F# Trying to write HTTP response to TCP stream - http

Question

I'm trying to make a simple HTTP server in F#. But unfortunately I'm stuck at the response stage, I'm trying to create a simple 404 response but my browser won't get it, it will simply load and load the page forever not going anywhere. I can't figure out where my code could be wrong.
let responseString = "HTTP/1.1 404 NOT FOUND";
let buffer = System.Text.Encoding.UTF8.GetBytes(responseString);
let processRequest (client: TcpClient) =
async { do printfn "Incoming HTTP request..."
use stream = client.GetStream()
use sr = new StreamReader(stream)
let! content = sr.ReadToEndAsync() |> Async.AwaitTask
do
printfn "Stream contains:\n%s" content
stream.Write(buffer, 0, buffer.Length)
stream.Flush() }
let ip = IPAddress.Parse("127.0.0.1")
let listener = TcpListener(ip, 8080)
let startServer =
async { do listener.Start()
do printfn "Starting server..."
while true do
let! context = listener.AcceptTcpClientAsync() |> Async.AwaitTask
do! processRequest context }
Async.Start startServer

Answer 1

The problem is, the TCP stream does not know when the client has sent all its data (unless you e.g. close the browser), so the StreamReader is blocked forever.
If you want to implement HTTP by yourself, you'd need (for starters) to read line by line and check whether the client is allowed to send any more data.

Answer 2

As #CaringDev points out, ReadToEnd doesn't terminate. That said for a simple HTTP server you'd only need to read the first line of the request. Here's an updated version of your code that reads the first line only and responds with a 200 OK:
open System.Net
let processRequest (client: Sockets.TcpClient) = async {
printfn "Incoming HTTP request..."
use stream = client.GetStream()
use sr = new System.IO.StreamReader(stream)
let line = sr.ReadLine()
printfn "Request: %s" line
let sw = new System.IO.StreamWriter(stream)
sw.WriteLine("HTTP/1.1 200 OK\r\n\r\nHello World")
sw.Flush()
}
let ip = IPAddress.Parse("127.0.0.1")
let listener = Sockets.TcpListener(ip, 8080)
let startServer = async {
do listener.Start()
do printfn "Starting server..."
while true do
let! context = listener.AcceptTcpClientAsync() |> Async.AwaitTask
processRequest context |> Async.Start
}
Async.Start startServer
I'd also be tempted to change do! processRequest context to processRequest context |> Async.Start so that you can process multiple requests simultaneously.