#!/usr/bin/env python3 """Functions for sending and receiving individual lines of text over a socket. A line is transmitted using one or more fixed-size packets of UTF-8 bytes containing: - Zero or more bytes of UTF-8, excluding \n and \0, followed by - Zero or more \0 bytes as required to pad the packet to PACKET_SIZE Originally from the UEDIN team of the ELITR project. """ PACKET_SIZE = 65536 def send_one_line(socket, text, pad_zeros=False): """Sends a line of text over the given socket. The 'text' argument should contain a single line of text (line break characters are optional). Line boundaries are determined by Python's str.splitlines() function [1]. We also count '\0' as a line terminator. If 'text' contains multiple lines then only the first will be sent. If the send fails then an exception will be raised. [1] https://docs.python.org/3.5/library/stdtypes.html#str.splitlines Args: socket: a socket object. text: string containing a line of text for transmission. """ text.replace('\0', '\n') lines = text.splitlines() first_line = '' if len(lines) == 0 else lines[0] # TODO Is there a better way of handling bad input than 'replace'? data = first_line.encode('utf-8', errors='replace') + b'\n' + (b'\0' if pad_zeros else b'') for offset in range(0, len(data), PACKET_SIZE): bytes_remaining = len(data) - offset if bytes_remaining < PACKET_SIZE: padding_length = PACKET_SIZE - bytes_remaining packet = data[offset:] + (b'\0' * padding_length if pad_zeros else b'') else: packet = data[offset:offset+PACKET_SIZE] socket.sendall(packet) def receive_one_line(socket): """Receives a line of text from the given socket. This function will (attempt to) receive a single line of text. If data is currently unavailable then it will block until data becomes available or the sender has closed the connection (in which case it will return an empty string). The string should not contain any newline characters, but if it does then only the first line will be returned. Args: socket: a socket object. Returns: A string representing a single line with a terminating newline or None if the connection has been closed. """ data = b'' while True: packet = socket.recv(PACKET_SIZE) if not packet: # Connection has been closed. return None data += packet if b'\0' in packet: break # TODO Is there a better way of handling bad input than 'replace'? text = data.decode('utf-8', errors='replace').strip('\0') lines = text.split('\n') return lines[0] + '\n' def receive_lines(socket): try: data = socket.recv(PACKET_SIZE) except BlockingIOError: return [] if data is None: # Connection has been closed. return None # TODO Is there a better way of handling bad input than 'replace'? text = data.decode('utf-8', errors='replace').strip('\0') lines = text.split('\n') if len(lines)==1 and not lines[0]: return None return lines