ConnectionResetError: [Errno 104] Connection reset by peer (tested)

ConnectionResetError: [Errno 104] Connection reset by peer means the other side aborted the TCP connection (sent RST) while you were reading or writing. We reproduced it with a local server, showed the requests version (Connection aborted.), and tested a retry with backoff.

1. Reproduce it: the other side aborts the connection

import socket, struct, threading

srv = socket.create_server(("127.0.0.1", 8965))
def handler():
    conn, _ = srv.accept()
    conn.recv(100)
    # close with SO_LINGER 0: the kernel sends RST instead of a normal FIN
    conn.setsockopt(socket.SOL_SOCKET, socket.SO_LINGER, struct.pack("ii", 1, 0))
    conn.close()
threading.Thread(target=handler).start()

c = socket.create_connection(("127.0.0.1", 8965))
c.sendall(b"GET / HTTP/1.0\r\n\r\n")
c.recv(100)

Output:

Traceback (most recent call last):
  File "/tmp/cr370/b1.py", line 14, in <module>
    c.recv(100)
    ~~~~~~^^^^^
ConnectionResetError: [Errno 104] Connection reset by peer

A reset means the peer sent a TCP RST instead of closing normally. Here the server forces one with SO_LINGER 0. In real life the usual causes are a server process that crashed or was restarted mid-request, a proxy, load balancer or firewall dropping an idle connection, the server rejecting the request (too large, bad TLS/protocol, rate limit) by cutting it off, or reusing a keep-alive connection the server already timed out.

2. It is ConnectionResetError, a ConnectionError

import errno, socket, struct, threading

srv = socket.create_server(("127.0.0.1", 8966))
def handler():
    conn, _ = srv.accept(); conn.recv(100)
    conn.setsockopt(socket.SOL_SOCKET, socket.SO_LINGER, struct.pack("ii", 1, 0)); conn.close()
threading.Thread(target=handler).start()

c = socket.create_connection(("127.0.0.1", 8966))
c.sendall(b"hello")
try:
    c.recv(100)
except ConnectionResetError as e:
    print(type(e).__name__, e.errno, errno.errorcode[e.errno])
    print("ConnectionError?", isinstance(e, ConnectionError), "| OSError?", isinstance(e, OSError))

Output:

ConnectionResetError 104 ECONNRESET
ConnectionError? True | OSError? True

Errno 104 (ECONNRESET) maps to ConnectionResetError, so except ConnectionResetError or except ConnectionError both catch it.

3. Through requests: Connection aborted

import socket, struct, threading, http.server, requests

class H(http.server.BaseHTTPRequestHandler):
    def log_message(self, *a): pass
    def do_GET(self):
        self.connection.setsockopt(socket.SOL_SOCKET, socket.SO_LINGER, struct.pack("ii", 1, 0))
        self.connection.close()                       # drop the client without a response
srv = http.server.HTTPServer(("127.0.0.1", 8967), H)
threading.Thread(target=srv.serve_forever, daemon=True).start()
try:
    requests.get("http://127.0.0.1:8967/", timeout=5)
except requests.exceptions.ConnectionError as e:
    print(type(e).__name__ + ":", e)

Output:

ConnectionError: ('Connection aborted.', ConnectionResetError(104, 'Connection reset by peer'))

requests reports it as requests.exceptions.ConnectionError: ('Connection aborted.', ConnectionResetError(104, ...)). The real cause is the server side: check its logs for a crash, a timeout or a rejected request at that moment.

4. Retry with backoff (for transient resets only)

import socket, struct, threading, time

srv = socket.create_server(("127.0.0.1", 8964))
def handler():
    while True:
        conn, _ = srv.accept(); conn.recv(100)
        conn.setsockopt(socket.SOL_SOCKET, socket.SO_LINGER, struct.pack("ii", 1, 0)); conn.close()
threading.Thread(target=handler, daemon=True).start()

def fetch(retries=3):
    for attempt in range(1, retries + 1):
        try:
            c = socket.create_connection(("127.0.0.1", 8964), timeout=5)
            c.sendall(b"ping"); return c.recv(100)
        except ConnectionResetError as e:
            print(f"attempt {attempt}: {e}")
            time.sleep(0.1 * 2 ** attempt)              # back off before retrying
    return None
print("result:", fetch())

Output:

attempt 1: [Errno 104] Connection reset by peer
attempt 2: [Errno 104] Connection reset by peer
attempt 3: [Errno 104] Connection reset by peer
result: None

Retrying helps when resets are transient (an idle connection dropped by a proxy, a server restart). Against a server that resets every request, as here, retries just fail three times; that points to a request the server refuses, so fix the request instead of retrying harder. With requests, a Session plus urllib3.util.Retry on the HTTPAdapter does the same.

Related: ECONNRESET (Node/browser) · [Errno 32] Broken pipe · requests exceptions list · socket errors and errno codes.

Written with AI assistance. Measured on 2026-10-23 with Python 3.13.5 and requests 2.32.3 on Linux, against local servers. Each block was run verbatim and the output pasted unedited. PlainHeaders is our extension; Python is free.