When I test it using echo hello | nc localhost 4100, everything is fine.
But when I use a custom client which concurrently starts 10 connections, I got below error, so confused.
13:25:12.299 [error] Task #PID<0.108.0> started from #PID<0.95.0> terminating
** (MatchError) no match of right hand side value: {:error, :closed}
lib/client.exs:14: Client.run/0
(elixir 1.14.3) lib/task/supervised.ex:89: Task.Supervised.invoke_mfa/2
(elixir 1.14.3) lib/task/supervised.ex:34: Task.Supervised.reply/4
(stdlib 4.2) proc_lib.erl:240: :proc_lib.init_p_do_apply/3
Function: #Function<1.124100197/0 in Client.run>
Args: []
13:25:12.299 [error] Task #PID<0.107.0> started from #PID<0.95.0> terminating
** (MatchError) no match of right hand side value: {:error, :closed}
lib/client.exs:14: Client.run/0
(elixir 1.14.3) lib/task/supervised.ex:89: Task.Supervised.invoke_mfa/2
(elixir 1.14.3) lib/task/supervised.ex:34: Task.Supervised.reply/4
(stdlib 4.2) proc_lib.erl:240: :proc_lib.init_p_do_apply/3
Function: #Function<1.124100197/0 in Client.run>
Args: []
My code is not the same as the linked one, the main process which owns the connection is always alive, so it should not cause the socket to be closed.
I modified the code to use :gen_tcp.controlling_process and I still got the error.
defmodule EchoServer do
require Logger
def start do
{:ok, socket} = :gen_tcp.listen(4100, [:binary, active: false, packet: :line])
Logger.info("Starting echo server")
accept(socket)
end
defp accept(socket) do
{:ok, conn} = :gen_tcp.accept(socket)
pid = spawn(fn -> recv(conn) end)
:ok = :gen_tcp.controlling_process(conn, pid)
send(pid, :start)
accept(socket)
end
defp recv(conn) do
receive do
:start ->
echo(conn)
end
end
defp echo(conn) do
case :gen_tcp.recv(conn, 0) do
{:ok, data} ->
:gen_tcp.send(conn, data)
echo(conn)
{:error, :closed} ->
:ok
end
end
end
When I ran the client, sometimes it’s all fine, sometimes I got {:error, :closed}, and sometimes I got {:error, :econnreset}.
I wrote a simple echo server in JS and I tested it using the same client elixir lib/client.exs and I found that no error showed, so I am sure that something is wrong with my server code, but I am really confused what is going wrong.
const net = require("net")
const server = net.createServer((socket) => {
console.log("Client connected")
socket.on("data", (data) => {
console.log(`Received data: ${data}`)
socket.write(data)
})
})
server.listen(4100, () => {
console.log("Server listening on port 4100")
})
Hi, telnet is fine, but the server returned error when it was concurrently requested.
This is the reduced code.
defmodule EchoServer do
require Logger
def start do
{:ok, socket} = :gen_tcp.listen(4100, [:binary, active: false, packet: :line])
Logger.info("Starting echo server")
accept(socket)
end
defp accept(socket) do
{:ok, conn} = :gen_tcp.accept(socket)
pid = spawn(fn -> recv(conn) end)
:ok = :gen_tcp.controlling_process(conn, pid)
send(pid, :start)
accept(socket)
end
defp recv(conn) do
receive do
:start ->
echo(conn)
end
end
defp echo(conn) do
case :gen_tcp.recv(conn, 0) do
{:ok, data} ->
:gen_tcp.send(conn, data)
echo(conn)
{:error, :closed} ->
:ok
end
end
end
EchoServer.start()
defmodule Client do
require Logger
def start() do
for _ <- 1..10 do
Task.async(&run/0)
end
|> Task.await_many()
end
def run() do
{:ok, socket} = :gen_tcp.connect(~c"localhost", 4100, [:binary, packet: :line, active: false])
:ok = :gen_tcp.send(socket, "hello\n")
case :gen_tcp.recv(socket, 0) do
{:ok, "hello\n"} ->
Logger.info("ok")
other ->
Logger.error("error: #{inspect(other)}")
end
end
end
Client.start()
Running multiple clients also works for me.
Maybe you can try to isolate your error even further. No Logger, no modules, etc.
As long as the behavior is inconsistent I don’t think we can help you that well.
