Changes per PR comments

src/Microsoft.AspNet.Mvc.Razor/Compilation/CompilerCache.cs

@@ -134,7 +134,7 @@ private CompilerCacheEntry GetOrAdd(RelativeFileInfo relativeFileInfo,
 
                 // Timestamp doesn't match but it might be because of deployment, compare the hash.
                 if (cacheEntry.IsPreCompiled &&
-                    cacheEntry.Hash == RazorFileHash.GetHash(fileInfo))
+                    cacheEntry.Hash == RazorFileHash.GetHash(fileInfo, cacheEntry.HashAlgorithmVersion))
                 {
                     // Cache hit, but we need to update the entry.
                     // Assigning to LastModified is an atomic operation and will result in a safe race if it is

src/Microsoft.AspNet.Mvc.Razor/Compilation/CompilerCacheEntry.cs

@@ -22,6 +22,7 @@ public CompilerCacheEntry([NotNull] RazorFileInfo info, [NotNull] Type compiledT
             Length = info.Length;
             LastModified = info.LastModified;
             Hash = info.Hash;
+            HashAlgorithmVersion = info.HashAlgorithmVersion;
             IsPreCompiled = true;
         }
 
@@ -63,6 +64,14 @@ public CompilerCacheEntry([NotNull] RelativeFileInfo info, [NotNull] Type compil
         /// </summary>
         public long Hash { get; }
 
+        /// <summary>
+        /// Gets the version of the hash algorithm used to generate <see cref="Hash"/>.
+        /// </summary>
+        /// <remarks>
+        /// This value is only initialized for precompiled views.
+        /// </remarks>
+        public int HashAlgorithmVersion { get; }
+
         /// <summary>
         /// Gets a flag that indicates if the file is precompiled.
         /// </summary>

src/Microsoft.AspNet.Mvc.Razor/Razor/PreCompileViews/RazorFileInfo.cs

@@ -31,5 +31,10 @@ public class RazorFileInfo
         /// A hash of the file content.
         /// </summary>
         public long Hash { get; set; }
+
+        /// <summary>
+        /// The version of hash algorithm used to generate <see cref="Hash"/>.
+        /// </summary>
+        public int HashAlgorithmVersion { get; set; }
     }
 }

src/Microsoft.AspNet.Mvc.Razor/Razor/PreCompileViews/RazorFileInfoCollectionGenerator.cs

@@ -51,7 +51,8 @@ protected virtual string GenerateFile([NotNull] RazorFileInfo fileInfo)
                                  fileInfo.Length,
                                  fileInfo.RelativePath,
                                  fileInfo.FullTypeName,
-                                 fileInfo.Hash);
+                                 fileInfo.Hash,
+                                 fileInfo.HashAlgorithmVersion);
         }
 
         protected virtual string Top
@@ -104,6 +105,7 @@ protected virtual string FileFormat
                 " + nameof(RazorFileInfo.RelativePath) + @" = @""{2}"",
                 " + nameof(RazorFileInfo.FullTypeName) + @" = @""{3}"",
                 " + nameof(RazorFileInfo.Hash) + @" = {4},
+                " + nameof(RazorFileInfo.HashAlgorithmVersion) + @" = {5},
             }};
             fileInfos.Add(info);
 ";

src/Microsoft.AspNet.Mvc.Razor/Razor/PreCompileViews/RazorPreCompiler.cs

@@ -167,7 +167,7 @@ protected virtual PrecompilationCacheEntry GetCacheEntry([NotNull] RelativeFileI
 
                     if (fullTypeName != null)
                     {
-                        var hash = RazorFileHash.GetHash(fileInfo.FileInfo);
+                        var hash = RazorFileHash.GetHash(fileInfo.FileInfo, RazorFileHash.HashAlgorthmVersion1);
                         var razorFileInfo = new RazorFileInfo
                         {
                             RelativePath = fileInfo.RelativePath,

src/Microsoft.AspNet.Mvc.Razor/Razor/RazorFileHash.cs

@@ -2,20 +2,30 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using System.IO;
 using Microsoft.AspNet.FileProviders;
 
 namespace Microsoft.AspNet.Mvc.Razor
 {
     public static class RazorFileHash
     {
-        public static long GetHash([NotNull] IFileInfo file)
+        /// <summary>
+        /// Version 1 of the hash algorithm used for generating hashes of Razor files.
+        /// </summary>
+        public static readonly int HashAlgorthmVersion1 = 1;
+
+        public static long GetHash([NotNull] IFileInfo file, int hashAlgorithmVersion)
         {
+            if (hashAlgorithmVersion != HashAlgorthmVersion1)
+            {
+                throw new ArgumentException(Resources.RazorHash_UnsupportedHashAlgorithm,
+                                            nameof(hashAlgorithmVersion));
+            }
+
             try
             {
                 using (var stream = file.CreateReadStream())
                 {
-                    return GetHash(stream);
+                    return Crc32.Calculate(stream);
                 }
             }
             catch (Exception)
@@ -24,10 +34,5 @@ public static long GetHash([NotNull] IFileInfo file)
                 return 0;
             }
         }
-
-        internal static long GetHash(Stream stream)
-        {
-            return Crc32.Calculate(stream);
-        }
     }
 }

src/Microsoft.AspNet.Mvc.Razor/Resources.resx

@@ -183,4 +183,7 @@
   <data name="ViewMustBeContextualized" xml:space="preserve">
     <value>The '{0}' method must be called before '{1}' can be invoked.</value>
   </data>
+  <data name="RazorHash_UnsupportedHashAlgorithm" xml:space="preserve">
+    <value>Unsupported hash algorithm.</value>
+  </data>
 </root>

test/Microsoft.AspNet.Mvc.Razor.Test/Compilation/CompilerCacheTest.cs

@@ -82,7 +82,8 @@ public ViewCollection()
                 Add(new RazorFileInfo()
                 {
                     FullTypeName = typeof(PreCompile).FullName,
-                    Hash = RazorFileHash.GetHash(GetMemoryStream(content)),
+                    Hash = Crc32.Calculate(GetMemoryStream(content)),
+                    HashAlgorithmVersion = 1,
                     LastModified = DateTime.FromFileTimeUtc(10000),
                     Length = length,
                     RelativePath = "ab",
@@ -127,7 +128,8 @@ public void GetOrAdd_UsesFilesFromCache_IfTimestampDiffers_ButContentAndLengthAr
             var razorFileInfo = new RazorFileInfo
             {
                 FullTypeName = typeof(PreCompile).FullName,
-                Hash = RazorFileHash.GetHash(GetMemoryStream(precompiledContent)),
+                Hash = Crc32.Calculate(GetMemoryStream(precompiledContent)),
+                HashAlgorithmVersion = 1,
                 LastModified = DateTime.FromFileTimeUtc(10000),
                 Length = Encoding.UTF8.GetByteCount(precompiledContent),
                 RelativePath = "ab",
@@ -169,7 +171,8 @@ public void GetOrAdd_RecompilesFile_IfContentAndLengthAreChanged(
             var razorFileInfo = new RazorFileInfo
             {
                 FullTypeName = typeof(PreCompile).FullName,
-                Hash = RazorFileHash.GetHash(GetMemoryStream(precompiledContent)),
+                Hash = Crc32.Calculate(GetMemoryStream(precompiledContent)),
+                HashAlgorithmVersion = 1,
                 LastModified = DateTime.FromFileTimeUtc(10000),
                 Length = Encoding.UTF8.GetByteCount(precompiledContent),
                 RelativePath = "ab",
@@ -210,7 +213,8 @@ public void GetOrAdd_UsesValueFromCache_IfViewStartHasNotChanged()
             fileProvider.AddFile("_ViewStart.cshtml", viewStartFileInfo);
             var viewStartRazorFileInfo = new RazorFileInfo
             {
-                Hash = RazorFileHash.GetHash(GetMemoryStream(viewStartContent)),
+                Hash = Crc32.Calculate(GetMemoryStream(viewStartContent)),
+                HashAlgorithmVersion = 1,
                 LastModified = viewStartFileInfo.LastModified,
                 Length = viewStartFileInfo.Length,
                 RelativePath = "_ViewStart.cshtml",
@@ -295,7 +299,8 @@ public void GetOrAdd_IgnoresCachedValueIfFileIsIdentical_ButViewStartWasDeletedS
                 FullTypeName = typeof(RuntimeCompileIdentical).FullName,
                 RelativePath = viewStartFileInfo.PhysicalPath,
                 LastModified = viewStartFileInfo.LastModified,
-                Hash = RazorFileHash.GetHash(viewStartFileInfo),
+                Hash = RazorFileHash.GetHash(viewStartFileInfo, hashAlgorithmVersion: 1),
+                HashAlgorithmVersion = 1,
                 Length = viewStartFileInfo.Length
             };
             fileProvider.AddFile(viewStartFileInfo.PhysicalPath, viewStartFileInfo);
@@ -332,7 +337,8 @@ public static IEnumerable<object[]> GetOrAdd_IgnoresCachedValue_IfViewStartWasCh
 
                 var razorFileInfo = new RazorFileInfo
                 {
-                    Hash = RazorFileHash.GetHash(contentStream),
+                    Hash = Crc32.Calculate(contentStream),
+                    HashAlgorithmVersion = 1,
                     LastModified = lastModified,
                     Length = length,
                     RelativePath = path
@@ -381,7 +387,8 @@ public void GetOrAdd_IgnoresCachedValue_IfViewStartWasChangedSinceCacheWasCreate
             var razorFileInfo = new RazorFileInfo
             {
                 FullTypeName = typeof(PreCompile).FullName,
-                Hash = RazorFileHash.GetHash(fileInfo),
+                Hash = RazorFileHash.GetHash(fileInfo, hashAlgorithmVersion: 1),
+                HashAlgorithmVersion = 1,
                 LastModified = lastModified,
                 Length = Encoding.UTF8.GetByteCount(content),
                 RelativePath = fileInfo.PhysicalPath,

test/Microsoft.AspNet.Mvc.Razor.Test/RazorHashTest.cs → test/Microsoft.AspNet.Mvc.Razor.Test/RazorFileHashTest.cs

@@ -4,15 +4,17 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.IO;
 using System.Linq;
 using System.Text;
 using Microsoft.AspNet.FileProviders;
+using Microsoft.AspNet.Testing;
 using Moq;
 using Xunit;
 
 namespace Microsoft.AspNet.Mvc.Razor
 {
-    public class RazorHashTest
+    public class RazorFileHashTest
     {
         public static IEnumerable<object[]> GetHashCodeData
         {
@@ -52,9 +54,25 @@ from readBytes in bytesToRead
             }
         }
 
+        [Theory]
+        [InlineData(-1)]
+        [InlineData(0)]
+        [InlineData(2)]
+        [InlineData(14)]
+        public void GetHash_ThrowsIfHashAlgorithmVersionIsUnknown(int hashAlgorithmVersion)
+        {
+            // Arrange
+            var file = new TestFileInfo();
+
+            // Act and Assert
+            ExceptionAssert.ThrowsArgument(() => RazorFileHash.GetHash(file, hashAlgorithmVersion),
+                                           "hashAlgorithmVersion",
+                                           "Unsupported hash algorithm.");
+        }
+
         [Theory]
         [MemberData(nameof(GetHashCodeData))]
-        public void GetHashCode_CalculatesHashCodeForFile(int bytesToRead, string content, long expected)
+        public void GetHash_CalculatesHashCodeForFile(int bytesToRead, string content, long expected)
         {
             // Arrange
             var bytes = Encoding.UTF8.GetBytes(content);
@@ -63,13 +81,13 @@ public void GetHashCode_CalculatesHashCodeForFile(int bytesToRead, string conten
                 .Returns(new SlowStream(bytes, bytesToRead));
 
             // Act
-            var result = RazorFileHash.GetHash(file.Object);
+            var result = RazorFileHash.GetHash(file.Object, hashAlgorithmVersion: 1);
 
             // Assert
             Assert.Equal(expected, result);
         }
 
-        private class SlowStream : System.IO.MemoryStream
+        private class SlowStream : MemoryStream
         {
             private readonly int _bytesToRead;