How to upload a JPG on to AWS Lambda (NodeJS)

Question

I am trying to do this:

Frontend: set up file to upload using <input type="file"> and <input type="button" onClick="...">
The File Object is retrieved using file[0] from the <input type="file">'s value.
Use Javascript Fetch api to call on my AWS API-Gateway Post API.

I have tried both multipart/form-data and application/json in the request.

On the AWS Lambda, I have used Buffer Object to consume the body.

I have tried using Buffer(body, "utf8"), Buffer(body, "base64"), Buffer(body, "binary").

This is, in turn, pushed up to S3 for storage using putObject.

Problem:

The file object that was set up in S3 has either filesize 0 or some random value that's not matching the original filesize.
The file downloaded from S3 cannot be opened.

Failed Approaches

I have considered multer and multiparty. These seem to be ExpressJS middleware and expects a HttpRequest object as input (this wasn't mentioned explicitly. It seems like I am ignorant enough not to assume that these can only work with HttpRequest object and it took me a while to find out). I am also ignorant enough not to know how to transform an AWS event object into a HttpRequest object. But that said, it seems excessive to use Express engine just for the sake of managing file upload.

Exposing my S3 bucket as public-read-write seems to be rather insecure. So I am not considering the frontend directly moving stuff in/out of my S3 bucket.

My Request

Can anyone tell me how to get this to work? And/or an alternative to this approach?

Bryan Jyh Herng Chong · Accepted Answer · 2018-09-22 03:11:28Z

This works for me:

Frontend

Specifically encoding File Object to base64 string. (How to convert file to base64 in JavaScript?)
Examining the encoded string-date of the file, you will find that it has a ; delimited header. This is also not explicitly mentioned anywhere. Use .split() and .join() to remove the header.
Now you can compose your request in whatever form you want. I took the easy way out and used JSON.

Here's some code that do what I have mentioned:

const getBase64fromFile = (file) => {
  return new Promise((resolve, reject) => {
    const reader = new FileReader();
    reader.readAsDataURL(file);
    reader.onload = () => {
      console.log(`getBase64fromFile success.`);
      const spliced = reader.result.split(',');
      const header = spliced[0];
      spliced.shift();
      resolve({
        header: header,
        body: spliced.join('')
      });
    };
    reader.onerror = (err) => {
      console.log(`getBase64fromFile failed.`);
      reject(err);
    };
  });
}

uploadHandler() { 
  console.log(this.state.selectedFile);

const selectedFile = this.state.selectedFile;
const email = this.state.email;
return getBase64fromFile(selectedFile)
.then((base64Data) => {
  return {
    name: selectedFile.name,
    header: base64Data.header,
    base64: base64Data.body,
    email: email
  }
})
.then((body) => {
  console.log(`${JSON.stringify(body)}`);
  return body;
})
.then((body) => {
  this.setState({status: "Begin uploading..."});
  return fetch(this.state.url+"/upload",
  { // Your POST endpoint
    method: 'POST',
    headers: {
      "Authorization": "Bearer " + this.state.token,
      "x-api-key": this.state.apikey,
      "Accept": "application/json",
    }, 
    body: JSON.stringify(body)
  });
})
.then(
  response => response.json() // if the response is a JSON object
)
.then(
  success => {
    console.log(success); // Handle the success response object
    this.setState({
      status: success.message
    });
  }
)
.catch(
  error => {console.log(error) ;// Handle the error response object
    this.setState({
      status: JSON.stringify(error)
    });
  })
;
}

(https://github.com/flameoftheforest/yaUserMan/blob/master/Tests/frontend/src/App.js)

AWS-Lambda

Now we know that the data is coming in as a base64 string, convert it to octet using Buffer.from(body, "base64").
The output of Buffer.from() is the <binary string> that putObject requires.

Here's some code that does what I have mentioned:

const params = {
  Bucket: process.env.IMAGE_BUCKET,
  Key: uuid() + event.body.name,
  Body: Buffer.from(event.body.base64, 'base64'),
  ACL: "public-read"
};

(https://github.com/flameoftheforest/yaUserMan/blob/master/yaUserMan/file2S3Helper.js)

Ref: https://medium.com/@olotintemitope/how-to-upload-files-to-amazon-s3-using-nodejs-lambda-and-api-gateway-bae665127907

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