Added very basic versions of WriteJsonAsync extension methods on Http…

…Request and HttpResponse.

samples/HelloWorld/Program.cs

@@ -10,7 +10,7 @@ static async Task Main(string[] args)
 
         app.MapGet("/", async context =>
         {
-            await context.Response.WriteAsync("Hello World");
+            await context.Response.WriteJsonAsync(new { message = "Hello World" });
         });
 
         await app.RunAsync();

src/FeatherHttp/JsonHttpContextExtensions.cs

@@ -0,0 +1,46 @@
+using System.Text.Json;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace Microsoft.AspNetCore.Http
+{
+    /// <summary>
+    /// Various extension methods to read and write JSON to and from the <see cref="HttpRequest"/> and <see cref="HttpResponse"/>.
+    /// </summary>
+    public static class JsonHttpContextExtensions
+    {
+        /// <summary>
+        /// Asynchronously reads the UTF-8 encoded text representing a single JSON value
+        /// into an instance of a type specified by a generic type parameter. The <see cref="HttpRequest"/> body
+        /// will be read to completion.
+        /// </summary>
+        /// <typeparam name="TValue">The target type of the JSON value.</typeparam>
+        /// <param name="request">The <see cref="HttpRequest"/> to read the JSON from.</param>
+        /// <param name="options">Options to control the behavior during reading.</param>
+        /// <param name="cancellationToken">A token that may be used to cancel the read operation.</param>
+        /// <returns>A TValue representation of the JSON value.</returns>
+        public static ValueTask<TValue> ReadJsonAsync<TValue>(this HttpRequest request, JsonSerializerOptions options = null, CancellationToken cancellationToken = default)
+        {
+            // TODO: Handle non-utf8 encoding
+            return JsonSerializer.DeserializeAsync<TValue>(request.Body, options, cancellationToken);
+        }
+
+        /// <summary>
+        /// Asynchronously converts a value of a type specified by a generic type parameter
+        /// to UTF-8 encoded JSON text and writes it to the <see cref="HttpResponse"/> body with an application/json content-type.
+        /// </summary>
+        /// <typeparam name="TValue">The type of the value to serialize.</typeparam>
+        /// <param name="response">The <see cref="HttpResponse"/> to write the JSON to.</param>
+        /// <param name="value">The value to convert</param>
+        /// <param name="options">Options to control behavior during writing.</param>
+        /// <param name="cancellationToken">A token that may be used to cancel the write operation.</param>
+        /// <returns>A task that represents the asynchronous write operation.</returns>
+        public static Task WriteJsonAsync<TValue>(this HttpResponse response, TValue value, JsonSerializerOptions options = null, CancellationToken cancellationToken = default)
+        {
+            // Set the content type to application/json if it's not already set
+            response.ContentType ??= "application/json";
+
+            return JsonSerializer.SerializeAsync(response.Body, value, options, cancellationToken);
+        }
+    }
+}