OneClientServer¶

class lsst.ts.tcpip.OneClientServer(host: str | None, port: int | None, log: Logger, connect_callback: Callable[[BaseClientOrServer], Awaitable[None]] | None = None, monitor_connection_interval: float = 0.1, name: str = '', encoding: str = 'utf-8', terminator: bytes = b'\r\n', **kwargs: Any)¶

Bases: BaseClientOrServer

A TCP/IP socket server that serves a single client.

If additional clients try to connect, they are rejected.

Parameters:

portint

IP port for this server. If 0 then randomly pick an available port (or ports, if listening on multiple sockets). 0 is strongly recommended for unit tests.

hoststr or None

IP address for this server. Common values include DEFAULT_LOCALHOST, LOCALHOST_IPV4 to force IPV4 or LOCALHOST_IPV6 for IPV6. If None then bind to all network interfaces (e.g. listen on an IPv4 socket and an IPv6 socket). Warning: None can cause trouble with port=0; see port in the Attributes section for more information.

loglogging.Logger

Logger.

connect_callbackcallable or None, optional

Asynchronous or (deprecated) synchronous function to call when when a client connects or disconnects. If the other end (client) closes the connection, it may take monitor_connection_interval seconds or longer to notice. The function receives one argument: this OneClientServer.

monitor_connection_intervalfloat, optional

Interval between checking if the connection is still alive (seconds). Defaults to DEFAULT_MONITOR_CONNECTION_INTERVAL. If ≤ 0 then do not monitor the connection at all. Monitoring is only useful if you do not regularly read from the reader using the read methods of this class (or copying what they do to detect and report hangups).

namestr, optional

Name used for log messages, e.g. “Commands” or “Telemetry”.

encodingstr

The encoding used by read_str and write_str, read_json,: and write_json.

terminatorbytes

The terminator used by read_str and write_str, read_json,: and write_json.

**kwargsdict [str, typing.Any]

Additional keyword arguments for asyncio.start_server, beyond host and port.

Notes

See tests/test_example.py for an example.

Always wait for start_task after constructing an instance, before using the instance. This indicates that the server has started listening for a connection.

You may wait for connected_task to wait until a client connects.

This class provides high-level read and write methods that monitor the connection (to call connect_callback as needed) and reject any attempt to read or write if not connected. Please use them.

Can be used as an async context manager, which may be useful for unit tests.

Attributes:

hoststr | None

IP address; the host constructor argument.

portint

The port on which this server is running.

If you specify port=0 and the server is only listening on one socket, then the port attribute is set to the randomly chosen port. However, if the server is listening on more than one socket, the port is ambiguous (since each socket will have a different port) and will be left at 0; in that case you will have to examine server.sockets to determine the port you want.

To make the server listen on only one socket with port=0, specify the host as a string instead of None. For example:

IP4: host=LOCALHOST_IPV4, port=0
IP6: host="::", port=0

An alternative that allows host=None is to specify family as socket.AF_INET for IPv4, or socket.AF_INET6 for IPv6.

connected_taskasyncio.Future

Future that is set done when a client connects. You may set replace it with a new asyncio.Future if you want to detect when another connection is made after the current client disconnects.

plus…

Attributes provided by parent class BaseClientOrServer.

Attributes Summary

connected

Return True if self._reader and self._writer are connected.

Methods Summary

`basic_close_client`()	Close the connected client socket, if any.
`call_connect_callback`()	Call self.__connect_callback.
`close`()	Close socket server and client socket, and set done_task done.
`close_client`()	Close the connected client socket, if any.
`read`(n)	Read up to n bytes.
`read_into`(struct)	Read binary data from a stream reader into a `ctypes.Structure`.
`read_json`()	Read JSON data.
`read_str`()	Read and decode a terminated str; strip the terminator.
`readexactly`(n)	Read exactly n bytes.
`readline`()	Read a sequence of bytes ending with `\n`.
`readuntil`([separator])	Read one line, where “line” is a sequence of bytes ending with `separator`.
`start`(**kwargs)	Start the TCP/IP server.
`write`(data)	Write data and call `drain`.
`write_from`(*structs)	Write binary data from one or more `ctypes.Structure`s.
`write_json`(data)	Write data in JSON format.
`write_str`(line)	Encode, terminate, and write a str.
`writelines`(lines)	Write an iterable of bytes and call `drain`.

Attributes Documentation

connected¶

Return True if self._reader and self._writer are connected.

Note: if the other end drops the connection and if you are not trying to read data (e.g. in a background loop), then it takes the operating system awhile to realize the connection is lost. So this can return true for some unknown time after the connection has been dropped.

Methods Documentation

async basic_close_client() → None¶

Close the connected client socket, if any.

Also:

Reset self.connected_task to a new Future.
Call connect_callback, if a client was connected.

Unlike close_client, this does not touch self.should_be_connected.

Always safe to call.

async call_connect_callback() → None¶

Call self.__connect_callback.

This is always safe to call. It only calls the callback function if that function is not None and if the connection state has changed since the last time this method was called.

async close() → None¶

Close socket server and client socket, and set done_task done.

Call connect_callback if a client was connected.

Always safe to call.

async close_client() → None¶

Close the connected client socket, if any.

Also:

Set self.should_be_connected false.
Reset self.connected_task to a new Future.
Call connect_callback, if a client was connected.

Always safe to call.

async read(n: int) → bytes¶

Read up to n bytes.

Parameters:

nint: The number of bytes to read. If -1 then block until the other end closes its writer, then return all data seen.

Raises:

ConnectionError: If the connection is lost before, or while, reading.

async read_into(struct: Structure) → None¶

Read binary data from a stream reader into a ctypes.Structure.

Parameters:

structctypes.Structure: Structure to set.

Raises:

ConnectionError: If the connection is lost before, or while, reading.
asyncio.IncompleteReadError: If EOF is reached before n bytes can be read. Use the IncompleteReadError.partial attribute to get the partially read data.

async read_json() → Any¶

Read JSON data.

Read the data with read_str and return the json-decoded result.

Returns:

datatyping.Any: Data decoded from JSON.

Raises:

ConnectionError: If the connection is lost before, or while, reading.
asyncio.IncompleteReadError: If EOF is reached before the complete separator is found and the internal buffer is reset.
LimitOverrunError: If the amount of data read exceeds the configured stream lmit. The data is left in the internal buffer and can be read again.
TypeError: If the data are of a type that cannot be decoded from JSON.
json.JSONDecodeError: If the data cannot be decoded from JSON.

async read_str() → str¶

Read and decode a terminated str; strip the terminator.

Read until self.terminator, strip the terminator, and decode the data as self.encoding with strict error handling.

Returns:

linestr: Line of data, as a str with the terminator stripped.

Raises:

ConnectionError: If the connection is lost before, or while, reading.
asyncio.IncompleteReadError: If EOF is reached before the complete separator is found and the internal buffer is reset.
LimitOverrunError: If the amount of data read exceeds the configured stream lmit. The data is left in the internal buffer and can be read again.
UnicodeError: If decoding fails.

async readexactly(n: int) → bytes¶

Read exactly n bytes.

Parameters:

nint: The number of bytes to read.

Raises:

ConnectionError: If the connection is lost before, or while, reading.
asyncio.IncompleteReadError: If EOF is reached before n bytes can be read. Use the IncompleteReadError.partial attribute to get the partially read data.

async readline() → bytes¶

Read a sequence of bytes ending with \n.

If EOF is received and \n was not found, the method returns partially read data.

Raises:

ConnectionError: If the connection is lost before, or while, reading.

async readuntil(separator: bytes = b'\n') → bytes¶

Read one line, where “line” is a sequence of bytes ending with separator.

Read data from the stream until separator is found.

On success, the data and separator will be removed from the internal buffer (consumed). Returned data will include the separator at the end.

See also read_str, which is more convenient for most use cases.

Parameters:

separatorbytes: The desired separator. The default matches the standard library, rather than using terminator.

Raises:

ConnectionError: If the connection is lost before, or while, reading.
asyncio.IncompleteReadError: If EOF is reached before the complete separator is found and the internal buffer is reset.
LimitOverrunError: If the amount of data read exceeds the configured stream lmit. The data is left in the internal buffer and can be read again.

async start(**kwargs: Any) → None¶

Start the TCP/IP server.

This is called automatically by the constructor, and is not intended to be called by the user. It is a public method so that subclasses can override it.

Parameters:

**kwargsdict [str, typing.Any]: Additional keyword arguments for asyncio.start_server, beyond host and port.

Raises:

RuntimeError: If start has already been called and has successfully constructed a server.

async write(data: bytes) → None¶

Write data and call drain.

Parameters:

databytes: The data to write.

Raises:

ConnectionError: If self.connected false before writing begins.

async write_from(*structs: Structure) → None¶

Write binary data from one or more ctypes.Structures.

Parameters:

structslist [ctypes.Structure]: Structures to write.

Raises:

ConnectionError: If self.connected false before writing begins.

async write_json(data: Any) → None¶

Write data in JSON format.

Encode the data as json and write the result with write_str.

Parameters:

dataany: The data to be written. Typically a dict, but any json-encodable data is acceptable.

Raises:

ConnectionError: If the connection is lost before, or while, reading.
UnicodeError: If encoding fails.
json.JSONEncodeError: If the data cannot be json-encoded.

async write_str(line: str) → None¶

Encode, terminate, and write a str.

Encode the str as self.encoding with strict error handling, and append self.terminator.

Parameters:

linestr: The line of data to be written.

Raises:

ConnectionError: If the connection is lost before, or while, reading.
UnicodeError: If encoding fails.

async writelines(lines: Iterable) → None¶

Write an iterable of bytes and call drain.

Parameters:

linescollections.abc.Iterable [bytes]: The data to write, as an iterable collection of bytes.

Raises:

ConnectionError: If self.connected false before writing begins.

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OneClientServer¶