/var/run/nscd/socket server in Python, https://github.com/termux/proot/issues/101

nscd.py

#!/data/data/com.termux/files/usr/bin/python3

import ipaddress
import os
import socket
import socketserver
import struct

# version, type, key_len
request_header = struct.Struct("<III")

# version, found, naddrs, addrslen, canonlen, error
ai_response_header = struct.Struct("<IIIIII")

class Handler(socketserver.StreamRequestHandler):
    def handle(self):
        version, req_type, key_len = request_header.unpack(self.rfile.read(request_header.size))
        if version in (2, 3) and req_type == 14 and key_len <= 1024:
            key = self.rfile.read(key_len).rstrip(b"\0").decode("latin1")
            try:
                addrinfo = socket.getaddrinfo(key, 0)
                familydata = bytearray()
                addrdata = bytearray()
                seen = set()
                for addrinfo_item in addrinfo:
                    addr = ipaddress.ip_address(addrinfo_item[4][0])
                    if addr in seen:
                        continue
                    seen.add(addr)
                    if addr.version == 4:
                        familydata.append(2)
                        addrdata.extend(addr.packed)
                    elif addr.version == 6:
                        familydata.append(10)
                        addrdata.extend(addr.packed)
                response = ai_response_header.pack(0, 1, len(familydata), len(addrdata), 0, 0) + addrdata + familydata
            except socket.gaierror:
                response = ai_response_header.pack(0, 0, 0, 0, 0, 0)
            self.wfile.write(response)

def serve(path):
    try:
        os.remove(path)
    except FileNotFoundError:
        pass
    s = socketserver.UnixStreamServer(path, Handler)
    s.serve_forever()

if __name__ == "__main__":
    # Note: Path to socket in guest is /var/run/nscd/socket
    #       If guest symlinks /var/run -> /run then "/var" should be omitted from path below,
    #       Otherwise it has to be added.
    #       You'll need to create "nscd" directory yourself and adjust path below.
    serve("/data/data/com.termux/files/home/ubuntu19-fs/run/nscd/socket")