Add optional IGenericRecordSerializer to Avro formatter

Signed-off-by: Kirner- <kirner10@gmail.com>

src/CloudNative.CloudEvents.Avro/AvroEventFormatter.cs

@@ -4,7 +4,7 @@
 
 using Avro;
 using Avro.Generic;
-using Avro.IO;
+using CloudNative.CloudEvents.Avro.Interfaces;
 using CloudNative.CloudEvents.Core;
 using System;
 using System.Collections.Generic;
@@ -41,30 +41,34 @@ namespace CloudNative.CloudEvents.Avro
         private const string DataName = "data";
 
         private static readonly string CloudEventAvroMediaType = MimeUtilities.MediaType + MediaTypeSuffix;
-        private static readonly RecordSchema avroSchema;
-        private static readonly DefaultReader avroReader;
-        private static readonly DefaultWriter avroWriter;
-        
-        static AvroEventFormatter()
+        private readonly IGenericRecordSerializer serializer;
+
+        /// <summary>
+        /// Creates an AvroEventFormatter using the default serializer.
+        /// </summary>
+        public AvroEventFormatter() : this(new BasicGenericRecordSerializer()) { }
+
+        /// <summary>
+        /// Creates an AvroEventFormatter that uses a custom <see cref="IGenericRecordSerializer"/>.
+        /// </summary>
+        /// <remarks>
+        /// It is recommended to use the default serializer before defining your own wherever possible.
+        /// </remarks>
+        public AvroEventFormatter(IGenericRecordSerializer genericRecordSerializer)
         {
-            // We're going to confidently assume that the embedded schema works. If not, type initialization
-            // will fail and that's okay since the type is useless without the proper schema.
-            using (var sr = new StreamReader(typeof(AvroEventFormatter).Assembly.GetManifestResourceStream("CloudNative.CloudEvents.Avro.AvroSchema.json")))
-            {
-                avroSchema = (RecordSchema) Schema.Parse(sr.ReadToEnd());
-            }
-            avroReader = new DefaultReader(avroSchema, avroSchema);
-            avroWriter = new DefaultWriter(avroSchema);
+            serializer = genericRecordSerializer;
         }
 
+        /// <summary>
+        /// Avro schema used to serialize and deserialize the CloudEvent.
+        /// </summary>
+        public static RecordSchema AvroSchema { get; } = ParseEmbeddedSchema();
+
         /// <inheritdoc />
         public override CloudEvent DecodeStructuredModeMessage(Stream body, ContentType? contentType, IEnumerable<CloudEventAttribute>? extensionAttributes)
         {
             Validation.CheckNotNull(body, nameof(body));
-
-            var decoder = new BinaryDecoder(body);
-            // The reuse parameter *is* allowed to be null...
-            var rawEvent = avroReader.Read<GenericRecord>(reuse: null!, decoder);
+            var rawEvent = serializer.Deserialize(body);
             return DecodeGenericRecord(rawEvent, extensionAttributes);
         }
 
@@ -146,7 +150,7 @@ namespace CloudNative.CloudEvents.Avro
             contentType = new ContentType(CloudEventAvroMediaType);
 
             // We expect the Avro encoded to detect data types that can't be represented in the schema.
-            GenericRecord record = new GenericRecord(avroSchema);
+            GenericRecord record = new GenericRecord(AvroSchema);
             record.Add(DataName, cloudEvent.Data);
             var recordAttributes = new Dictionary<string, object>();
             recordAttributes[CloudEventsSpecVersion.SpecVersionAttribute.Name] = cloudEvent.SpecVersion.VersionId;
@@ -162,9 +166,7 @@ namespace CloudNative.CloudEvents.Avro
                 recordAttributes[attribute.Name] = avroValue;
             }
             record.Add(AttributeName, recordAttributes);
-            MemoryStream memStream = new MemoryStream();
-            BinaryEncoder encoder = new BinaryEncoder(memStream);
-            avroWriter.Write(record, encoder);
+            var memStream = serializer.Serialize(record);
             return memStream.ToArray();
         }
 
@@ -176,5 +178,16 @@ namespace CloudNative.CloudEvents.Avro
         /// <inheritdoc />
         public override void DecodeBinaryModeEventData(ReadOnlyMemory<byte> body, CloudEvent cloudEvent) =>
             throw new NotSupportedException("The Avro event formatter does not support binary content mode");
+
+        private static RecordSchema ParseEmbeddedSchema()
+        {
+            // We're going to confidently assume that the embedded schema works. If not, type initialization
+            // will fail and that's okay since the type is useless without the proper schema.
+            using var sr = new StreamReader(typeof(AvroEventFormatter)
+                .Assembly
+                .GetManifestResourceStream("CloudNative.CloudEvents.Avro.AvroSchema.json"));
+
+            return (RecordSchema) Schema.Parse(sr.ReadToEnd());
+        }
     }
 }

src/CloudNative.CloudEvents.Avro/BasicGenericRecordSerializer.cs

@@ -0,0 +1,47 @@
+// Copyright (c) Cloud Native Foundation.
+// Licensed under the Apache 2.0 license.
+// See LICENSE file in the project root for full license information.
+
+using Avro.Generic;
+using Avro.IO;
+using CloudNative.CloudEvents.Avro.Interfaces;
+using System;
+using System.IO;
+
+namespace CloudNative.CloudEvents.Avro;
+
+/// <summary>
+/// The default implementation of the <see cref="IGenericRecordSerializer"/>.
+/// </summary>
+/// <remarks>
+/// Makes use of the Avro <see cref="DefaultReader"/> and <see cref="DefaultWriter"/>
+/// together with the embedded Avro schema.
+/// </remarks>
+internal sealed class BasicGenericRecordSerializer : IGenericRecordSerializer
+{
+    private readonly DefaultReader avroReader;
+    private readonly DefaultWriter avroWriter;
+
+    public BasicGenericRecordSerializer()
+    {
+        avroReader = new DefaultReader(AvroEventFormatter.AvroSchema, AvroEventFormatter.AvroSchema);
+        avroWriter = new DefaultWriter(AvroEventFormatter.AvroSchema);
+    }
+
+    /// <inheritdoc />
+    public ReadOnlyMemory<byte> Serialize(GenericRecord record)
+    {
+        var memStream = new MemoryStream();
+        var encoder = new BinaryEncoder(memStream);
+        avroWriter.Write(record, encoder);
+        return memStream.ToArray();
+    }
+
+    /// <inheritdoc />
+    public GenericRecord Deserialize(Stream rawMessagebody)
+    {
+        var decoder = new BinaryDecoder(rawMessagebody);
+        // The reuse parameter *is* allowed to be null...
+        return avroReader.Read<GenericRecord>(reuse: null!, decoder);
+    }
+}

src/CloudNative.CloudEvents.Avro/Interfaces/IGenericRecordSerializer.cs

@@ -0,0 +1,39 @@
+using Avro.Generic;
+using System;
+using System.IO;
+
+namespace CloudNative.CloudEvents.Avro.Interfaces;
+
+/// <summary>
+/// Used to serialize and deserialize an Avro <see cref="GenericRecord"/>
+/// matching the <see href="https://github.com/cloudevents/spec/blob/main/cloudevents/formats/cloudevents.avsc">
+/// CloudEvent Avro schema</see>.
+/// </summary>
+/// <remarks>
+/// <para>
+/// An implementation of this interface can optionally be supplied to the <see cref="AvroEventFormatter"/> in cases
+/// where a custom Avro serialiser is required for integration with pre-existing tools/infrastructure.
+/// </para>
+/// <para>
+/// It is recommended to use the default serializer before defining your own wherever possible.
+/// </para>
+/// </remarks>
+public interface IGenericRecordSerializer
+{
+    /// <summary>
+    /// Serialize an Avro <see cref="GenericRecord"/>.
+    /// </summary>
+    /// <remarks>
+    /// The record is guaranteed to match the
+    /// <see href="https://github.com/cloudevents/spec/blob/main/cloudevents/formats/cloudevents.avsc">
+    /// CloudEvent Avro schema</see>.
+    /// </remarks>
+    ReadOnlyMemory<byte> Serialize(GenericRecord value);
+
+    /// <summary>
+    /// Deserialize a <see cref="GenericRecord"/> matching the
+    /// <see href="https://github.com/cloudevents/spec/blob/main/cloudevents/formats/cloudevents.avsc">
+    /// CloudEvent Avro schema</see>, represented as a stream.
+    /// </summary>
+    GenericRecord Deserialize(Stream messageBody);
+}

test/CloudNative.CloudEvents.UnitTests/Avro/AvroEventFormatterTest.cs

@@ -3,6 +3,7 @@
 // See LICENSE file in the project root for full license information.
 
 using CloudNative.CloudEvents.NewtonsoftJson;
+using CloudNative.CloudEvents.UnitTests.Avro.Helpers;
 using System;
 using System.Net.Mime;
 using Xunit;
@@ -83,5 +84,43 @@ namespace CloudNative.CloudEvents.Avro.UnitTests
 
             Assert.Equal("value", cloudEvent[extensionAttribute]);
         }
+
+        [Fact]
+        public void StructuredParseSerializationWithCustomSerializer()
+        {
+            var serializer = new FakeGenericRecordSerializer();
+            var jsonFormatter = new JsonEventFormatter();
+            var avroFormatter = new AvroEventFormatter(serializer);
+
+            var expectedSerializedData = new byte[] { 0x1, 0x2, 0x3, };
+            serializer.SetSerializeResponse(expectedSerializedData);
+
+            var inputCloudEvent = jsonFormatter.DecodeStructuredModeText(jsonv10);
+            var avroData = avroFormatter
+                .EncodeStructuredModeMessage(inputCloudEvent, out var _)
+                .ToArray();
+
+            Assert.Equal(1, serializer.SerializeCalls);
+            Assert.Equal(expectedSerializedData, avroData);
+        }
+
+        [Fact]
+        public void StructuredParseDeserializationWithCustomSerializer()
+        {
+            var serializer = new FakeGenericRecordSerializer();
+            var avroFormatter = new AvroEventFormatter(serializer);
+            var expectedCloudEventId = "4321";
+            var expectedCloudEventType = "MyBrilliantEvent";
+            var expectedCloudEventSource = "https://cloudevents.io.test/test-event";
+            serializer.SetDeserializeResponseAttributes(
+                expectedCloudEventId, expectedCloudEventType, expectedCloudEventSource);
+
+            var actualCloudEvent = avroFormatter.DecodeStructuredModeMessage(Array.Empty<byte>(), null, null);
+
+            Assert.Equal(1, serializer.DeserializeCalls);
+            Assert.Equal(expectedCloudEventId, actualCloudEvent.Id);
+            Assert.Equal(expectedCloudEventType, actualCloudEvent.Type);
+            Assert.Equal(expectedCloudEventSource, actualCloudEvent.Source!.ToString());
+        }
     }
 }

test/CloudNative.CloudEvents.UnitTests/Avro/Helpers/FakeGenericRecordSerializer.cs

@@ -0,0 +1,47 @@
+// Copyright (c) Cloud Native Foundation.
+// Licensed under the Apache 2.0 license.
+// See LICENSE file in the project root for full license information.
+
+using Avro.Generic;
+using CloudNative.CloudEvents.Avro.Interfaces;
+using System;
+using System.Collections.Generic;
+using System.IO;
+
+namespace CloudNative.CloudEvents.UnitTests.Avro.Helpers;
+
+internal class FakeGenericRecordSerializer : IGenericRecordSerializer
+{
+    public byte[]? SerializeResponse { get; private set; }
+    public GenericRecord DeserializeResponse { get; private set; }
+    public int DeserializeCalls { get; private set; } = 0;
+    public int SerializeCalls { get; private set; } = 0;
+
+    public FakeGenericRecordSerializer()
+    {
+        DeserializeResponse = new GenericRecord(CloudEvents.Avro.AvroEventFormatter.AvroSchema);
+    }
+
+    public GenericRecord Deserialize(Stream messageBody)
+    {
+        DeserializeCalls++;
+        return DeserializeResponse;
+    }
+
+    public ReadOnlyMemory<byte> Serialize(GenericRecord value)
+    {
+        SerializeCalls++;
+        return SerializeResponse;
+    }
+
+    public void SetSerializeResponse(byte[] response) => SerializeResponse = response;
+
+    public void SetDeserializeResponseAttributes(string id, string type, string source) =>
+        DeserializeResponse.Add("attribute", new Dictionary<string, object>()
+        {
+            { CloudEventsSpecVersion.SpecVersionAttribute.Name, CloudEventsSpecVersion.Default.VersionId },
+            { CloudEventsSpecVersion.Default.IdAttribute.Name, id},
+            { CloudEventsSpecVersion.Default.TypeAttribute.Name, type},
+            { CloudEventsSpecVersion.Default.SourceAttribute.Name, source}
+        });
+}

test/CloudNative.CloudEvents.UnitTests/CloudNative.CloudEvents.UnitTests.csproj

@@ -28,4 +28,7 @@
     <ProjectReference Include="..\..\src\CloudNative.CloudEvents\CloudNative.CloudEvents.csproj" />
   </ItemGroup>
 
+  <ItemGroup>
+    <EmbeddedResource Include="..\..\src\CloudNative.CloudEvents.Avro\AvroSchema.json" />
+  </ItemGroup>
 </Project>