First working version

.gitignore

@@ -1,4 +1,11 @@
 # ---> Python
+
+# Configuration file
+*config.py
+
+# Data folder
+data/
+
 # Byte-compiled / optimized / DLL files
 __pycache__/
 *.py[cod]

README.md

@@ -1,3 +1,53 @@
 # filebridging
 
-Share files via a bridge server.
+Share files via a bridge server using TCP over SSL and end-to-end encryption.
+
+## Requirements
+Python3.8+ is needed for this package.
+
+## Usage
+If you need a virtual environment, create it.
+```bash
+python3.8 -m venv env;
+alias pip="env/bin/pip";
+alias python="env/bin/python";
+```
+
+Install filebridging and read the help.
+```bash
+pip install filebridging
+python -m filebridging.server --help
+python -m filebridging.client --help
+```
+
+## Examples
+* Client-server example
+    ```bash
+    # 3 distinct tabs
+    python -m filebridging.server --host localhost --port 5000 --certificate ~/.ssh/server.crt --key ~/.ssh/server.key
+    python -m filebridging.client s --host localhost --port 5000 --certificate ~/.ssh/server.crt --token 12345678 --password supersecretpasswordhere --path ~/file_to_send 
+    python -m filebridging.client r --host localhost --port 5000 --certificate ~/.ssh/server.crt --token 12345678 --password supersecretpasswordhere --path ~/Downloads 
+    ```
+
+* Client-client example
+    ```bash
+    # 2 distinct tabs
+    python -m filebridging.client s --host localhost --port 5000 --certificate ~/.ssh/server.crt --key ~/.ssh/private.key --token 12345678 --password supersecretpasswordhere --path ~/file_to_send --standalone
+    python -m filebridging.client r --host localhost --port 5000 --certificate ~/.ssh/server.crt --token 12345678 --password supersecretpasswordhere --path ~/Downloads 
+    ```
+    The receiver client may be standalone as well: just add the `--key` parameter (for SSL-secured sessions) and the `--standalone` flag. 
+
+* Configuration file example
+    ```python
+    #!/bin/python
+    
+    host = "www.example.com"
+    port = 5000
+    certificate = "/path/to/public.crt"
+    key = "/path/to/private.key"
+    
+    action = 'r'
+    password = 'verysecretpassword'
+    token = 'sessiontok'
+    file_path = '.'
+    ```

filebridging/__init__.py

@@ -0,0 +1,18 @@
+"""General information about this package.
+
+Python 3.8+ is needed to use this package.
+```python3.8+
+from filebridging.client import Client
+from filebridging.server import Server
+help(Client)
+help(Server)
+```
+"""
+
+__author__ = "Davide Testa"
+__email__ = "davide@davte.it"
+__credits__ = []
+__license__ = "GNU General Public License v3.0"
+__version__ = "0.0.1"
+__maintainer__ = "Davide Testa"
+__contact__ = "t.me/davte"

filebridging/client.py

@@ -0,0 +1,795 @@
+"""Receiver and sender client class.
+
+Arguments
+    - host: localhost, IPv4 address or domain (e.g. www.example.com)
+    - port: port to reach (must be enabled)
+    - action: either [S]end or [R]eceive
+    - file_path: file to send / destination folder
+    - token: session token (6-10 alphanumerical characters)
+    - certificate [optional]: server certificate for SSL
+    - key [optional]: needed only for standalone clients
+    - password [optional]: necessary to end-to-end encryption
+    - standalone [optional]: allow client-to-client communication (the host
+    must be reachable by both clients)
+"""
+
+import argparse
+import asyncio
+import collections
+import logging
+import os
+import random
+import ssl
+import string
+import sys
+from typing import Union
+
+from . import utilities
+
+
+class Client:
+    """Sender or receiver client.
+
+    Create a Client object providing host, port and other optional parameters.
+    Then, run it with `Client().run()` method
+    """
+    def __init__(self, host='localhost', port=5000, ssl_context=None,
+                 action=None,
+                 standalone=False,
+                 buffer_chunk_size=10 ** 4,
+                 buffer_length_limit=10 ** 4,
+                 file_path=None,
+                 password=None,
+                 token=None):
+        self._host = host
+        self._port = port
+        self._ssl_context = ssl_context
+        self._action = action
+        self._standalone = standalone
+        self._stopping = False
+        self._reader = None
+        self._writer = None
+        # Shared queue of bytes
+        self.buffer = collections.deque()
+        # How many bytes per chunk
+        self._buffer_chunk_size = buffer_chunk_size
+        # How many chunks in buffer
+        self._buffer_length_limit = buffer_length_limit
+        self._file_path = file_path
+        self._working = False
+        self._token = token
+        self._password = password
+        self._ssl_context = None
+        self._encryption_complete = False
+        self._file_name = None
+        self._file_size = None
+        self._file_size_string = None
+
+    @property
+    def host(self) -> str:
+        """Host to reach.
+
+        For standalone clients, you must be able to listen this host.
+        """
+        return self._host
+
+    @property
+    def port(self) -> int:
+        """Port number."""
+        return self._port
+
+    @property
+    def action(self) -> str:
+        """Client role.
+
+        Possible values:
+        - `send`
+        - `receive`
+        """
+        return self._action
+
+    @property
+    def standalone(self) -> bool:
+        """Tell whether client should run as server as well."""
+        return self._standalone
+
+    @property
+    def stopping(self) -> bool:
+        return self._stopping
+
+    @property
+    def reader(self) -> asyncio.StreamReader:
+        return self._reader
+
+    @property
+    def writer(self) -> asyncio.StreamWriter:
+        return self._writer
+
+    @property
+    def buffer_length_limit(self) -> int:
+        """Max number of buffer chunks in memory.
+
+        You may want to reduce this limit to allocate less memory, or increase
+        it to boost performance.
+        """
+        return self._buffer_length_limit
+
+    @property
+    def buffer_chunk_size(self) -> int:
+        """Length (bytes) of buffer chunks in memory.
+
+        You may want to reduce this limit to allocate less memory, or increase
+        it to boost performance.
+        """
+        return self._buffer_chunk_size
+
+    @property
+    def file_path(self) -> str:
+        """Path of file to send or destination folder."""
+        return self._file_path
+
+    @property
+    def working(self) -> bool:
+        return self._working
+
+    @property
+    def ssl_context(self) -> ssl.SSLContext:
+        return self._ssl_context
+
+    def set_ssl_context(self, ssl_context: ssl.SSLContext):
+        self._ssl_context = ssl_context
+
+    @property
+    def token(self):
+        """Session token.
+
+        6-10 alphanumerical characters to provide to server to link sender and
+        receiver.
+        """
+        return self._token
+
+    @property
+    def password(self):
+        """Password for file encryption or decryption."""
+        return self._password
+
+    @property
+    def encryption_complete(self):
+        return self._encryption_complete
+
+    @property
+    def file_name(self):
+        return self._file_name
+
+    @property
+    def file_size(self):
+        return self._file_size
+
+    @property
+    def file_size_string(self):
+        """Formatted file size (e.g. 64.22 MB)."""
+        return self._file_size_string
+
+    async def run_client(self) -> None:
+        if self.action == 'send':
+            file_name = os.path.basename(os.path.abspath(self.file_path))
+            file_size = os.path.getsize(os.path.abspath(self.file_path))
+            # File size increases after encryption
+            # "Salted_" (8 bytes) + salt (8 bytes)
+            # Then, 1-16 bytes are added to make file_size a multiple of 16
+            # i.e., (32 - file_size mod 16) bytes are added to original size
+            if self.password:
+                file_size += 32 - (file_size % 16)
+            self.set_file_information(
+                file_name=file_name,
+                file_size=file_size
+            )
+        if self.standalone:
+            server = await asyncio.start_server(
+                ssl=self.ssl_context,
+                client_connected_cb=self._connect,
+                host=self.host,
+                port=self.port,
+            )
+            async with server:
+                logging.info("Running at `{s.host}:{s.port}`".format(s=self))
+                await server.serve_forever()
+        else:
+            try:
+                reader, writer = await asyncio.open_connection(
+                    host=self.host,
+                    port=self.port,
+                    ssl=self.ssl_context
+                )
+            except (ConnectionRefusedError, ConnectionResetError) as exception:
+                logging.error(f"Connection error: {exception}")
+                return
+            await self.connect(reader=reader, writer=writer)
+
+    async def _connect(self, reader: asyncio.StreamReader,
+                       writer: asyncio.StreamWriter):
+        """Wrap connect method to catch exceptions.
+
+        This is required since callbacks are never awaited and potential
+        exception would be logged at loop.close().
+        Only standalone clients need this wrapper, regular clients might use
+        connect method directly.
+        """
+        try:
+            return await self.connect(reader, writer)
+        except KeyboardInterrupt:
+            print()
+        except Exception as e:
+            logging.error(e)
+
+    async def connect(self,
+                      reader: asyncio.StreamReader,
+                      writer: asyncio.StreamWriter):
+        """Communicate with the server or the other client.
+
+        Send information about the client (connection token, role, file name
+        and size), get information from the server (file name and size), wait
+        for start signal and then send or receive the file.
+        """
+        self._reader = reader
+        self._writer = writer
+
+        async def _write(message: Union[list, str, bytes],
+                         terminate_line=True) -> int:
+            """Framework for `asyncio.StreamWriter.write` method.
+
+            Create string from list, encode it, send and drain writer.
+            Return 0 on success, 1 on error.
+            """
+            # Adapt
+            if type(message) is list:
+                message = '|'.join(map(str, message))
+            if type(message) is str:
+                if terminate_line:
+                    message += '\n'
+                message = message.encode('utf-8')
+            if type(message) is not bytes:
+                return 1
+            try:
+                writer.write(message)
+                await writer.drain()
+            except ConnectionResetError:
+                logging.error("Client disconnected.")
+            except Exception as e:
+                logging.error(f"Unexpected exception:\n{e}", exc_info=True)
+            else:
+                return 0  # On success, return 0
+            # On exception, return 1
+            return 1
+
+        if self.action == 'send' or not self.standalone:
+            if await _write(
+                    [self.action[0], self.token,
+                     self.file_name, self.file_size]
+            ):
+                return
+        # Wait for server start signal
+        while 1:
+            server_hello = await self.reader.readline()
+            if not server_hello:
+                logging.error("Server disconnected.")
+                return
+            server_hello = server_hello.decode('utf-8').strip('\n').split('|')
+            if self.action == 'receive' and server_hello[0] == 's':
+
+                self.set_file_information(file_name=server_hello[2],
+                                          file_size=server_hello[3])
+            elif (
+                    self.standalone
+                    and self.action == 'send'
+                    and server_hello[0] == 'r'
+            ):
+                # Check token
+                if server_hello[1] != self.token:
+                    if await _write("Invalid session token!"):
+                        return
+                    return
+            elif server_hello[0] == 'start!':
+                break
+            else:
+                logging.info(f"Server said: {'|'.join(server_hello)}")
+            if self.standalone:
+                if await _write("start!"):
+                    return
+                break
+        if self.action == 'send':
+            await self.send(writer=self.writer)
+        else:
+            await self.receive(reader=self.reader)
+
+    async def encrypt_file(self, input_file, output_file):
+        """Use openssl to encrypt the input_file.
+
+        The encrypted file will overwrite `output_file` if it exists.
+        """
+        self._encryption_complete = False
+        logging.info("Encrypting file...")
+        stdout, stderr = ''.encode(), ''.encode()
+        try:
+            _subprocess = await asyncio.create_subprocess_shell(
+                "openssl enc -aes-256-cbc "
+                "-md sha512 -pbkdf2 -iter 100000 -salt "
+                f"-in \"{input_file}\" -out \"{output_file}\" "
+                f"-pass pass:{self.password}"
+            )
+            stdout, stderr = await _subprocess.communicate()
+        except Exception as e:
+            logging.error(
+                "Exception {e}:\n{o}\n{er}".format(
+                    e=e,
+                    o=stdout.decode().strip(),
+                    er=stderr.decode().strip()
+                )
+            )
+        logging.info("Encryption completed.")
+        self._encryption_complete = True
+
+    async def send(self, writer: asyncio.StreamWriter):
+        """Encrypt and send the file.
+
+        Caution: if no password is provided, the file will be sent as clear
+        text.
+        """
+        self._working = True
+        file_path = self.file_path
+        if self.password:
+            file_path = self.file_path + '.enc'
+            # Remove already-encrypted file if present (salt would differ)
+            if os.path.isfile(file_path):
+                os.remove(file_path)
+            asyncio.ensure_future(
+                self.encrypt_file(
+                    input_file=self.file_path,
+                    output_file=file_path
+                )
+            )
+            # Give encryption an edge
+            while not os.path.isfile(file_path):
+                await asyncio.sleep(.5)
+        logging.info("Sending file...")
+        bytes_sent = 0
+        with open(file_path, 'rb') as file_to_send:
+            while not self.stopping:
+                output_data = file_to_send.read(self.buffer_chunk_size)
+                if not output_data:
+                    # If encryption is in progress, wait and read again later
+                    if self.password and not self.encryption_complete:
+                        await asyncio.sleep(1)
+                        continue
+                    break
+                try:
+                    writer.write(output_data)
+                    await asyncio.wait_for(writer.drain(), timeout=3.0)
+                except ConnectionResetError:
+                    print()  # New line after progress_bar
+                    logging.error('Server closed the connection.')
+                    self.stop()
+                    break
+                except asyncio.exceptions.TimeoutError:
+                    print()  # New line after progress_bar
+                    logging.error('Server closed the connection.')
+                    self.stop()
+                    break
+                bytes_sent += len(output_data)
+                new_progress = min(
+                    int(bytes_sent / self.file_size * 100),
+                    100
+                )
+                self.print_progress_bar(
+                    progress=new_progress,
+                    bytes_=bytes_sent,
+                )
+        print()  # New line after progress_bar
+        writer.close()
+        return
+
+    async def receive(self, reader: asyncio.StreamReader):
+        """Download the file and decrypt it.
+
+        If no password is provided, the file cannot be decrypted.
+        """
+        self._working = True
+        file_path = os.path.join(
+            os.path.abspath(
+                self.file_path
+            ),
+            self.file_name
+        )
+        original_file_path = file_path
+        if self.password:
+            file_path += '.enc'
+        logging.info("Receiving file...")
+        with open(file_path, 'wb') as file_to_receive:
+            bytes_received = 0
+            while not self.stopping:
+                input_data = await reader.read(self.buffer_chunk_size)
+                bytes_received += len(input_data)
+                new_progress = min(
+                    int(bytes_received / self.file_size * 100),
+                    100
+                )
+                self.print_progress_bar(
+                    progress=new_progress,
+                    bytes_=bytes_received
+                )
+                if not input_data:
+                    break
+                file_to_receive.write(input_data)
+        print()  # New line after sys.stdout.write
+        if bytes_received < self.file_size:
+            logging.warning("Transmission terminated too soon!")
+            if self.password:
+                logging.error("Partial files can not be decrypted!")
+                return
+        logging.info("File received.")
+        if self.password:
+            logging.info("Decrypting file...")
+            stdout, stderr = ''.encode(), ''.encode()
+            try:
+                _subprocess = await asyncio.create_subprocess_shell(
+                    "openssl enc -aes-256-cbc "
+                    "-md sha512 -pbkdf2 -iter 100000 -salt -d "
+                    f"-in \"{file_path}\" -out \"{original_file_path}\" "
+                    f"-pass pass:{self.password}"
+                )
+                stdout, stderr = await _subprocess.communicate()
+                logging.info("Decryption completed.")
+            except Exception as e:
+                logging.error(
+                    "Exception {e}:\n{o}\n{er}".format(
+                        e=e,
+                        o=stdout.decode().strip(),
+                        er=stderr.decode().strip()
+                    )
+                )
+                logging.info("Decryption failed", exc_info=True)
+
+    def stop(self, *_):
+        if self.working:
+            logging.info("Received interruption signal, stopping...")
+            self._stopping = True
+            if self.writer:
+                self.writer.close()
+        else:
+            raise KeyboardInterrupt("Not working yet...")
+
+    def set_file_information(self, file_name=None, file_size=None):
+        if file_name is not None:
+            self._file_name = file_name
+        if file_size is not None:
+            self._file_size = int(file_size)
+            self._file_size_string = utilities.get_file_size_representation(
+                self.file_size
+            )
+
+    def run(self):
+        loop = asyncio.get_event_loop()
+        try:
+            loop.run_until_complete(
+                self.run_client()
+            )
+        except KeyboardInterrupt:
+            print()
+            logging.error("Interrupted")
+            for task in asyncio.all_tasks(loop):
+                task.cancel()
+            if self.writer:
+                self.writer.close()
+            loop.run_until_complete(
+                self.wait_closed()
+            )
+        loop.close()
+
+    def print_progress_bar(self, progress: int, bytes_: int):
+        """Print client progress bar.
+
+        `progress` % = `bytes_string` transferred
+        out of `self.file_size_string`.
+        """
+        action = {
+            'send': "Sending",
+            'receive': "Receiving"
+        }[self.action]
+        bytes_string = utilities.get_file_size_representation(
+            bytes_
+        )
+        utilities.print_progress_bar(
+            prefix=f"\t\t\t{action} `{self.file_name}`: ",
+            done_symbol='#',
+            pending_symbol='.',
+            progress=progress,
+            scale=5,
+            suffix=(
+                " completed "
+                f"({bytes_string} "
+                f"of {self.file_size_string})"
+            )
+        )
+
+    @staticmethod
+    async def wait_closed() -> None:
+        """Give time to cancelled tasks to end properly.
+
+        Sleep .1 second and return.
+        """
+        await asyncio.sleep(.1)
+
+
+def get_action(action):
+    """Parse abbreviations for `action`."""
+    if not isinstance(action, str):
+        return
+    elif action.lower().startswith('r'):
+        return 'receive'
+    elif action.lower().startswith('s'):
+        return 'send'
+
+
+def get_file_path(path, action='receive'):
+    """Check that file `path` is correct and return it."""
+    path = os.path.abspath(
+        os.path.expanduser(path)
+    )
+    if (
+            isinstance(path, str)
+            and action == 'send'
+            and os.path.isfile(path)
+    ):
+        return path
+    elif (
+            isinstance(path, str)
+            and action == 'receive'
+            and os.access(os.path.dirname(path), os.W_OK)
+    ):
+        return path
+    elif path is not None:
+        logging.error(f"Invalid file: `{path}`")
+
+
+def main():
+    # noinspection SpellCheckingInspection
+    log_formatter = logging.Formatter(
+        "%(asctime)s [%(module)-15s %(levelname)-8s]     %(message)s",
+        style='%'
+    )
+    root_logger = logging.getLogger()
+    root_logger.setLevel(logging.DEBUG)
+
+    # noinspection PyUnresolvedReferences
+    asyncio.selector_events.logger.setLevel(logging.ERROR)
+
+    console_handler = logging.StreamHandler()
+    console_handler.setFormatter(log_formatter)
+    console_handler.setLevel(logging.DEBUG)
+    root_logger.addHandler(console_handler)
+
+    # Parse command-line arguments
+    cli_parser = argparse.ArgumentParser(description='Run client',
+                                         allow_abbrev=False)
+    cli_parser.add_argument('--host', type=str,
+                            default=None,
+                            required=False,
+                            help='server address')
+    cli_parser.add_argument('--port', type=int,
+                            default=None,
+                            required=False,
+                            help='server port')
+    cli_parser.add_argument('--certificate', type=str,
+                            default=None,
+                            required=False,
+                            help='server SSL certificate')
+    cli_parser.add_argument('--key', type=str,
+                            default=None,
+                            required=False,
+                            help='server SSL key (required only for '
+                                 'SSL-secured standalone client)')
+    cli_parser.add_argument('--action', type=str,
+                            default=None,
+                            required=False,
+                            help='[S]end or [R]eceive')
+    cli_parser.add_argument('--path', type=str,
+                            default=None,
+                            required=False,
+                            help='File path to send / folder path to receive')
+    cli_parser.add_argument('--password', '--p', '--pass', type=str,
+                            default=None,
+                            required=False,
+                            help='Password for file encryption or decryption')
+    cli_parser.add_argument('--token', '--t', '--session_token', type=str,
+                            default=None,
+                            required=False,
+                            help='Session token '
+                                 '(must be the same for both clients)')
+    cli_parser.add_argument('--standalone',
+                            action='store_true',
+                            help='Run both as client and server')
+    cli_parser.add_argument('others',
+                            metavar='R or S',
+                            nargs='*',
+                            help='[S]end or [R]eceive (see `action`)')
+    args = vars(cli_parser.parse_args())
+    host = args['host']
+    port = args['port']
+    certificate = args['certificate']
+    key = args['key']
+    action = get_action(args['action'])
+    file_path = args['path']
+    password = args['password']
+    token = args['token']
+    standalone = args['standalone']
+
+    # If host and port are not provided from command-line, try to import them
+    sys.path.append(os.path.abspath('.'))
+    if host is None:
+        try:
+            from config import host
+        except ImportError:
+            host = None
+    if port is None:
+        try:
+            from config import port
+        except ImportError:
+            port = None
+    # Take `s`, `r` etc. from command line as `action`
+    if action is None:
+        for arg in args['others']:
+            action = get_action(arg)
+            if action:
+                break
+    if action is None:
+        try:
+            from config import action
+            action = get_action(action)
+        except ImportError:
+            action = None
+    if file_path is None:
+        try:
+            from config import file_path
+            file_path = get_action(file_path)
+        except ImportError:
+            file_path = None
+    if password is None:
+        try:
+            from config import password
+        except ImportError:
+            password = None
+    if token is None:
+        try:
+            from config import token
+        except ImportError:
+            token = None
+    if certificate is None or not os.path.isfile(certificate):
+        try:
+            from config import certificate
+        except ImportError:
+            certificate = None
+    if key is None or not os.path.isfile(key):
+        try:
+            from config import key
+        except ImportError:
+            key = None
+
+    # If import fails, prompt user for host or port
+    new_settings = {}  # After getting these settings, offer to store them
+    while host is None:
+        host = input("Enter host:\t\t\t\t\t\t")
+        new_settings['host'] = host
+    while port is None:
+        try:
+            port = int(input("Enter port:\t\t\t\t\t\t"))
+        except ValueError:
+            logging.info("Invalid port. Enter a valid port number!")
+            port = None
+        new_settings['port'] = port
+    while action is None:
+        action = get_action(
+            input("Do you want to (R)eceive or (S)end a file?\t\t")
+        )
+    if file_path is not None and (
+            (action == 'send'
+             and not os.path.isfile(os.path.abspath(file_path)))
+            or (action == 'receive'
+                and not os.path.isdir(os.path.abspath(file_path)))
+    ):
+        file_path = None
+    while file_path is None:
+        if action == 'send':
+            file_path = get_file_path(
+                path=input(f"Enter file to send:\t\t\t\t\t"),
+                action=action
+            )
+            if file_path and not os.path.isfile(os.path.abspath(file_path)):
+                file_path = None
+        elif action == 'receive':
+            file_path = get_file_path(
+                path=input(f"Enter destination folder:\t\t\t\t"),
+                action=action
+            )
+            if file_path and not os.path.isdir(os.path.abspath(file_path)):
+                file_path = None
+    if password is None:
+        logging.warning(
+            "You have provided no password for file encryption.\n"
+            "Your file will be unencoded unless you provide a password in "
+            "config file."
+        )
+    if token is None and action == 'send':
+        # Generate a random [6-10] chars-long alphanumerical token
+        token = ''.join(
+            random.SystemRandom().choice(
+                string.ascii_uppercase + string.digits
+            )
+            for _ in range(random.SystemRandom().randint(6, 10))
+        )
+        logging.info(
+            "You have not provided a token for this connection.\n"
+            f"A token has been generated for you:\t\t\t{token}\n"
+            "Your peer must be informed of this token.\n"
+            "For future connections, you may provide a custom token writing "
+            "it in config file."
+        )
+    while token is None or not (6 <= len(token) <= 10):
+        token = input("Please enter a 6-10 chars token.\t\t\t")
+    if new_settings:
+        answer = utilities.timed_input(
+            "You may store the following configuration values in "
+            "`config.py`.\n\n" + '\n'.join(
+                '\t\t'.join(map(str, item))
+                for item in new_settings.items()
+            ) + '\n\n'
+                'Do you want to store them?\t\t\t\t',
+            timeout=3
+        )
+        if answer:
+            with open('config.py', 'a') as configuration_file:
+                configuration_file.writelines(
+                    [
+                        f'{name} = "{value}"\n'
+                        if type(value) is str
+                        else f'{name} = {value}\n'
+                        for name, value in new_settings.items()
+                    ]
+                )
+            logging.info("Configuration values stored.")
+        else:
+            logging.info("Proceeding without storing values...")
+    ssl_context = None
+    if certificate and key and standalone:  # Standalone client
+        ssl_context = ssl.create_default_context(
+            purpose=ssl.Purpose.CLIENT_AUTH
+        )
+        ssl_context.load_cert_chain(certificate, key)
+    elif certificate:  # Server-dependent client
+        ssl_context = ssl.create_default_context(
+            purpose=ssl.Purpose.SERVER_AUTH
+        )
+        ssl_context.load_verify_locations(certificate)
+    else:
+        logging.warning(
+            "Please consider using SSL. To do so, add in `config.py` or "
+            "provide via Command Line Interface the path to a valid SSL "
+            "certificate. Example:\n\n"
+            "certificate = 'path/to/certificate.crt'"
+        )
+    logging.info("Starting client...")
+    client = Client(
+        host=host,
+        port=port,
+        ssl_context=ssl_context,
+        action=action,
+        standalone=standalone,
+        file_path=file_path,
+        password=password,
+        token=token
+    )
+    client.run()
+    logging.info("Stopped client")
+
+
+if __name__ == '__main__':
+    main()

filebridging/server.py

@@ -0,0 +1,378 @@
+"""Server class.
+
+May be a local server or a publicly reachable server.
+
+Arguments
+    - host: localhost, IPv4 address or domain (e.g. www.example.com)
+    - port: port to reach (must be enabled)
+    - certificate [optional]: server certificate for SSL
+    - key [optional]: needed only for standalone clients
+"""
+
+import argparse
+import asyncio
+import collections
+import logging
+import os
+import ssl
+from typing import Union
+
+
+class Server:
+    def __init__(self, host='localhost', port=5000, ssl_context=None,
+                 buffer_chunk_size=10 ** 4, buffer_length_limit=10 ** 4):
+        self._host = host
+        self._port = port
+        self._ssl_context = ssl_context
+        self.connections = collections.OrderedDict()
+        # Dict of queues of bytes
+        self.buffers = collections.OrderedDict()
+        # How many bytes per chunk
+        self._buffer_chunk_size = buffer_chunk_size
+        # How many chunks in buffer
+        self._buffer_length_limit = buffer_length_limit
+        self._working = False
+        self._server = None
+        self._ssl_context = None
+
+    @property
+    def host(self) -> str:
+        return self._host
+
+    @property
+    def port(self) -> int:
+        return self._port
+
+    @property
+    def buffer_length_limit(self) -> int:
+        return self._buffer_length_limit
+
+    @property
+    def buffer_chunk_size(self) -> int:
+        return self._buffer_chunk_size
+
+    @property
+    def working(self) -> bool:
+        return self._working
+
+    @property
+    def server(self) -> asyncio.base_events.Server:
+        return self._server
+
+    @property
+    def ssl_context(self) -> ssl.SSLContext:
+        return self._ssl_context
+
+    @property
+    def buffer_is_full(self):
+        return (
+                sum(len(buffer)
+                    for buffer in self.buffers.values())
+                >= self.buffer_length_limit
+        )
+
+    def set_ssl_context(self, ssl_context: ssl.SSLContext):
+        self._ssl_context = ssl_context
+
+    async def run_reader(self, reader, connection_token):
+        while 1:
+            try:
+                # Wait one second if buffer is full
+                while self.buffer_is_full:
+                    await asyncio.sleep(1)
+                    continue
+                input_data = await reader.read(self.buffer_chunk_size)
+                if connection_token not in self.buffers:
+                    break
+                self.buffers[connection_token].append(input_data)
+            except ConnectionResetError as e:
+                logging.error(e)
+                break
+            except Exception as e:
+                logging.error(f"Unexpected exception:\n{e}", exc_info=True)
+
+    async def run_writer(self, writer, connection_token):
+        consecutive_interruptions = 0
+        errors = 0
+        while connection_token in self.buffers:
+            try:
+                input_data = self.buffers[connection_token].popleft()
+            except IndexError:
+                # Slow down if buffer is empty; after 1.5 s of silence, break
+                consecutive_interruptions += 1
+                if consecutive_interruptions > 3:
+                    break
+                await asyncio.sleep(.5)
+                continue
+            else:
+                consecutive_interruptions = 0
+            if not input_data:
+                break
+            try:
+                writer.write(input_data)
+                await writer.drain()
+            except ConnectionResetError as e:
+                logging.error(e)
+                break
+            except Exception as e:
+                logging.error(e, exc_info=True)
+                errors += 1
+                if errors > 3:
+                    break
+                await asyncio.sleep(0.5)
+        writer.close()
+
+    async def connect(self,
+                      reader: asyncio.StreamReader,
+                      writer: asyncio.StreamWriter):
+        """Connect with client.
+
+        Decide whether client is sender or receiver and start transmission.
+        """
+        client_hello = await reader.readline()
+        client_hello = client_hello.decode('utf-8').strip('\n').split('|')
+        if len(client_hello) != 4:
+            await self.refuse_connection(writer=writer,
+                                         message="Invalid client_hello!")
+            return
+        connection_token = client_hello[1]
+        if connection_token not in self.connections:
+            self.connections[connection_token] = dict(
+                sender=False,
+                receiver=False
+            )
+
+        async def _write(message: Union[list, str, bytes],
+                         terminate_line=True) -> int:
+            # Adapt
+            if type(message) is list:
+                message = '|'.join(map(str, message))
+            if type(message) is str:
+                if terminate_line:
+                    message += '\n'
+                message = message.encode('utf-8')
+            if type(message) is not bytes:
+                return 1
+            try:
+                writer.write(message)
+                await writer.drain()
+            except ConnectionResetError:
+                logging.error("Client disconnected.")
+            except Exception as e:
+                logging.error(f"Unexpected exception:\n{e}", exc_info=True)
+            else:
+                return 0  # On success, return 0
+            # On exception, disconnect and return 1
+            self.disconnect(connection_token=connection_token)
+            return 1
+
+        if client_hello[0] == 's':  # Sender client connection
+            if self.connections[connection_token]['sender']:
+                await self.refuse_connection(
+                    writer=writer,
+                    message="Invalid token! "
+                            "A sender client is already connected!\n"
+                )
+                return
+            self.connections[connection_token]['sender'] = True
+            self.connections[connection_token]['file_name'] = client_hello[2]
+            self.connections[connection_token]['file_size'] = client_hello[3]
+            self.buffers[connection_token] = collections.deque()
+            logging.info("Sender is connecting...")
+            index, step = 0, 1
+            while not self.connections[connection_token]['receiver']:
+                index += 1
+                if index >= step:
+                    if await _write("Waiting for receiver..."):
+                        return
+                    step += 1
+                    index = 0
+                await asyncio.sleep(.5)
+            # Send start signal to client
+            if await _write("start!"):
+                return
+            logging.info("Incoming transmission starting...")
+            await self.run_reader(reader=reader,
+                                  connection_token=connection_token)
+            logging.info("Incoming transmission ended")
+        elif client_hello[0] == 'r':  # Receiver client connection
+            if self.connections[connection_token]['receiver']:
+                await self.refuse_connection(
+                    writer=writer,
+                    message="Invalid token! "
+                            "A receiver client is already connected!\n"
+                )
+                return
+            self.connections[connection_token]['receiver'] = True
+            logging.info("Receiver is connecting...")
+            index, step = 0, 1
+            while not self.connections[connection_token]['sender']:
+                index += 1
+                if index >= step:
+                    if await _write("Waiting for sender..."):
+                        return
+                    step += 1
+                    index = 0
+                await asyncio.sleep(.5)
+            # Send file information and start signal to client
+            if await _write(
+                    ['s',
+                     'hidden_token',
+                     self.connections[connection_token]['file_name'],
+                     self.connections[connection_token]['file_size']]
+            ):
+                return
+            if await _write("start!"):
+                return
+            await self.run_writer(writer=writer,
+                                  connection_token=connection_token)
+            logging.info("Outgoing transmission ended")
+            self.disconnect(connection_token=connection_token)
+        else:
+            await self.refuse_connection(writer=writer,
+                                         message="Invalid client_hello!")
+            return
+
+    def disconnect(self, connection_token: str) -> None:
+        del self.buffers[connection_token]
+        del self.connections[connection_token]
+
+    def run(self):
+        loop = asyncio.get_event_loop()
+        logging.info("Starting file bridging server...")
+        try:
+            loop.run_until_complete(self.run_server())
+        except KeyboardInterrupt:
+            print()
+            logging.info("Stopping...")
+            # Cancel connection tasks (they should be done but are pending)
+            for task in asyncio.all_tasks(loop):
+                task.cancel()
+            loop.run_until_complete(
+                self.server.wait_closed()
+            )
+        loop.close()
+        logging.info("Stopped.")
+
+    async def run_server(self):
+        self._server = await asyncio.start_server(
+            ssl=self.ssl_context,
+            client_connected_cb=self.connect,
+            host=self.host,
+            port=self.port,
+        )
+        async with self.server:
+            logging.info("Running at `{s.host}:{s.port}`".format(s=self))
+            await self.server.serve_forever()
+
+    @staticmethod
+    async def refuse_connection(writer: asyncio.StreamWriter,
+                                message: str = None):
+        """Send a `message` via writer and close it."""
+        if message is None:
+            message = "Connection refused!\n"
+        writer.write(
+            message.encode('utf-8')
+        )
+        await writer.drain()
+        writer.close()
+
+
+def main():
+    # noinspection SpellCheckingInspection
+    log_formatter = logging.Formatter(
+        "%(asctime)s [%(module)-15s %(levelname)-8s]     %(message)s",
+        style='%'
+    )
+    root_logger = logging.getLogger()
+    root_logger.setLevel(logging.DEBUG)
+
+    # noinspection PyUnresolvedReferences
+    asyncio.selector_events.logger.setLevel(logging.ERROR)
+
+    console_handler = logging.StreamHandler()
+    console_handler.setFormatter(log_formatter)
+    console_handler.setLevel(logging.DEBUG)
+    root_logger.addHandler(console_handler)
+
+    # Parse command-line arguments
+    cli_parser = argparse.ArgumentParser(description='Run server',
+                                         allow_abbrev=False)
+    cli_parser.add_argument('--host', type=str,
+                            default=None,
+                            required=False,
+                            help='server address')
+    cli_parser.add_argument('--port', type=int,
+                            default=None,
+                            required=False,
+                            help='server port')
+    cli_parser.add_argument('--certificate', type=str,
+                            default=None,
+                            required=False,
+                            help='server SSL certificate')
+    cli_parser.add_argument('--key', type=str,
+                            default=None,
+                            required=False,
+                            help='server SSL key')
+    args = vars(cli_parser.parse_args())
+    host = args['host']
+    port = args['port']
+    certificate = args['certificate']
+    key = args['key']
+
+    # If host and port are not provided from command-line, try to import them
+    if host is None:
+        try:
+            from config import host
+        except ImportError:
+            host = None
+    if port is None:
+        try:
+            from config import port
+        except ImportError:
+            port = None
+
+    # If import fails, prompt user for host or port
+    while host is None:
+        host = input("Enter host:\t\t\t\t\t\t")
+    while port is None:
+        try:
+            port = int(input("Enter port:\t\t\t\t\t\t"))
+        except ValueError:
+            logging.info("Invalid port. Enter a valid port number!")
+            port = None
+
+    try:
+        if certificate is None or not os.path.isfile(certificate):
+            from config import certificate
+        if key is None or not os.path.isfile(key):
+            from config import key
+        if not os.path.isfile(certificate):
+            certificate = None
+        if not os.path.isfile(key):
+            key = None
+    except ImportError:
+        certificate = None
+        key = None
+    ssl_context = None
+    if certificate and key:
+        ssl_context = ssl.create_default_context(ssl.Purpose.CLIENT_AUTH)
+        ssl_context.load_cert_chain(certificate, key)
+    else:
+        logging.warning(
+            "Please consider using SSL. To do so, add in `config.py` or "
+            "provide via Command Line Interface the path to a valid SSL "
+            "key and certificate. Example:\n\n"
+            "key = 'path/to/secret.key'\n"
+            "certificate = 'path/to/certificate.crt'"
+        )
+    server = Server(
+        host=host,
+        port=port,
+        ssl_context=ssl_context
+    )
+    server.run()
+
+
+if __name__ == '__main__':
+    main()

filebridging/utilities.py

@@ -0,0 +1,69 @@
+"""Useful functions."""
+
+import logging
+import signal
+import sys
+
+units_of_measurements = {
+    1: 'bytes',
+    1000: 'KB',
+    1000 * 1000: 'MB',
+    1000 * 1000 * 1000: 'GB',
+    1000 * 1000 * 1000 * 1000: 'TB',
+}
+
+
+def get_file_size_representation(file_size):
+    scale, unit = get_scale_and_unit(file_size=file_size)
+    if scale < 10:
+        return f"{file_size} {unit}"
+    return f"{(file_size // (scale / 100)) / 100:.2f} {unit}"
+
+
+def get_scale_and_unit(file_size):
+    scale, unit = min(units_of_measurements.items())
+    for scale, unit in sorted(units_of_measurements.items(), reverse=True):
+        if file_size > scale:
+            break
+    return scale, unit
+
+
+def print_progress_bar(prefix='',
+                       suffix='',
+                       done_symbol="#",
+                       pending_symbol=".",
+                       progress=0,
+                       scale=10):
+    progress_showed = (progress // scale) * scale
+    sys.stdout.write(
+        f"{prefix}"
+        f"{done_symbol * (progress_showed // scale)}"
+        f"{pending_symbol * ((100 - progress_showed) // scale)}\t"
+        f"{progress}%"
+        f"{suffix}      \r"
+    )
+    sys.stdout.flush()
+
+
+def timed_input(message: str = None,
+                timeout: int = 5):
+    class TimeoutExpired(Exception):
+        pass
+
+    def interrupted(signal_number, stack_frame):
+        """Called when read times out."""
+        raise TimeoutExpired
+
+    if message is None:
+        message = f"Enter something within {timeout} seconds"
+
+    signal.alarm(timeout)
+    signal.signal(signal.SIGALRM, interrupted)
+    try:
+        given_input = input(message)
+    except TimeoutExpired:
+        given_input = None
+        print()  # Print end of line
+        logging.info("Timeout!")
+    signal.alarm(0)
+    return given_input

setup.py

@@ -0,0 +1,75 @@
+"""Setup."""
+
+import codecs
+import os
+import re
+import setuptools
+import sys
+
+if sys.version_info < (3, 8):
+    raise RuntimeError("Python3.8+ is needed to use this library")
+
+here = os.path.abspath(os.path.dirname(__file__))
+
+
+def read(*parts):
+    """Read file in `part.part.part.part.ext`.
+
+    Start from `here` and follow the path given by `*parts`
+    """
+    with codecs.open(os.path.join(here, *parts), 'r') as fp:
+        return fp.read()
+
+
+def find_information(info, *file_path_parts):
+    """Read information in file."""
+    version_file = read(*file_path_parts)
+    version_match = re.search(
+        r"^__{info}__ = ['\"]([^'\"]*)['\"]".format(
+            info=info
+        ),
+        version_file,
+        re.M
+    )
+    if version_match:
+        return version_match.group(1)
+    raise RuntimeError("Unable to find version string.")
+
+
+with open("README.md", "r") as readme_file:
+    long_description = readme_file.read()
+
+setuptools.setup(
+    name='filebridging',
+    version=find_information("version", "filebridging", "__init__.py"),
+    author=find_information("author", "filebridging", "__init__.py"),
+    author_email=find_information("email", "filebridging", "__init__.py"),
+    description=(
+        "Share files via a bridge server using TCP over SSL and end-to-end "
+        "encryption."
+    ),
+    license=find_information("license", "filebridging", "__init__.py"),
+    long_description=long_description,
+    long_description_content_type="text/markdown",
+    url="https://gogs.davte.it/davte/filebridging",
+    packages=setuptools.find_packages(),
+    platforms=['any'],
+    install_requires=[],
+    classifiers=[
+        "Development Status :: 5 - Production/Stable",
+        "Environment :: Console",
+        "Framework :: AsyncIO",
+        "Intended Audience :: End Users/Desktop",
+        "License :: OSI Approved :: GNU General Public License v3 (GPLv3)",
+        "Natural Language :: English",
+        "Operating System :: OS Independent",
+        "Programming Language :: Python :: 3 :: Only",
+        "Topic :: Communications :: File Sharing",
+    ],
+    keywords=(
+        'file share '
+        'tcp ssl tls end-to-end encryption '
+        'python asyncio async'
+    ),
+    include_package_data=True,
+)