1 files changed, 112 insertions, 0 deletions
diff --git a/src/DotNetOpenAuth.BuildTasks/CompareFiles.cs b/src/DotNetOpenAuth.BuildTasks/CompareFiles.cs
new file mode 100644
index 0000000..51fcee4
--- /dev/null
+++ b/src/DotNetOpenAuth.BuildTasks/CompareFiles.cs
@@ -0,0 +1,112 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using Microsoft.Build.Utilities;
+using Microsoft.Build.Framework;
+using System.IO;
+
+namespace DotNetOpenAuth.BuildTasks {
+	public class CompareFiles : Task {
+		/// <summary>
+		/// One set of items to compare.
+		/// </summary>
+		[Required]
+		public ITaskItem[] OriginalItems { get; set; }
+
+		/// <summary>
+		/// The other set of items to compare.
+		/// </summary>
+		[Required]
+		public ITaskItem[] NewItems { get; set; }
+
+		/// <summary>
+		/// Gets whether the items lists contain items that are identical going down the list.
+		/// </summary>
+		[Output]
+		public bool AreSame { get; private set; }
+
+		/// <summary>
+		/// Same as <see cref="AreSame"/>, but opposite.
+		/// </summary>
+		[Output]
+		public bool AreChanged { get { return !AreSame; } }
+
+		public override bool Execute() {
+			AreSame = AreFilesIdentical();
+			return true;
+		}
+
+		private bool AreFilesIdentical() {
+			if (OriginalItems.Length != NewItems.Length) {
+				return false;
+			}
+
+			for (int i = 0; i < OriginalItems.Length; i++) {
+				if (!IsContentOfFilesTheSame(OriginalItems[i].ItemSpec, NewItems[i].ItemSpec)) {
+					return false;
+				}
+			}
+
+			return true;
+		}
+
+		private bool IsContentOfFilesTheSame(string file1, string file2) {
+			// If exactly one file is missing, that's different.
+			if (File.Exists(file1) ^ File.Exists(file2)) return false;
+			// If both are missing, that's the same.
+			if (!File.Exists(file1)) return true;
+			// If both are present, we need to do a content comparison.
+			using (FileStream fileStream1 = File.OpenRead(file1)) {
+				using (FileStream fileStream2 = File.OpenRead(file2)) {
+					if (fileStream1.Length != fileStream2.Length) return false;
+					byte[] buffer1 = new byte[4096];
+					byte[] buffer2 = new byte[buffer1.Length];
+					int bytesRead;
+					do {
+						bytesRead = fileStream1.Read(buffer1, 0, buffer1.Length);
+						if (fileStream2.Read(buffer2, 0, buffer2.Length) != bytesRead) {
+							// We should never get here since we compared file lengths, but
+							// this is a sanity check.
+							return false;
+						}
+						for (int i = 0; i < bytesRead; i++) {
+							if (buffer1[i] != buffer2[i]) {
+								return false;
+							}
+						}
+					} while (bytesRead == buffer1.Length);
+				}
+			}
+
+			return true;
+		}
+
+		/// <summary>
+		/// Tests whether a file is up to date with respect to another,
+		/// based on existence, last write time and file size.
+		/// </summary>
+		/// <param name="sourcePath">The source path.</param>
+		/// <param name="destPath">The dest path.</param>
+		/// <returns><c>true</c> if the files are the same; <c>false</c> if the files are different</returns>
+		internal static bool FastFileEqualityCheck(string sourcePath, string destPath) {
+			FileInfo sourceInfo = new FileInfo(sourcePath);
+			FileInfo destInfo = new FileInfo(destPath);
+			
+			if (sourceInfo.Exists ^ destInfo.Exists) {
+				// Either the source file or the destination file is missing.
+				return false;
+			}
+
+			if (!sourceInfo.Exists) {
+				// Neither file exists.
+				return true;
+			}
+
+			// We'll say the files are the same if their modification date and length are the same.
+			return
+				sourceInfo.LastWriteTimeUtc == destInfo.LastWriteTimeUtc &&
+				sourceInfo.Length == destInfo.Length;
+		}
+	}
+}