Python套接字掛起連接/接受

我正在嘗試使用 發送資料包sockets，并且直到今天早上都可以這樣做。我不確定發生了什么事。資料包顯示在其中，tcpdump但服務器和客戶端無法相互連接。

網貓

import socket
import argparse
import sys
import os
import re
import threading


def convertContent(content: str = "") -> bytes:
    byteContent = []
    # grab the hex from the content
    for i in range(len(content)):
        if content[i] == "\\" and content[i 1] == "x":
            byteContent.append(f"{content[i 2]}{content[i 3]}")

    # grab the non hex from the content, split it on the hex
    stringContent = re.split(r"\\x.{2}", content)

    byteIndex = 0
    newContent = b""
    # Re add the non-hex content, and the hex content
    for word in stringContent:
        newContent  = word.encode()
        if byteIndex < len(byteContent):
            newContent  = bytes.fromhex(byteContent[byteIndex])
            byteIndex  = 1
    newContent = newContent.replace(b"\\n", b"\n").replace(b"\\r", b"\r")
    return newContent


class Netcat():
    '''
    Netcat class that can be used to send/receive TCP packets
    '''
    BUFFER_SIZE = 1024

    def __init__(self):
        pass

    @classmethod
    def createSocket(cls):
        sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        # Address might be in a TIME_WAIT status, ignore this
        sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
        # Port might be in a TIME_WAIT status, ignore this
        sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEPORT, 1)
        return sock

    @classmethod
    def send(cls, hostname: str = "127.0.0.1", srcPort: int = 0, destPort: int = 9999, content: str = "", buffer_size: int = 1024):
        srcPort = int(srcPort)
        destPort = int(destPort)
        try:
            content = convertContent(content=content)
        except:
            pass
        sock = cls.createSocket()

        # Set the source port before sending
        sock.connect((hostname, destPort))
        sock.sendall(content)
        # shutdown might be redundant/unnecessary (tells connected host that we're done sending data)
        sock.shutdown(socket.SHUT_WR)
        while True:
            data = sock.recv(buffer_size)
            if len(data) == 0:
                break
        sock.close()

    @classmethod
    def receive(cls, port: int = 9999, buffer_size: int = 1024):
        if port <= 1024 and os.geteuid() != 0:
            print(f"Listening on port {port} requires superuser privileges!")
            return
        host = ""
        sock = cls.createSocket()
        sock.bind((host, port))
        sock.listen(10)
        conn, addr = sock.accept()
        while True:
            data = conn.recv(buffer_size)
            if not data:
                break
        conn.close()

threading.Thread(target=Netcat.receive,daemon=True).start()
Netcat.send(content="test")

注意：我將資料包從一個 VM 發送到另一個 VM，而不是發送給我自己，但是要求人們啟動一堆 VM 來重現這一點會很多。hostnamesend方法中的param應該是接收機器的實際IP

我拋出了一些列印陳述句，服務器停止sock.accept()，而客戶端掛起sock.connect((hostname, destPort))

I checked the hostname for the server, and it's listening on (0.0.0.0, 8888) (assuming 8888 is the port param), which means its listening on all interfaces on that port, so I dont know why its refusing to connect

I tcpdumped on the server, and its getting the packets, it gets a SYN, then sends out a SYN, ACK, but the rest of the packets are marked as re-transmissions.

I've tried looping the accept & connect lines, thinking maybe some sort of race condition was occurring, but no matter what I do the client can't connect to the server.

Edit: This works on my local machine, but still breaks when I try to send packets over the network. The first 2 steps of the handshake go through SYN & SYN, ACK, but not the third ACK

uj5u.com熱心網友回復：

不要在客戶端系結。下面的作業示例，但對制作獨立腳本進行了微小的更改：

import socket
import threading

def receive(port: int = 9999, buffer_size: int = 1024):
    host = ""
    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    # Address might be in a TIME_WAIT status, ignore this
    sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
    sock.bind((host, port))
    sock.listen()
    conn, addr = sock.accept()
    while True:
        data = conn.recv(buffer_size)
        if not data:
            break
        print(data)
    conn.close()

def send(hostname: str = "127.0.0.1", destPort: int = 9999, content: str = b"test", buffer_size: int = 1024):
    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    # Address might be in a TIME_WAIT status, ignore this
    sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)

    # Removed bind
    sock.connect((hostname, destPort))
    sock.sendall(content)
    # shutdown might be redundant/unnecessary (tells connected host that we're done sending data)
    sock.shutdown(socket.SHUT_WR)
    while True:
        data = sock.recv(buffer_size)
        if len(data) == 0:
            break
    sock.close()
    
threading.Thread(target=receive,daemon=True).start()
send()

輸出：

b'test'

標籤：python sockets tcp

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