10 REST API File Upload Best Practices

File uploads are a common feature in web applications. They are used to upload files to the server, such as images, videos, and documents. While this feature is commonly used, there are a few things to consider when designing a REST API for file uploads. In this article, we will discuss 10 best practices for designing a REST API for file uploads.

1. Use PUT for file uploads

When you use PUT for file uploads, the entire file is uploaded in a single request. This means that there’s no need to worry about incomplete or failed uploads, since the entire file will either be uploaded successfully or not at all.

Additionally, using PUT for file uploads allows you to easily resume an interrupted upload from the point of interruption. This is because the server will know exactly where the file should continue from, since the entire file was uploaded in the first place.

Finally, using PUT for file uploads means that you can use any type of file, including binary files. This is because the entire file is uploaded as a single request, so there’s no need to worry about encoding the file beforehand.

2. Include the Content-Length header

The Content-Length header is used to indicate the size of the file being uploaded in bytes. This is important because it allows the server to allocate the appropriate amount of memory for the file, and it also allows the client to display a progress bar during the upload.

If the Content-Length header is not included, the server will have to read the entire file into memory before it can start processing it, which could cause out-of-memory errors. Additionally, the client will not be able to display a progress bar, so the user will have no idea how long the upload will take.

So, always remember to include the Content-Length header when uploading files via the REST API!

3. Don’t forget to validate the content type of the uploaded file

The content type is a critical part of the request header, and it tells the server what kind of file is being uploaded. If this information is not accurate, it could allow an attacker to upload malicious files to your server that could then be executed.

To validate the content type, you can use the PHP function finfo_file(), which will return the correct content type for a given file. You can then compare this against the expected content type for the file you’re expecting to be uploaded.

4. If you want to allow users to upload files from a web page, use multipart/form-data as the form encoding

The multipart/form-data encoding type allows you to upload files as part of the request body. This is different from the other common form encoding type, application/x-www-form-urlencoded, which encodes the data in the request body as a string.

The advantage of using multipart/form-data is that it allows you to upload files without having to encode them first. This can be helpful if you’re dealing with large files, or if you want to avoid potential encoding issues.

It’s also worth noting that the multipart/form-data encoding type is the only one that supports file uploads in the HTML specification. So, if you want to allow users to upload files from a web page, this is the encoding type you should use.

5. Use POST requests when uploading large amounts of data (over 1 MB)

When sending data to a server, the POST request method is used when the size of the data being sent is too large for a GET request. This is because the data is sent in the body of the request, rather than in the URL like it is with GET requests.

This means that the data is not stored in the browser’s history or in the web server’s logs, which can be a security concern. It also means that the data is not cached by the browser or by any intermediate proxies, which can improve performance.

So, if you’re sending large amounts of data to a server, make sure to use a POST request.

6. Consider using chunked transfer encoding if you need to support really large files or streams

Chunked transfer encoding is a streaming data transfer mechanism in which data is divided into small chunks before being sent over the network. This has several advantages, including the fact that it allows you to send large files without having to first load them into memory, and it also makes it possible to resume an interrupted transfer more easily.

If you’re not familiar with chunked transfer encoding, then I recommend reading this excellent article from Mozilla Developer Network, which provides a detailed explanation of how it works.

So, if you need to support really large file uploads or streams, then consider using chunked transfer encoding. It’s one of the most important REST API file upload best practices.

7. When possible, avoid sending binary data in the request body and send it as part of the URL instead

When you’re sending binary data in the request body, the entire request payload has to be Base64 encoded, which increases the size of the request by about 33%. In addition, if the file is large, it might not fit in a single HTTP request, which would require the use of chunked encoding, adding even more overhead.

Instead, when possible, avoid sending binary data in the request body and send it as part of the URL instead. For example, if you’re uploading an image, you can send the image data as part of the URL using a data: URL scheme. This way, the data doesn’t have to be Base64 encoded, saving you bandwidth and reducing the size of the request.

8. Always consider security implications when allowing file uploads

When you allow file uploads, you’re also allowing potential attackers to upload malicious files that could be used to compromise your system. For example, an attacker could upload a PHP script that allows them to execute arbitrary code on your server.

To mitigate this risk, it’s important to only allow file uploads from trusted sources. You can do this by verifying the user’s identity before allowing them to upload a file. Additionally, you should also check the file type and contents of the file before allowing it to be uploaded.

9. Make sure that your API is able to handle concurrent uploads

When a user is uploading a file, they are likely going to be on a slow internet connection. This means that the upload is going to take some time, and during that time, the user might try to upload another file.

If your API can’t handle concurrent uploads, then the second upload is going to fail. This is because the first upload is going to take up all of the bandwidth, and the second upload is going to be stuck waiting.

To avoid this, make sure that your API is able to handle concurrent uploads. This way, the second upload will start as soon as the first one is finished, and the user won’t have to wait.

10. Test your API with various types of files

When you’re building a file upload feature into your API, it’s important to consider the various types of files that your users might want to upload. For example, image files might need to be a certain size or format in order for your application to process them correctly. Similarly, video files might need to be encoded in a specific way before they can be used in your application.

By testing your API with various types of files, you can ensure that your API is able to handle all types of file uploads correctly. This will give your users the confidence that they need to use your API, and it will help to avoid any unexpected errors or issues.