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WIZ5100 : how many sockets does the HttpListener class need?


Hello !

I am running into a strange behavior of the HttpListener class.
It’s maybe just that I am not properly undertanding the way it works.
It’s like to treat a single http request, the class would be using 2 sockets ?

For an example,
In the following code, I am reserving one socket for the W5100 class;
I am reserving 2 sockets for "other use"
There should be one left, enough to serve a single simple test page.
However, it is throwing a “No free sockets” exception when trying to load the page.
If I comment the s2 socket out, this works fine
I first thought that the browser was opening 2 tcp connections simultaneously (trying /favicon.ico or ???) but after checking with WireShark, or manualy opening a “telnet 80”, the result is the same : exception.

// Let's enable the W5100 network chip with static IPs and ReserveSocket=true
WIZnet_W5100.Enable(SPI.SPI_module.SPI1, (Cpu.Pin)FEZ_Pin.Digital.Di10, (Cpu.Pin)FEZ_Pin.Digital.Di9, true);
NetworkInterface.EnableStaticIP(new byte[] { 192, 168, 0, 10 }, 
				new byte[] { 255, 255, 255, 0 }, 
				new byte[] { 192, 168, 0, 1 }, 
				new byte[] { 0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA });
// Here we should have 3 sockets left

// Let's reserve 2 sockets for other uses
Socket s1 = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
Socket s2 = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);

// Here we should have one socket left

// instead of the following code, we can reserve another "s3" socket
// like s1 & s2 and it will not throw exceptions       
HttpListener Listener = new HttpListener("http", 80);
HttpListenerContext ctx;
HttpListenerResponse Response;
string s= "<html><body>Hello, World !</body></html>";
byte[] b= Encoding.UTF8.GetBytes(s);

while (true) // Listen to http requests, and reply them with a simple test message
	ctx = Listener.GetContext(); 
        // this is throwing a "No free sockets" exception at 1st request ?!!
	Debug.Print("Serving a page...");
	Response = ctx.Response;
	Response.ContentLength64 = b.Length;
	Response.ContentType = "text/html";
	Response.OutputStream.Write(b, 0, b.Length);
	Debug.Print(" Done with the page.");

What am I doing wrong or misanderstanding ?
Thank you in advance for any help !



wiznet chipset accepts only 4 simultaneous sockets to be opened
One is reserved according to the settings

WIZnet_W5100.Enable(SPI.SPI_module.SPI1, (Cpu.Pin)FEZ_Pin.Digital.Di10, (Cpu.Pin)FEZ_Pin.Digital.Di9, true);

You said you are reserving other 2.

and The HttpListener requires at least two sockets, one that is always open that polls for incoming connection. then when it receives the a request it opens another socket that will handle the incoming request session.

So as total, you are using the four sockets and you are requesting more.

In your application you should be wise using the 4 sockets you got. Don’t keep open sockets if you are not using them.


Thank you, that makes sense now ! :wink: