Expose Headers on NatsSvcMsg (#371)

* Expose headers on NatsSvcMsg and aa test for passing headers in svc requests

* Revert accidental format change

---------

Co-authored-by: Niklas Petersen <niklasfp@users.noreply.github.com>

Author: niklasfp

src/NATS.Client.Services/NatsSvcMsg.cs

@@ -47,6 +47,11 @@ public NatsSvcMsg(NatsMsg<T> msg, NatsSvcEndpointBase? endPoint, Exception? exce
     /// </summary>
     public string? ReplyTo => _msg.ReplyTo;
 
+    /// <summary>
+    /// Pass additional information using name-value pairs.
+    /// </summary>
+    public NatsHeaders? Headers => _msg.Headers;
+
     /// <summary>
     /// Send a reply with an empty message body.
     /// </summary>

tests/NATS.Client.Services.Tests/ServicesTests.cs

@@ -264,4 +264,62 @@ public async Task Add_multiple_service_listeners_ping_info_and_stats()
         Assert.Equal("1.0.0", stats.First(s => s.Name == "s1").Version);
         Assert.Equal("2.0.0", stats.First(s => s.Name == "s2").Version);
     }
+
+    [Fact]
+    public async Task Pass_headers_to_request_and_in_response()
+    {
+        var cts = new CancellationTokenSource(TimeSpan.FromSeconds(10));
+        var cancellationToken = cts.Token;
+
+        await using var server = NatsServer.Start();
+        await using var nats = server.CreateClientConnection();
+        var svc = new NatsSvcContext(nats);
+
+        await using var s1 = await svc.AddServiceAsync("s1", "1.0.0", cancellationToken: cancellationToken);
+
+        await s1.AddEndpointAsync<int>(
+            name: "e1",
+            handler: async m =>
+            {
+                if (m.Headers != null)
+                {
+                    var headers = m.Headers;
+                    if (headers.TryGetValue("foo", out var foo))
+                    {
+                        if (foo != "bar")
+                        {
+                            await m.ReplyErrorAsync(m.Data, "Expected 'foo' = 'bar' header", cancellationToken: cancellationToken);
+                            return;
+                        }
+
+                        await m.ReplyAsync(m.Data, headers: new NatsHeaders { { "bar", "baz" } }, cancellationToken: cancellationToken);
+                        return;
+                    }
+                }
+
+                await m.ReplyErrorAsync(m.Data, "Missing 'foo' header", cancellationToken: cancellationToken);
+            },
+            cancellationToken: cancellationToken);
+
+        // With headers
+        var headers = new NatsHeaders { { "foo", "bar" } };
+        var response = await nats.RequestAsync<int, int>("e1", 999, headers, cancellationToken: cancellationToken);
+        Assert.Equal(999, response.Data);
+        Assert.Equal("baz", response.Headers?["bar"]);
+
+        // With headers, but not the expected one.
+        headers = new NatsHeaders
+        {
+            { "not-the-expected", "4711" },
+            { "also-not-the-expected", "4242" },
+        };
+        response = await nats.RequestAsync<int, int>("e1", 999, headers, cancellationToken: cancellationToken);
+        Assert.Equal("999", response.Headers?["Nats-Service-Error-Code"]);
+        Assert.Equal("Missing 'foo' header", response.Headers?["Nats-Service-Error"]);
+
+        // No headers.
+        response = await nats.RequestAsync<int, int>("e1", 999, cancellationToken: cancellationToken);
+        Assert.Equal("999", response.Headers?["Nats-Service-Error-Code"]);
+        Assert.Equal("Missing 'foo' header", response.Headers?["Nats-Service-Error"]);
+    }
 }