How to chain writeFile() and OCR with NodeJS in Google Cloud Functions? - node.js

Question

The scenario is as follows:
From an Amazon S3 bucket a file is fetched, then it is stored in a temporary folder and then Object Character Recognition is to be performed using the API.
Unfortunately, this doesn't work, I think it's due to the asynchronous/synchronous execution, but I've already tried several variants with callbacks/promises and didn't get any further.
If someone can give me a hint on how to construct this scenario I would be grateful!
The current error is:
TypeError: Cannot read property 'writeFile' of undefined at Response.<anonymous> (/srv/index.js:38:32) (it's the 'await fs.writeFile(dir,data);' line)
/**
* Responds to any HTTP request.
*
* #param {!express:Request} req HTTP request context.
* #param {!express:Response} res HTTP response context.
*/
const AWS = require('aws-sdk');
const fs = require('fs').promises;
const Vision = require('#google-cloud/vision');
var os = require('os');
exports.helloWorld = async (req,res) => {
var bucket, fileName, fileUrl;
req.on('data', chunk => {
body += chunk.toString();
data.push(chunk);
});
req.on('end', () => {
bucket = JSON.parse(data).value1;
fileName = JSON.parse(data).value2;
fileUrl = JSON.parse(data).value3;
var s3 = new AWS.S3();
s3.getObject({
Bucket: bucket,
Key: fileName
},
async function(error, data) {
if (error != null) {
console.log("Failed to retrieve an object: " + error);
} else {
console.log("Loaded " + data.ContentType + " bytes");
var tmpdir = os.tmpdir();
var dir = tmpdir+'/'+fileName;
try{
await fs.writeFile(dir,data);
const vision = new Vision.ImageAnnotatorClient();
let text;
await vision
.textDetection('/tmp/' + fileName)
.then(([detections]) => {
const annotation = detections.textAnnotations[0];
console.log(1);
text = annotation ? annotation.description : '';
console.log(`Extracted text from image (${text.length} chars)`);
console.log(1);
console.log(text);
resolve("Finished ocr successfully");
})
.catch(error =>{
console.log(error);
reject("Error with OCR");
})
}catch(error){
console.log(error);
}
}
},
);
let message = bucket + fileName + fileUrl;
res.status(200).send(message);
});
};

Answer 1

You're getting that error, because you're running on an older version of Node (< 10.0.0), where fs.promises is not available. That's why fs is undefined, and you're getting:
TypeError: Cannot read property 'writeFile' of undefined at Response.<anonymous> (/srv/index.js:38:32) (it's the 'await fs.writeFile(dir,data);' line)
Either use a newer version, or just promisify the code.
const { promisify } = require('util');
const fs = require('fs');
// const fs = require('fs').promises
const writeFile = promisify(fs.writeFile);
And now use writeFile instead of fs.writeFile in your code.
Aside from that, there are a few issues with your code.
req.on('data', chunk => {
body += chunk.toString();
data.push(chunk);
});
data is not defined anywhere, and it doesn't make sense to push data into an array and then running JSON.parse on that array, given the next few lines.
bucket = JSON.parse(data).value1;
fileName = JSON.parse(data).value2;
fileUrl = JSON.parse(data).value3;
Furthermore, JSON.parse should be called only once, instead of parsing the same string (which is an array in your code, and will yield an error) 3 times.
const values = JSON.parse(body); // should be body instead of data with the posted code
bucket = values.value1;
fileName = values.value2;
fileUrl = values.value3;
This can be improved greatly by just posting bucket, fileName & fileUrl in the JSON instead of valueN.
const { bucket, fileName, fileUrl } = JSON.parse(body);
The whole code can be rewritten into:
const AWS = require('aws-sdk');
const { promisify } = require('util');
const fs = require('fs');
const Vision = require('#google-cloud/vision');
const os = require('os');
const path = require('path');
const writeFile = promisify(fs.writeFile);
exports.helloWorld = async (req,res) => {
let body = '';
req.on('data', chunk => {
body += chunk.toString();
});
req.on('end', async() => {
// post { "bucket": "x", "fileName": "x", "fileUrl": "x" }
const { bucket, fileName, fileUrl } = JSON.parse(body);
var s3 = new AWS.S3();
try {
const data = await s3.getObject({
Bucket: bucket,
Key: fileName
}).promise();
const tmpdir = os.tmpdir();
const filePath = path.join(tmpdir, fileName)
await writeFile(filePath, data);
const vision = new Vision.ImageAnnotatorClient();
const [detections] = await vision.textDetection(filePath)
const annotation = detections.textAnnotations[0];
const text = annotation ? annotation.description : '';
console.log(`Extracted text from image (${text.length} chars)`);
let message = bucket + fileName + fileUrl;
res.status(200).send(message);
} catch(e) {
console.error(e);
res.status(500).send(e.message);
}
});
};
NOTE: I don't know if Vision API works like this, but I used the same logic and parameters that you're using.