Uploading to AWS from Unity

Ever found yourself needing to upload content to AWS S3 storage, but had no luck finding up-to-date documentation? Well, REWIND’s here to help! This article will explain how to upload to S3 using simple C# in Unity, WebRequests and streams. The code was tested in Unity 2019.x.

AMAZON

Implementation

Before you write any actual code, you will first need to create a bucket via the AWS Web GUI — this will define the root location where all files will be uploaded. Whilst you’re there, you’ll also need to collect the following information:

• Bucket name — the name of the created bucket.
• Access key — required for establishing a connection with AWS3.
• Secret key — also required for establishing a connection with AWS3.

Here are our using directives:

using System;
using System.IO;
using System.Net;
using System.Security.Cryptography;
using System.Text;
using UnityEngine;

With them we can create our very first members at the top of our class:

private const string awsBucketName = "MyTestBucket";
private const string awsAccessKey = "XXXxxxXXXxxx";
private const string awsSecretKey = "XXXXxxxxxxXXXxxxXXX";

We will also need a member to store our base virtual URL :

private string awsURLBaseVirtual = "";

We then fill in the base virtual URL in MonoBehavior’s Start:

void Start()
{
   awsURLBaseVirtual = "https://" + 
      awsBucketName + ".s3.amazonaws.com/";  
}

OK, so let’s assume that you want to upload a single file to your test bucket. Let’s create a function named UploadFileToAWS3, which takes the filepath and filename as it's arguments.

public void UploadFileToAWS3(string FileName, string FilePath)

We’ll start the function by creating an AWS3 header. To do so, first we need to create a current-date string:

string currentAWS3Date = System.DateTime.UtcNow.ToString(
   "ddd, dd MMM yyyy HH:mm:ss ") +
   "GMT";
string canonicalString = 
   "PUT\n\n\n\nx-amz-date:" +
   currentAWS3Date + "\n/" +
   awsBucketName + "/" + FileName;

Now we need to encode our secret:

   UTF8Encoding encode = new UTF8Encoding();
   HMACSHA1 signature = new HMACSHA1();
   signature.Key = encode.GetBytes(awsSecretKey);
   byte[] bytes = encode.GetBytes(canonicalString);
   byte[] moreBytes = signature.ComputeHash(bytes);
   string encodedCanonical = Convert.ToBase64String(moreBytes);

With the encoded secret, we can create an AWS3 header:

string aws3Header = "AWS " + awsAccessKey + ":" + encodedCanonical;

Now, it’s time for a WebRequest. To do that, we have to create a URL that defines the destination path. We do this by combining the base virtual URL with the specified filename.

string URL3 = awsURLBaseVirtual + FileName;

The WebRequest itself needs our newly created URL (to know where to point at), our header and date.

WebRequest requestS3 = (HttpWebRequest)WebRequest.Create(URL3); requestS3.Headers.Add("Authorization", aws3Header);
requestS3.Headers.Add("x-amz-date", currentAWS3Date);

Next, let’s read byte data from our local file.

byte[] fileRawBytes = File.ReadAllBytes(FilePath);
requestS3.ContentLength = fileRawBytes.Length;

Now, it’s very important to set a proper RESTful method on the request itself. Since we are uploading, we use PUT.

requestS3.Method = "PUT";

Finally, we can upload the file to AWS via a Stream.

Stream S3Stream = requestS3.GetRequestStream();
S3Stream.Write(fileRawBytes, 0, fileRawBytes.Length);
Debug.Log(
   "Sent bytes: " +
   requestS3.ContentLength +
   ", for file: " +
   FileName);

Don’t forget to close your Stream after!

S3Stream.Close();

Putting it all together

Now we have all the pieces, we can put them together in a complete class!

using System;
using System.IO;
using System.Net;
using System.Security.Cryptography;
using System.Text;
using UnityEngine;
public class AWS3 : MonoBehaviour
{
    private const string awsBucketName = "MyTestBucket";
    private const string awsAccessKey = "XXXxxxXXXxxx";
    private const string awsSecretKey = "XXXXxxxxxxXXXxxxXXX";
    private string awsURLBaseVirtual = "";
 
    void Start()
    {
        awsURLBaseVirtual = "https://" +
           awsBucketName +
           ".s3.amazonaws.com/";
    }
    public void UploadFileToAWS3(string FileName, string FilePath)
    {
        string currentAWS3Date =  
            System.DateTime.UtcNow.ToString(
                "ddd, dd MMM yyyy HH:mm:ss ") +
                "GMT";
        string canonicalString =
            "PUT\n\n\n\nx-amz-date:" +
            currentAWS3Date + "\n/" +
            awsBucketName + "/" + FileName;
        UTF8Encoding encode = new UTF8Encoding();
        HMACSHA1 signature = new HMACSHA1();
        signature.Key = encode.GetBytes(awsSecretKey);
        byte[] bytes = encode.GetBytes(canonicalString);
        byte[] moreBytes = signature.ComputeHash(bytes);
        string encodedCanonical = Convert.ToBase64String(moreBytes);
        string aws3Header = "AWS " +
            awsAccessKey + ":" +
            encodedCanonical;
        string URL3 = awsURLBaseVirtual + FileName;
        WebRequest requestS3 = 
           (HttpWebRequest)WebRequest.Create(URL3);
        requestS3.Headers.Add("Authorization", aws3Header);
        requestS3.Headers.Add("x-amz-date", currentAWS3Date);
        byte[] fileRawBytes = File.ReadAllBytes(FilePath);
        requestS3.ContentLength = fileRawBytes.Length;
        requestS3.Method = "PUT";
        Stream S3Stream = requestS3.GetRequestStream();
        S3Stream.Write(fileRawBytes, 0, fileRawBytes.Length);
        Debug.Log("Sent bytes: " +
            requestS3.ContentLength +
            ", for file: " +
            FileName);
        S3Stream.Close();
    }
}

You can easily extend this functionality to support folders that will be replicated on AWS3, and even encapsulate the whole process to run on async task.

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