[Unity] Build Asset Bundle, and upload to AWS-S3

UnityAssetBundleBuilder.cs

using UnityEngine;
using UnityEngine.Networking;
using UnityEditor;
using System.Collections.Generic;
using System.IO;
using System.Security.Cryptography;
using System.Text;
using System;


// Usage
// 1. Put this script to Assets/Editor/
// 2. Execute [Menu] -> [Build] -> [Build Asset Bundle]
public class UnityAssetBundleBuilder {

	// Enter your s3 informations
	private const string s3Bucket = "";
	private const string s3KeyBase = "";
	private const string s3AccessKeyId = "";
	private const string s3SecretAccessKey = "";

	private const string baseDir = "AssetBundles";
	private const string s3PostUrl = "http://" + s3Bucket + ".s3.amazonaws.com/";

	private static readonly BuildTarget[] buildTargets =
		new BuildTarget[] { BuildTarget.iOS, BuildTarget.Android };

	private static readonly Dictionary<string, string> postParams = new Dictionary<string, string> {
		{ "acl", "public-read" },
		{ "Content-Type", "application/octet-stream" },
		{ "x-amz-meta-uuid", "14365123651274" },
		{ "AWSAccessKeyId", s3AccessKeyId },
	};

	private const string policyBase = "{{" +
		"\"expiration\": \"{0}\"," +
		"\"conditions\": [" +
		"    {{\"bucket\": \"" + s3Bucket + "\"}}," +
		"    [\"starts-with\", \"$key\", \"{1}\"]," +
		"    {{\"acl\": \"public-read\"}}," +
		"    [\"starts-with\", \"$Content-Type\", \"application/octet-stream\"]," +
		"    {{\"x-amz-meta-uuid\": \"14365123651274\"}}" +
		"  ]" +
		"}}";


	[MenuItem("Build/Build AssetBundles")]
	public static void Build() {
		if (Directory.Exists(baseDir)) {
			Directory.Delete(baseDir, true);
		}
		Directory.CreateDirectory(baseDir);

		foreach (BuildTarget target in buildTargets) {
			buildForPlatform(target);
		}
	}

	private static void buildForPlatform(BuildTarget target) {
		var platform = target.ToString().ToLower();
		string dir = Path.Combine(baseDir, platform);
		Directory.CreateDirectory(dir);

		BuildPipeline.BuildAssetBundles(dir,
		                                BuildAssetBundleOptions.ChunkBasedCompression,
		                                target);

		var dirInfo = new DirectoryInfo(dir);
		foreach (var fileInfo in dirInfo.GetFiles()) {
			Debug.Log("upload : " + fileInfo.FullName);
			uploadToS3(platform, fileInfo);
		}
	}

	private static void uploadToS3(string platform, FileInfo fileInfo) {

		var form = new WWWForm();
		foreach (KeyValuePair<string, string> pair in postParams) {
			form.AddField(pair.Key, pair.Value);
		}

		string s3Key = Path.Combine(s3KeyBase, platform + "/" + fileInfo.Name);
		form.AddField("key", s3Key);

		string expiration = DateTime.Now.AddMinutes(1).ToString("yyyy-MM-ddTHH:mm:ss.fffZ");
		string policy = string.Format(policyBase, expiration, s3Key);
		string base64Policy = Convert.ToBase64String(Encoding.UTF8.GetBytes(policy));

		var hmac = new HMACSHA1(Encoding.UTF8.GetBytes(s3SecretAccessKey));
		string signature = Convert.ToBase64String(hmac.ComputeHash(Encoding.UTF8.GetBytes(base64Policy)));

		form.AddField("Policy", base64Policy);
		form.AddField("Signature", signature);

		byte[] fileBytes = File.ReadAllBytes(fileInfo.FullName);
		form.AddBinaryData("file", fileBytes, fileInfo.Name, "application/octet-stream");

		if (!postRequestWithRetry(s3Key, form)) {
			Debug.LogError("Upload failed : " + s3Key);
		}
	}

	private static bool postRequestWithRetry(string s3Key, WWWForm form, int retryLimit = 5) {
		for (int i = 0; i < retryLimit; i++) {
			if (postRequest(s3Key, form)) {
				return true;
			}
			Debug.Log("Retry : " + (i + 1));
		}
		return false;
	}

	private static bool postRequest(string s3Key, WWWForm form) {
		using (UnityWebRequest www = UnityWebRequest.Post(s3PostUrl, form)) {
			var s = www.Send();
			long startTick = DateTime.Now.Ticks;
			while (!s.isDone) {
				if (DateTime.Now.Ticks > startTick + 10L * 10000000L) {
					Debug.LogWarning("Timeout");
					break;
				}
			}

			if (string.IsNullOrEmpty(www.error)) {
				Debug.Log("Uploaded : " + s3PostUrl + s3Key);
				return true;

			} else {
				Debug.LogWarning("Error : " + www.error);
				return false;
			}
		}
	}

}

You can please tell me where i find the s3KeyBase?

// Enter your s3 informations
private const string s3Bucket = "";
private const string s3KeyBase = "";
private const string s3AccessKeyId = "";
private const string s3SecretAccessKey = "";

Based on cross referencing other source codes, since the "key" in AddField("key", s3Key) implies the name that you'd insert for the file you're uploading onto s3, it would seem that s3KeyBase is any root name that you would want your item to retain on the s3 bucket. For example, if your bucket has some kind of "folder" structure like Project1/Username/platform/filename, then your s3Keybase in this case would be Project1/Username/

Getting 400 bad request.

Can you tell me if this script can be used as a Post Process Build Script in Unity Cloud Build?
If so is the baseDir going to be different?

In this doc: https://docs.unity3d.com/Manual/UnityCloudBuildAddressables.html
It says:

The Addressable content for your build is located at $WORKSPACE/.build/last/<BUILD_TARGET_ID>/extra_data/addrs/

Can I access the $WORKSPACE variable to get the root path?

Thanks in advance