---
title: Cloudflare
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---
import current from '/version.js';
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[Cloudflare](https://www.cloudflare.com/) is a cloud services
platform which includes "Serverless
Functions" and cloud storage.
[SheetJS](https://sheetjs.com) is a JavaScript library for reading and writing
data from spreadsheets.
This demo explores two key Cloudflare offerings:
- ["Cloudflare Workers"](#cloudflare-workers) explores the serverless
computing offering. The demo creates a JavaScript function that can process
user-submitted files and generate spreadsheets.
- ["Cloudflare R2"](#cloudflare-r2) explores the cloud storage ("R2") offering. The
demo uses the NodeJS connection library to read spreadsheets from R2 and write
spreadsheets to an R2 bucket.
:::note Tested Deployments
This demo was last tested on 2024 April 02.
:::
## Cloudflare Workers
Cloudflare offers NodeJS runtimes for running JavaScript serverless functions.[^1]
The [SheetJS NodeJS module](/docs/getting-started/installation/nodejs) can be
required in Lambda functions. Cloudflare provides a convenient cli called Wrangler [^2]
which can streamline development and deployment
:::note pass
In this demo, Wrangler is used as that is Cloudflare's recommended way of developing and deploying to
Workers
:::
### Reading Data
In the Lambda handler, the `event.body` attribute is a Base64-encoded string
representing the HTTP request form data. This body must be parsed.
#### Processing Form Bodies
The `busboy` body parser[^2] is battle-tested in NodeJS deployments.
`busboy` fires a `'file'` event for every file in the form body. The callback
receives a NodeJS stream that should be collected into a Buffer:
```js
/* accumulate the files manually */
var files = {};
bb.on('file', function(fieldname, file, filename) {
/* concatenate the individual data buffers */
var buffers = [];
file.on('data', function(data) { buffers.push(data); });
file.on('end', function() { files[fieldname] = Buffer.concat(buffers); });
});
```
`busboy` fires a `'finish'` event when the body parsing is finished. Callbacks
can assume every file in the form body has been stored in NodeJS Buffer objects.
#### Processing NodeJS Buffers
The SheetJS `read` method[^3] can read the Buffer objects and generate SheetJS
workbook objects[^4] which can be processed with other API functions.
For example, a handler can use `sheet_to_csv`[^5] to generate CSV text:
```js
/* on the finish event, all of the fields and files are ready */
bb.on('finish', function() {
/* grab the first file */
var f = files["upload"];
if(!f) callback(new Error("Must submit a file for processing!"));
/* f[0] is a buffer */
// highlight-next-line
var wb = XLSX.read(f[0]);
/* grab first worksheet and convert to CSV */
var ws = wb.Sheets[wb.SheetNames[0]];
callback(null, { statusCode: 200, body: XLSX.utils.sheet_to_csv(ws) });
});
```
Complete Code Sample (click to show)
This example takes the first uploaded file submitted with the key `upload`,
parses the file and returns the CSV content of the first worksheet.
```js
const XLSX = require('xlsx');
var Busboy = require('busboy');
exports.handler = function(event, context, callback) {
/* set up busboy */
var ctype = event.headers['Content-Type']||event.headers['content-type'];
var bb = Busboy({headers:{'content-type':ctype}});
/* busboy is evented; accumulate the fields and files manually */
var fields = {}, files = {};
bb.on('error', function(err) { callback(null, { body: err.message }); });
bb.on('field', function(fieldname, val) {fields[fieldname] = val });
// highlight-start
bb.on('file', function(fieldname, file, filename) {
/* concatenate the individual data buffers */
var buffers = [];
file.on('data', function(data) { buffers.push(data); });
file.on('end', function() { files[fieldname] = [Buffer.concat(buffers), filename]; });
});
// highlight-end
/* on the finish event, all of the fields and files are ready */
bb.on('finish', function() {
/* grab the first file */
var f = files["upload"];
if(!f) callback(new Error("Must submit a file for processing!"));
/* f[0] is a buffer */
// highlight-next-line
var wb = XLSX.read(f[0]);
/* grab first worksheet and convert to CSV */
var ws = wb.Sheets[wb.SheetNames[0]];
callback(null, { statusCode: 200, body: XLSX.utils.sheet_to_csv(ws) });
});
/* start the processing */
// highlight-next-line
bb.end(Buffer.from(event.body, "base64"));
};
```
Complete Code Sample (click to show)
This example creates a sample workbook object and sends the file in the response:
```js
var XLSX = require('xlsx');
exports.handler = function(event, context, callback) {
/* make workbook */
var wb = XLSX.read("S,h,e,e,t,J,S\n5,4,3,3,7,9,5", {type: "binary"});
/* write to XLSX file in Base64 encoding */
// highlight-next-line
var body = XLSX.write(wb, { type: "base64", bookType: "xlsx" });
/* mark as attached file */
var headers = { "Content-Disposition": 'attachment; filename="SheetJSLambda.xlsx"'};
/* Send back data */
callback(null, {
statusCode: 200,
// highlight-next-line
isBase64Encoded: true,
body: body,
headers: headers
});
};
```