Monthly Archives: August 2013

C++ || Multi-Hash Interprocess Communication Using Fork, Popen, & Pipes

The following is another homework assignment which was presented in an Operating Systems Concepts class. Using two pipes, the following is a program which implements the computing of hash values on a file using the MD5, SHA1, SHA224, SHA256, SHA384, and SHA512 hashing algorithms provided on Unix based systems.

REQUIRED KNOWLEDGE FOR THIS PROGRAM

How To Use Fork
How To Use Pipe
How To Use Popen

==== 1. OVERVIEW ====

Hash algorithms map large data sets of variable length (e.g. files), to data sets of a fixed length. For example, the contents of a 1GB file may be hashed into a single 128-bit integer. Many hash algorithms exhibit an important property called an avalanche effect – slight changes in the input data trigger significant changes in the hash value.

Hash algorithms are often used for verifying the integrity of files downloaded from the WEB. For example, websites hosting a file usually post the hash value of the file using the MD5 hash algorithm. By doing this, the user can then verify the integrity of the downloaded file by computing the MD5 algorithm on their own, and compare their hash value against the hash value posted on the website. The user will know if the download was valid only if the two hash values match.

==== 2. TECHNICAL DETAILS ====

The following implements a program for computing the hash value of a file using the MD5, SHA1, SHA224, SHA256, SHA384, and SHA512 hashing algorithms provided on Unix based systems.

This program takes the name of the target file being analyzed as a command line argument, and does the following:

1. Check to make sure the file exists.
2. Create two pipes.
3. Create a child process.
4. The parent transmits the name of the file to the child (over the first pipe).
5. The child receives the name of the file and computes the hash of the file using the MD5 algorithm (using Linux program md5sum).
6. The child transmits the computed hash to the parent (over the second pipe) and terminates.
7. The parent receives the hash, prints it, and calls wait().
8. Repeat the same process starting with step 3, but using algorithms SHA1...SHA512.
9. The parent terminates after all hashes have been computed.

The use of the popen function is used in order to launch the above programs and capture their output into a character array buffer.

This program also uses two pipes. The two pipes created are the following:

(1) Parent to child pipe: Used by the parent to transfer the name of the file to the child. The parent writes to this pipe and the child reads it.

(2) Child to parent pipe: Used by the child to transfer the computed hashes to the parent. The child writes to this pipe and the parent reads it.


QUICK NOTES:
The highlighted lines are sections of interest to look out for.

The code is heavily commented, so no further insight is necessary. If you have any questions, feel free to leave a comment below.

Using the following example input file located here, the following is sample output:

C++ || Snippet – How To Use Popen & Save Results Into A Character Array

The following is sample code which demonstrates the use of the “popen” function call on Unix based systems.

The “popen” function call opens a process by creating a pipe, forking, and invoking the shell. It does this by executing the command specified by the incoming string function parameter. It creates a pipe between the calling program and the executed command, and returns a pointer to a stream that can be used to either read from or write to the pipe.

The following example demonstrates how to save the results of the popen command into a char array.


QUICK NOTES:
The highlighted lines are sections of interest to look out for.

The code is heavily commented, so no further insight is necessary. If you have any questions, feel free to leave a comment below.

The following is sample output:


Program output: fa97c59cc414e42d4e0e853ddf5b4745 /bin/ls

C++ || Serial & Parallel Multi Process File Downloader Using Fork & Execlp

The following is another homework assignment which was presented in an Operating Systems Concepts class. The following are two multi-process programs using commandline arguments, which demonstrates more practice using the fork() and execlp() system calls on Unix based systems.

==== 1. OVERVIEW ====

File downloaders are programs used for downloading files from the Internet. The following programs listed on this page implement two distinct type of multi-process downloaders:

1. a serial file downloader which downloads files one by one.
2. a parallel file downloader which dowloads multiple files in parallel.

In both programs, the parent process first reads a file via the commandline. This file which is read is the file that contains the list of URLs of the files to be downloaded. The incoming url file that is read has the following format:

[URL1]
[URL2]
.
.
.
[URLN]

Where [URL] is an http internet link with a valid absolute file path extension.
(i.e: http://newsimg.ngfiles.com/270000/270173_0204618900-cc-asmbash.jpg)

After the url file is parsed, next the parent process forks a child process. Each created child process uses the execlp() system call to replace its executable image with that of the “wget” program. The use of the wget program performs the actual file downloading.

==== 2. SERIAL DOWNLOADER ====

The serial downloader downloads files one at a time. After the parent process has read and parsed the incoming url file from the commandline, the serial downloader proceeds as follows:

1. The parent forks off a child process.
2. The child uses execlp("/usr/bin/wget", "wget", [URL STRING1], NULL) system call in order to replace its program with wget program that will download the first file in urls.txt (i.e. the file at URL ).
3. The parent executes a wait() system call until the child exits.
4. The parent forks off another child which downloads the next file specified in url.txt.
5. Repeat the same process until all files are downloaded.

The following is implemented below:

Since the serial downloader downloads files one at a time, that can become very slow. That is where the parallel downloader comes in handy!

==== 3. PARALLEL DOWNLOADER ====

The parallel downloader downloads files all at once and is implemented much like the serial downloader. The parallel downloader proceeds as follows:

1. The parent forks off n children, where n is the number of URLs in url.txt.
2. Each child executes execlp("/usr/bin/wget", "wget", [URL STRING], NULL) system call where each is a distinct URL in url.txt.
3. The parent calls wait() (n times in a row) and waits for all children to terminate.
4. The parent exits.

The following is implemented below:


QUICK NOTES:
The highlighted lines are sections of interest to look out for.

The code is heavily commented, so no further insight is necessary. If you have any questions, feel free to leave a comment below.

Also note, while the parallel downloader executes, the outputs from different children may intermingle.

C++ || Snippet – How To Use Fork & Pipe For Interprocess Communication

The following is sample code which demonstrates the use of the fork, read, and write function calls for use with pipes on Unix based systems.

A pipe is a mechanism for interprocess communication. Data written to a pipe by one process can be read by another process. Creating a pipe is achieved by using the pipe function, which creates both the reading and writing ends of the pipe file descriptor.

In typical use, a parent process creates a pipe just before it forks one or more child processes. The pipe is then used for communication between either the parent or child processes, or between two sibling processes.

A real world example of this kind of communication can be seen in all operating system terminal shells. When you type a command in a shell, it will spawn the executable represented by that command with a call to fork. A pipe is opened to the new child process, and its output is read and printed by the terminal.


QUICK NOTES:
The highlighted lines are sections of interest to look out for.

The code is heavily commented, so no further insight is necessary. If you have any questions, feel free to leave a comment below.

The following is sample output:

Parent is forking a child.
Parent is now waiting for child id #12776 to complete..

Starting the child process..

Message from the parent via the pipe: Greetings From Your Parent!

Program is now exiting...

The child process is complete and has terminated!

Program is now exiting...

C++ || Snippet – How To Use Fork & Execlp For Interprocess Communication

The following is sample code which demonstrates the use of the “fork” and “execlp” function calls on Unix based systems.

The “fork” function call creates a new process by duplicating the calling process; or in more simpler terms, it creates a duplicate process (a child) of the calling (parent) process.

This new process, referred to as the child, is an exact duplicate of the calling process, referred to as the parent.

The “execlp” function call is part of a family of functions which replaces a current running process image with a new process image. That means by using the “execlp” function call, you are basically replacing the entire current running process with a new user defined program.

Though fork and execlp are not required to be used together, they are often used in conjunction with one another as a way of creating a new program running as a child of another process.


QUICK NOTES:
The highlighted lines are sections of interest to look out for.

The code is heavily commented, so no further insight is necessary. If you have any questions, feel free to leave a comment below.

The following is sample output:

Parent is forking a child.
Parent is now waiting for child id #10872 to complete..

Starting the child process..

total 1466
-rw-r--r-- 1 admin admin 468 Apr 27 2012 nautilus-computer.desktop
-rwxrwxr-x 1 admin admin 9190 Aug 19 15:17 ForkExample
-rw-rw-r-- 1 admin admin 1640 Aug 19 15:17 ForkExample.cpp

The child process is complete and has terminated!

Parent is now exiting...

Python || Aku Aku Snake Game Using Pygame

The following is another homework assignment which was presented in an Introduction to Game Design and Production class. This project is an implementation of the classic “Snake” game using Python 3.2 and Pygame 1.9.2a0.

REQUIRED KNOWLEDGE FOR THIS PROGRAM

Pygame - How To Install
Pygame - Download Here
How To Use Pygame
How To Create Executable Python Programs
Aku Aku Snake! Source Code - Click Here To Download
Aku Aku Snake! Executable File - Click Here To Download

==== 1. DESCRIPTION ====

Aku Aku Snake is a new take on the classic “snake” game. It features ten levels, with characters and sounds taken from the PlayStation hit: “Crash Bandicoot 2: Cortex Strikes Back.” The purpose of this game is to successfully complete all ten levels in the fewest amount of retries possible.

To advance in the game, each round the player must consume a specified number of fruit items. Once the required score is obtained during each round, a new one is started. This process is repeated until the player finishes all ten levels. But watch out! The game gets harder as the game progresses.

==== 2. USAGE ====

This game utilizes the python “pygame” module. To play this game, it is assumed that the user already has python 3 and pygame installed on their computer. If that is not the case, here are documents explaining how to obtain the necessary resources for play.

How to install Python:


Install Python

How to install Pygame:


Pygame - How To Install
Pygame - Download Here

After the required resources are obtained, to start the game, the easiest way this to do would be to extract the entire .zip file into the directory of your choice, and to simply run the “main.py” source file through the python interpreter. Once the “main.py” source file is ran through the python interpreter, the game should automatically start.

NOTE: Python and Pygame are not needed to play the executable file!

==== 3. EXTERNAL DEPENDENCIES ====

Other than the pygame module and the “main.py” file mentioned above, there are eight other source files this program depends on. The additional source files should be saved within the “libs” folder, which is located in the directory: “data -> libs”

The following is a brief description of each additional source file.

• “gameBoard.py” sets up the game board and background images for display. This class also reads files (images/fonts) from the “img” & “fnt” directory for use within this program.

• “gameMusic.py” sets up the game sounds and music. This class also reads files (.ogg) from the “snd” directory for use within this program.

• “gameSave.py” sets up the game to have the ability to save its current status. This class uses the “pickle” module to save the players current progress to a file.

• “snake.py” sets up the snake for display on the game board. This class also reads files (images) from the “img” directory for use within this program.

• “fruit.py” sets up the fruit for display on the game board. This class also reads files (images) from the “img” directory for use within this program.

• “enemy.py” sets up the enemies for display on the game board. This class also reads files (images) from the “img” directory, and uses the “spriteStripAnim” class for use within this program.

• “spriteSheet.py” handles sprite sheet animations.

• “spriteStripAnim.py” extends the spriteSheet.py module, providing an iterator (iter() and next() methods), and a __add__() method for joining strips, which comes in handy when a strip wraps to the next row.

These additional files are located within the directory: “data -> libs” folder.

==== 4. FEATURES ====

This game features various colorful images and background music which are taken from the original Crash Bandicoot game. Each level in this game features background music that are unique to each level.

The most useful feature implemented in this game is the “save game” element, which allows a player to save their current progress at any moment during gameplay. This allows a player to save their current status and continue playing the game at a later date if they desire.

To save the game, during gameplay simply click on the boss image in the upper right corner. Once the save is complete, a sound jingle will play confirming the successful save.

This game also features two modes of operation: “Easy” and “Hard” mode. When easy mode is selected, the game saves the user’s current game progress every time they die, but when hard mode is selected, that feature is turned off and the user HAS to save their current progress manually, or else it will be lost after each death.

Here are screenshots of the game during play. (on all images, click to enlarge)

Spoiler Inside: Aku Aku Snake! Screenshots SelectShow

==== 5. DOWNLOAD AND PLAY ====

Aku Aku Snake! Source Code - Click Here To Download
Aku Aku Snake! Executable File - Click Here To Download

NOTE: Python and Pygame are not needed to play the executable file!

Python || Brainy Memory Game Using Pygame

The following is another homework assignment which was presented in an Introduction to Game Design and Production class. This project is an implementation of the classic “Memory” game using Python 3.2 and Pygame 1.9.2a0.

REQUIRED KNOWLEDGE FOR THIS PROGRAM

Pygame - How To Install
Pygame - Download Here
How To Use Pygame
How To Create Executable Python Programs
Brainy Memory Game Source Code - Click Here To Download
Brainy Memory Game Executable File - Click Here To Download

==== 1. DESCRIPTION ====

Brainy Memory Game is a mind stimulating educational card game in which an assortment of cards are laid face down on a surface, and the player tries to find and uncover two identical pairs. If the two selected cards match, they are removed from gameplay. If the two selected cards do not match, both of the cards are turned back over, and the process repeats until all identical matching cards have been uncovered! The object of this game is to find identical pairs of two matching cards in the fewest number of turns possible. This game can be played alone or with multiple players, and is especially challenging for children and adults alike.

==== 2. USAGE ====

This game utilizes the python “pygame” module. To play this game, it is assumed that the user already has python and pygame installed on their computer. If that is not the case, here are documents explaining how to obtain the necessary resources for play.

How to install Python:


Install Python

How to install Pygame:


Pygame - How To Install
Pygame - Download Here

After the required resources are obtained, to start the game, the easiest way to do this would be to extract the entire .zip file into the directory of your choice, and to simply run the “memory.py” source file through the python interpreter. Once the “memory.py” source file is ran through the python interpreter, the game should automatically start.

NOTE: Python and Pygame are not needed to play the executable file!

==== 3. EXTERNAL DEPENDENCIES ====

Other than the pygame module and the memory.py file mentioned above, there are two other source files this program depends on. They are named “gameBoard.py” and “gameMusic.py.”

• “gameBoard.py” sets up the game board and playing cards for display. It also reads files (images/fonts) from the “img” & “fnt “directory for use within this program.

• “gameMusic.py” sets up the game sounds and music. It also reads files (.ogg/.wav) from the “snd” directory for use within this program.

Both of these source files should be located in the same directory as “memory.py”

==== 4. FEATURES ====

This game features various colorful images and sounds for a pleasant user experience. By default, there are 27 playing cards (image size: 80×80) for use located in the “img” folder, and more can be added by the player in the future if they desire.

There are four attainable memory ranks available in this game, with two of them being displayed below. Play the full game to discover the rest!

Here are screenshots of the game during play. (on all images, click to enlarge)

Spoiler Inside: Brainy Memory Game Screenshots SelectShow

==== 5. DOWNLOAD AND PLAY ====


Brainy Memory Game Source Code - Click Here To Download
Brainy Memory Game Executable File - Click Here To Download

NOTE: Python and Pygame are not needed to play the executable file!

Python || Random Number Guessing Game Using Random MyRNG & While Loop

Here is another homework assignment which was presented in introduction class. The following is a simple guessing game using commandline arguments, which demonstrates the use of generating random numbers.

REQUIRED KNOWLEDGE FOR THIS PROGRAM

How To Get User Input
Getting Commandline Arguments
While Loops
MyRNG.py - Random Number Class

==== 1. DESCRIPTION ====

The following program is a simple guessing game which demonstrates how to generate random numbers using python. This program will seed the random number generator (located in the file MyRNG.py), select a number at random, and then ask the user for a guess. Using a while loop, the user will keep attempting to guess the selected random number until the correct guess is obtained, afterwhich the user will have the option of continuing play or exiting.

==== 2. USAGE ====

The user enters various options into the program via the commandline. An example of how the commandline can be used is given below.


python3 guess.py [-h] [-v] -s [seed] -m 2 -M 353

Where the brackets are meant to represent features which are optional, meaning the user does not have to specify them at run time.

The -m and -M options are mandatory.

• -M is best picked as a large prime integer
• -m is best picked as an integer in the range of 2,3,..,M-1

NOTE: The use of commandline arguments is not mandatory. If any of the mandatory options are not selected, the program uses its own logic to generate random numbers.

==== 3. FEATURES ====

The following lists and explains the command line argument options.

-s (seed): Seed takes an integer as a parameter and is used to seed the random number generator. When omitted, the program uses its own logic to seed the generator

-v (verbose): Turn on debugging messages.

-h (help): Print out a help message which tells the user how to run the program and a brief description of the program.

-m (minimum): Set the minimum of the range of numbers the program will select its numbers from.

-M (maximum): Set the maximum of the range of numbers the program will select its numbers from.


QUICK NOTES:
The highlighted lines are sections of interest to look out for.

The code is heavily commented, so no further insight is necessary. If you have any questions, feel free to leave a comment below.

Once compiled, you should get this as your output:

Seed = 806189064, Minimum = 1, Maximum = 1000

I'm thinking of a number between 1 and 1000. Go ahead and make your first guess.
>> 500

Sorry that was not correct, please try again...

>> 400

WARMER

>> 600

COLDER

>> 300

WARMER

>> 150

WARMER

>> 100

COLDER

>> 180

COLDER

>> 190

COLDER

>> 130

WARMER

>> 128

WINNER! You have guessed correctly!
It took you 10 attempt(s) to find the answer!

Would you like to play again? (Yes or No): y

------------------------------------------------------------

Make a guess between 1 and 1000

>> 500

Sorry that was not correct, please try again...

>> 600

COLDER

>> 400

WARMER

>> 300

WARMER

>> 280

WARMER

>> 260

WARMER

>> 250

COLDER

>> 256

WINNER! You have guessed correctly!
It took you 8 attempt(s) to find the answer!

Would you like to play again? (Yes or No): n

Thanks for playing!!

Python || Custom Random Number Generator Class MyRNG

The following is sample code for a simple random number generator class. This random number generator is based on the Park & Miller paper “Random Number Generators: Good Ones Are Hard To Find.

This class has three functions. The constructor initializes data members “m_min” and “m_max” which stores the minimum and maximum range of values in which the random numbers will generate.

The “Seed()” function stores the value of the current seed within the class, and the “Next()” function returns a random number to the caller using an algorithm based on the Park & Miller paper listed in the paragraph above. Each time the “Next()” function is called, a new random number is generated and returned to the caller.


QUICK NOTES:
The highlighted lines are sections of interest to look out for.

The code is heavily commented, so no further insight is necessary. If you have any questions, feel free to leave a comment below.

===== DEMONSTRATION HOW TO USE =====

Use of the above class is very simple to use. A sample function demonstrating its use is provided on line #64 in the above code snippet.

After running the code, the following is sample output:

SAMPLE OUTPUT:


1037, 1296, 1123, 1900, 1375, 1676, 1798, 662, 664, 674, 746, 1249, 793, 1578, 1112,

Python || Pdf Merge Using PyPdf

The following is a simple pdf file merger program which utilizes the “pyPdf” library to manipulate pdf files. This program has the ability to merge entire selected pdf files together, and save the selected files into one single new pdf file.

REQUIRED KNOWLEDGE FOR THIS PROGRAM

PyPdf - What Is It?
How To Create Executable Python Programs
Display The Time In Python
Metadata With PyPdf
Pdf Merge Executable File - Click Here To Download

This program first asks the user to place the pdf file(s) they wish to merge into a specified folder. The default input folder is titled “Files To Merge.” After the input pdf file(s) have been placed into the specified input folder, the program prompts the user to select which file(s) they wish to merge together. As soon as the input pdf file(s) have been selected, the file merging begins, with the files being saved to the output pdf file in the exact same order as specified by the user. As soon as the file merging is complete, the single merged pdf file is saved into an output folder titled “Completed Merged Files.”


QUICK NOTES:
The highlighted lines are sections of interest to look out for.

The code is heavily commented, so no further insight is necessary. If you have any questions, feel free to leave a comment below.

Click here to download a Windows executable file demonstrating the above use.

Python || Pdf Split & Extract Using PyPdf

The following is a simple pdf file split & extractor program which utilizes the “pyPdf” library to manipulate pdf files. This program has the ability to extract selected pages from an existing pdf file, and save the extracted pages into a new pdf file.

REQUIRED KNOWLEDGE FOR THIS PROGRAM

PyPdf - What Is It?
How To Create Executable Python Programs
Display The Time In Python
Metadata With PyPdf
Pdf Split Executable File - Click Here To Download

This program first asks the user to place the pdf file(s) they wish to extract pages from into a specified folder. The default input folder is titled “Files To Extract.” After the input pdf file(s) have been placed into the specified input folder, the program prompts the user to select which file they wish to extract pages from. As soon as an input pdf file has been selected, the user is asked to enter in the page numbers they wish to extract from the specified input pdf file. After the page extraction is completed, the selected pages are merged into one single pdf file, and is saved into an output folder titled “Completed Extracted Files.”


QUICK NOTES:
The highlighted lines are sections of interest to look out for.

The code is heavily commented, so no further insight is necessary. If you have any questions, feel free to leave a comment below.

Click here to download a Windows executable file demonstrating the above use.