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discard """
disabled: "windows"
exitcode: 0
"""
# AsyncSocketBug.nim
# Jens Alfke (@snej) -- 16 July 2020
# Demonstrates data loss by Nim's AsyncSocket.
# Just run it, and it will raise an assertion failure within a minute.
import asyncdispatch, asyncnet, strformat, strutils, sugar
const FrameSize = 9999 # Exact size not important, but larger sizes fail quicker
proc runServer() {.async.} =
# Server side:
var server = newAsyncSocket()
server.bindAddr(Port(9001))
server.listen()
let client = await server.accept()
echo "Server got client connection"
var lastN = 0
while true:
let frame = await client.recv(FrameSize)
assert frame.len == FrameSize
let n = frame[0..<6].parseInt()
echo "RCVD #", n, ": ", frame[0..80], "..."
if n != lastN + 1:
echo &"******** ERROR: Server received #{n}, but last was #{lastN}!"
assert n == lastN + 1
lastN = n
await sleepAsync 100
proc main() {.async.} =
asyncCheck runServer()
# Client side:
let socket = newAsyncSocket(buffered = false)
await socket.connect("localhost", Port(9001))
echo "Client socket connected"
var sentCount = 0
var completedCount = 0
while sentCount < 2000:
sentCount += 1
let n = sentCount
var message = &"{n:06} This is message #{n} of ∞. Please stay tuned for more. "
#echo ">>> ", message
while message.len < FrameSize:
message = message & message
let frame = message[0..<FrameSize]
capture n:
socket.send(frame).addCallback proc(f: Future[void]) =
# Callback when the send completes:
assert not f.failed
echo "SENT #", n
if n != completedCount + 1:
echo &"******** ERROR: Client completed #{n}, but last completed was #{completedCount}!"
# If this assert is enabled, it will trigger earlier than the server-side assert above:
assert n == completedCount + 1
completedCount = n
await sleepAsync 1
waitFor main()
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