Makes the hashing algorithm used for ETags pluggable.

Author: Bart Koelman

src/JsonApiDotNetCore/Configuration/JsonApiApplicationBuilder.cs

@@ -285,6 +285,7 @@ private void AddSerializationLayer()
             _services.AddScoped(typeof(AtomicOperationsResponseSerializer));
             _services.AddScoped(sp => sp.GetRequiredService<IJsonApiSerializerFactory>().GetSerializer());
             _services.AddScoped<IResourceObjectBuilder, ResponseResourceObjectBuilder>();
+            _services.AddSingleton<IFingerprintGenerator, FingerprintGenerator>();
             _services.AddSingleton<IETagGenerator, ETagGenerator>();
         }
 

src/JsonApiDotNetCore/Serialization/ETagGenerator.cs

@@ -1,46 +1,26 @@
-using System.Linq;
-using System.Security.Cryptography;
-using System.Text;
 using Microsoft.Net.Http.Headers;
 
 namespace JsonApiDotNetCore.Serialization
 {
     /// <inheritdoc />
     internal sealed class ETagGenerator : IETagGenerator
     {
-        private static readonly uint[] LookupTable = Enumerable.Range(0, 256).Select(ToLookupEntry).ToArray();
+        private readonly IFingerprintGenerator _fingerprintGenerator;
 
-        private static uint ToLookupEntry(int index)
+        public ETagGenerator(IFingerprintGenerator fingerprintGenerator)
         {
-            string hex = index.ToString("X2");
-            return hex[0] + ((uint)hex[1] << 16);
+            ArgumentGuard.NotNull(fingerprintGenerator, nameof(fingerprintGenerator));
+
+            _fingerprintGenerator = fingerprintGenerator;
         }
 
         /// <inheritdoc />
         public EntityTagHeaderValue Generate(string requestUrl, string responseBody)
         {
-            byte[] buffer = Encoding.UTF8.GetBytes(requestUrl + "|" + responseBody);
-
-            using HashAlgorithm hashAlgorithm = MD5.Create();
-            byte[] hash = hashAlgorithm.ComputeHash(buffer);
+            string fingerprint = _fingerprintGenerator.Generate(ArrayFactory.Create(requestUrl, responseBody));
+            string eTagValue = "\"" + fingerprint + "\"";
 
-            string eTagValue = "\"" + ByteArrayToHex(hash) + "\"";
             return EntityTagHeaderValue.Parse(eTagValue);
         }
-
-        // https://stackoverflow.com/questions/311165/how-do-you-convert-a-byte-array-to-a-hexadecimal-string-and-vice-versa
-        private static string ByteArrayToHex(byte[] bytes)
-        {
-            char[] buffer = new char[bytes.Length * 2];
-
-            for (int index = 0; index < bytes.Length; index++)
-            {
-                uint value = LookupTable[bytes[index]];
-                buffer[2 * index] = (char)value;
-                buffer[2 * index + 1] = (char)(value >> 16);
-            }
-
-            return new string(buffer);
-        }
     }
 }

src/JsonApiDotNetCore/Serialization/FingerprintGenerator.cs

@@ -0,0 +1,54 @@
+using System.Collections.Generic;
+using System.Linq;
+using System.Security.Cryptography;
+using System.Text;
+
+namespace JsonApiDotNetCore.Serialization
+{
+    /// <inheritdoc />
+    internal sealed class FingerprintGenerator : IFingerprintGenerator
+    {
+        private static readonly byte[] Separator = Encoding.UTF8.GetBytes("|");
+        private static readonly uint[] LookupTable = Enumerable.Range(0, 256).Select(ToLookupEntry).ToArray();
+
+        private static uint ToLookupEntry(int index)
+        {
+            string hex = index.ToString("X2");
+            return hex[0] + ((uint)hex[1] << 16);
+        }
+
+        /// <inheritdoc />
+        public string Generate(IEnumerable<string> elements)
+        {
+            ArgumentGuard.NotNull(elements, nameof(elements));
+
+            using var hasher = IncrementalHash.CreateHash(HashAlgorithmName.MD5);
+
+            foreach (string element in elements)
+            {
+                byte[] buffer = Encoding.UTF8.GetBytes(element);
+                hasher.AppendData(buffer);
+                hasher.AppendData(Separator);
+            }
+
+            byte[] hash = hasher.GetHashAndReset();
+            return ByteArrayToHex(hash);
+        }
+
+        private static string ByteArrayToHex(byte[] bytes)
+        {
+            // https://stackoverflow.com/questions/311165/how-do-you-convert-a-byte-array-to-a-hexadecimal-string-and-vice-versa
+
+            char[] buffer = new char[bytes.Length * 2];
+
+            for (int index = 0; index < bytes.Length; index++)
+            {
+                uint value = LookupTable[bytes[index]];
+                buffer[2 * index] = (char)value;
+                buffer[2 * index + 1] = (char)(value >> 16);
+            }
+
+            return new string(buffer);
+        }
+    }
+}

src/JsonApiDotNetCore/Serialization/IFingerprintGenerator.cs

@@ -0,0 +1,15 @@
+using System.Collections.Generic;
+
+namespace JsonApiDotNetCore.Serialization
+{
+    /// <summary>
+    /// Provides a method to generate a fingerprint for a collection of string values.
+    /// </summary>
+    public interface IFingerprintGenerator
+    {
+        /// <summary>
+        /// Generates a fingerprint for the specified elements.
+        /// </summary>
+        public string Generate(IEnumerable<string> elements);
+    }
+}

src/JsonApiDotNetCore/Serialization/JsonApiReader.cs

@@ -86,7 +86,7 @@ public async Task<InputFormatterResult> ReadAsync(InputFormatterContext context)
 
         private async Task<string> GetRequestBodyAsync(Stream bodyStream)
         {
-            using var reader = new StreamReader(bodyStream);
+            using var reader = new StreamReader(bodyStream, leaveOpen: true);
             return await reader.ReadToEndAsync();
         }
 

test/TestBuildingBlocks/IntegrationTest.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Net.Http;
 using System.Net.Http.Headers;
+using System.Text;
 using System.Threading.Tasks;
 using JsonApiDotNetCore.Middleware;
 using Newtonsoft.Json;
@@ -60,6 +61,7 @@ public abstract class IntegrationTest
             {
                 requestText = requestText.Replace("atomic__", "atomic:");
                 request.Content = new StringContent(requestText);
+                request.Content.Headers.ContentLength = Encoding.UTF8.GetByteCount(requestText);
 
                 if (contentType != null)
                 {