refactor(Storage): Smplify final chunk detection in resumable uploads

Removes the IsFinalChunk(string) helper method and replaces it with a
direct check on HashingStream.EndOfStreamReached.

By leveraging the fact that the HashingStream wrapper already observes
when 0 bytes are read from the source, we can accurately identify the
terminal request without redundant string parsing or range header
calculations.

Author: mahendra-google

apis/Google.Cloud.Storage.V1/Google.Cloud.Storage.V1/CustomMediaUpload.cs

@@ -17,7 +17,6 @@
 using Google.Apis.Upload;
 using System;
 using System.IO;
-using System.Linq;
 using System.Net.Http;
 using System.Threading;
 using System.Threading.Tasks;
@@ -73,16 +72,10 @@ public Task InterceptAsync(HttpRequestMessage request, CancellationToken cancell
                 {
                     return Task.CompletedTask;
                 }
-
-                if (request.Method == System.Net.Http.HttpMethod.Put && request.Content?.Headers.Contains("Content-Range") is true)
+                if (_hashingStream.EndOfStreamReached)
                 {
-                    var rangeHeader = request.Content.Headers.GetValues("Content-Range").First();
-
-                    if (IsFinalChunk(rangeHeader))
-                    {
-                        var calculatedHash = _hashingStream.GetBase64Hash();
-                        request.Headers.TryAddWithoutValidation(GoogleHashHeader, $"crc32c={calculatedHash}");
-                    }
+                     var calculatedHash = _hashingStream.GetBase64Hash();
+                     request.Headers.TryAddWithoutValidation(GoogleHashHeader, $"crc32c={calculatedHash}");
                 }
                 return Task.CompletedTask;
             }
@@ -102,51 +95,6 @@ private void OnProgressChanged(IUploadProgress progress)
                     _mediaUpload.ProgressChanged -= OnProgressChanged;
                 }
             }
-
-            private bool IsFinalChunk(string rangeHeader)
-            {
-                // Expected format: "bytes {start}-{end}/{total}" or "bytes */{total}" for the final request.
-                // We are interested in the final chunk of a known-size upload.
-                const string prefix = "bytes ";
-                if (!rangeHeader.StartsWith(prefix, StringComparison.OrdinalIgnoreCase))
-                {
-                    return false;
-                }
-
-                ReadOnlySpan<char> span = rangeHeader.AsSpan(prefix.Length);
-                int slashIndex = span.IndexOf('/');
-                if (slashIndex == -1)
-                {
-                    return false;
-                }
-
-                var totalSpan = span.Slice(slashIndex + 1);
-                if (totalSpan.IsEmpty || totalSpan[0] == '*')
-                {
-                    return false;
-                }
-
-                if (!long.TryParse(totalSpan.ToString(), System.Globalization.NumberStyles.Integer, System.Globalization.CultureInfo.InvariantCulture, out long totalSize))
-                {
-                    return false;
-                }
-
-                var rangeSpan = span.Slice(0, slashIndex);
-                int dashIndex = rangeSpan.IndexOf('-');
-                if (dashIndex == -1)
-                {
-                    return false;
-                }
-
-                var endByteSpan = rangeSpan.Slice(dashIndex + 1);
-                if (!long.TryParse(endByteSpan.ToString(), System.Globalization.NumberStyles.Integer, System.Globalization.CultureInfo.InvariantCulture, out long endByte))
-                {
-                    return false;
-                }
-
-                // If endByte is the last byte of the file, it's the final chunk.
-                return (endByte + 1) == totalSize;
-            }
         }
 
         internal sealed class HashingStream : Stream
@@ -155,6 +103,12 @@ internal sealed class HashingStream : Stream
             private readonly Crc32c _hasher;
             private long _maxPositionHashed = 0;
 
+            ///<summary>
+            /// Returns true if the underlying stream has returned 0 bytes, 
+            /// indicating the end of the stream has been reached.
+            ///</summary>
+            public bool EndOfStreamReached { get; private set; }
+
             public HashingStream(Stream stream)
             {
                 _stream = stream;
@@ -179,7 +133,11 @@ public override async Task<int> ReadAsync(byte[] buffer, int offset, int count,
 
             private void ProcessBytes(byte[] buffer, int offset, int bytesRead, long startingPos)
             {
-                if (bytesRead <= 0) return;
+                if (bytesRead <= 0)
+                {
+                    EndOfStreamReached = true;
+                    return;
+                }
 
                 // Only hash bytes that are beyond the furthest point we've already hashed.
                 // This handles the rewind and re-read scenario during retries.