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<title>CSCI 4061 Project 2: Blather Chat Server/Client</title>
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<div id="preamble" class="status">
<i>Last Updated: 2017-11-29 Wed 17:46</i>
</div>
<div id="content">
<h1 class="title">CSCI 4061 Project 2: Blather Chat Server/Client</h1>
<ul class="org-ul">
<li><b>Due: 11:59pm Tue 12/12/2017</b>
</li>
<li><i>Approximately 20.0% of total grade</i>
</li>
<li>Submit to <a href="https://canvas.umn.edu/"><b>Canvas</b></a>
</li>
<li>Projects may be done in groups of 1 or 2. Indicate groups in the
<code>GROUP-MEMBERS.txt</code> file.
</li>
<li>No additional collaboration with other students is allowed. Seek
help from course staff if you get stuck for too long.
</li>
</ul>
<div id="outline-container-sec-0-0-1" class="outline-4">
<h4 id="sec-0-0-1">CODE DISTRIBUTION: <a href="http://www-users.cs.umn.edu/~kauffman/4061/p2-code.zip">p2-code.zip</a></h4>
</div>
<div id="outline-container-sec-0-0-2" class="outline-4">
<h4 id="sec-0-0-2">TEST CODE: <i>Not posted</i></h4>
<div class="outline-text-4" id="text-0-0-2">
</div>
</div>
<div id="outline-container-sec-0-0-3" class="outline-4">
<h4 id="sec-0-0-3">CHANGELOG:</h4>
<div class="outline-text-4" id="text-0-0-3">
<dl class="org-dl">
<dt> Tue Nov 28 15:33:01 CST 2017 </dt><dd> Corrected project weight. Re-ordered to put optional ADVANCED
features at end. Described unlinking the semaphore for final
ADVANCED feature.
</dd>
</dl>
<div id="table-of-contents">
<h2>Table of Contents</h2>
<div id="text-table-of-contents">
<ul>
<li><a href="http://www-users.cs.umn.edu/~kauffman/4061/p2.html#sec-1">1. Introduction: A Chat Service</a>
<ul>
<li><a href="http://www-users.cs.umn.edu/~kauffman/4061/p2.html#sec-1-1">1.1. Basic Features</a></li>
<li><a href="http://www-users.cs.umn.edu/~kauffman/4061/p2.html#sec-1-2">1.2. ADVANCED Features : Extra Credit</a></li>
</ul>
</li>
<li><a href="http://www-users.cs.umn.edu/~kauffman/4061/p2.html#sec-2">2. Download Code and Setup</a></li>
<li><a href="http://www-users.cs.umn.edu/~kauffman/4061/p2.html#sec-3">3. Demo / ScreenShot</a></li>
<li><a href="http://www-users.cs.umn.edu/~kauffman/4061/p2.html#sec-4">4. Overall Architecture</a>
<ul>
<li><a href="http://www-users.cs.umn.edu/~kauffman/4061/p2.html#sec-4-1">4.1. What Needs to be Implemented</a></li>
<li><a href="http://www-users.cs.umn.edu/~kauffman/4061/p2.html#sec-4-2">4.2. What's Already Done</a></li>
<li><a href="http://www-users.cs.umn.edu/~kauffman/4061/p2.html#sec-4-3">4.3. Provide a Makefile</a></li>
<li><a href="http://www-users.cs.umn.edu/~kauffman/4061/p2.html#sec-4-4">4.4. No malloc() / free() required</a></li>
</ul>
</li>
<li><a href="http://www-users.cs.umn.edu/~kauffman/4061/p2.html#sec-5">5. Basic Protocol and Architecture</a>
<ul>
<li><a href="http://www-users.cs.umn.edu/~kauffman/4061/p2.html#sec-5-1">5.1. Server and Clients</a></li>
<li><a href="http://www-users.cs.umn.edu/~kauffman/4061/p2.html#sec-5-2">5.2. Joining</a></li>
<li><a href="http://www-users.cs.umn.edu/~kauffman/4061/p2.html#sec-5-3">5.3. Normal Messages</a></li>
<li><a href="http://www-users.cs.umn.edu/~kauffman/4061/p2.html#sec-5-4">5.4. Departures and Removing Clients</a></li>
<li><a href="http://www-users.cs.umn.edu/~kauffman/4061/p2.html#sec-5-5">5.5. Protocol Data Types</a></li>
</ul>
</li>
<li><a href="http://www-users.cs.umn.edu/~kauffman/4061/p2.html#sec-6">6. The Server</a>
<ul>
<li><a href="http://www-users.cs.umn.edu/~kauffman/4061/p2.html#sec-6-1">6.1. Server and Client Data</a></li>
<li><a href="http://www-users.cs.umn.edu/~kauffman/4061/p2.html#sec-6-2">6.2. Server Operations: <code>server.c</code></a></li>
<li><a href="http://www-users.cs.umn.edu/~kauffman/4061/p2.html#sec-6-3">6.3. Messages Handled by the Server</a></li>
<li><a href="http://www-users.cs.umn.edu/~kauffman/4061/p2.html#sec-6-4">6.4. Other Messages Sent by the Server</a></li>
<li><a href="http://www-users.cs.umn.edu/~kauffman/4061/p2.html#sec-6-5">6.5. <code>bl-server.c</code> main function</a></li>
</ul>
</li>
<li><a href="http://www-users.cs.umn.edu/~kauffman/4061/p2.html#sec-7">7. The Client</a>
<ul>
<li><a href="http://www-users.cs.umn.edu/~kauffman/4061/p2.html#sec-7-1">7.1. Simplified Terminal I/O</a></li>
<li><a href="http://www-users.cs.umn.edu/~kauffman/4061/p2.html#sec-7-2">7.2. <code>bl-client.c</code> Features</a></li>
<li><a href="http://www-users.cs.umn.edu/~kauffman/4061/p2.html#sec-7-3">7.3. Client Main Approach</a></li>
</ul>
</li>
<li><a href="http://www-users.cs.umn.edu/~kauffman/4061/p2.html#sec-8">8. Manual Inspection Criteria (50%)</a></li>
<li><a href="http://www-users.cs.umn.edu/~kauffman/4061/p2.html#sec-9">9. ADVANCED Features</a>
<ul>
<li><a href="http://www-users.cs.umn.edu/~kauffman/4061/p2.html#sec-9-1">9.1. Server Ping and Disconnected Clients (10%)</a></li>
<li><a href="http://www-users.cs.umn.edu/~kauffman/4061/p2.html#sec-9-2">9.2. Binary Server Log File (10%)</a></li>
<li><a href="http://www-users.cs.umn.edu/~kauffman/4061/p2.html#sec-9-3">9.3. Last Messages for Client (10%)</a></li>
<li><a href="http://www-users.cs.umn.edu/~kauffman/4061/p2.html#sec-9-4">9.4. <code>who_t</code> for Client and Server (10%)</a></li>
</ul>
</li>
<li><a href="http://www-users.cs.umn.edu/~kauffman/4061/p2.html#sec-10">10. Automatic Testing (50%)</a></li>
<li><a href="http://www-users.cs.umn.edu/~kauffman/4061/p2.html#sec-11">11. Zip and Submit</a>
<ul>
<li><a href="http://www-users.cs.umn.edu/~kauffman/4061/p2.html#sec-11-1">11.1. Submit to Canvas</a></li>
<li><a href="http://www-users.cs.umn.edu/~kauffman/4061/p2.html#sec-11-2">11.2. Late Policies</a></li>
</ul>
</li>
</ul>
</div>
</div>
</div>
</div>
<div id="outline-container-sec-1" class="outline-2">
<h2 id="sec-1"><span class="section-number-2">1</span> Introduction: A Chat Service</h2>
<div class="outline-text-2" id="text-1">
<p>
Systems programming is often associated with communication as this
invariably requires coordinating multiple entities that are related
only based on their desire to share information. This project focuses
on developing a simple <b>chat server and client</b> called <code>blather</code>. The
basic usage is in two parts.
</p>
<dl class="org-dl">
<dt> Server </dt><dd> Some user starts <code>bl-server</code> which manages the chat "room". The
server is non-interactive and will likely only print debugging
output as it runs.
</dd>
<dt> Client </dt><dd> Any user who wishes to chat runs <code>bl-client</code> which takes input
typed on the keyboard and sends it to the server. The server
broadcasts the input to all other clients who can respond by
typing their own input.
</dd>
</dl>
<p>
Chat servers are an old idea dating to the late 1970's and if you have
never used one previously, get online a bit more or <a href="https://en.wikipedia.org/wiki/Online_chat">read about them on
Wikipedia</a>. Even standard Unix terminals have a built-in ability to
communicate with other users through <a href="http://man7.org/linux/man-pages/man1/mesg.1.html">commands like <code>write</code>, <code>wall</code>,
and <code>talk</code></a>.
</p>
<p>
Unlike standard internet chat services, <code>blather</code> will be restricted
to a single Unix machine and to users with permission to read related
files. However, extending the programs to run via the internet will
be the subject of some discussion.
</p>
<p>
Like most interesting projects, <code>blather</code> utilizes a combination of
many different system tools. Look for the following items to arise.
</p>
<ul class="org-ul">
<li>Multiple communicating processes: clients to servers
</li>
<li>Communication through FIFOs
</li>
<li>Signal handling for graceful server shutdown
</li>
<li>Alarm signals for periodic behavior
</li>
<li>Input multiplexing with <code>select()</code>
</li>
<li>Multiple threads in the client to handle typed input versus info
from the server
</li>
</ul>
<p>
Finally, this project includes some <b>advanced features</b> which may be
implemented for extra credit.
</p>
</div>
<div id="outline-container-sec-1-1" class="outline-3">
<h3 id="sec-1-1"><span class="section-number-3">1.1</span> Basic Features</h3>
<div class="outline-text-3" id="text-1-1">
<p>
The specification below is mainly concerned with basic features of the
<code>blather</code> server and client. Implementing these can garner full credit
for the assignment.
</p>
</div>
</div>
<div id="outline-container-sec-1-2" class="outline-3">
<h3 id="sec-1-2"><span class="section-number-3">1.2</span> ADVANCED Features : Extra Credit</h3>
<div class="outline-text-3" id="text-1-2">
<p>
Some portions of the specification and code are marked ADVANCED to
indicate optional features that can be implemented for extra
credit. Some of these have dependencies so take care to read
carefully.
</p>
<p>
ADVANCED features may be evaluated using tests and manual inspection
criteria that are made available after the standard tests are
distributed.
</p>
</div>
</div>
</div>
<div id="outline-container-sec-2" class="outline-2">
<h2 id="sec-2"><span class="section-number-2">2</span> Download Code and Setup</h2>
<div class="outline-text-2" id="text-2">
<p>
As in labs, download the code pack linked at the top of the
page. Unzip this which will create a folder and create your files in
that folder.
</p>
<table border="2" cellspacing="0" cellpadding="6" rules="groups" frame="hsides">
<colgroup>
<col class="left">
<col class="left">
<col class="left">
</colgroup>
<thead>
<tr>
<th scope="col" class="left">File</th>
<th scope="col" class="left">State</th>
<th scope="col" class="left">Notes</th>
</tr>
</thead>
<tbody>
<tr>
<td class="left">GROUP-MEMBERS.txt</td>
<td class="left">Edit</td>
<td class="left">Fill in names of group members to indicate partnerships</td>
</tr>
<tr>
<td class="left">Makefile</td>
<td class="left">Create</td>
<td class="left">Build project, run tests</td>
</tr>
<tr>
<td class="left">server.c</td>
<td class="left">Create</td>
<td class="left">Service routines for the server</td>
</tr>
<tr>
<td class="left">bl-server.c</td>
<td class="left">Create</td>
<td class="left">Main function for <code>bl-server</code> executable</td>
</tr>
<tr>
<td class="left">bl-client.c</td>
<td class="left">Create</td>
<td class="left">Main function for <code>bl-client</code> executable</td>
</tr>
</tbody>
<tbody>
<tr>
<td class="left">blather.h</td>
<td class="left">Provided</td>
<td class="left">Header file which contains required structs, defines, and prototypes</td>
</tr>
<tr>
<td class="left">util.c</td>
<td class="left">Provided</td>
<td class="left">Utility methods debug messages and checking system call returns</td>
</tr>
<tr>
<td class="left">simpio.c</td>
<td class="left">Provided</td>
<td class="left">Simplified terminal I/O to get nice interactive sessions</td>
</tr>
<tr>
<td class="left">simpio-demo.c</td>
<td class="left">Provided</td>
<td class="left">Demonstrates simpio features, model for <code>bl-client.c</code></td>
</tr>
</tbody>
</table>
</div>
</div>
<div id="outline-container-sec-3" class="outline-2">
<h2 id="sec-3"><span class="section-number-2">3</span> Demo / ScreenShot</h2>
<div class="outline-text-2" id="text-3">
<p>
Demonstrating an interactive, dynamic chat session between multiple
users is difficult but the screenshot below attempts to do so. It
shows the server and several clients mid-chat.
</p>
<ul class="org-ul">
<li>The server <code>bl-server</code> is started in the large terminal on the left
and shows output about what is going on. There is no specific output
required and that shown is for debugging purposes.
</li>
<li>There are 4 <code>bl-client</code> instances run by various users who log into
the server and specify their name. The lower-right user <code>Barbara</code>
joins later while the upper left user <code>Bruce</code> logs out near the end
of the session.
</li>
</ul>
<div class="center">
<div class="figure">
<p><img src="./readme_files/blather-demo.png" alt="blather-demo.png" width="100%" style="max-width:100%;">
</p>
<p><span class="figure-number">Figure 1:</span> Sample <code>blather</code> server and client runs.</p>
</div>
</div>
</div>
</div>
<div id="outline-container-sec-4" class="outline-2">
<h2 id="sec-4"><span class="section-number-2">4</span> Overall Architecture</h2>
<div class="outline-text-2" id="text-4">
</div><div id="outline-container-sec-4-1" class="outline-3">
<h3 id="sec-4-1"><span class="section-number-3">4.1</span> What Needs to be Implemented</h3>
<div class="outline-text-3" id="text-4-1">
<p>
<code>blather</code> has two parts: the server and client. Both need to be
written along with service routines in <code>server.c</code>
</p>
</div>
<div id="outline-container-sec-4-1-1" class="outline-4">
<h4 id="sec-4-1-1"><code>server.c</code> data structure manipulations</h4>
<div class="outline-text-4" id="text-4-1-1">
<p>
Implement the functions in this file to manipulate the <code>server_t</code> and
<code>client_t</code> data that will ultimately be used by the server to fulfill
its role.
</p>
</div>
</div>
<div id="outline-container-sec-4-1-2" class="outline-4">
<h4 id="sec-4-1-2"><code>bl-server.c</code> main function and signal handlers</h4>
<div class="outline-text-4" id="text-4-1-2">
<p>
Implement the server which manages the interactions between clients in
this file making use of the service functions in <code>server.c</code> to get the
job done.
</p>
</div>
</div>
<div id="outline-container-sec-4-1-3" class="outline-4">
<h4 id="sec-4-1-3"><code>bl-client.c</code> main function and thread workers</h4>
<div class="outline-text-4" id="text-4-1-3">
<p>
Implement the client which allows a single user to communicate with
the server in this file. The client must have multiple threads so you
will need to implement some worker functions as thread entry points
here.
</p>
</div>
</div>
</div>
<div id="outline-container-sec-4-2" class="outline-3">
<h3 id="sec-4-2"><span class="section-number-3">4.2</span> What's Already Done</h3>
<div class="outline-text-3" id="text-4-2">
<p>
Examine the provided files closely as they give some insight into what
work is already done.
</p>
<ul class="org-ul">
<li><code>blather.h</code> can be included in most files to make programs aware of
the data structures and required functions. It contains
documentation of the central data structures.
</li>
<li><code>util.c</code> contains a few functions for debugging and checking system
calls.
</li>
<li><code>simpio.c</code> and <code>simpio-demo.c</code> provide a small library and data
structure to do terminal I/O nicely. The demo program shows how it
works.
</li>
</ul>
</div>
</div>
<div id="outline-container-sec-4-3" class="outline-3">
<h3 id="sec-4-3"><span class="section-number-3">4.3</span> Provide a Makefile</h3>
<div class="outline-text-3" id="text-4-3">
<p>
Provide a <code>Makefile</code> which has at least the following targets.
</p>
<ul class="org-ul">
<li><code>bl-server</code> : builds the server executable, be included in the
default targets.
</li>
<li><code>bl-client</code> : builds the client executable, be included in the
default targets.
</li>
<li><code>test-binary</code> : compile and run the binary tests
</li>
<li><code>test-shell</code> : run the shell scripts associated with integration
tests
</li>
</ul>
</div>
</div>
<div id="outline-container-sec-4-4" class="outline-3">
<h3 id="sec-4-4"><span class="section-number-3">4.4</span> No malloc() / free() required</h3>
<div class="outline-text-3" id="text-4-4">
<p>
It may come as a surprise, but this set of programs is specifically
oriented so that no dynamic memory allocation is required. All of the
data structures are fixed size, strings have a maximum length, and
communication is done through FIFOs. Keep this in mind as you code
and avoid <code>malloc()</code> unless you see no other way around it as it will
likely make things harder than they need to be.
</p>
</div>
</div>
</div>
<div id="outline-container-sec-5" class="outline-2">
<h2 id="sec-5"><span class="section-number-2">5</span> Basic Protocol and Architecture</h2>
<div class="outline-text-2" id="text-5">
<p>
Clients communicate with the server along the following lines.
</p>
<ul class="org-ul">
<li><code>bl-server</code> creates a FIFO at startup time. The FIFO is created with
a name specified according to naming convention at startup. Examples:
<div class="org-src-container">
<pre class="src src-sh">$> bl-server server1 # creates the server1.fifo
$> bl-server batcave # creates the batcave.fifo
$> bl-server fortress-of-solitude # creates the fortress-of-solitude.fifo
</pre>
</div>
<p>
This FIFO is <b>only for join requests</b> to the server. The name of
this file must be known for the clients to connect to server.
</p>
</li>
<li>The server then waits for clients to write join requests to join
FIFO.
</li>
<li><code>bl-client</code> creates two FIFOs on startup:
<ul class="org-ul">
<li>A <b>to-client FIFO</b> for the server to write data intended for the
client. The client reads this FIFO.
</li>
<li>A <b>to-server FIFO</b> to which the client writes and from which the
server reads.
</li>
<li>The names of these files are inconsequential so long as they are
fairly unique. Basing names for the FIFOs on the PID of the client
is an easy way to do this. This avoids multiple clients in the
same directory mistakenly using each other's FIFOs.
</li>
</ul>
</li>
<li>A client writes a join request to the server which includes the
names of its to-client and to-server FIFOs. All subsequent
communication between client and server is done through the
to-client and to-server FIFOs.
</li>
<li>A client reads typed input from users. When input is ready, it is
sent as a <b>mesg<sub>t</sub></b> to the server.
</li>
<li>As a server receives messages from clients, it will <b>broadcast</b> the
message to all clients including the sender.
</li>
<li>The server sends notices of other kinds to the clients such as when
a new client <b>joins</b>. Clients may send <b>departure</b> notices which are
re-broadcast by the server.
</li>
</ul>
<p>
The sections below give graphical depictions of some of the ideas of
the protocols.
</p>
</div>
<div id="outline-container-sec-5-1" class="outline-3">
<h3 id="sec-5-1"><span class="section-number-3">5.1</span> Server and Clients</h3>
<div class="outline-text-3" id="text-5-1">
<p>
The following diagram illustrates the single server <code>server1</code> with 2
clients connected. Each client has its own FIFOs for communication
with the server and the server knows about these FIFOs.
</p>
<div class="center">
<div class="figure">
<p><img src="./readme_files/schematic.svg" alt="schematic.svg" width="50%" style="max-width:100%;">
</p>
<p><span class="figure-number">Figure 2:</span> Schematic of server data which has been joined by 2 clients.</p>
</div>
</div>
</div>
</div>
<div id="outline-container-sec-5-2" class="outline-3">
<h3 id="sec-5-2"><span class="section-number-3">5.2</span> Joining</h3>
<div class="outline-text-3" id="text-5-2">
<p>
This diagram illustrates how a new client can join the server. It
creates FIFOs for communication and then writes a <code>join_t</code> request on
the server's FIFO. The server then adds the client information to its
array and broadcasts the join to all clients.
</p>
<div class="center">
<div class="figure">
<p><img src="./readme_files/join-request.svg" alt="join-request.svg" width="100%" style="max-width:100%;">
</p>
<p><span class="figure-number">Figure 3:</span> New client joining the server which has two existing clients.</p>
</div>
</div>
</div>
</div>
<div id="outline-container-sec-5-3" class="outline-3">
<h3 id="sec-5-3"><span class="section-number-3">5.3</span> Normal Messages</h3>
<div class="outline-text-3" id="text-5-3">
<p>
A client wanting to communicate with others sends a normal <code>mesg_t</code> to
the server with its name and body filled in. The client's to-server
FIFO is used for this. The server then broadcasts the same message to
all clients including the sender.
</p>
<div class="center">
<div class="figure">
<p><img src="./readme_files/broadcast.svg" alt="broadcast.svg" width="100%" style="max-width:100%;">
</p>
<p><span class="figure-number">Figure 4:</span> Client sending a message which is broadcast to all other clients.</p>
</div>
</div>
</div>
</div>
<div id="outline-container-sec-5-4" class="outline-3">
<h3 id="sec-5-4"><span class="section-number-3">5.4</span> Departures and Removing Clients</h3>
<div class="outline-text-3" id="text-5-4">
<p>
A client can indicate it is leaving by sending an appropriate
message. The server will remove its FIFOs and shift all elements in
its clients array. The departure is broadcast to all clients.
</p>
<div class="center">
<div class="figure">
<p><img src="./readme_files/depart.svg" alt="depart.svg" width="100%" style="max-width:100%;">
</p>
<p><span class="figure-number">Figure 5:</span> Client sending a message which is broadcast to all other clients.</p>
</div>
</div>
</div>
</div>
<div id="outline-container-sec-5-5" class="outline-3">
<h3 id="sec-5-5"><span class="section-number-3">5.5</span> Protocol Data Types</h3>
<div class="outline-text-3" id="text-5-5">
<p>
The header file <code>blather.h</code> describes several data types associated
with basic communication operations. One of these is the <code>mesg_t</code>
struct which is used to convey information between clients and server.
</p>
<pre class="example">// mesg_t: struct for messages between server/client
typedef struct {
mesg_kind_t kind; // kind of message
char name[MAXNAME]; // name of sending client or subject of event
char body[MAXLINE]; // body text, possibly empty depending on kind
} mesg_t;
</pre>
<p>
Each message has a <b>kind</b> which helps determine what to do with the
messages. The kinds are defined in the <code>mesg_kind_t</code> enumeration which
sets up specific integers associated with each kind.
</p>
<pre class="example">// mesg_kind_t: Kinds of messages between server/client
typedef enum {
BL_MESG = 10, // normal messasge from client with name/body
BL_JOINED = 20, // client joined the server, name only
BL_DEPARTED = 30, // client leaving/left server normally, name only
BL_SHUTDOWN = 40, // server to client : server is shutting down, no name/body
BL_DISCONNECTED = 50, // ADVANCED: client disconnected abnormally, name only
BL_PING = 60, // ADVANCED: ping to ask or show liveness
} mesg_kind_t;
</pre>
<p>
Messages are sent both from client to server and from server to client
through the FIFOs that connect them. The specification below will
describe what actions need be taken on receiving messages.
</p>
<p>
Finally, when the a client wishes to initially join the server, it
fills in and sends a <code>join_t</code>.
</p>
<pre class="example">// join_t: structure for requests to join the chat room
typedef struct {
char name[MAXPATH]; // name of the client joining the server
char to_client_fname[MAXPATH]; // name of file server writes to to send to client
char to_server_fname[MAXPATH]; // name of file client writes to to send to server
} join_t;
</pre>
</div>
</div>
</div>
<div id="outline-container-sec-6" class="outline-2">
<h2 id="sec-6"><span class="section-number-2">6</span> The Server</h2>
<div class="outline-text-2" id="text-6">
<p>
The <code>bl-server.c</code> program is responsible for allowing clients to
connect, become aware of one another, and communicate. It's main
functionality is to <b>broadcast</b> messages from one client to all others
and to broadcast status changes such as new clients that join or
depart.
</p>
</div>
<div id="outline-container-sec-6-1" class="outline-3">
<h3 id="sec-6-1"><span class="section-number-3">6.1</span> Server and Client Data</h3>
<div class="outline-text-3" id="text-6-1">
<p>
To that end, the server process should maintain a <code>server_t</code> data
structure which is defined in <code>blather.h</code> as below
</p>
<pre class="example">// server_t: data pertaining to server operations
typedef struct {
char server_name[MAXPATH]; // name of server which dictates file names for joining and logging
int join_fd; // file descriptor of join file/FIFO
int join_ready; // flag indicating if a join is available
int n_clients; // number of clients communicating with server
client_t client[MAXCLIENTS]; // array of clients populated up to n_clients
int time_sec; // ADVANCED: time in seconds since server started
int log_fd; // ADVANCED: file descriptor for log
sem_t *log_sem; // ADVANCED: posix semaphore to control who_t section of log file
} server_t;
</pre>
<p>
The most prominent features of this structure are as follows.
</p>
<ul class="org-ul">
<li>The <code>server_name</code> which determines the name of the FIFO filename for
joining and a few other things.
</li>
<li>A <code>join_fd</code> file descriptor which should be attached to a FIFO to
read requests from clients to join the server.
</li>
<li>The <code>client[][</code> array of <code>client_t</code> structs that track clients
connected to the server. The field <code>n_clients</code> determines how full
this array is.
</li>
</ul>
<p>
Associated closely with the <code>server_t</code> is the <code>client_t</code> struct which
contains data on each client.
</p>
<pre class="example">// client_t: data on a client connected to the server
typedef struct {
char name[MAXPATH]; // name of the client
int to_client_fd; // file descriptor to write to to send to client
int to_server_fd; // file descriptor to read from to receive from client
char to_client_fname[MAXPATH]; // name of file (FIFO) to write into send to client
char to_server_fname[MAXPATH]; // name of file (FIFO) to read from receive from client
int data_ready; // flag indicating a mesg_t can be read from to_server_fd
int last_contact_time; // ADVANCED: server time at which last contact was made with client
} client_t;
</pre>
<p>
While the client program <code>bl-client</code> may make use of this struct as
well its main purpose is to help track data for the server. Prominent
features are as follows.
</p>
<ul class="org-ul">
<li>The user name of the client which is provided when it joins.
</li>
<li>Names and file descriptors of the to-client and to-server FIFOs. The
file descriptors are opened by the server based on the file names
the provided by the client and used for communication between them.
</li>
<li>A <code>data_ready</code> flag which is set and cleared by the server as
messages are available.
</li>
</ul>
</div>
</div>
<div id="outline-container-sec-6-2" class="outline-3">
<h3 id="sec-6-2"><span class="section-number-3">6.2</span> Server Operations: <code>server.c</code></h3>
<div class="outline-text-3" id="text-6-2">
<p>
To facilitate operations of <code>bl-server</code> main program, complete the
<code>server.c</code> file which provides service routines that mainly manipulate
<code>server_t</code> structures. Each of these has a purpose to serve in the
ultimate goal of the server.
</p>
<pre class="example">client_t *server_get_client(server_t *server, int idx);
// Gets a pointer to the client_t struct at the given index. If the
// index is beyond n_clients, the behavior of the function is
// unspecified and may cause a program crash.
void server_start(server_t *server, char *server_name, int perms);
// Initializes and starts the server with the given name. A join fifo
// called "server_name.fifo" should be created. Removes any existing
// file of that name prior to creation. Opens the FIFO and stores its
// file descriptor in join_fd._
//
// ADVANCED: create the log file "server_name.log" and write the
// initial empty who_t contents to its beginning. Ensure that the
// log_fd is position for appending to the end of the file. Create the
// POSIX semaphore "/server_name.sem" and initialize it to 1 to
// control access to the who_t portion of the log.
void server_shutdown(server_t *server);
// Shut down the server. Close the join FIFO and unlink (remove) it so
// that no further clients can join. Send a BL_SHUTDOWN message to all
// clients and proceed to remove all clients in any order.
//
// ADVANCED: Close the log file. Close the log semaphore and unlink
// it.
int server_add_client(server_t *server, join_t *join);
// Adds a client to the server according to the parameter join which
// should have fileds such as name filed in. The client data is
// copied into the client[] array and file descriptors are opened for
// its to-server and to-client FIFOs. Initializes the data_ready field
// for the client to 0. Returns 0 on success and non-zero if the
// server as no space for clients (n_clients == MAXCLIENTS).
int server_remove_client(server_t *server, int idx);
// Remove the given client likely due to its having departed or
// disconnected. Close fifos associated with the client and remove
// them. Shift the remaining clients to lower indices of the client[]
// array and decrease n_clients.
int server_broadcast(server_t *server, mesg_t *mesg);
// Send the given message to all clients connected to the server by
// writing it to the file descriptors associated with them.
//
// ADVANCED: Log the broadcast message unless it is a PING which
// should not be written to the log.
void server_check_sources(server_t *server);
// Checks all sources of data for the server to determine if any are
// ready for reading. Sets the servers join_ready flag and the
// data_ready flags of each of client if data is ready for them.
// Makes use of the select() system call to efficiently determine
// which sources are ready.
int server_join_ready(server_t *server);
// Return the join_ready flag from the server which indicates whether
// a call to server_handle_join() is safe.
int server_handle_join(server_t *server);
// Call this function only if server_join_ready() returns true. Read a
// join request and add the new client to the server. After finishing,
// set the servers join_ready flag to 0.
int server_client_ready(server_t *server, int idx);
// Return the data_ready field of the given client which indicates
// whether the client has data ready to be read from it.
int server_handle_client(server_t *server, int idx);
// Process a message from the specified client. This function should
// only be called if server_client_ready() returns true. Read a
// message from to_server_fd and analyze the message kind. Departure
// and Message types should be broadcast to all other clients. Ping
// responses should only change the last_contact_time below. Behavior
// for other message types is not specified. Clear the client's
// data_ready flag so it has value 0.
//
// ADVANCED: Update the last_contact_time of the client to the current
// server time_sec.
void server_tick(server_t *server);
// ADVANCED: Increment the time for the server
void server_ping_clients(server_t *server);
// ADVANCED: Ping all clients in the server by broadcasting a ping.
void server_remove_disconnected(server_t *server, int disconnect_secs);
// ADVANCED: Check all clients to see if they have contacted the
// server recently. Any client with a last_contact_time field equal to
// or greater than the parameter disconnect_secs should be
// removed. Broadcast that the client was disconnected to remaining
// clients. Process clients from lowest to highest and take care of
// loop indexing as clients may be removed during the loop
// necessitating index adjustments.
void server_write_who(server_t *server);
// ADVANCED: Write the current set of clients logged into the server
// to the BEGINNING the log_fd. Ensure that the write is protected by
// locking the semaphore associated with the log file. Since it may
// take some time to complete this operation (acquire semaphore then
// write) it should likely be done in its own thread to preven the
// main server operations from stalling. For threaded I/O, consider
// using the pwrite() function to write to a specific location in an
// open file descriptor which will not alter the position of log_fd so
// that appends continue to write to the end of the file.
void server_log_message(server_t *server, mesg_t *mesg);
// ADVANCED: Write the given message to the end of log file associated
// with the server.
</pre>
</div>
</div>
<div id="outline-container-sec-6-3" class="outline-3">
<h3 id="sec-6-3"><span class="section-number-3">6.3</span> Messages Handled by the Server</h3>
<div class="outline-text-3" id="text-6-3">
<p>
The function <code>server_handle_client()</code> is a workhorse that will read a
message from a client and respond take appropriate action. Here are
the messages that the server should accept and respond to.
</p>
<table border="2" cellspacing="0" cellpadding="6" rules="groups" frame="hsides">
<colgroup>
<col class="left">
<col class="left">
<col class="left">
<col class="left">
</colgroup>
<thead>
<tr>
<th scope="col" class="left">kind</th>
<th scope="col" class="left">Name</th>
<th scope="col" class="left">Body?</th>
<th scope="col" class="left">Action</th>
</tr>
</thead>
<tbody>
<tr>
<td class="left"><code>BL_MESG</code></td>
<td class="left">Yes</td>
<td class="left">Yes</td>
<td class="left">Broadcast message to all clients.</td>
</tr>
<tr>
<td class="left"><code>BL_DEPARTED</code></td>
<td class="left">Yes</td>
<td class="left">No</td>
<td class="left">Broadcast message to all clients.</td>
</tr>
</tbody>
</table>
</div>
</div>
<div id="outline-container-sec-6-4" class="outline-3">
<h3 id="sec-6-4"><span class="section-number-3">6.4</span> Other Messages Sent by the Server</h3>
<div class="outline-text-3" id="text-6-4">
<p>
The server will broadcast several other kinds of messages to clients
under the following circumstances.
</p>
<table border="2" cellspacing="0" cellpadding="6" rules="groups" frame="hsides">
<colgroup>
<col class="left">
<col class="left">
<col class="left">
<col class="left">
</colgroup>
<thead>
<tr>
<th scope="col" class="left">kind</th>
<th scope="col" class="left">Name</th>
<th scope="col" class="left">Body?</th>
<th scope="col" class="left">Circumstance</th>
</tr>
</thead>
<tbody>
<tr>
<td class="left"><code>BL_JOINED</code></td>
<td class="left">Yes</td>
<td class="left">No</td>
<td class="left">Broadcast when a new client joins the server</td>
</tr>
<tr>
<td class="left"><code>BL_SHUTDOWN</code></td>
<td class="left">No</td>
<td class="left">No</td>
<td class="left">Broadcast when the server starts shutting down</td>
</tr>
</tbody>
<tbody>
<tr>
<td class="left">ADVANCED</td>
<td class="left"> </td>
<td class="left"> </td>
<td class="left"> </td>
</tr>
<tr>
<td class="left"><code>BL_PING</code></td>
<td class="left">No</td>
<td class="left">No</td>
<td class="left">Broadcast periodically, clients should respond with a ping to indicate liveness</td>
</tr>
<tr>
<td class="left"><code>BL_DISCONNECTED</code></td>
<td class="left">Yes</td>
<td class="left">No</td>
<td class="left">Broadcast when a client has not pinged in a while to indicate disconnection.</td>
</tr>
</tbody>
</table>
</div>
</div>
<div id="outline-container-sec-6-5" class="outline-3">
<h3 id="sec-6-5"><span class="section-number-3">6.5</span> <code>bl-server.c</code> main function</h3>
<div class="outline-text-3" id="text-6-5">
<p>
Define a <code>main()</code> entry point in <code>bl-server</code> that ties all of the
server operations together into a function unit.
</p>
</div>
<div id="outline-container-sec-6-5-1" class="outline-4">
<h4 id="sec-6-5-1">Listen, Select, Respond</h4>
<div class="outline-text-4" id="text-6-5-1">
<p>
The server <code>main()</code> function in its simplest form boils down to the
following pseudocode.
</p>
<div class="org-src-container">
<pre class="src src-text">REPEAT:
check all sources
handle a join request if on is ready
for each client{
if the client is ready handle data from it
}
}
</pre>
</div>
<p>
The advanced features build somewhat on this but not by much.
</p>
</div>
</div>
<div id="outline-container-sec-6-5-2" class="outline-4">
<h4 id="sec-6-5-2">Signal Handling</h4>
<div class="outline-text-4" id="text-6-5-2">
<p>
The server should run indefinitely without interaction from an
interactive user. To stop it, send signals. The server should handle
<code>SIGTERM</code> and <code>SIGINT</code> by shutting down gracefully: exit the main
computation, call <code>server_shutdown()</code> and return 0.
</p>
</div>
</div>
</div>
</div>
<div id="outline-container-sec-7" class="outline-2">
<h2 id="sec-7"><span class="section-number-2">7</span> The Client</h2>
<div class="outline-text-2" id="text-7">
<p>
While <code>bl-server</code> is a perpetual, non-interactive program, it is not
interesting with clients to connect to it allowing users to
communicate. <code>bl-client</code> is such a program. It allows a user to type
into the terminal to send text to the server and receive text back
from the server which is printed to the screen. The sections below
describe how to build it.
</p>
</div>
<div id="outline-container-sec-7-1" class="outline-3">
<h3 id="sec-7-1"><span class="section-number-3">7.1</span> Simplified Terminal I/O</h3>
<div class="outline-text-3" id="text-7-1">
<p>
Standard terminal input and output work well in many situations but
the <code>bl-client</code> must intermingle the user typing while data may be
printed to the screen. This calls for somewhat finer control. To
simplify the murky area that is terminal control, the file <code>simpio.c</code>
provides functions which have the following net effect.
</p>
<ul class="org-ul">
<li>A prompt can be set that is always displayed as the last final
advancing line in the terminal.
</li>
<li>Text can be typed and deleted by the user.
</li>
<li>Any thread printing with the <code>iprintf()</code> function will advance the
prompt forwards without disrupting the text a user may be typing.
</li>
</ul>
<p>
The program <code>simpio-demo.c</code> demonstrates this facility by spinning up
a user and background thread which both print to the screen. Text
printed by the background thread using <code>iprintf()</code> does not disrupt
text being typed by the user at the prompt.
</p>
<p>
Use <code>simpio-demo.c</code> as a template to begin you development on
<code>bl-client.c</code> noting the following.
</p>
<ul class="org-ul">
<li>Initialize the simplified terminal I/O with the following sequence
<div class="org-src-container">
<pre class="src src-c">simpio_set_prompt(simpio, prompt); // set the prompt
simpio_reset(simpio); // initialize io
simpio_noncanonical_terminal_mode(); // set the terminal into a compatible mode
</pre>
</div>
</li>
<li>When threads want to print, use the <code>iprintf()</code> function. It works
like <code>printf()</code> but takes as its first argument a <code>simpio_t</code> object
which manages the prompt and typed text.
</li>
<li>Analyze the input loop in <code>simpio-demo.c</code> to see how to read
characters from the prompt, detect a completed line, and end of
input.
</li>
</ul>
</div>
</div>
<div id="outline-container-sec-7-2" class="outline-3">
<h3 id="sec-7-2"><span class="section-number-3">7.2</span> <code>bl-client.c</code> Features</h3>
<div class="outline-text-3" id="text-7-2">
<p>
Unlike the server, there are no required C functions for the
client. Instead, there are a series of required features and
suggestions on how to implement them.
</p>
</div>
<div id="outline-container-sec-7-2-1" class="outline-4">
<h4 id="sec-7-2-1">Client Name and FIFO Creation</h4>
<div class="outline-text-4" id="text-7-2-1">
<p>
The client program is run as follows
</p>
<div class="org-src-container">
<pre class="src src-sh">$> bl-client server1 Lois
# join the server1 as a user Lois
$> bl-client dc-serv Bruce
# join the dc-serv server as user Bruce
</pre>
</div>
<p>
The first argument is the server to join and corresponds to a FIFO
name that is owned by the server.
</p>
<p>
The client should create its own to-client and to-server FIFOs which
become part of the join request to the server. The names of these
FIFOs can be selected arbitrarily so long as they do not conflict with
other user FIFO names. Examples are to create temporary file names or
use the PID of the client process to choose the FIFO names.
</p>
</div>
</div>
<div id="outline-container-sec-7-2-2" class="outline-4">
<h4 id="sec-7-2-2">Joining the Server</h4>
<div class="outline-text-4" id="text-7-2-2">
<p>
The client should construct a <code>join_t</code> with its name and the names of
its to-client and to-server FIFOs. This should be written to the name
of the server's FIFO which will notify the server and other clients of
the new user's arrival.
</p>
</div>
</div>
<div id="outline-container-sec-7-2-3" class="outline-4">
<h4 id="sec-7-2-3">Messages Handled by Client</h4>
<div class="outline-text-4" id="text-7-2-3">
<p>
The client should handle the following kinds of messages from the server.
</p>
<table border="2" cellspacing="0" cellpadding="6" rules="groups" frame="hsides">
<colgroup>
<col class="left">
<col class="left">
<col class="left">
<col class="left">
<col class="left">
</colgroup>
<thead>
<tr>
<th scope="col" class="left">kind</th>
<th scope="col" class="left">Name</th>
<th scope="col" class="left">Body?</th>
<th scope="col" class="left">Action</th>
<th scope="col" class="left">Print Format / Example</th>
</tr>
</thead>
<tbody>
<tr>
<td class="left"><code>BL_MESG</code></td>
<td class="left">Yes</td>
<td class="left">Yes</td>
<td class="left">Print</td>
<td class="left"><code>[Bruce] : check this out</code></td>
</tr>
<tr>
<td class="left"><code>BL_JOINED</code></td>
<td class="left">Yes</td>
<td class="left">No</td>
<td class="left">Print</td>
<td class="left"><code>-- Bruce JOINED --</code></td>
</tr>
<tr>
<td class="left"><code>BL_DEPARTED</code></td>
<td class="left">Yes</td>
<td class="left">No</td>
<td class="left">Print</td>
<td class="left"><code>-- Clark DEPARTED --</code></td>
</tr>
<tr>
<td class="left"><code>BL_SHUTDOWN</code></td>
<td class="left">No</td>
<td class="left">No</td>
<td class="left">Print</td>
<td class="left"><code>!!! server is shutting down !!!</code></td>
</tr>
</tbody>
<tbody>
<tr>
<td class="left">ADVANCED</td>
<td class="left"> </td>
<td class="left"> </td>
<td class="left"> </td>
<td class="left"> </td>
</tr>
<tr>
<td class="left"><code>BL_DISCONNECTED</code></td>
<td class="left">Yes</td>
<td class="left">No</td>
<td class="left">Print</td>
<td class="left"><code>-- Clark DISCONNECTED --</code></td>
</tr>
<tr>
<td class="left"><code>BL_PING</code></td>
<td class="left">No</td>
<td class="left">No</td>
<td class="left">Reply</td>
<td class="left">Send <code>BL_PING</code> message back to server</td>
</tr>
</tbody>
</table>
</div>
</div>
<div id="outline-container-sec-7-2-4" class="outline-4">
<h4 id="sec-7-2-4">User Input and Messages from the Server</h4>
<div class="outline-text-4" id="text-7-2-4">
<p>
To make the user experience reasonable, server messages should be
received and printed to the screen as soon as they are available.
Printing server messages should not disrupt the text input too
much. This combination of requirements suggests the following.
</p>
<ul class="org-ul">
<li><b>Use two threads</b>, one for user interactions and the other for
server interactions.
</li>
<li>The user thread performs an input loop until the user has completed
a line. It then writes message data into the to-server FIFO to get
it to the server and goes back to reading user input.
</li>
<li>The server thread reads data from the to-client FIFO and prints to
the screen as data is read.
</li>
<li>Both user and server threads use the <code>iprintf()</code> function to ensure
that data appears correctly on the screen and cooperates with input
being typed.
</li>
</ul>
<p>
A few additional notes are in order on the interaction of these two
threads.
</p>
<ul class="org-ul">
<li>Should the user thread receive and end of input, it should send a
message to the server with kind <code>BL_DEPARTED</code> to indicate the client
is shutting down. This will notify other users of the departure. The
user thread should cancel the server thread and return.
</li>
<li>If the server thread receives a <code>BL_SHUTDOWN</code> message, the server is
shutting down. This means the client should exit as well. The server
thread should cancel the user thread and return.
</li>
</ul>
</div>
</div>
<div id="outline-container-sec-7-2-5" class="outline-4">
<h4 id="sec-7-2-5">Typed Input is Sent to the Server, not Printed</h4>
<div class="outline-text-4" id="text-7-2-5">
<p>
When users type input, it is echoed onto the screen by <code>simpio</code> at the
prompt. However, on hitting enter, the data is sent immediately to the
server as a <code>mesg_t</code> with kind <code>MESG</code>, <code>name</code> filled in with the
user's name and <code>body</code> filled in with the text line typed.
</p>
<p>
Though the message body is known by the client which just sent it, the
body is not printed to the screen. Instead, the client waits for the
server to broadcast the message back and prints its own message just
as if it were a message from another user. This ensures that no
special actions need to be taken to avoid duplicate messages.
</p>
<p>
This "print only what the server sends" feature restriction is
somewhat modified by some of the advanced features described later.
</p>
</div>
</div>
</div>
<div id="outline-container-sec-7-3" class="outline-3">
<h3 id="sec-7-3"><span class="section-number-3">7.3</span> Client Main Approach</h3>
<div class="outline-text-3" id="text-7-3">
<p>
To summarize, <code>bl-client</code> will roughly take the following steps.
</p>
<div class="org-src-container">
<pre class="src src-text">read name of server and name of user from command line args
create to-server and to-client FIFOs
write a join_t request to the server FIFO
start a user thread to read inpu
start a server thread to listen to the server
wait for threads to return
restore standard terminal output
user thread{
repeat:
read input using simpio
when a line is ready
create a mesg_t with the line and write it to the to-server FIFO
until end of input
write a DEPARTED mesg_t into to-server
cancel the server thread
server thread{
repeat:
read a mesg_t from to-client FIFO
print appropriate response to terminal with simpio
until a SHUTDOWN mesg_t is read
cancel the user thread
</pre>
</div>
</div>
</div>
</div>
<div id="outline-container-sec-8" class="outline-2">
<h2 id="sec-8"><span class="section-number-2">8</span> Manual Inspection Criteria (50%)</h2>
<div class="outline-text-2" id="text-8">
<p>
The following criteria will be examined during manual inspection of
code by graders. Use this as a guide to avoid omitting important steps
or committing bad style fouls.
</p>
<table border="2" cellspacing="0" cellpadding="6" rules="groups" frame="hsides">
<colgroup>
<col class="left">
<col class="right">
<col class="left">
</colgroup>
<thead>
<tr>
<th scope="col" class="left">Location</th>
<th scope="col" class="right">Wgt</th>
<th scope="col" class="left">Criteria</th>
</tr>
</thead>
<tbody>
<tr>
<td class="left"><b>Makefile</b></td>
<td class="right">5</td>
<td class="left">A Makefile is provided which compiles commando</td>
</tr>
<tr>
<td class="left"> </td>
<td class="right"> </td>
<td class="left">Any required test targets are present.</td>
</tr>
</tbody>
<tbody>
<tr>
<td class="left"><b>server.c</b></td>
<td class="right"> </td>
<td class="left"> </td>
</tr>
</tbody>
<tbody>
<tr>
<td class="left"><code>server_start()</code></td>
<td class="right">5</td>
<td class="left">creates and opens FIFO correctly for joins, removes existing FIFO</td>
</tr>
<tr>
<td class="left"><code>server_shutdown()</code></td>
<td class="right"> </td>
<td class="left">closes and removes FIFO to prevent additional joins</td>
</tr>
<tr>
<td class="left"> </td>
<td class="right"> </td>
<td class="left">broadcasts a shutdown message</td>
</tr>
<tr>
<td class="left"> </td>
<td class="right"> </td>
<td class="left">does basic error checking of system calls</td>
</tr>
</tbody>
<tbody>
<tr>
<td class="left"><code>server_add_client()</code></td>
<td class="right">5</td>
<td class="left">does bounds checking to prevent overflow on add</td>
</tr>
<tr>
<td class="left"> </td>
<td class="right"> </td>
<td class="left">adds client to end of array and increments <code>n_clients</code></td>
</tr>
<tr>
<td class="left"> </td>
<td class="right"> </td>
<td class="left">fills in fixed fields of client data based on join parameter</td>
</tr>
<tr>
<td class="left"> </td>
<td class="right"> </td>
<td class="left">makes use of strncpy() to prevent buffer overruns</td>
</tr>
<tr>
<td class="left"> </td>
<td class="right"> </td>
<td class="left">opens to-client and to-server FIFOs for reading</td>
</tr>
</tbody>
<tbody>
<tr>
<td class="left"><code>server_remove_client()</code></td>
<td class="right">5</td>
<td class="left">uses <code>server_get_client()</code> for readability</td>
</tr>
<tr>
<td class="left"> </td>
<td class="right"> </td>
<td class="left">closes to-client and from-client FIFOs</td>
</tr>
<tr>
<td class="left"> </td>
<td class="right"> </td>
<td class="left">correctly shifts array of clients to maintain contiguous client array</td>
</tr>
</tbody>
<tbody>
<tr>
<td class="left"><code>server_check_sources()</code></td>
<td class="right">5</td>
<td class="left">makes use of <code>select()</code> system call to detect ready clients/joins</td>
</tr>
<tr>
<td class="left"> </td>
<td class="right"> </td>
<td class="left">checks join FIFO and all clients in <code>select()</code> call</td>
</tr>
<tr>
<td class="left"> </td>
<td class="right"> </td>
<td class="left">does not read data but sets <code>read</code> flags for join and clients</td>
</tr>
<tr>
<td class="left"> </td>
<td class="right"> </td>
<td class="left">does basic error checking of system calls</td>
</tr>
</tbody>
<tbody>
<tr>
<td class="left"><code>server_handle_join()</code></td>
<td class="right">5</td>
<td class="left">reads a <code>join_t</code> from join FIFO correctly</td>
</tr>
<tr>
<td class="left"> </td>
<td class="right"> </td>
<td class="left">adds client with <code>server_add_client()</code></td>
</tr>
<tr>
<td class="left"> </td>
<td class="right"> </td>
<td class="left">broadcasts join</td>
</tr>
<tr>
<td class="left"><code>server_handle_client()</code></td>
<td class="right"> </td>
<td class="left">reads a <code>mesg_t</code> from the to-server FIFO</td>
</tr>
<tr>
<td class="left"> </td>
<td class="right"> </td>
<td class="left">processes message properly and broadcasts if needed</td>
</tr>
<tr>
<td class="left"> </td>
<td class="right"> </td>
<td class="left">does basic error checking of system calls</td>
</tr>
</tbody>
<tbody>
<tr>
<td class="left"><b>bl-server.c</b></td>
<td class="right"> </td>
<td class="left"> </td>
</tr>
<tr>
<td class="left"> </td>
<td class="right">5</td>
<td class="left">main loop makes use of the <code>server.c</code> routines extensively</td>
</tr>
<tr>
<td class="left"> </td>
<td class="right"> </td>
<td class="left">clear code to check input sources and handle ready input</td>
</tr>
<tr>
<td class="left"> </td>
<td class="right"> </td>
<td class="left">signal handling for graceful shutdown is clear</td>
</tr>
</tbody>
<tbody>
<tr>
<td class="left"><b>bl-client.c</b></td>
<td class="right"> </td>
<td class="left"> </td>
</tr>
<tr>
<td class="left">main and overall</td>
<td class="right">5</td>
<td class="left">proper setup of terminal with simpio</td>
</tr>
<tr>
<td class="left"> </td>
<td class="right"> </td>
<td class="left">use of simpio for input and output</td>
</tr>
<tr>
<td class="left"> </td>
<td class="right"> </td>
<td class="left">clear creation and joining of threads</td>
</tr>
<tr>
<td class="left"> </td>
<td class="right"> </td>
<td class="left">resets terminal at end of run</td>
</tr>
</tbody>
<tbody>
<tr>
<td class="left">user thread</td>
<td class="right">5</td>
<td class="left">clear use of a user thread to handle typed input</td>
</tr>
<tr>
<td class="left"> </td>
<td class="right"> </td>
<td class="left">user thread sends data to server</td>
</tr>
<tr>
<td class="left"> </td>
<td class="right"> </td>
<td class="left">cancels server thread at end of input before returning</td>
</tr>
</tbody>
<tbody>
<tr>
<td class="left">server thread</td>
<td class="right">5</td>
<td class="left">clear use of a server thread to listen data on to-client FIFO</td>
</tr>
<tr>
<td class="left"> </td>
<td class="right"> </td>
<td class="left">clear handling of different kinds of messages coming from server</td>
</tr>
<tr>
<td class="left"> </td>
<td class="right"> </td>
<td class="left">cancels user thread on receiving shutdown message and returns</td>
</tr>
</tbody>
<tbody>
<tr>
<td class="left"> </td>
<td class="right">50</td>
<td class="left">Total</td>
</tr>
</tbody>
</table>
</div>
</div>
<div id="outline-container-sec-9" class="outline-2">
<h2 id="sec-9"><span class="section-number-2">9</span> ADVANCED Features</h2>
<div class="outline-text-2" id="text-9">
<p>
The following advanced features may be implemented to garner extra
credit on the total project score for the semester. Each additional
feature is worth the extra credit indicated.
</p>
</div>
<div id="outline-container-sec-9-1" class="outline-3">
<h3 id="sec-9-1"><span class="section-number-3">9.1</span> Server Ping and Disconnected Clients (10%)</h3>
<div class="outline-text-3" id="text-9-1">
<p>
Clients may terminate abruptly in the real world before they have a
chance to send a <code>BL_DEPARTED</code> message to the server. This additional
feature adds period <b>pinging</b> to the server and clients. A ping is a
short message just to establish whether a communication partner is
still present. In this case, it is a message with kind <code>BL_PING</code>.
</p>
<p>
Implementing this feature will cause the server broadcast a ping to
all clients every second. Clients should respond immediately by
sending a ping back.
</p>
<p>
To detect disconnected clients, the server should maintain its
<code>time_sec</code> incrementing it each second. Whenever a message is
received from a client, including <code>BL_PING</code> messages, the server
updates the client's <code>last_contact_time</code> to the current server
time. Any client that abruptly departs will eventually have a large
gap between its <code>last_contact_time</code> and the <code>time_sec</code>.
</p>
<p>
Every second, the server runs the function
<code>server_remove_disconnected(server, disconnect_secs)</code>. If any client
with a difference in <code>last_contact_time</code> and
<code>server_remove_disconnected</code> that is larger than the argument
<code>disconnect_secs</code> should be removed. A <code>BL_DISCONNECTED</code> message
should be broadcast for this client to notify other clients of the
change.
</p>
<p>
<b>A good way to implement periodic activity</b> is to use the <code>alarm()</code>
function. This arranges for a periodic signal to be sent to the server
process. This should be done in <code>main()</code> for <code>bl-server.c</code>. The
signal handler for the <code>SIGALRM</code> that is raised can set a variable to
indicate that 1 second has passed. In the main loop of the server, a
condition checks this variable and performs the ping broadcast and
checks for disconnected clients.
</p>
<p>
All changes for this feature are on the server side. Additional
functions to write or modify are as follows.
</p>
<div class="org-src-container">
<pre class="src src-c">// server.c
// Modify
int server_handle_client(server_t *server, int idx)
// Write
void server_tick(server_t *server)
void server_ping_clients(server_t *server)
void server_remove_disconnected(server_t *server, int disconnect_secs)
// bl-server.c
int main(int argc, char *argv[])
</pre>
</div>
</div>
</div>
<div id="outline-container-sec-9-2" class="outline-3">
<h3 id="sec-9-2"><span class="section-number-3">9.2</span> Binary Server Log File (10%)</h3>
<div class="outline-text-3" id="text-9-2">
<p>
There is cause to want a log of all messages that pass through a
server. This feature will cause the server to write such a log in a
binary file.
</p>
<p>
The file should be named after the server name similarly to the join
FIFO. For example
</p>
<div class="org-src-container">
<pre class="src src-sh">$> bl-server server1
# creates server1.fifo
# creates server1.log
$> bl-server batcave
# creates batcave.fifo
# creates batcave.log
</pre>
</div>
<p>
The format of this binary log file is as follows.
</p>
<ul class="org-ul">
<li>The first part should contain a binary <code>who_t</code> structure which has
the active users in it. To complete the logging feature, the
<code>who_t</code> does not need to be kept to date.
</li>
<li>After the <code>who_t</code> is a growing sequence of <code>mesg_t</code> structs in the
log file. Any message that is broadcast by the server EXCEPT for
pings is written to the end of this log, NOT in text format but as
the direct binary representation of a <code>mesg_t</code>.
</li>
<li>Each new message that is broadcast is appended to the end of the log
in binary format.
</li>
</ul>
<p>
When the server starts up, the log file should be created and the
<code>log_fd</code> field filled with its file descriptor. A good place to write
log messages is during <code>server_broadcast()</code>. In it, any message that
is not a ping should be written to the end of log.
</p>
<p>
When the server shuts down, close the file descriptor of the log but
do not remove the file. On startup, re-open any existing log and
continue appending to it.
</p>
<p>
This feature is implemented entirely in the server and requires
modification of the following functions.
</p>
<div class="org-src-container">
<pre class="src src-c">// server.c
void server_start(server_t *server, char *server_name, int perms)
void server_shutdown(server_t *server)
int server_broadcast(server_t *server, mesg_t *mesg)
void server_write_who(server_t *server)
void server_log_message(server_t *server, mesg_t *mesg)
// bl-server.c
int main(int argc, char *argv[])
</pre>
</div>
<p>
In addition, provide a file called <code>bl-showlog.c</code> which will read the
binary log file and print its output. This should include the <code>who_t</code>
at the beginning and all log messages. Here is a demo run including
the presumed <code>Makefile</code> target. Output is nearly identical to what is
shown in the client.
</p>
<div class="org-src-container">
<pre class="src src-text">> make bl-showlog
gcc -Wall -g -c bl-showlog.c
gcc -Wall -g -c util.c
gcc -Wall -g -o bl-showlog bl-showlog.o util.o -lpthread
> file server1.log
server1.log: data
> ./bl-showlog server1.log
3 CLIENTS
0: Batman
1: Clark
2: Barbara
MESSAGES
-- Bruce JOINED --
-- Clark JOINED --
-- Lois JOINED --
[Bruce] : hey, want to know secret identity?
[Clark] : dude, I have x-ray vision
[Lois] : wait, you have x-ray vision
[Clark] : ah, er, I mean...
[Bruce] : ha ha. I'd never do something dumb like that.
[Lois] : why not?
[Clark] : oh boy, here it comes...
[Bruce] : because...
[Lois] : ??
[Bruce] : AHYM BAAATMAN!!!
[Clark] : walked into that one
[Lois] : yup
-- Barbara JOINED --
[Barbara] : hey guys
[Clark] : hey Barbara
[Lois] : what up!
[Barbara] : Did I miss anything important?
[Clark] : the big "reveal" from Bruce...
[Barbara] : what, that he's Batman?
[Lois] : yup
[Bruce] : wait, how did you know that?
[Barbara] : you told me when we were dating
[Lois] : me too
[Bruce] : awkward. time for a SMOKE BOMB!!!
-- Bruce DEPARTED --
[Barbara] : that guy
>
</pre>
</div>
</div>
</div>
<div id="outline-container-sec-9-3" class="outline-3">
<h3 id="sec-9-3"><span class="section-number-3">9.3</span> Last Messages for Client (10%)</h3>
<div class="outline-text-3" id="text-9-3">
<p>
This feature requires the Binary Server Log File Feature.
</p>
<p>
Clients that recently join a server have no idea what has transpired
prior to their joining. This can be ameliorated if clients can access
the binary log to examine the last N messages. For example:
</p>
<div class="org-src-container">
<pre class="src src-text">$> bl-client server1 Lois
-- Lois JOINED --
[Clark] : eek!
-- Clark DEPARTED --
[Lois] : what's his deal?
[Bruce] : um..
Lois> %last 10
====================
LAST 10 MESSAGES
[Bruce] : what up man?
[Clark] : not much, just down in the fortress of solitude
[Bruce] : with lois
[Clark] : nope. lana
[Bruce] : nice
-- Lois JOINED --
[Clark] : eek!
-- Clark DEPARTED --
[Lois] : what's his deal?
[Bruce] : um..
====================
Lois>> wtf?!?
</pre>
</div>
<p>
To accomplish this <code>bl-client</code> should examine the typed line that is
entered to see if it starts with the string <code>%last</code> in which case it
will be followed by an integer which is the number of messages
requested.
</p>
<p>
On detecting this command request, client should open the binary log
file for the server and seek to the end of it using <code>lseek()</code>. Note
that the exact position in the binary log file can be calculated
immediately by using.
</p>
<ul class="org-ul">
<li><code>sizeof(mesg_t</code>
</li>
<li>The number of messages requested
</li>
<li>The argument <code>SEEK_END</code> to <code>lseek()</code>
</li>
</ul>
<p>
Thus no looping is required to find that position.
</p>
<p>
The client should then read off these messages and print them to the
screen. It is a good idea to write function that will print logged
messages to keep the main loop and thread loops simple in the client.
</p>
<p>
<b>No server interaction</b> is required for this feature so long as the
server is producing the binary log file. Modify only <code>bl-client.c</code>.
</p>
<p>
Modify the following code for this feature.
</p>
<div class="org-src-container">
<pre class="src src-c">// bl-client.c
// helper functions and maybe main()
int main(int argc, char *argv[])
</pre>
</div>
</div>
</div>
<div id="outline-container-sec-9-4" class="outline-3">
<h3 id="sec-9-4"><span class="section-number-3">9.4</span> <code>who_t</code> for Client and Server (10%)</h3>
<div class="outline-text-3" id="text-9-4">
<p>
Users who log into the server have no way of knowing who is logged
in. This feature ameliorates that.
</p>
<ul class="org-ul">
<li>The server writes its active users as a <code>who_t</code> structure to the
beginning of its binary log every second at the same time as it
would check for disconnected users.
</li>
<li>Clients can read the <code>who_t</code> at the beginning of the log file to
determine which users are connected to the server. The client the
provides a <code>%who</code> command which prints active users.
</li>
<li>To prevent the server from writing the <code>who_t</code> structure while a
client is reading or vice versa, the server creates a semaphore
which must be acquired to access this part of the log.
</li>
</ul>
<p>
The <code>who_t</code> structure is a simple, fixed size array of strings.
</p>
<pre class="example">// who_t: data to write into server log for current clients (ADVANCED)
typedef struct {
int n_clients; // number of clients on server
char names[MAXCLIENTS][MAXNAME]; // names of clients
} who_t;
</pre>
<p>
This fixed size means every time it is written it will overwrite the
same bytes. The server should write it every second in the same block
using the same approach as is used to check for disconnected clients
(<code>alarm(1)</code>). Use of <code>pwrite()</code> is suggested to allow the <code>log_fd</code> to
stay in position to write to the end of the log file.
</p>
<p>
The client should implement the <code>%who</code> command by checking the
<code>simpio->buf</code> for the string. It should then acquire the semaphore,
read the <code>who_t</code> and print the results the screen similar to the
following.
</p>
<div class="org-src-container">
<pre class="src src-text">-- Barbara JOINED --
[Barbara] : Bruce?
[Barbara] : Bruce, are you there?
[Clark] : Ummm....
[Barbara] : hang on
Barbara>> %who
====================
3 CLIENTS
0: Batman
1: Clark
2: Barbara
====================
[Barbara] : (sigh) Batman?
[Batman] : I AM THE NIGHT!
Barbara>>
</pre>
</div>
<p>
The server is responsible for creating the semaphore which controls
access to the <code>who_t</code> portion of the log. Follow the same naming
convention as before.
</p>
<div class="org-src-container">
<pre class="src src-sh">$> bl-server server1
# creates server1.fifo FIFO
# creates server1.log binary log file
# creates /server1.sem POSIX semaphore
$> bl-server batcave
# creates batcave.fifo FIFO
# creates batcave.log binary log file
# creates /batcave.sem POSIX semaphore
</pre>
</div>
<p>
A few notes on POSIX semaphores.
</p>
<ul class="org-ul">
<li>They are created / accessed with the <code>sem_open()</code> function which
takes a name which must start with a forward slash, thus the
<code>/server1.sem</code> convention.
</li>
<li>POSIX semaphores are singular, not arrays of semaphores like System
V semaphores. The have only <code>sem_wait()</code> (decrement) and
<code>sem_post()</code> (increment) operations. However, these are sufficient
for the present purpose.
</li>
<li>When the server wants to write a <code>who_t</code> into the log, it acquires
the semaphore with <code>sem_wait()</code>, writes, then releases with
<code>sem_post()</code>.
</li>
<li>Clients follow a similar protocol when reading the <code>who_t</code>.
</li>
<li>When shutting down the, server should unlink the semaphore with
<code>sem_unlink()</code>.
</li>
</ul>
<p>
Modify the following code for this feature.
</p>
<div class="org-src-container">
<pre class="src src-c">// server.c
void server_start(server_t *server, char *server_name, int perms)
void server_shutdown(server_t *server)
void server_write_who(server_t *server)
// bl-server.c
int main(int argc, char *argv[])
// bl-client.c
// helper functions and maybe main()
int main(int argc, char *argv[])
</pre>
</div>
</div>
</div>
</div>
<div id="outline-container-sec-10" class="outline-2">
<h2 id="sec-10"><span class="section-number-2">10</span> <a id="testing" name="testing"></a> Automatic Testing (50%) <span class="tag"><span class="grading">grading</span></span></h2>
<div class="outline-text-2" id="text-10">
<p>
<i>Brewing</i>
</p>
</div>
</div>
<div id="outline-container-sec-11" class="outline-2">
<h2 id="sec-11"><span class="section-number-2">11</span> Zip and Submit</h2>
<div class="outline-text-2" id="text-11">
</div><div id="outline-container-sec-11-1" class="outline-3">
<h3 id="sec-11-1"><span class="section-number-3">11.1</span> Submit to Canvas</h3>
<div class="outline-text-3" id="text-11-1">
<p>
Once your are confident your code is working, you are ready to
submit. Ensure your folder has all of the required files. Create a
zip archive of your lab folder and submit it to blackboard.
</p>
<p>
On Canvas:
</p>
<ul class="org-ul">
<li>Click on the <i>Assignments</i> section
</li>
<li>Click on the appropriate link for this lab
</li>
<li>Scroll down to "Attach a File"
</li>
<li>Click "Browse My Computer"
</li>
<li>Select you Zip file and press OK
</li>
</ul>
</div>
</div>
<div id="outline-container-sec-11-2" class="outline-3">
<h3 id="sec-11-2"><span class="section-number-3">11.2</span> Late Policies</h3>
<div class="outline-text-3" id="text-11-2">
<p>
You may wish to review the policy on late project submission which
will cost you late tokens to submit late or credit if you run out of
tokens.
</p>
<p>
<a href="http://www-users.cs.umn.edu/~kauffman/4061/syllabus.html#late-projects">http://www-users.cs.umn.edu/~kauffman/4061/syllabus.html#late-projects</a>
</p>
<p>
<b>No projects will be accepted more than 48 hours after the deadline.</b>
</p>
</div>
</div>
</div>
</div>
<div id="postamble" class="status">
<hr> <i> Author: Chris Kauffman (<a href="mailto:kauffman@umn.edu">kauffman@umn.edu</a>) <br> Date: 2017-11-29 Wed 17:46 <br> </i>
</div>
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