event.value.fields

  name = getFileName(name.stringValue)
  appointment = appointment.stringValue

  console.log(`Processing document ${name} in appointment ${appointment}`)

  const tempDir = createTempDir(appointment)

  const tmpDocumentPath = await downloadPdf(tempDir, name, appointment)
  const imagePath = await convertPdfToImage(tmpDocumentPath)
  await uploadImage(imagePath, appointment)

  deleteDir(tempDir)
}

function getFileName (name) {
  const nameParts = name.split('/')
  return nameParts[nameParts.length - 1]
}

function createTempDir (appointment) {
  const tempDir = `${os.tmpdir()}/${appointment}_${Math.random()}`
  fs.mkdirSync(tempDir)
  console.log(`Created dir ${tempDir}`)
  return tempDir
}

async function downloadPdf (tempDir, name, appointment) {
  const destination = `${tempDir}/${name}`
  await storage.bucket(GOOGLE_STORAGE_BUCKET_NAME).file(`${appointment}/${name}`).download({ destination })
  console.log(`Successfully downloaded document ${name}`)
  return destination
}

async function convertPdfToImage (pdfPath) {
  const imagePath = pdfPath.replace('pdf', 'png')

  return new Promise(function (resolve, reject) {
    try {
      gs()
        .batch()
        .nopause()
        .device('png16m')
        .output(imagePath)
        .input(pdfPath)
        .exec(function (err, stdout, stderr) {
          if (!err) {
            console.log('gs executed w/o error')
            console.log('stdout', stdout)
            console.log('stderr', stderr)
            resolve(imagePath)
          } else {
            console.log('gs error:', err)
            reject(err)
          }
        })
    } catch (error) {
      console.log(error)
    }
  })
}

async function uploadImage (imagePath, appointment) {
  const imagePathParts = imagePath.split('/')
  const imageName = imagePathParts[imagePathParts.length - 1]

  console.log(`Starting upload for ${imageName} at ${imagePath} to storage ${appointment}/${imageName}`)

  await storage.bucket(GOOGLE_STORAGE_BUCKET_NAME).upload(imagePath, {
    destination: `${appointment}/${imageName}`,
    metadata: {
      metadata: { appointment }
    }
  })

  console.log(`Successfully uploaded image for appointment ${appointment}`)
}

function deleteDir (dir) {
  rimraf.sync(dir)
}

Cloud Functions for Firebase - Converting PDF to image

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