UTSA CS 3733 Operating Systems Assignment 4 Fall 2001

CS 3733 Operating Systems, Fall 2001 Assignment 4

Due Monday, November 12, 2001

Introduction
In this assignment you will use the library you created in Assignment 1 to create a server to keep a database of song locations. Since we do not yet know how to communicate over a network, we will use named pipes to have processes on the same machine communicate.

This assignment has 5 parts. Each part builds on the previous one. For each part, create a new directory and copy the files from the previous part into this directory. Each part should have a separate makefile which can run lint on the programs for that part. In parts 3 and 4 you will use your library from Assignment 1 to write a program that can create a music database and receive queries on that database. In part 2 you will write a program that can be used to test parts 3 and 4. In part 1 you will write a utility routine that you will need.

In this assignment you will be sending strings from one process to another. For testing purposes it is sometimes easier to generate and look at lines rather than strings. You can find two useful filters, string2line and line2string in /usr/local/courses/cs3733/fall2001/assign4.

Part 0:
Make sure the datalib library you created in assignment 1 is working correctly. If you think you are too far from having this working, you can use my library (at a 3-point penalty) available in /usr/local/courses/cs3733/fall2001/assign1/workinglib.

Part 1:
Write a function with the following prototype:
int read_string_from_fd(int fd, char *buf, int bufsize);
that reads a string from the given file descriptor and puts it in buf if it fits. This will read one character at a time until a string terminator is found, putting the result in buf. At most bufsize bytes will be read. If and end-of-file occurs before any input, return 0. If no string terminator is found or an I/O error occurs, return -1. Otherwise, return 1 to indicate success. In this case buf should contain a valid string.

Put this function in a file called myiolib.c. Create a file called myiolib.h containing the prototypes of the public functions in myiolib.c. Write a separate main program that checks to see that this function is working correctly. One way to do this is to write a main program called iotest that reads strings from file descriptor 0 using read_string_from_fd and sends the corresponding line to standard output. This program should check for the errors that can be returned by read_string_from_fd. You can generate input strings from the command line using:
line2string | iotest

Part 2:
Write a main program called musictester that takes two named pipes inpipe and outpipe as command line parameters. It does the following:

Prompts the user for a character. It reads a line of characters from standard input, opens outpipe for writing, and sends the first byte of the line read to outpipe.
Enters a loop in which it prompts the user to enter data from the command line. Each line is converted to a string and sent to outpipe along with the string terminator, but without the newline. You may assume that an input line of more than 100 bytes is an invalid input. This should cause your program to terminate gracefully.
When it receives end-of-file from standard input (or an error), it closes outpipe and opens inpipe for read.
Everything it receives from inpipe it sends to the screen.

This program should only terminate if it receives invalid input from standard input or an end-of-file from inpipe.

Think about using fgets for user input. Be sure that your program does not have a buffer overflow problem.

Do this using three windows.
In the first window run musictester:
musictester inpipe outpipe
In the second window, look at what is going into outpipe:
cat outpipe | string2line
In the third window, generate input for inpipe:
cat > inpipe.

Part 3:
Write a main program called musicinfo that takes two named pipes as command line parameters. I will refer to these as inpipe and outpipe. The main program opens outpipe for reading and writing and performs an infinite loop that does the following:

Open inpipe for reading.
Read one byte from inpipe, called the command byte.
Take action based on the command byte.
Close inpipe.

For this part, if the command byte is not '0', take no action.

If the command byte is '0', do the following:

Use read_string_from_fd to read three strings from inpipe.
The first string will be interpreted as a host name.
The second will be interpreted as a port number.
The third string will be interpreted as a key.
You may assume a maximum length of 128 bytes for each string.
Insert the corresponding entry in your data library.
If both of the above operations are successful, send a single byte of '0' to outpipe.
If either operation in unsuccessful, send a single byte of '1' to outpipe.

You can test this in one of two ways:
Using Part 2:

Use 2 windows.
In window 1 execute:
musicinfo inpipe outpipe
In window 2 execute:
musictester outpipe inpipe

Without Part 2:

Use 4 windows.
In the first window run musicinfo:
musicinfo inpipe outpipe
In the second window, create the command byte:
cat > inpipe
In the third window, generate the strings:
line2string > inpipe
In the last window, look at the output generated:
cat outpipe | string2line
Note that you need 2 different windows to send to inpipe, since the command is a single byte. When you generate this, be sure to use CTRL-D so that it gets sent to the pipe without waiting for a newline.

Part 4
Have musicinfo handle the following additional command bytes:

Command byte '1':

Read a single string from inpipe. Use this as the key parameter to getdata.
If getdata was unsuccessful, send a single byte of '1' to outpipe.
If successful, send a byte of '0' to outpipe followed by strings for the host name, port number, and key.

Command byte '2':
This is just like command byte '1', but uses findentry.

Command byte '3':
This is like command byte '1', but uses deleteentry. It will only send one byte to outpipe indicating success ('0') or failure ('1').

If an invalid command byte is received, take no action.

Handing in the program
Use the cover page provided when handing in your assignment.

The output you provide is determined what which parts of the assignment you have working. In each case, remove any unnecessary print statements that would obscure your output.

If Parts 2 and 3 are both working correctly:
Use the 2-window method of testing described above, running musicinfo in one window and musictester in another. Use musicinfo with command '0' to create three entries in the music database in the following order: Entry host port key 1. myhost1 23 my first key 2. ten10.cs.utsa.edu 10034 myfile.1 3. ten24.cs.utsa.edu 10036 myfile.2 If Part 4 is also working also do the following:

send a '1' command with key myfile.1
send a '2' command with key first

Use cut-and-paste to gather the output from the two windows and handle them in (clearly labeled) with your assignment. The part gathered should start with the prompt before the program is run and end with the prompt after is has terminated. If Part 3 is working but Part 2 is not Do exactly the same as above, but use the 4-window method that does not need musictester. Gather the output for each window using cut-and-paste and turn it in with your printout. Make sure the output of each window is clearly labeled. If Part 2 is working, but not part 3 Use the 3-window method described in Part 2 and use musictester to send the same information as in the above tests. Gather the results of the three windows, label them clearly, and turn them in with your assignment.

Entry	host	port	key
1.	myhost1	23	my first key
2.	ten10.cs.utsa.edu	10034	myfile.1
3.	ten24.cs.utsa.edu	10036	myfile.2