# Working with the filesystem in Node.js

You'll commonly need to work with files in a workflow, for example: downloading content from some service to upload to another. This doc explains how to work with files in Pipedream workflows and provides some sample code for common operations.

# The /tmp directory

Within a workflow, you have full read-write access to the /tmp directory. You have 512 MB of available space in /tmp to save any file.

# Managing /tmp across workflow runs

The /tmp directory is stored on the virtual machine that runs your workflow. We call this the execution environment ("EE"). More than one EE may be created to handle high-volume workflows. And EEs can be destroyed at any time (for example, after about 10 minutes of receiving no events). This means that you should not expect to have access to files across invocations. At the same time, files may remain, so you should clean them up to make sure that doesn't affect your workflow. Use the tmp-promise package to cleanup files after use, or delete the files manually.

# Writing a file to /tmp

Use the fs module to write data to /tmp:

import fs from "fs"
import { file } from 'tmp-promise'

const { path, cleanup } = await file();
await fs.promises.appendFile(path, Buffer.from("hello, world"))
await cleanup();

# Listing files in /tmp

Return a list of the files saved in /tmp:

import fs from "fs";

return fs.readdirSync("/tmp");

# Reading a file from /tmp

This example uses step exports to return the contents of a test file saved in /tmp, returned as a string (fs.readFileSync returns a Buffer):

import fs from "fs";

this.fileData = (await fs.promises.readFile('/tmp/your-file')).toString()

# Delete a file

import fs from "fs";

return await fs.promises.unlink('/tmp/your-file')

# Download a file to /tmp

See this example to learn how to download a file to /tmp.

# Upload a file from /tmp

See this example to learn how to upload a file from /tmp in an HTTP request.

# Download a file, uploading it in another multipart/form-data request

This workflow provides an example of how to download a file at a specified Download URL, uploading that file to an Upload URL as form data.

# Download email attachments to /tmp, upload to Amazon S3

This workflow is triggered by incoming emails. When copied, you'll get a workflow-specific email address you can send any email to. This workflow takes any attachments included with inbound emails, saves them to /tmp, and uploads them to Amazon S3.

You should also be aware of the inbound payload limits associated with the email trigger.