Network Programming in .NET

Assuming you have an Azure account, if you open up a Computer vision service under Cognitive Services, and grab an API key, you can use Azure to recognise the content of images. – Great for tagging images in blogs, or making sure nobody uploads a nude pic as their profile image on your website – For which you should check out AvatarApi.com for this!

So, lets see some code – I’m using C#, and Newtonsoft to parse the Json;

const string strUrl = “https://westeurope.api.cognitive.microsoft.com/vision/v1.0/analyze?visualFeatures=Tags”;
var wc = new WebClient();
wc.Headers[“Ocp-Apim-Subscription-Key”] = “xxxxxxx”;
var jPost = new { url = Url };
var strPost = JsonConvert.SerializeObject(jPost, Formatting.Indented);
var strJson = wc.UploadString(strUrl, “POST”, strPost);
var jResult = JObject.Parse(strJson);

Depending on your image of course, this will return JSON similar to the following;

{
  "tags": [
    {
      "name": "car",
      "confidence": 0.99999725818634
    },
    {
      "name": "outdoor",
      "confidence": 0.99585741758347
    },
    {
      "name": "transport",
      "confidence": 0.82641708850861
    },
    {
      "name": "blue",
      "confidence": 0.51219713687897
    },
    {
      "name": "roof",
      "confidence": 0.091790720820427
    },
    {
      "name": "automotive",
      "confidence": 0.01434036432286
    },
    {
      "name": "summer",
      "confidence": 0.0078773201327271
    }
  ],
  "requestId": "e0010f8b-189f-4481-ad02-5b71b3ac2b2b",
  "metadata": {
    "width": 1600,
    "height": 1200,
    "format": "Jpeg"
  }
}

TL;DR;

You can grab the code for this demo here https://github.com/infiniteloopltd/udp

Internet traffic can be thought of as layers, normally the stack for viewing a website is IP at the bottom, TCP/IP in the middle, and HTTP at the top.

IP just gets data from A to B , TCP/IP makes sure that data doesn’t get jumbled or dropped in between, and HTTP does things specific to serving websites, like HTTP redirects, HTTP error messages etc.

But, instead of TCP/IP you can also use UDP/IP or simply “UDP”, which is TCP’s messy little brother. It still has the concept of ports like TCP has, but offers no guarantee of jumbled or dropped data.

For this reason, UDP is only used in situations where low latency is much more important than data integrity, like audio / video streaming or gaming. It’s terrible for file transfer.

One other key use of UDP is it’s lower bandwidth usage, which makes it useful for IOT applications over expensive mobile data networks.

If you want to read more about Network programming, check out my book- which you can Buy at Amazon US or Buy at Amazon UK

Javascript promises are a key feature of modern asyncronous javascript, but, if you’re developing a mass-market website, cross-browser support may trump the syntactical sugar, especially if you’re facing down business-types, rather than other developers.

Specifically, IE11 does not support Javascript promises, and if you are looking to support a wide range of browsers, then there is a polyfill available from Taylor Hakes, that can get round that error message, that simply says “‘Promise’ is undefined” in IE11

So, working with an example from SMTPJS v3 – which now uses promises, and arrow functions, you need include the following script tags;

https://cdn.jsdelivr.net/npm/promise-polyfill@8/dist/polyfill.min.js
https://smtpjs.com/v3/smtp.js

Then adjust the code to use an inline function instead of an arrow function:

Email.send({
Host : “email-smtp.eu-west-1.amazonaws.com”,
Username : “******”,
Password : “*****”,
To : ‘them@gmail.com’,
From : “you@website.com”,
Subject : “This is the subject”,
Body : “My useragent is ” + navigator.userAgent
}).then(
function(message) { alert(message) } // FOR IE
);

In case you’ve missed it, SMTPJS.com has just released the V3 Library, this offers a cleaner object model, promises, and new features, such as multiple attachments, Reply-to, and sender name

Here’s an example on how to send multiple attachments:

Email.send({
SecureToken : “XXXXX-XXXX-XXXX-XXXX-XXXXXXX”,
To : “recipient@website.com”,
From : “sender@website.com”,
FromName: “Joe Sender”,
ReplyAddress: “noreply@website.com”,
Subject : “This is the subject”,
Body : “This is the body”,
Attachments : [
{
name : “padlock.png”,
path : “https://www.smtpjs.com/img/ipad.png”
},
{
name : “spam.png”,
path : “https://www.smtpjs.com/img/iphone.png”
}
]
}).then(
message => alert(message)
);

Obviously, you need to change the secureToken property above, or pass in naked SMTP credentials.

Here’s another example, imagine you want to offer an upload form, so people can upload a file to be sent to you – without putting the file on your server.

First, here’s the required line of HTML:

<input type=”file” id=”fileupload” onchange=”uploadFileToServer()” />

Then here’s the uploadFileToServer() method;

function uploadFileToServer() {
var file = event.srcElement.files[0];
var reader = new FileReader();
reader.readAsBinaryString(file);
reader.onload = function () {
var datauri = “data:” + file.type + “;base64,” + btoa(reader.result);
Email.send({
SecureToken : “XXXX-XXXX-XXXX-XXXX-XXXX”,
To : “recipient@website.com”,
From : “sender@isp.com”,
Subject : “The subject”,
Body : “See file attached”,
Attachments : [
{
name : file.name,
data : datauri
}
]
}).then(
message => alert(message)
);
};
reader.onerror = function() {
console.log(‘there are some problems’);
};
}

Need to find vehicle details of a motorcycle registered in Spain via an API?, this new addition to our suite lets you do this; you should use an alternative API endpoint, as follows;

http://www.matriculaapi.com/api/bespokeapi.asmx?op=CheckMotorBikeSpain

Which returns data in the following format:

{

 “Description”: “SUZUKI DL 650 V-STROM”,

 “CarMake”: {

   “CurrentTextValue”: “SUZUKI”

 },

 “CarModel”: {

   “CurrentTextValue”: “DL 650”

 },

 “MakeDescription”: {

   “CurrentTextValue”: “SUZUKI”

 },

 “ModelDescription”: {

   “CurrentTextValue”: “DL 650”

 },

 “EngineSize”: “645”,

 “VehicleIdentificationNumber”: “”,

 “RegistrationYear”: “2003”,

 “RegistrationDate”: “01/11/2003”,

 “Variation”: “V-STROM”,

 “Seats”: 1,

 “VariantType”: “”,

 “VehicleType”: “MOTOCICLETA”,

 “Fuel”: “GASOLINA”,

 “IndicativePrice”: “7909.79”,

 “Doors”: 0,

 “AllTerain”: 0,

 “KType”: 0,

 “ImageUrl”: “http://matriculaapi.com/image.aspx/@U1VaVUtJIERMIDY1MHxtb3RvcmN5Y2xl&#8221;,

 “Transmission”: “MANUAL”,

 “DynamicPower”: “68”,

 “Stolen”: null

}

Making your website accessible by both IPv4 (What everyone is familiar with) and IPv6, those wierd long IP addresses with hex numbers in them, is as simple as

(1) finding your IPv6 address, which you can do by doing a IPConfig /all on your desktop

And getting the IPv6 address from the “6TO4 adapter”

Tunnel adapter 6TO4 Adapter:

Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : Microsoft 6to4 Adapter
Physical Address. . . . . . . . . : 00-00-00-00-00-00-00-E0
DHCP Enabled. . . . . . . . . . . : No
Autoconfiguration Enabled . . . . : Yes
IPv6 Address. . . . . . . . . . . : 2002:5f9a:f46a::5f9a:f46a(Preferred)
Default Gateway . . . . . . . . . : 2002:c058:6301::1
DHCPv6 IAID . . . . . . . . . . . : 469762048
DHCPv6 Client DUID. . . . . . . . : 00-01-00-01-21-42-14-1B-00-25-90-1E-04-94

(2) Then adding a DNS entry for an AAAA record pointing to the IPv6 address that you found above.

I doubt it will make much difference today or tomorrow, since IPv4 will take a long long time to die out completely, but slowly, IPv6 will become the norm, and it’s best to be ahead of the curve, rather than being behind it.

Yes, it’s possible to host ASP.NET on linux, and there are plenty of great tutorials out there, and this is just a quick post with a few of my tips thrown in…

I followed the tutorial at https://www.microsoft.com/net/learn/web/aspnet-hello-world-tutorial, using a EC2 instance from Amazon.

However, at the point where it says, “point a browser at https://localhost:5001&#8221; I had to get a bit inventive,

So, I opened up port 5001 in security settings, and I created a release build

dotnet build –configuration Release

Navigated to the “publish” folder and ran this command to have the app listen on all hosts, not just localhost.

dotnet myWebAppp.dll –urls https://0.0.0.0:5001

Then from my mac, I could navigate to https://%5BIP%5D:5001, and dismissed the bad cert warning.

This example uses the AvatarAPI.com service, but a new JSON based API which is a bit more modern than the XML / SOAP based API.

<html>
<body>
<?php
$curl = curl_init();
curl_setopt_array($curl, array(
CURLOPT_RETURNTRANSFER => 1,
CURLOPT_URL => ‘https://www.avatarapi.com/json.aspx/helen.smith@gmail.com‘,
CURLOPT_USERPWD => “arnoldtest:test123″
));
$resp = curl_exec($curl);
curl_close($curl);
$avatar = json_decode($resp);
?>

<img src=”<?php echo $avatar->Image ?>”><br>
<?php echo $avatar->Name ?>

</body>
</html>

The username and password should be substituted with your own username/password which is available at the website.

To skip to the code example, here it is on GitHub;

https://github.com/infiniteloopltd/HelloWorldGTK/

GTK# is an option that is available under Visual Studio for Mac under Other > .NET > GTK# 2.0, and it allows you to create windows-forms like GUIs that work cross platform, using the .NET Core framework. Above is a simple application that shows the user’s current IP address.

using System;
using System.Net;
using Gtk;

public partial class MainWindow : Gtk.Window
{
    public MainWindow() : base(Gtk.WindowType.Toplevel)
    {
        Build();

        WebClient wc = new WebClient();
        var strIP = wc.DownloadString(“http://icanhazip.com&#8221;);
        label2.Text = strIP;

    }

    protected void OnDeleteEvent(object sender, DeleteEventArgs a)
    {
        Application.Quit();
        a.RetVal = true;
    }
}

Socks5 is a proxy server that operates on the TCP level, rather than the HTTP/S level, which makes it possible to proxy IP trafic such as email, FTP, voip, etc. Normally, you use a forwarding proxy like Squid, privoxy, or Polipo to bridge the HTTP / Socks5 layer, but you can also interface at socket level from C#

This example is modified from Zahmed on CodeProject, https://www.codeproject.com/articles/5954/c-class-for-connecting-via-a-socks-proxy-server – so credit due there.

So, here’s the modified helper class;

using System;
using System.Net;
using System.Net.Sockets;
using System.Text;

/*
* zahmed
* Date 23 Jan 2004
* Socks 5 RFC is available at http://www.faqs.org/rfcs/rfc1928.html.
* https://www.codeproject.com/articles/5954/c-class-for-connecting-via-a-socks-proxy-server
*/
namespace LMKR
{
public class ConnectionException:ApplicationException
{
public ConnectionException(string message)
:base(message) {}
}

/// <summary>
/// Provides sock5 functionality to clients (Connect only).
/// </summary>
public class SocksProxy
{

private SocksProxy(){}

#region ErrorMessages
private static string[] errorMsgs= {
“Operation completed successfully.”,
“General SOCKS server failure.”,
“Connection not allowed by ruleset.”,
“Network unreachable.”,
“Host unreachable.”,
“Connection refused.”,
“TTL expired.”,
“Command not supported.”,
“Address type not supported.”,
“Unknown error.”
};
#endregion
public static Socket ConnectToSocks5Proxy(string proxyAdress, ushort proxyPort, string destAddress, ushort destPort)
{
IPAddress destIP = null;
IPAddress proxyIP = null;
byte[] request = new byte[257];
byte[] response = new byte[257];
ushort nIndex;

try
{
proxyIP = IPAddress.Parse(proxyAdress);
}
catch(FormatException)
{ // get the IP address
proxyIP = Dns.GetHostByAddress(proxyAdress).AddressList[0];
}

// Parse destAddress (assume it in string dotted format “212.116.65.112” )
try
{
destIP = IPAddress.Parse(destAddress);
}
catch(FormatException)
{
// wrong assumption its in domain name format “www.microsoft.com”
}

IPEndPoint proxyEndPoint = new IPEndPoint(proxyIP,proxyPort);

// open a TCP connection to SOCKS server…
Socket s = new Socket(AddressFamily.InterNetwork,SocketType.Stream,ProtocolType.Tcp);
s.Connect(proxyEndPoint);

nIndex = 0;
request[nIndex++]=0x05; // Version 5.
request[nIndex++]=0x02; // 2 Authentication methods are in packet…
request[nIndex++]=0x00; // NO AUTHENTICATION REQUIRED
request[nIndex++]=0x00; // NO AUTHENTICATION REQUIRED
//request[nIndex++]=0x02; // USERNAME/PASSWORD
// Send the authentication negotiation request…
s.Send(request,nIndex,SocketFlags.None);

// Receive 2 byte response…
int nGot = s.Receive(response,2,SocketFlags.None);
if (nGot!=2)
throw new ConnectionException(“Bad response received from proxy server.”);

if (response[1]==0xFF)
{ // No authentication method was accepted close the socket.
s.Close();
throw new ConnectionException(“None of the authentication method was accepted by proxy server.”);
}

byte[] rawBytes;
// This version only supports connect command.
// UDP and Bind are not supported.

// Send connect request now…
nIndex = 0;
request[nIndex++]=0x05; // version 5.
request[nIndex++]=0x01; // command = connect.
request[nIndex++]=0x00; // Reserve = must be 0x00

if (destIP != null)
{// Destination adress in an IP.
switch(destIP.AddressFamily)
{
case AddressFamily.InterNetwork:
// Address is IPV4 format
request[nIndex++]=0x01;
rawBytes = destIP.GetAddressBytes();
rawBytes.CopyTo(request,nIndex);
nIndex+=(ushort)rawBytes.Length;
break;
case AddressFamily.InterNetworkV6:
// Address is IPV6 format
request[nIndex++]=0x04;
rawBytes = destIP.GetAddressBytes();
rawBytes.CopyTo(request,nIndex);
nIndex+=(ushort)rawBytes.Length;
break;
}
}
else
{// Dest. address is domain name.
request[nIndex++]=0x03; // Address is full-qualified domain name.
request[nIndex++]=Convert.ToByte(destAddress.Length); // length of address.
rawBytes = Encoding.Default.GetBytes(destAddress);
rawBytes.CopyTo(request,nIndex);
nIndex+=(ushort)rawBytes.Length;
}

// using big-edian byte order
byte[] portBytes = BitConverter.GetBytes(destPort);
for (int i=portBytes.Length-1;i>=0;i–)
request[nIndex++]=portBytes[i];

// send connect request.
s.Send(request,nIndex,SocketFlags.None);
s.Receive(response); // Get variable length response…
if (response[1]!=0x00)
throw new ConnectionException(errorMsgs[response[1]]);
// Success Connected…
return s;
}
}
}

Which is the same as on codeproject, without the username/password requirement, and here’s how it’s called;

byte[] bytesReceived = new byte[1024];
Socket client;
client = LMKR.SocksProxy.ConnectToSocks5Proxy(“127.0.0.1”, 9050, “www.icanhazip.com”, 80);
string strGet = “GET /\r\n\r\n”;
client.Send(Encoding.ASCII.GetBytes(strGet));
var bytes = client.Receive(bytesReceived, bytesReceived.Length, 0);
var page = Encoding.ASCII.GetString(bytesReceived, 0, bytes);
Console.WriteLine(page);
client.Close();