C# native host with Chrome Native Messaging

Assuming the manifest is set up properly, here is a complete example for talking to a C# host using the "port" method:

using System;using System.IO;using Newtonsoft.Json;using Newtonsoft.Json.Linq;namespace NativeMessagingHost{   class Program   {      public static void Main(string[] args)      {         JObject data;         while ((data = Read()) != null)         {            var processed = ProcessMessage(data);            Write(processed);            if (processed == "exit")            {               return;            }         }      }      public static string ProcessMessage(JObject data)      {         var message = data["text"].Value<string>();         switch (message)         {            case "test":               return "testing!";            case "exit":               return "exit";            default:               return "echo: " + message;         }      }      public static JObject Read()      {         var stdin = Console.OpenStandardInput();         var length = 0;         var lengthBytes = new byte[4];         stdin.Read(lengthBytes, 0, 4);         length = BitConverter.ToInt32(lengthBytes, 0);         var buffer = new char[length];         using (var reader = new StreamReader(stdin))         {            while (reader.Peek() >= 0)            {               reader.Read(buffer, 0, buffer.Length);            }         }         return (JObject)JsonConvert.DeserializeObject<JObject>(new string(buffer));      }      public static void Write(JToken data)      {         var json = new JObject();         json["data"] = data;         var bytes = System.Text.Encoding.UTF8.GetBytes(json.ToString(Formatting.None));         var stdout = Console.OpenStandardOutput();         stdout.WriteByte((byte)((bytes.Length >> 0) & 0xFF));         stdout.WriteByte((byte)((bytes.Length >> 8) & 0xFF));         stdout.WriteByte((byte)((bytes.Length >> 16) & 0xFF));         stdout.WriteByte((byte)((bytes.Length >> 24) & 0xFF));         stdout.Write(bytes, 0, bytes.Length);         stdout.Flush();      }   }}

If you don't need to actively communicate with the host, using runtime.sendNativeMessage will work fine. To prevent the host from hanging, simply remove the while loop and do Read/Write once.

To test this, I used the example project provided by Google here: https://chromium.googlesource.com/chromium/src/+/master/chrome/common/extensions/docs/examples/api/nativeMessaging

Note: I'm using Json.NET to simplify the json serialization/de-serialization process.

I hope this is helpful to somebody!