CODEWITHSUNDEEP
netcatsocat
Sam Liddicott
Sam Liddicott

Reputation: 1386

socat equivalent of netcat -N

I have a dumb network service that receives an entire file up to EOF and then emits a response.

I can use it like this:

netcat -N $SERVER $PORT < input > output

netcat's -N option causes a shutdown(..., SHUT_WR) to be send when the file is read, so that the server will process and send the output.

I can't find a socat equivalent.

It is something like:

socat - TCP:$SERVER:$PORT,linger=5000,shut-down < input > output

but I never manage to get the response data.

Upvotes: 1

Views: 916

Answers (1)

Bill
Bill

Reputation: 281

Here is a small python server which after discussion minimally mimics the server you describe.

import asyncio
import time

class FileReceiver(asyncio.Protocol):

    def connection_made(self, transport):
        print("connection_made")
        self.transport = transport

    def data_received(self, data):
        print(data)

    def eof_received(self):
        time.sleep(2)
        self.transport.write("hello\n".encode());
        if self.transport.can_write_eof():
            self.transport.write_eof()
        return True    

async def main(host, port):
    loop = asyncio.get_event_loop()
    server = await loop.create_server(FileReceiver, host, port)
    await server.serve_forever()

asyncio.run(main('127.0.0.1', 5000))

It correctly returns the hello\n with

netcat -N $SERVER $PORT < input > output

does not return the hello\n when -N is dropped

netcat $SERVER $PORT < input > output

but does not work with

socat - TCP:$SERVER:$PORT < input > output

socat by default sends the SHUT_WR so shut-down is not needed, the shutdowns are the same for netcat -N and socat. The problem is in the timing. socat works if the time.sleep is excluded so socat is shutting down too quickly. The default delay for socat to shutdown the channel is 0.5 second. This can be extended with the -t option. The following works correctly.

socat -t 5 - TCP:$SERVER:$PORT < input > output

Upvotes: 1

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