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A Client Process Speaking to a Server Process

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A Client Process Speaking to a Server Process

Introduction
In this assignment, you will write a client program that connects to a given server. The server
defines a communication protocol, which the client has to implement by sending properly
formulated messages over a communication pipe. The server hosts several electrocardiogram
(ecg) data points of 15 patients suffering from various cardiac diseases. The client’s goal,
thereby your goal, is to obtain these data points by sending properly formatted messages
that the server understands. In addition, the server supports is capable of sending raw files
potentially in several segments (i.e., when the file is larger than some internal buffer size).
Your client must implement this file transfer functionality as well such that it can collect
files of arbitrary size using a series of requests/responese.
We obtained the above dataset from physionet.org.
1 Starter Code
You are given a source directory with the following files:
• A makefile that compiles and builds the source files when you type make command
in the terminal.
• FIFORequestChannel class (FIFORequestChannel.cpp/.h) that implements a pipebased communication channel. You can use this to communicate with another process.
This class has a read and a write function to receive and send data to/from the server,
respectively. The usage of the function is demonstrated in the given client.cpp. No
change in this class is necessary for PA2.
• A server.cpp that contains the server logic. When compiled with the makefile, an
executable called server is made. You need to run this executable to start the server.
Although nothing will change in this server for this PA, you will have to refer to its
code to understand the server protocol and then implement the client functionality
based on that.
• The client program in client.cpp that, for the time being, is capable of connecting
to the server using the FIFORequestChannel class. The client also sends a sample
message to the server and receives a response. Once compiled, an executable file
client is generated, which you would run to start the client program. This is the file
where you will make most of the changes needed for this assignment.
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CSCE 313 Spring 2020
• A common.h and a common.cpp file that contain different useful classes and functions
potentially shared between the server and the client. For instance, if you decide to
create classes for different types of messages (e.g., data message, file message), you
should put them in these files.
Download the source and unzip it. Open a terminal, navigate to the directory, and then
build using make command. After that, run the ./server to start the server. Now, open
another terminal, navigate to the same directory, and run client. At this point, the client
will connect to the server, exchange a simple message and then the client will exit. Since
pipe is a point-to-point connection, when either the client or the server exits, the other side
will exit as well after receiving SIGPIPE signal for “broken pipe”.
Server Specification
The server supports several functionalities. The client requests a certain functionality by
sending the appropriate message to the server. Internally, the server will execute the correct
functionality, prepare a reply message for the client and send it back.
Connecting to the Server
You will see the following in the server main function:
FIFORequestChannel control_chan (“control”, FIFORequestChannel::SERVER_SIDE);
which sets up a communication channel over an OS-provided IPC mechanism called “named
pipe”. Note that the first argument in the channel constructor is the name of the channel.
To connect to this server, the client has to create an instance with the same name, but with
CLIENT SIDE as the second argument:
FIFORequestChannel control_chan (“control”, FIFORequestChannel::CLIENT_SIDE);
Requesting Data Points
After creating the channel, the server then goes in a “infinite” loop that processes client
requests based on the type. Now, let us find out how the server works. The server maintains
ECG values (at 2 contact points) for each patient in a time series where there are 2 data
points (i.e., ecg1 and ecg2) collected every 4ms (see any of the .csv files under the BIMDC/
directory) for the duration of a minute. That means there is 15K data points for each patient
in each file and there are 15 such patients. Hence, there are 15 files each with 15K data
points.
The client requests a data point by specifying:
• Message type is DATA MSG. Data type is MESSAGE TYPE defined in common.h. There are
a number of message types, each serving a different purpose.
• Which patient. There are 15 patients total. Required data type is an int with value
in range [1, 15]
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CSCE 313 Spring 2020
• At what time in seconds. Data types is double with range [0.00, 59.996]
• Which ecg record: 1 or 2, indicating which ecg record the client is interested to obtain.
The data type is integer.
You will find this request format in common.h as datamsg. In response to a properly formatted
data message, the server replies with the ecg value as a double. Your first task is to prepare
and send a data message to the server and collect its response.
The following is an example of requesting ecg2 for patient 10 at time 59.004 from the
command line when you run the client:
$ ./client -p 10 -t 59.00 -e 2
In the above, the argument “-p” is for which patient, “-t” for time, and “-e” for ecg no.
Requesting Files
To request a file, you need to package the following information in a message:
• Message type set to FILE MSG indicating that it is a file request. Data type is MESSAGE TYPE
defined in common.h
• Starting offset in the file. Data type is int64 t because of the fact that the file can
be large and a usual 32-bit integer will not be sufficient.
• How many bytes to transfer beginning from the starting offset. Data type is int.
• The name of the file as NULL terminated string, relative to the directory BIMDC/
The type filemsg in common.h encodes these information. However, you won’t see a field
for the file name, because it is a variable length field. If you were to use a data type, you
would need to know the length exactly, which is impossible beforehand. You can just think
of the name as variable length payload data in the packet that follows the header, which is
a filemsg object.
The reason for using offset and length is the fact that a file can be very long and may
not fit in the buffers allocated in this PA. For instance, if the file is 20GB long and if you
must send the file in a single message, that message must be 20GB long, requiring the same
amount of physical memory and bogging the server down. To avoid this, we set the limit of
each transfer by the variable called buffercapacity in both client.cpp and server.cpp.
This variable defaults to the constant MAX MESSAGE defined in common.h. However, you can
change that providing the optional argument -m as follows, which changes capacity to 5000
bytes:
$ ./client -m 5000
Note that the change must be done for both client and server to make it effective (e.g., seeing
faster/slower performance).
Therefore, instead of requesting the whole file, you just request a portion of the file where
the bytes are in range [offset, offset+length]. As a result, you can allocate a buffer that is
only length bytes long, but use multiple packets to transfer a single file.
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CSCE 313 Spring 2020
Furthermore, a client would not know the length of a file unless the server informs. To
achieve that, the client should first send a special file message by setting offset and length
both to 0. In response, the server just sends back the length of the file as a int64 t. Note
that int64 t is a 64-bit integer which is necessary for files over 4GB size (i.e., the max
number represented by an unsigned 32-bit integer is 232 = 4GB). From the file length, the
client then knows how many transfers it has to request, because each transfer is limited to
max MAX MESSAGE.
Also, note that the requested filename is relative to the BIMDC/ directory. Therefore,
to request the file BIMDC/1.csv, the client would put “1.csv” as the file name. The client
should store the received files under received/ directory and with the same name (i.e.,
received/1.csv). Furthermore, take into account that you are receiving portions of the file
in response to each request. Therefore, you must prepare the file appropriately so that the
received chunk of the file is put in the right place.
The following is an example request for getting file “10.csv” from the client command
line:
$ ./client -f 10.csv
where the argument “-f” is for specifying file name.
Requesting New Channel Creation
The client can ask the server to create a new channel of communication. This feature will
be implemented in this PA and used extensively in the following ones when you write multithreaded client. The client sends a special message with message type set to NEWCHANNEL MSG.
In response, the server creates a new request channel object, returns the name back, which the
client uses to join into the same channel. This is shown in the server’s process new channel
function.
The following is a request a new channel:
$ ./client -c
.
Your Task
The following are your tasks:
• Requesting Data Points: (15 pts) Request all data points for person 1 by (both ecg1
and ecg2), collect the responses, and put them in a file called x1.csv. Compare the file
against the original BIMDC/1.csv using a file compare tool (e.g., fc) and demonstrate
that they are exactly same. Also, measure the time do the entire thing by using
gettimeofday function.
• Requesting Files: (35 points)
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CSCE 313 Spring 2020
– (20 pts) Request an entire file by first sending a file message to get its length, and
then a series of file messages to get the actual content of the file. Put received file
under the received directory with the same name as the original file. Compare
the file against the original using linux command diff and demonstrate that they
are exactly same. Measure the time for the transfer.
– (10 pts) Make sure to treat the file as binary, because we will use this same
program to transfer any type of file. Putting the data in a STL string will not
work, because C++ strings are NULL terminated. To demonstrate that your file
transfer is capable of handling binary files as well, make a large empty file under
the BIMDC/ directory using the truncate command (see man pages on how to use
truncate), transfer that file, and then compare to make sure they are identical
using the diff command.
– (5 pts) Experiment with transferring larger files (e.g., 100MB), and document required time. What is the main bottleneck here? Can you change the transfer time
by varying the bottleneck? [Hint: the most likely bottleneck is buffer capacity]
• Requesting a New Channel: (15 pts) Ask the server to create a new channel for you by
sending a special NEWCHANNEL MSG request and join that channel. After the channel is
created, demonstrate that you can use that to speak to the server. Sending a few data
point requests and receiving their responses is adequate for that demonstration.
• Run the Server as a child process (15 pts) Run the server process as a child of the
client process using fork() and exec() such that you do need two terminals: 1 for
the client and another for the server. The outcome is that you open a single terminal,
run the client which first runs the server and then connects to it. Also, to make sure
that the server does not keep running after the client dies, sent a special QUIT MSG to
the server and call wait() function to wait for its finish.
• Closing Channelsworth 5 pts You must also ensure that there are NO open connections
at the end and NO temporary files remaining in the directory either. The server would
clean up this resources as long as you send QUIT MSG at the end. This part is worth 5
points. Note that the given client.cpp already does this for the control channel.
• Report (15 points): Write a report describing the design, and the timing data you
collected for data points, text file, and binary files. Compare the difference in time
between transferring data points vs entire file.
2 Submission Instruction
Put everything excluding the BIMDC directory in a single directory, zip it and submit on
ecampus. Do not forget to make necessary changes to the makefile should you decide to
add other .h/.cpp files. Please do not include any data file because that will make your
zip file very large. Make sure that your directory has everything needed to compile your
program.
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