Set content-type properly and don't send body until after we send status code

Author: Christopher Anderson

src/WebJobs.Script/Binding/Http/RawScriptResult.cs

@@ -12,6 +12,7 @@
 using Microsoft.AspNetCore.Mvc.Formatters;
 using Microsoft.AspNetCore.WebUtilities;
 using Microsoft.Azure.WebJobs.Script.WebHost.Formatters;
+using Microsoft.Net.Http.Headers;
 using Newtonsoft.Json;
 
 namespace Microsoft.Azure.WebJobs.Script.Binding
@@ -45,16 +46,27 @@ public async Task ExecuteResultAsync(ActionContext context)
             {
                 foreach (var header in Headers)
                 {
-                    response.Headers.Add(header.Key, header.Value?.ToString() ?? string.Empty);
+                    if (header.Key.Equals("content-type", StringComparison.OrdinalIgnoreCase))
+                    {
+                        if (header.Value == null)
+                        {
+                            throw new InvalidOperationException("content-type header cannot be null");
+                        }
+                        response.ContentType = header.Value.ToString();
+                    }
+                    else
+                    {
+                        response.Headers.Add(header.Key, header.Value?.ToString() ?? string.Empty);
+                    }
                 }
             }
 
-            await WriteResponseBodyAsync(response, Content);
-
             if (StatusCode != null)
             {
                 response.StatusCode = StatusCode.Value;
             }
+
+            await WriteResponseBodyAsync(response, Content);
         }
 
         private async Task WriteResponseBodyAsync(HttpResponse response, object content)
@@ -83,11 +95,15 @@ private async Task WriteResponseBodyAsync(HttpResponse response, object content)
 
         private static OutputFormatterWriteContext CreateFormatterContext(HttpResponse response, object content)
         {
-            return new OutputFormatterWriteContext(
+            var context = new OutputFormatterWriteContext(
                 response.HttpContext,
                 (s, e) => new HttpResponseStreamWriter(s, e),
                 content?.GetType(),
                 content);
+
+            context.ContentType = response.ContentType;
+
+            return context;
         }
 
         private static IOutputFormatter SelectedFormatter(OutputFormatterWriteContext formatterContext)

test/WebJobs.Script.Tests.Integration/NodeContentTests.cs

@@ -22,6 +22,7 @@
 using System.Web.Http.Results;
 using Moq;
 using Microsoft.Azure.WebJobs.Script.Binding;
+using Microsoft.Azure.WebJobs.Host;
 
 namespace Microsoft.Azure.WebJobs.Script.Tests
 {
@@ -58,6 +59,15 @@ public async Task StringTextPlainRaw()
             Assert.Equal(str, content);
         }
 
+        [Fact]
+        public async Task BadContentType_ThrowsExpectedException()
+        {
+            await Assert.ThrowsAsync<FunctionInvocationException>(async () =>
+            {
+                var content = await Response("asdf", null);
+            });
+        }
+
         [Fact]
         public async Task ByteArrayTextPlainResponse()
         {