Webforms Cache Buster

Fingerprint.cs

sing System.Collections.Concurrent;
using System.IO;
using System.Security.Cryptography;
using System.Text;
using System.Web;

/**
 * Solution from https://stefanolsen.com/posts/cache-busting-with-asp-net-mvc/
 * https://www.madskristensen.net/blog/cache-busting-in-aspnet/
 * https://stefanolsen.com/posts/cache-busting-2-0-an-update-for-asp-net-core/
 */
public static class Fingerprint
{
	private static readonly ConcurrentDictionary<string, string> CachedFileHashes = new ConcurrentDictionary<string, string>();

	public static string Version(string contentPath)
	{
			var physicalPath = HttpContext.Current.Server.MapPath(key);
			// Check if we already cached the file hash in the cache. If not, add it using the inner method.
			string fileHash = CachedFileHashes.GetOrAdd(physicalPath, key =>
			{
				var fileInfo = new FileInfo(key);

				// If file exists, generate a hash of it, otherwise return null.
				return fileInfo.Exists ? ComputeFileHash(fileInfo.OpenRead()) : null;
			});

		return $"{contentPath}?v={fileHash}";
	}

	private static string ComputeFileHash(Stream fileStream)
	{
		using(SHA256 hasher = new SHA256Managed())
		using(fileStream)
		{
			byte[] hashBytes = hasher.ComputeHash(fileStream);
			var sb = new StringBuilder(hashBytes.Length * 2);

			foreach(byte hashByte in hashBytes)
			{
				sb.AppendFormat("{0:x2}", hashByte);
			}

			return sb.ToString();
		}
	}
}