chore: Fix null reference complaints under .NET 8.0

Signed-off-by: Jon Skeet <jonskeet@google.com>

src/CloudNative.CloudEvents.Amqp/AmqpExtensions.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Cloud Native Foundation.
+// Copyright (c) Cloud Native Foundation.
 // Licensed under the Apache 2.0 license.
 // See LICENSE file in the project root for full license information.
 
@@ -8,6 +8,7 @@ using Amqp.Types;
 using CloudNative.CloudEvents.Core;
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.IO;
 using System.Net.Mime;
 
@@ -145,7 +146,7 @@ namespace CloudNative.CloudEvents.Amqp
             }
         }
 
-        private static bool HasCloudEventsContentType(Message message, out string? contentType)
+        private static bool HasCloudEventsContentType(Message message, [NotNullWhen(true)] out string? contentType)
         {
             contentType = message.Properties.ContentType?.ToString();
             return MimeUtilities.IsCloudEventsContentType(contentType);
@@ -249,4 +250,4 @@ namespace CloudNative.CloudEvents.Amqp
             return applicationProperties;
         }
     }
-}
+}

src/CloudNative.CloudEvents.Amqp/CloudNative.CloudEvents.Amqp.csproj

@@ -12,6 +12,8 @@
     <PackageReference Include="AMQPNetLite" Version="2.4.2" />
     <PackageReference Include="AMQPNetLite.Serialization" Version="2.4.2" />
     <ProjectReference Include="..\CloudNative.CloudEvents\CloudNative.CloudEvents.csproj" />
+    <!-- Source-only package with nullable reference annotations. -->
+    <PackageReference Include="Nullable" Version="1.3.1" PrivateAssets="All" />
   </ItemGroup>
 
 </Project>

src/CloudNative.CloudEvents.Avro/AvroEventFormatter.cs

@@ -185,9 +185,9 @@ namespace CloudNative.CloudEvents.Avro
             // 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"));
+                .GetManifestResourceStream("CloudNative.CloudEvents.Avro.AvroSchema.json")!);
 
             return (RecordSchema) Schema.Parse(sr.ReadToEnd());
         }
     }
-}
+}

src/CloudNative.CloudEvents.NewtonsoftJson/JsonEventFormatter.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Cloud Native Foundation.
+// Copyright (c) Cloud Native Foundation.
 // Licensed under the Apache 2.0 license.
 // See LICENSE file in the project root for full license information.
 
@@ -345,7 +345,7 @@ namespace CloudNative.CloudEvents.NewtonsoftJson
             {
                 throw new ArgumentException($"Structured mode property '{DataBase64PropertyName}' must be a string, when present.");
             }
-            cloudEvent.Data = Convert.FromBase64String((string?) dataBase64Token);
+            cloudEvent.Data = Convert.FromBase64String((string) dataBase64Token!);
         }
 
         /// <summary>
@@ -498,7 +498,7 @@ namespace CloudNative.CloudEvents.NewtonsoftJson
         /// </summary>
         /// <param name="data">The CloudEvent to infer the data content from. Must not be null.</param>
         /// <returns>The inferred data content type, or null if no inference is performed.</returns>
-        protected override string? InferDataContentType(object data) => data is byte[]? null : JsonMediaType;
+        protected override string? InferDataContentType(object data) => data is byte[] ? null : JsonMediaType;
 
         /// <summary>
         /// Encodes structured mode data within a CloudEvent, writing it to the specified <see cref="JsonWriter"/>.
@@ -524,7 +524,14 @@ namespace CloudNative.CloudEvents.NewtonsoftJson
             }
             else
             {
-                ContentType dataContentType = new ContentType(GetOrInferDataContentType(cloudEvent));
+                string? dataContentTypeText = GetOrInferDataContentType(cloudEvent);
+                // This would only happen in a derived class which overrides GetOrInferDataContentType further...
+                // This class infers application/json for anything other than byte arrays.
+                if (dataContentTypeText is null)
+                {
+                    throw new ArgumentException("Data content type cannot be inferred");
+                }
+                ContentType dataContentType = new ContentType(dataContentTypeText);
                 if (IsJsonMediaType(dataContentType.MediaType))
                 {
                     writer.WritePropertyName(DataPropertyName);
@@ -710,4 +717,4 @@ namespace CloudNative.CloudEvents.NewtonsoftJson
         protected override void DecodeStructuredModeDataBase64Property(JToken dataBase64Token, CloudEvent cloudEvent) =>
             throw new ArgumentException($"Data unexpectedly represented using '{DataBase64PropertyName}' within structured mode CloudEvent.");
     }
-}
+}

src/CloudNative.CloudEvents/CloudEventFormatterAttribute.cs

@@ -56,7 +56,7 @@ namespace CloudNative.CloudEvents
                 throw new ArgumentException($"The {nameof(CloudEventFormatterAttribute)} on type {targetType} has no converter type specified.", nameof(targetType));
             }
 
-            object instance;
+            object? instance;
             try
             {
                 instance = Activator.CreateInstance(formatterType);

src/CloudNative.CloudEvents/Core/BinaryDataUtilities.cs

@@ -65,7 +65,7 @@ namespace CloudNative.CloudEvents.Core
         public static MemoryStream AsStream(ReadOnlyMemory<byte> memory)
         {
             var segment = GetArraySegment(memory);
-            return new MemoryStream(segment.Array, segment.Offset, segment.Count, false);
+            return new MemoryStream(segment.Array!, segment.Offset, segment.Count, false);
         }
 
         /// <summary>
@@ -79,7 +79,7 @@ namespace CloudNative.CloudEvents.Core
 
             // TODO: If we introduce an additional netstandard2.1 target, we can use encoding.GetString(memory.Span)
             var segment = GetArraySegment(memory);
-            return encoding.GetString(segment.Array, segment.Offset, segment.Count);
+            return encoding.GetString(segment.Array!, segment.Offset, segment.Count);
         }
 
         /// <summary>
@@ -92,7 +92,7 @@ namespace CloudNative.CloudEvents.Core
         {
             Validation.CheckNotNull(destination, nameof(destination));
             var segment = GetArraySegment(source);
-            await destination.WriteAsync(segment.Array, segment.Offset, segment.Count).ConfigureAwait(false);
+            await destination.WriteAsync(segment.Array!, segment.Offset, segment.Count).ConfigureAwait(false);
         }
 
         /// <summary>
@@ -108,13 +108,14 @@ namespace CloudNative.CloudEvents.Core
             var segment = GetArraySegment(memory);
             // We probably don't actually need to check the offset: if the count is the same as the length,
             // I can't see how the offset can be non-zero. But it doesn't *hurt* as a check.
-            return segment.Offset == 0 && segment.Count == segment.Array.Length
+            return segment.Offset == 0 && segment.Count == segment.Array!.Length
                 ? segment.Array
                 : memory.ToArray();
         }
 
+        // Note: when this returns, the Array property of the returned segment is guaranteed not to be null.
         private static ArraySegment<byte> GetArraySegment(ReadOnlyMemory<byte> memory) =>
-            MemoryMarshal.TryGetArray(memory, out var segment)
+            MemoryMarshal.TryGetArray(memory, out var segment) && segment.Array is not null
                 ? segment
                 : new ArraySegment<byte>(memory.ToArray());
     }

src/CloudNative.CloudEvents/Core/MimeUtilities.cs

@@ -1,8 +1,9 @@
-// Copyright 2021 Cloud Native Foundation.
+// Copyright 2021 Cloud Native Foundation.
 // Licensed under the Apache 2.0 license.
 // See LICENSE file in the project root for full license information.
 
 using System;
+using System.Diagnostics.CodeAnalysis;
 using System.Net.Http.Headers;
 using System.Net.Mime;
 using System.Text;
@@ -57,7 +58,7 @@ namespace CloudNative.CloudEvents.Core
             var header = new MediaTypeHeaderValue(contentType.MediaType);
             foreach (string parameterName in contentType.Parameters.Keys)
             {
-                header.Parameters.Add(new NameValueHeaderValue(parameterName, contentType.Parameters[parameterName].ToString()));
+                header.Parameters.Add(new NameValueHeaderValue(parameterName, contentType.Parameters[parameterName]));
             }
             return header;
         }
@@ -76,7 +77,7 @@ namespace CloudNative.CloudEvents.Core
         /// </summary>
         /// <param name="contentType">The content type to check. May be null, in which case the result is false.</param>
         /// <returns>true if the given content type denotes a (non-batch) CloudEvent; false otherwise</returns>
-        public static bool IsCloudEventsContentType(string? contentType) =>
+        public static bool IsCloudEventsContentType([NotNullWhen(true)] string? contentType) =>
             contentType is string &&
             contentType.StartsWith(MediaType, StringComparison.InvariantCultureIgnoreCase) &&
             !contentType.StartsWith(BatchMediaType, StringComparison.InvariantCultureIgnoreCase);
@@ -86,7 +87,7 @@ namespace CloudNative.CloudEvents.Core
         /// </summary>
         /// <param name="contentType">The content type to check. May be null, in which case the result is false.</param>
         /// <returns>true if the given content type represents a CloudEvent batch; false otherwise</returns>
-        public static bool IsCloudEventsBatchContentType(string? contentType) =>
+        public static bool IsCloudEventsBatchContentType([NotNullWhen(true)] string? contentType) =>
             contentType is string && contentType.StartsWith(BatchMediaType, StringComparison.InvariantCultureIgnoreCase);
     }
 }

src/CloudNative.CloudEvents/Http/HttpClientExtensions.cs

@@ -1,10 +1,11 @@
-// Copyright (c) Cloud Native Foundation.
+// Copyright (c) Cloud Native Foundation.
 // Licensed under the Apache 2.0 license.
 // See LICENSE file in the project root for full license information.
 
 using CloudNative.CloudEvents.Core;
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Net.Http;
 using System.Net.Http.Headers;
@@ -130,7 +131,7 @@ namespace CloudNative.CloudEvents.Http
             return ToCloudEventInternalAsync(httpRequestMessage.Headers, httpRequestMessage.Content, formatter, extensionAttributes, nameof(httpRequestMessage));
         }
 
-        private static async Task<CloudEvent> ToCloudEventInternalAsync(HttpHeaders headers, HttpContent content,
+        private static async Task<CloudEvent> ToCloudEventInternalAsync(HttpHeaders headers, HttpContent? content,
             CloudEventFormatter formatter, IEnumerable<CloudEventAttribute>? extensionAttributes, string paramName)
         {
             Validation.CheckNotNull(formatter, nameof(formatter));
@@ -142,7 +143,7 @@ namespace CloudNative.CloudEvents.Http
             }
             else
             {
-                string? versionId = MaybeGetVersionId(headers) ?? MaybeGetVersionId(content.Headers);
+                string? versionId = MaybeGetVersionId(headers) ?? MaybeGetVersionId(content?.Headers);
                 if (versionId is null)
                 {
                     throw new ArgumentException($"Request does not represent a CloudEvent. It has neither a {HttpUtilities.SpecVersionHttpHeader} header, nor a suitable content type.", nameof(paramName));
@@ -151,7 +152,8 @@ namespace CloudNative.CloudEvents.Http
                     ?? throw new ArgumentException($"Unknown CloudEvents spec version '{versionId}'", paramName);
 
                 var cloudEvent = new CloudEvent(version, extensionAttributes);
-                foreach (var header in headers.Concat(content.Headers))
+                var allHeaders = content is null ? headers : headers.Concat(content.Headers);
+                foreach (var header in allHeaders)
                 {
                     string? attributeName = HttpUtilities.GetAttributeNameFromHeaderName(header.Key);
                     if (attributeName is null || attributeName == CloudEventsSpecVersion.SpecVersionAttribute.Name)
@@ -231,7 +233,7 @@ namespace CloudNative.CloudEvents.Http
             return ToCloudEventBatchInternalAsync(httpRequestMessage.Content, formatter, extensionAttributes, nameof(httpRequestMessage));
         }
 
-        private static async Task<IReadOnlyList<CloudEvent>> ToCloudEventBatchInternalAsync(HttpContent content,
+        private static async Task<IReadOnlyList<CloudEvent>> ToCloudEventBatchInternalAsync(HttpContent? content,
             CloudEventFormatter formatter, IEnumerable<CloudEventAttribute>? extensionAttributes, string paramName)
         {
             Validation.CheckNotNull(formatter, nameof(formatter));
@@ -331,16 +333,16 @@ namespace CloudNative.CloudEvents.Http
         }
 
         private static ByteArrayContent ToByteArrayContent(ReadOnlyMemory<byte> content) =>
-            MemoryMarshal.TryGetArray(content, out var segment)
+            MemoryMarshal.TryGetArray(content, out var segment) && segment.Array is not null
             ? new ByteArrayContent(segment.Array, segment.Offset, segment.Count)
             // TODO: Just throw?
             : new ByteArrayContent(content.ToArray());
 
         // TODO: This would include "application/cloudeventsarerubbish" for example...
-        private static bool HasCloudEventsContentType(HttpContent content) =>
+        private static bool HasCloudEventsContentType([NotNullWhen(true)] HttpContent? content) =>
             MimeUtilities.IsCloudEventsContentType(content?.Headers?.ContentType?.MediaType);
 
-        private static bool HasCloudEventsBatchContentType(HttpContent content) =>
+        private static bool HasCloudEventsBatchContentType([NotNullWhen(true)] HttpContent? content) =>
             MimeUtilities.IsCloudEventsBatchContentType(content?.Headers?.ContentType?.MediaType);
 
         private static string? MaybeGetVersionId(HttpHeaders? headers) =>
@@ -348,4 +350,4 @@ namespace CloudNative.CloudEvents.Http
             ? headers.GetValues(HttpUtilities.SpecVersionHttpHeader).First()
             : null;
     }
-}
+}

src/CloudNative.CloudEvents/Http/HttpListenerExtensions.cs

@@ -179,7 +179,7 @@ namespace CloudNative.CloudEvents.Http
             }
             else
             {
-                string versionId = httpListenerRequest.Headers[HttpUtilities.SpecVersionHttpHeader];
+                string? versionId = httpListenerRequest.Headers[HttpUtilities.SpecVersionHttpHeader];
                 if (versionId is null)
                 {
                     throw new ArgumentException($"Request does not represent a CloudEvent. It has neither a {HttpUtilities.SpecVersionHttpHeader} header, nor a suitable content type.", nameof(httpListenerRequest));
@@ -191,12 +191,18 @@ namespace CloudNative.CloudEvents.Http
                 var headers = httpListenerRequest.Headers;
                 foreach (var key in headers.AllKeys)
                 {
+                    // It would be highly unusual for either the key or the value to be null, but
+                    // the contract claims it's possible. Skip it if so.
+                    if (key is null || headers[key] is not string headerValue)
+                    {
+                        continue;
+                    }
                     string? attributeName = HttpUtilities.GetAttributeNameFromHeaderName(key);
                     if (attributeName is null || attributeName == CloudEventsSpecVersion.SpecVersionAttribute.Name)
                     {
                         continue;
                     }
-                    string attributeValue = HttpUtilities.DecodeHeaderValue(headers[key]);
+                    string attributeValue = HttpUtilities.DecodeHeaderValue(headerValue);
                     cloudEvent.SetAttributeFromString(attributeName, attributeValue);
                 }