Why does BeginReceiveFrom never time out?
- by James Hugard
I am writing an asynchronous Ping using Raw Sockets in F#, to enable parallel requests using as few threads as possible ("System.Net.NetworkInformation.Ping" appears to use one thread per request, but have not tested this... also am interested in using F# async workflows). The synchronous version below correctly times out when the target host does not exist/respond, but the asynchronous version hangs. Both work when the host does respond... Any ideas?
(note: the process must run as Admin for this code to work)
This throws a timeout:
let result = Ping.Ping ( IPAddress.Parse( "192.168.33.22" ), 1000 )
However, this hangs:
let result = Ping.PingAsync ( IPAddress.Parse( "192.168.33.22" ), 1000 )
|> Async.RunSynchronously
Here's the code...
module Ping
open System
open System.Net
open System.Net.Sockets
open System.Threading
//---- ICMP Packet Classes
type IcmpMessage (t : byte) =
let mutable m_type = t
let mutable m_code = 0uy
let mutable m_checksum = 0us
member this.Type
with get() = m_type
member this.Code
with get() = m_code
member this.Checksum = m_checksum
abstract Bytes : byte array
default this.Bytes
with get() =
[|
m_type
m_code
byte(m_checksum)
byte(m_checksum >>> 8)
|]
member this.GetChecksum() =
let mutable sum = 0ul
let bytes = this.Bytes
let mutable i = 0
// Sum up uint16s
while i < bytes.Length - 1 do
sum <- sum + uint32(BitConverter.ToUInt16( bytes, i ))
i <- i + 2
// Add in last byte, if an odd size buffer
if i <> bytes.Length then
sum <- sum + uint32(bytes.[i])
// Shuffle the bits
sum <- (sum >>> 16) + (sum &&& 0xFFFFul)
sum <- sum + (sum >>> 16)
sum <- ~~~sum
uint16(sum)
member this.UpdateChecksum() =
m_checksum <- this.GetChecksum()
type InformationMessage (t : byte) =
inherit IcmpMessage(t)
let mutable m_identifier = 0us
let mutable m_sequenceNumber = 0us
member this.Identifier = m_identifier
member this.SequenceNumber = m_sequenceNumber
override this.Bytes
with get() =
Array.append (base.Bytes)
[|
byte(m_identifier)
byte(m_identifier >>> 8)
byte(m_sequenceNumber)
byte(m_sequenceNumber >>> 8)
|]
type EchoMessage() =
inherit InformationMessage( 8uy )
let mutable m_data = Array.create 32 32uy
do base.UpdateChecksum()
member this.Data
with get() = m_data
and set(d) = m_data <- d
this.UpdateChecksum()
override this.Bytes
with get() =
Array.append (base.Bytes)
(this.Data)
//---- Synchronous Ping
let Ping (host : IPAddress, timeout : int ) =
let mutable ep = new IPEndPoint( host, 0 )
let socket = new Socket( AddressFamily.InterNetwork, SocketType.Raw, ProtocolType.Icmp )
socket.SetSocketOption( SocketOptionLevel.Socket, SocketOptionName.SendTimeout, timeout )
socket.SetSocketOption( SocketOptionLevel.Socket, SocketOptionName.ReceiveTimeout, timeout )
let packet = EchoMessage()
let mutable buffer = packet.Bytes
try
if socket.SendTo( buffer, ep ) <= 0 then
raise (SocketException())
buffer <- Array.create (buffer.Length + 20) 0uy
let mutable epr = ep :> EndPoint
if socket.ReceiveFrom( buffer, &epr ) <= 0 then
raise (SocketException())
finally
socket.Close()
buffer
//---- Entensions to the F# Async class to allow up to 5 paramters (not just 3)
type Async with
static member FromBeginEnd(arg1,arg2,arg3,arg4,beginAction,endAction,?cancelAction): Async<'T> =
Async.FromBeginEnd((fun (iar,state) -> beginAction(arg1,arg2,arg3,arg4,iar,state)), endAction, ?cancelAction=cancelAction)
static member FromBeginEnd(arg1,arg2,arg3,arg4,arg5,beginAction,endAction,?cancelAction): Async<'T> =
Async.FromBeginEnd((fun (iar,state) -> beginAction(arg1,arg2,arg3,arg4,arg5,iar,state)), endAction, ?cancelAction=cancelAction)
//---- Extensions to the Socket class to provide async SendTo and ReceiveFrom
type System.Net.Sockets.Socket with
member this.AsyncSendTo( buffer, offset, size, socketFlags, remoteEP ) =
Async.FromBeginEnd( buffer, offset, size, socketFlags, remoteEP,
this.BeginSendTo,
this.EndSendTo )
member this.AsyncReceiveFrom( buffer, offset, size, socketFlags, remoteEP ) =
Async.FromBeginEnd( buffer, offset, size, socketFlags, remoteEP,
this.BeginReceiveFrom,
(fun asyncResult -> this.EndReceiveFrom(asyncResult, remoteEP) ) )
//---- Asynchronous Ping
let PingAsync (host : IPAddress, timeout : int ) =
async {
let ep = IPEndPoint( host, 0 )
use socket = new Socket( AddressFamily.InterNetwork, SocketType.Raw, ProtocolType.Icmp )
socket.SetSocketOption( SocketOptionLevel.Socket, SocketOptionName.SendTimeout, timeout )
socket.SetSocketOption( SocketOptionLevel.Socket, SocketOptionName.ReceiveTimeout, timeout )
let packet = EchoMessage()
let outbuffer = packet.Bytes
try
let! result = socket.AsyncSendTo( outbuffer, 0, outbuffer.Length, SocketFlags.None, ep )
if result <= 0 then
raise (SocketException())
let epr = ref (ep :> EndPoint)
let inbuffer = Array.create (outbuffer.Length + 256) 0uy
let! result = socket.AsyncReceiveFrom( inbuffer, 0, inbuffer.Length, SocketFlags.None, epr )
if result <= 0 then
raise (SocketException())
return inbuffer
finally
socket.Close()
}
