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Simple reliable transport (Cal EE 122 Project 1, Fall 2011)

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README
EE 122 Fall 2011
Project 1

In this folder you'll find the sample receiver, code for computing and
validating checksums, as well as example sender code. 

Quick! What do I have to write?
===============================
Sender.py is the file in which you will implement your reliable sender. You do
not need to modify any other included files to complete this project, unless of
course you are implementing one of the bells and whistles that requires you to
do so. It provides all the scaffolding you need to handle the command line
arguments we will use in the grading of your project.

The Receiver
============
Receiver.py is the sample receiver. What you've received is largely identical
to what we will use for grading your projects (what we actually use may include
additional instrumentation to assist in grading, but should not vary
significantly in functionality). Feel free to modify it, but keep in mind that
we will be testing against our own version of the sender, not yours (except, of
course, if you're implementing an extra credit option that requires extending
the receiver we provided). If bugs are found or changes made to the sample
receiver, we'll notify you and post an updated copy. Additionally, the latest
version of the sample receiver will usually be running on
harpua.cs.berkeley.edu, port 33122, and you are welcome to test your senders
against that receiver.

BasicSender and Friends
=======================
The BasicSender class in BasicSender.py provides a skeleton upon which to build
your reliable sender. It provides the following methods:

    __init__(self,dest,port,filename): Creates a BasicSender. Specify the
        destination's hostname, the port at which the receiver is listening,
        and a filename to transmit. If no filename is provided, it will read
        from STDIN.
    
    receive(self, timeout): Receive a packet. Waits for a packet before
        returning. Optionally you can specify a maximum timeout to wait for a
        packet. Returns the received packet as a string, or None if receive
        times out.

    send(self,message): Sends message to the receiver specified when you
        created the sender.

    make_packet(self,msg_type,seqno,message): Creates a BEARS-TP packet from
        the specified message type, sequence number, and message. Generates the
        appropriate checksum, and returns the full BEARS-TP packet with
        checksum appended.

    split_packet(self,packet): Given a BEARS-TP packet, splits a packet into a
        tuple of the form (msg_type, seqno, data, checksum). For packets
        without a data field, the data element will be the empty string.

In addition, it defines one method which you must implement:

    start(self): Starts the Sender.

We provide three example senders that build upon the BasicSender; you are
welcome to base your design upon these:

UnreliableSender.py: While it provides no reliability, it will read from a file
or STDIN and send to a receiver using our protocol.

InteractiveSender.py: A simple interactive sender. It will send any message you
type to the specified receiver. It then waits for a response before prompting
you for a new message. 

StanfurdSender.py: Almost identical to InteractiveSender.py, it's not very good
at counting and sometimes loses track of sequence numbers. You can use this to
see how the receiver behaves when loss occurs.

Checksums
=========
Checksum.py includes two functions for validating and generating checksums for
your packets:

    validate_checksum(message): Returns true if the message's checksum matches
        the message, and false otherwise. This function assumes the last field
        of the message the checksum.

    generate_checksum(message): Returns the checksum string for a message. This
        function assumes the message includes the trailing delimiter. The
        checksum is ONLY valid if you simply append this function's result to
        the message you pass in.

Problems and Questions
======================
Direct any problems or questions you have to your recitation section GSI. If
you find problems or bugs in the provided code, you may also file an issue
ticket on this project's Github page:

    https://github.com/shaddi/bears-tp
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