TCP socket RESET's the connection when not reading the entire read buffer

Port, board and/or hardware

W5500-EVB-Pico, Raspberry Pi Pico W

MicroPython version

MicroPython v1.24.1 on 2024-11-29; W5500-EVB-Pico with RP2040

Reproduction

When not reading the entire TCP message, micropython will RESET the connection, instead of doing a proper TCP connection teardown.

Example:

import network
from machine import SPI, Pin
import time
import asyncio

def w5x00_init():
    # https://github.com/Wiznet/RP2040-HAT-MicroPython/blob/main/Ethernet%20Example%20Getting%20Started%20%5BMicropython%5D.md
    spi=SPI(0,2_000_000, mosi=Pin(19),miso=Pin(16),sck=Pin(18))
    nic = network.WIZNET5K(spi,Pin(17),Pin(20))
    nic.active(True)
    nic.ifconfig('dhcp')
    while not nic.isconnected():
        time.sleep(1)
        print(nic.regs())
    print(nic.ifconfig())

async def handle_client_read_1000(r, w):
    await r.read(1000)
    w.write(b'HTTP/1.0 200 OK\r\nContent-Length: 2\r\nContent-Type: text/plain\r\n\r\nhi')
    w.close()
    await w.wait_closed()

async def server_async(handle_client):
    await asyncio.start_server(handle_client, '0.0.0.0', 80)
    while True:
        await asyncio.sleep(1)
        
w5x00_init()
asyncio.run(server_async(handle_client_read_1000))

Expected behaviour

Reading parts of the TCP stream/reading the entire stream/not reading the stream should not change the behavior of writing into the stream.

When running the same code (except the network setup) in CPython it does a proper TCP connection teardown and does not send RESET.

Observed behaviour

When doing

curl 192.168.2.127

we get a TCP connection teardown after the payload has been send (FIN-ACK):

But when sending a message longer then the buffer (here 1000B) via

curl 192.168.2.127/hiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii

we get

I.e. it sends RESET instead of doing a proper connection teardown.

This causes various strange behaviors as seen in the original discussion.

Additional Information

See the original discussion

Code of Conduct

Yes, I agree