Fix reverse proxy no longer relaying Content-* headers

Modules/ReverseProxy/Http/HttpProxy.cs

@@ -91,6 +91,14 @@ private HttpRequestMessage ConfigureRequest(IRequest request)
 
         var req = new HttpRequestMessage(new HttpMethod(request.Header.Method.ToString()), GetRequestUri(request));
 
+        // important: set the body before the header so we can override "Content-" related headers here
+        var content = request.GetBody();
+
+        if (content is not null && CanSendBody(request))
+        {
+            req.Content = new RequestBody(content);
+        }
+
         for (var i = 0; i < headers.Count; i++)
         {
             var header = headers.GetStringEntry(i);
@@ -119,13 +127,6 @@ private HttpRequestMessage ConfigureRequest(IRequest request)
 
         req.Headers.Add("Forwarded", string.Join(", ", forwardings.Select(GetForwarding)));
 
-        var content = request.GetBody();
-
-        if (content is not null && CanSendBody(request))
-        {
-            req.Content = new RequestBody(content);
-        }
-
         return req;
     }
 

Testing/Acceptance/Modules/ReverseProxy/ReverseProxyTests.cs

@@ -63,6 +63,26 @@ public async Task TestHead(ServerEngine engine)
         await headed.AssertStatusAsync(HttpStatusCode.OK);
     }
 
+    [TestMethod]
+    [MultiEngineTest]
+    public async Task TestContentTypeIsRelayed(ServerEngine engine)
+    {
+        await using var setup = await TestSetup.CreateAsync(engine, r =>
+        {
+            var contentType = r.Header.Headers.GetEntry("Content-Type");
+            return r.Respond().Content(contentType ?? "(none)").Build();
+        });
+
+        var runner = setup.Runner;
+
+        var request = runner.GetRequest(method: new HttpMethod("SEARCH"));
+        request.Content = new StringContent("<x/>", System.Text.Encoding.UTF8, "application/xml");
+
+        using var response = await runner.GetResponseAsync(request);
+
+        Assert.AreEqual("application/xml; charset=utf-8", await response.GetContentAsync());
+    }
+
     [TestMethod]
     [MultiEngineTest]
     public async Task TestForwardingChainIsRelayed(ServerEngine engine)