Fix Forwarded header for IPv4 with dual stack sockets (#2509)

* prefer IPv4 addresses

* Handling remote and local IPs

* nit: formatting

* Code style

---------

Co-authored-by: Ryan Karg <rkarg@blizzard.com>
Co-authored-by: Miha Zupan <mihazupan.zupan1@gmail.com>

src/ReverseProxy/Transforms/RequestHeaderForwardedTransform.cs

@@ -141,6 +141,12 @@ private void AppendBy(HttpContext context, ref ValueStringBuilder builder)
     // https://tools.ietf.org/html/rfc7239#section-6
     private void AppendNode(IPAddress? ipAddress, int port, NodeFormat format, ref ValueStringBuilder builder)
     {
+        // Prefer IPv4 formatting
+        if (ipAddress is { IsIPv4MappedToIPv6: true })
+        {
+            ipAddress = ipAddress.MapToIPv4();
+        }
+
         // "It is important to note that an IPv6 address and any nodename with
         // node-port specified MUST be quoted, since ":" is not an allowed
         // character in "token"."

test/ReverseProxy.Tests/Transforms/RequestHeaderForwardedTransformTests.cs

@@ -95,6 +95,9 @@ await transform.ApplyAsync(new RequestTransformContext()
     [InlineData("", "127.0.0.1", 2, NodeFormat.Ip, ForwardedTransformActions.Set, "for=127.0.0.1")]
     [InlineData("", "127.0.0.1", 2, NodeFormat.IpAndPort, ForwardedTransformActions.Append, "for=\"127.0.0.1:2\"")]
     [InlineData("", "127.0.0.1", 2, NodeFormat.IpAndRandomPort, ForwardedTransformActions.Append, "for=\"127.0.0.1:_abcdefghi\"")]
+    [InlineData("", "::ffff:127.0.0.1", 2, NodeFormat.Ip, ForwardedTransformActions.Set, "for=127.0.0.1")]
+    [InlineData("", "::ffff:127.0.0.1", 2, NodeFormat.IpAndPort, ForwardedTransformActions.Append, "for=\"127.0.0.1:2\"")]
+    [InlineData("", "::ffff:127.0.0.1", 2, NodeFormat.IpAndRandomPort, ForwardedTransformActions.Append, "for=\"127.0.0.1:_abcdefghi\"")]
     [InlineData("", "::1", 2, NodeFormat.Random, ForwardedTransformActions.Set, "for=_abcdefghi")]
     [InlineData("", "::1", 2, NodeFormat.RandomAndPort, ForwardedTransformActions.Append, "for=\"_abcdefghi:2\"")]
     [InlineData("", "::1", 2, NodeFormat.RandomAndRandomPort, ForwardedTransformActions.Append, "for=\"_abcdefghi:_jklmnopqr\"")]
@@ -139,6 +142,9 @@ await transform.ApplyAsync(new RequestTransformContext()
     [InlineData("", "127.0.0.1", 2, NodeFormat.Ip, ForwardedTransformActions.Set, "by=127.0.0.1")]
     [InlineData("", "127.0.0.1", 2, NodeFormat.IpAndPort, ForwardedTransformActions.Append, "by=\"127.0.0.1:2\"")]
     [InlineData("", "127.0.0.1", 2, NodeFormat.IpAndRandomPort, ForwardedTransformActions.Append, "by=\"127.0.0.1:_abcdefghi\"")]
+    [InlineData("", "::ffff:127.0.0.1", 2, NodeFormat.Ip, ForwardedTransformActions.Set, "by=127.0.0.1")]
+    [InlineData("", "::ffff:127.0.0.1", 2, NodeFormat.IpAndPort, ForwardedTransformActions.Append, "by=\"127.0.0.1:2\"")]
+    [InlineData("", "::ffff:127.0.0.1", 2, NodeFormat.IpAndRandomPort, ForwardedTransformActions.Append, "by=\"127.0.0.1:_abcdefghi\"")]
     [InlineData("", "::1", 2, NodeFormat.Random, ForwardedTransformActions.Set, "by=_abcdefghi")]
     [InlineData("", "::1", 2, NodeFormat.RandomAndPort, ForwardedTransformActions.Append, "by=\"_abcdefghi:2\"")]
     [InlineData("", "::1", 2, NodeFormat.RandomAndRandomPort, ForwardedTransformActions.Append, "by=\"_abcdefghi:_jklmnopqr\"")]