socket_eagain_error_handling.py

import errno
import select
import socket
import time

HOST = "example.com"
PORT = 80
REQUEST = b"GET / HTTP/1.1\r\nHost: example.com\r\nConnection: close\r\n\r\n"
CONNECT_TIMEOUT = 5
READ_TIMEOUT = 5
MAX_RETRIES = 3
BUFFER_SIZE = 4096


def wait_for_socket(sock, wait_for_write=False, timeout=READ_TIMEOUT):
    readers = [] if wait_for_write else [sock]
    writers = [sock] if wait_for_write else []
    readable, writable, _ = select.select(readers, writers, [], timeout)
    return bool(writable if wait_for_write else readable)


def connect_socket():
    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    sock.setblocking(False)

    try:
        sock.connect((HOST, PORT))
    except BlockingIOError:
        pass

    if not wait_for_socket(sock, wait_for_write=True, timeout=CONNECT_TIMEOUT):
        sock.close()
        raise TimeoutError(f"Timed out while connecting to {HOST}:{PORT}")

    connect_error = sock.getsockopt(socket.SOL_SOCKET, socket.SO_ERROR)
    if connect_error != 0:
        sock.close()
        raise OSError(connect_error, f"Socket connect failed for {HOST}:{PORT}")

    return sock


def read_response(sock):
    response_chunks = []
    retries = 0

    while True:
        try:
            chunk = sock.recv(BUFFER_SIZE)
            if not chunk:
                break
            response_chunks.append(chunk)
            retries = 0
        except BlockingIOError as exc:
            if exc.errno not in (errno.EAGAIN, errno.EWOULDBLOCK):
                raise

            retries += 1
            if retries > MAX_RETRIES:
                raise TimeoutError("Socket stayed unavailable after repeated retries.") from exc

            if not wait_for_socket(sock, timeout=READ_TIMEOUT):
                raise TimeoutError("Timed out while waiting for the socket to become readable.") from exc

            time.sleep(0.2)

    return b"".join(response_chunks)


def main():
    sock = connect_socket()
    try:
        sock.sendall(REQUEST)
        response = read_response(sock)
        print(response.decode("utf-8", errors="replace"))
    finally:
        sock.close()


if __name__ == "__main__":
    main()