The sliplib module implements the encoding and decoding
functionality for SLIP packets, as described in
RFC 1055.
It defines encoding, decoding, and validation functions,
as well as a driver class that can be used to implement
a SLIP protocol stack, and higher-level classes that
apply the SLIP protocol to TCP connections or IO streams.
Read the documentation
for detailed information.
The SLIP protocol is described in RFC 1055 (A Nonstandard for Transmission of IP Datagrams over Serial Lines: SLIP, J. Romkey, June 1988). The original purpose of the protocol is to provide a mechanism to indicate the boundaries of IP packets, in particular when the IP packets are sent over a connection that does not provide a framing mechanism, such as serial lines or dial-up connections.
There is, however, nothing specific to IP in the SLIP protocol. SLIP offers a generic framing method that can be used for any type of data that must be transmitted over a (continuous) byte stream. In fact, the main reason for creating this module was the need to communicate with a third-party application that used SLIP over TCP (which is a continuous byte stream) to frame variable length data structures.
To install the sliplib module, use
pip install sliplib
The recommended basic usage is to run all encoding and decoding operations
through an instantiation driver of the Driver class, in combination
with the appropriate I/O code.
The Driver class itself works without any I/O, and can therefore be used with
any networking code, or any bytestream like pipes, serial I/O, etc.
It can work in synchronous as well as in asynchronous environments.
The Driver class offers the methods
send and receive to handle
the conversion between messages and SLIP-encoded packets.
The module also provides a SlipWrapper abstract baseclass
that provides the methods send_msg and recv_msg to send
and receive single SLIP-encoded messages. This base class
wraps an instance of the Driver class with a user-provided stream.
Two concrete subclasses of SlipWrapper are provided:
SlipStreamallows the wrapping of a byte IO stream.SlipSocketallows the wrapping of a TCP socket.
In addition, the module also provides a SlipRequestHandler
to facilitate the creation of TCP servers that can handle
SLIP-encoded messages.
Contrary to the reference implementation described in :rfc:1055,
which chooses to essentially ignore protocol errors,
the functions and classes in the sliplib module
use a ProtocolError exception
to indicate protocol errors, i.e. SLIP packets with invalid byte sequences.
The Driver class raises a ProtocolError exception
when an attempt is made to get() a message from such a packet.