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CITS2002 Systems Programming - Project 2 2023
Background
We increasingly use multiple computers,
such as those at university, at places of employment,
personal desktop computers, and laptops.
Unfortunately,
because cloud-based services such as Dropbox and OneDrive
are not always available,
we may have only a subset of our files on the computer we're using.
We (should also) employ portable storage devices, such as USB thumb-drives
to backup and transport copies of our files between computers but, over time,
we need to manually identify the most up-to-date
version of a file before we overwrite another file of the same name.
We'd like to synchronise files between our computers and
our USB thumb-drive
(so that both hold the most up-to-date copy of the same files),
travel home,
and then synchronise our USB thumb-drive with our home computer or laptop.
Eventually, all three locations will hold identical copies of the same files.
The activity of ensuring that two sets of files are identical,
is termed file synchronization,
or just syncing.
For this project,
two sets of files are deemed identical if
each file exists in the same relative location below a 'top-level' directory,
with the same filename,
and with identical contents.
The goal of this project
is to design and develop a command-line utility program,
named mysync,
to synchronise the contents of two or more directories.
Successful completion of the project will develop and enhance
your understanding of advanced features of the C11 programming language,
POSIX function calls,
and the use of the make utility.
Program invocation
Your program will be invoked from the command-line
with zero-or-more options (switches) and two-or-more directory names:
prompt> ./mysync [options] directory1 directory2 [directory3 ...]
The program's options are:
| -a |
By default, 'hidden' and configuration files
(those beginning with a '.' character) are not synchronised
because they do not change very frequently.
The -a option requests that all files,
regardless of whether they begin with a '.' or not,
should be considered for synchronisation.
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| -i pattern |
Filenames matching the indicated pattern should be ignored;
all other (non-matching) filenames should be considered for synchronisation.
The -i option may be provided multiple times.
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| -n |
By default, mysync determines what files need to be synchronised
and then silently performs the necessary copying.
The -n option requests that any files to be copied are identified,
but they are not actually synchronised.
Setting the -n option also sets the -v option.
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| -o pattern |
Only filenames matching the indicated pattern should be considered for synchronisation;
all other (non-matching) filenames should be ignored.
The -o option may be provided multiple times.
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| -p |
By default,
after a file is copied from one directory to another,
the new file will have the current modification time and default file
permissions.
The -p option requests that
the new copy of the file have the same modification time
and the same file permissions as the old file.
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| -r |
By default, only files found immediately within the named directories are
synchronised.
The -r option requests that any directories found
within the named directories are recursively processed.
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| -v |
By default, mysync performs its actions silently.
No output appears on the stdout stream,
although some errors may be reported on the stderr stream.
The -v option requests that mysync be more
verbose in its output,
reporting its actions to stdout.
There is no required format for the (your) debug printing (it will be ignored during marking).
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File patterns
Globbing, also known as
wildcard expansion,
is a feature in Unix-like operating systems
(including Linux and macOS) that allows you to use special characters,
termed wildcards,
to match and specify multiple files and directories in a concise way.
The wildcard characters *, ?, [ ], and { } are widely supported.
Normally, globbing is performed by the shell before it passes the expanded patterns
as arguments to a new child process.
Within our own programs, such as mysync with its -i and -o options,
we need to perform globbing ourselves.
A simple way to determine if a glob-pattern matches a given filename,
is to first convert the glob-pattern to a regular-expression,
and to then see if the regular expression matches the filename.
The provided function
glob2regex
performs the first part of this process,
and the library functions regcomp and regexec,
used in sequence,
perform the second.
Note that, because the shell expands wildcards, that you'll need to enclose
your file patterns within single-quotation characters.
For example, the following command will (only) synchronise your C11 files:
prompt> ./mysync -o '*.[ch]' ....
and the following command will synchronise all files except your laboratory exercises:
prompt> ./mysync -i 'lab?-Q*.*' ....
Examples
Assume that you have a USB thumb-drive,
imaginatively named "myUSB",
and that you plug it in:
- if using a CSSE lab Linux computer,
your thumb-drive should be mounted at "/media/UNIWA 2xxxxxxx/myUSB"
(yes, there's an annoying space in that pathname).
- if using your own laptop running macOS,
your thumb-drive should be mounted at "/Volumes/myUSB".
- if using your own laptop running Linux,
you can use the df command to find the name of your thumb-drive's mount point.
Consider the following typical invocations of mysync
(which employ the simpler macOS pathname):
prompt> ./mysync ~ /Volumes/myUSB
this command will synchronise files between your home directory
and your USB thumb-drive.
prompt> ./mysync -a /Volumes/myUSB ~
this command will synchronise all files
(including configuration files)
between your home directory and your USB thumb-drive.
prompt> ./mysync -n -r /Volumes/myUSB cits2002
this command will recursively determine which files require
synchronization, it will report the actions that would be taken
in synchronizing them, but no actual copying will be performed.
prompt> ./mysync -p -v /Volumes/myUSB cits2002
this command will synchronise Systems Programming directory and your USB thumb-drive,
ensuring that all files eventually have the same modification time
and protection modes.
At the same time, all actions taken will be reported.
prompt> ./mysync -r /Volumes/myUSB cits2002 ~/backup/cits2002
this command will recursively synchronise files between 3 directories -
your Systems Programming (working) directory,
your USB thumb-drive,
and a local copy of all your cits2002 work.
WARNING: until you are very confident that your mysync program
is working, and is copying files correctly,
you are strongly advised NOT to use your mysync program
to backup your project!
Getting started
There is no required sequence of steps to undertake the project,
and no sequence of steps will guarantee success.
However, the following sequence is strongly recommended
(and this is how the sample solution was built).
It is assumed (considered essential for success!) that each step:
- is extensively tested before you proceed to the next step, and
- if any errors are found,
the first error should be reported to stderr,
and the program should immediately terminate.
The recommended initial steps (some will take 2 minutes, others make take a day):
- find a project partner.
- determine what activities are to be performed by the program.
Determine what data needs to be stored during the execution of the
program. Design one of more data types and data structures to store
this long-term data, and create a new mysync.h header file to
define these constructs.
- break up the activities into fairly independent sets.
Write a number of "empty" C files,
each of which includes your mysync.h header file,
to implement the activities.
Ensure that the main() function is in a file named mysync.c
- write a Makefile to compile and link your C files,
each of which will be dependent on the header file.
- write the main() function,
whose initial task is simply to receive and validate the command-line
options and arguments.
Write a usage() function to report the program's synopsis,
should command-line processing detect any errors.
- ensure that the actual command-line arguments are the names of
directories that you can read.
- open and read each directory,
locating all regular files in the directory.
At this stage, limit your project to support just two directories,
and to just print each filename as it is found.
- add support for the -a command-line option when finding files.
- store the name (location) and modification time of each file found
in each directory.
- having finished reading the directories,
identify all files that exist in one directory but not in the other,
or the newer of two files if they exist in both directories.
- if the -n command-line option is not provided,
copy the unique (or newer) file from one directory to the other.
- add support for three or more directories.
- add support for the -r command-line option
when finding files.
- add support for the -p command-line option
when copying files.
-
armed with a fully tested program, and overflowing with confidence,
support the -i and -o options.
It is anticipated
that a successful project will use (most of)
the following Linux system-calls, and standard C11 & POSIX functions:
perror,
getopt,
malloc,
realloc,
strdup,
free,
opendir,
readdir,
closedir,
stat,
mkdir,
open,
read,
write,
close,
chmod,
utime,
and
glob2regex(provided),
regcomp
and
regexec.
Project requirements and fine print
- Your project must be developed in
multiple C11 source files and (at least one) header file.
- Your submission will be compiled with the C11 compiler
arguments -std=c11 -Wall -Werror,
and marks will not be awarded if your submission does not compile.
- Compilation and linking of your project must be supported
by a Makefile,
employing approriate variable definitions and automatic variables.
- The default target of your Makefile must be named
mysync,
and invocation of the make command must produce an executable program named
mysync.
- Note that in this project,
nothing is ever deleted - our sets of synchronised files just keep growing.
- The directories to be synchronised will contain (only) regular-files and other (sub)directories.
All other file types may be ignored.
- Your project must not invoke the standard utility programs
cp or mkdir,
or call the library function system()
- You may leave all 'debug printing'
(to either stdout or stderr) in your submitted program -
it will all be ignored.
Assessment
The project is due
5:00pm Friday 20th October (end of week 12).
- The project is worth 25% of your final mark for CITS2002.
It will be marked out of 50.
- The project may be completed individually or in teams of two
(but not teams of three).
The choice of project partners is up to you -
you will not be automatically assigned a project partner.
- If the project is undertaken by a team of two,
both students will receive the same mark for the project.
- Requests for extensions will not be granted for students
working in a team of two.
This also applies if any member of a team of two
has a registered University Academic Adjustment Plan (UAAP).
- Your submission will be examined, compiled, and run on
a contemporary Ubuntu Linux system (such as in CSSE labs).
While you may develop your project on other computers, excuses such as
"it worked at laptop, just not when you tested it!" will
not be accepted.
- This project is subject to UWA's
Policy on Assessment - particularly §5.3
Principles of submission and penalty for late submission,
and
Policy on Academic Conduct.
In accordance with these policies, you may discuss with other students
the general principles required to understand this project,
but the work you submit must be the result of your own team's efforts.
All projects will be compared using software that detects significant
similarities between source code files.
Students suspected of plagiarism will be interviewed and will be required to
demonstrate their full understanding of their project submission.
- 25 of the possible 50 marks will come from assessing your design and programming style,
including your use of meaningful comments;
well chosen identifier names;
appropriate choice of basic data-structures, data-types and functions;
and
appropriate choice of control-flow constructs (manual marking).
- 25 of the possible 50 marks will come from the correctness of your solution
(automated marking),
which will assessed by having the correct output (measurements line)
when tested with a number of sysconfig and command input files..
During the marking, attention will
obviously be given to the correctness of your solution. However, a correct
and efficient solution should not be considered as the perfect, nor
necessarily desirable, form of solution. Preference will be given to well
presented, well documented solutions that use the appropriate features of
the language to complete tasks in an easy to understand and easy to follow
manner. That is, do not expect to receive full marks for your project simply
because it works correctly. Remember, a computer program should not only
convey a message to the computer, but also to other human programmers.
Good luck!
Chris McDonald.
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