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Editorial Team
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Asked: 2026-05-27T00:50:14+00:00

I’m playing around with a simple webserver written in F#. As I have noticed,

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I’m playing around with a simple webserver written in F#. As I have noticed, if I hit refresh in Firefox, after some tries, I get an error page saying:

The connection was reset

The connection to the server was reset while the page was loading.

Why does this occur seemingly randomly (increasing the backlog to 1000 didn’t help)? Also, why is Firefox the only browser which displays the response of my webserver? I guess my response is not valid, is that right?

The code of the webserver:

module Program

open System
open System.Net.Sockets
open System.IO

type TcpListener with
   member this.AsyncAcceptSocket =
    Async.FromBeginEnd(this.BeginAcceptSocket, this.EndAcceptSocket)

type Main =
    static member Init () =
        let tcpListener = new TcpListener(80)        
        tcpListener.Start()

        let rec loop =
            async{                                
                let! socket = tcpListener.AsyncAcceptSocket
                Async.Start(loop)
                let stream = new NetworkStream(socket)
                let streamWriter = new StreamWriter(stream)                
                
                streamWriter.WriteLine("HTTP/1.0 200 OK");
                streamWriter.WriteLine("Date: Fri, 15 Nov 2011 23:59:59 GMT");
                streamWriter.WriteLine("Content-Type: text/html");
                streamWriter.WriteLine("Content-Length: 13540");
                streamWriter.WriteLine("")
                streamWriter.WriteLine("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\" \"http://www.w3.org/TR/html4/loose.dtd\">");
                streamWriter.WriteLine("<html>");
                streamWriter.WriteLine("<body>");
                streamWriter.WriteLine("<h1>This is the title</h1>");
                streamWriter.WriteLine("</body>");
                streamWriter.Write("</html>");                
                streamWriter.Flush()                        
                stream.Close()
                socket.Close()
            }

        Async.Start(loop)

        Console.ReadLine()

Main.Init()

EDIT

It seems the problem isn’t related to the way I invoked loop in the previous solution. I have reduced the program to this (and my problems still persist):

module Program

open System
open System.Net.Sockets
open System.IO

let tcpListener = new TcpListener(80)        
tcpListener.Start()

while true do                            
    let socket = tcpListener.AcceptSocket()
    let stream = new NetworkStream(socket)
    let streamWriter = new StreamWriter(stream)                
                
    streamWriter.WriteLine("response");             
    streamWriter.Flush()                        
    stream.Close()
    socket.Close()

Console.ReadLine()
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1 Answer

  1. Editorial Team

    Here’s a working version. I’d use TcpClient instead of socket so you don’t have to manage its underlining stream.

    module Program

open System
open System.Net
open System.Net.Sockets
open System.IO

type TcpListener with
   member this.AsyncAcceptTcpClient() =
    Async.FromBeginEnd(this.BeginAcceptTcpClient, this.EndAcceptTcpClient)

type Main =
    static member Init() =
        let tcpListener = new TcpListener(IPAddress.Loopback, 80)
        tcpListener.Start()

        let writeContent() =
            let stream = new MemoryStream()
            let streamWriter = new StreamWriter(stream)
            streamWriter.WriteLine("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\" \"http://www.w3.org/TR/html4/loose.dtd\">")
            streamWriter.WriteLine("<html>")
            streamWriter.WriteLine("<body>")
            streamWriter.WriteLine("<h1>This is the title</h1>")
            streamWriter.WriteLine("</body>")
            streamWriter.Write("</html>")
            streamWriter.Flush()
            stream

        let rec loop() =
            async {
                use! tcp = tcpListener.AsyncAcceptTcpClient()
                let stream = tcp.GetStream()
                use streamWriter = new StreamWriter(stream)
                use content = writeContent()

                streamWriter.WriteLine("HTTP/1.0 200 OK")
                streamWriter.WriteLine("Date: Fri, 15 Nov 2011 23:59:59 GMT")
                streamWriter.WriteLine("Content-Type: text/html")
                streamWriter.WriteLine("Content-Length: {0}", content.Length)
                streamWriter.WriteLine("")
                streamWriter.Flush()

                content.WriteTo stream
                stream.Flush()
                return! loop()
            }

        Async.Start(loop())

        Console.ReadLine() |> ignore

Main.Init()
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