Handling multipart/form-data in aws lambda - amazon-web-services

Question

I'm trying to send a request with an image to a lambda function through API gateway.
I'm using this piece of code to parse the form-data-object received by my lambda function. I then upload the image to S3, but when downloading and opening the image from S3, I see that it's corrupt.
I have tried the following npm packages:
parse-multipart
parse-multipart-data
Both do not work, because I get an empty parts-array. The piece of code I use does get results in the array, but the buffers seems to be corrupt.
The problem seems to be in this line of code:
Buffer.from(item.slice(item.search(/Content-Type:\s.+/g) + item.match(/Content-Type:\s.+/g)[0].length + 4, -4), 'binary')
Does anyone has a solution for me?

Answer 1

You can use busboy to parse the multipart form data before uploading to S3 as shown below:
// This code is written in ECMAScript 6 (ES6), not CommonJS syntax.
// So, make sure you add <"type": "module"> in your package.json.
import {S3Client, PutObjectCommand} from '#aws-sdk/client-s3';
import Busboy from 'busboy';
// Initialize the clients outside the function handler to take advantage of execution environment reuse.
const s3Client = new S3Client({region: process.env.AWS_REGION});
// Function handler.
export async function handler(event) {
const {
ContentType: contentType = '',
File: file = '',
} = await FORM.parse(event['body'], event['headers']);
try {
// Adds an object to a bucket. We must have `WRITE` permissions on a bucket to add an object to it.
await s3Client.send(new PutObjectCommand({
Body: file,
Bucket: 'BUCKET_NAME',
ContentType: contentType,
Key: 'SOME_KEY',
}));
return {
isBase64Encoded: false,
statusCode: 200,
body: JSON.stringify({
message: 'Everything is gonna be alright.',
}),
}
} catch (e) {
return {
isBase64Encoded: false,
statusCode: 404,
body: JSON.stringify(e),
}
}
}
const FORM = {
parse(body, headers) {
return new Promise((resolve, reject) => {
const data = {};
const buffer = Buffer.from(body, 'base64');
const bb = Busboy({
headers: Object.keys(headers).reduce((newHeaders, key) => {
// busboy expects lower-case headers.
newHeaders[key.toLowerCase()] = headers[key];
return newHeaders;
}, {}),
limits: {
fileSize: 10485760, // Set as desired.
files: 1,
},
});
bb.on('file', (name, stream, info) => {
const chunks = [];
stream.on('data', (chunk) => {
if (name === 'File') {
chunks.push(chunk);
}
}).on('limit', () => {
reject(new Error('File size limit has been reached.'));
}).on('close', () => {
if (name === 'File') {
data[name] = Buffer.concat(chunks);
data['ContentType'] = info.mimeType;
}
});
});
bb.on('error', (err) => {
reject(err);
});
bb.on('close', () => {
resolve(data);
});
bb.end(buffer);
});
}
};