[SOLVED] Csci493.66 assignment 5- autoscroll – a self-scrolling file viewer p0

Overview
This assignment is designed to give you practice with several parts of the kernel API: signal handling, a bit of terminal control, and file I/O. It is probably the most algorithmically challenging of the assignments you’ve had so far, but it does not require a long program. Because you haven’t yet learned how to control terminals, the program will not use many features of terminals. It will use the ANSI escape sequences that I explained and showed examples of in class to control the position of the cursor and the screen contents.
The assignment is specified by the following man-page-like description. Your job is to write a program that satisfies these requirements. The information regarding program submission is at the end of the assignment.
NAME
autoscroll — display a file, automatically scrolling upward one line per second if needed
SYNOPSIS
autoscroll [-s secs] textfile where secs is a positive integer < 60
DESCRIPTION
When run with any size plain text file in a terminal window with R rows and C columns, autoscroll displays the first R-1 lines of the file in the terminal. If the number of lines in the file is R-1 or less, it terminates after displaying these lines. Otherwise, every N seconds, with N=1 by default, it scrolls the file up one line, so that the topmost line disappears and the next line in the file is displayed; but see below for further details. It also updates a clock display and an indicator of the visible lines in the file.
Terminal windows have a coordinate system in which the upper-left corner is (1,1). The bottom row of the terminal window, which I’ll call the status bar, is reserved for status information and never shows any file content. In particular, it displays the current time in the format “HH:MM:SS” in the leftmost position of row R, and starting in column 10 of row R , it displays the range of line numbers of the file that are currently displayed in the format “Lines: num1-num2”, where num1 and num2 are integers, such as “Lines: 100-122”.
While the program is auto-scrolling, the cursor is parked at position (R,C-2). At any time, the user can enter one of two key combinations to pause and restart autoscrolling: CTRL-Z or CTRL-C. CTRL-Z pauses scrolling. When the user enters CTRL-Z, the clock display continues to keep time but the file is not scrolled upward in the terminal. When the display is paused and the user enters CTRL-C, autoscrolling restarts. If scrolling is not paused, CTRL-C has no effect and when it is paused, CTRL-Z has no effect. The user can terminate the program at any time by sending any other terminating signal, such as SIGTERM, SIGQUIT, or SIGKILL or by by entering CTRL- on the keyboard. When any terminating signal is delivered to the process, the screen is cleared and the shell prompt returns. The following figure shows a sample of how the terminal’s area is used.

• If the -s option is supplied, the rate at which the file is scrolled should be once every secs seconds.
IMPLEMENTATION ISSUES
• Because alarm() is not a timer, in order to get repeated alarms, the handler must set it every time it runs.
(80+80+40 on each of 3 lines). autoscroll needs to reduce the range of lines it displays by 2 because of this long line. If the next line to be scrolled into view in the file is a long line, it should not display it until there is room in the terminal for the entire line, including wrapped content, to be visible. This implies that there will be space at the bottom until it can fit that line into the text display region.
• In order to display the file as if it is scrolled, the program clears the screen above the status line and redraws the new range of lines. It does this every N seconds. Most terminals have a scroll buffer that saves what was in the terminal as it advances. autoscroll should clear that buffer as well.
• The signal handler for the signal that alarm() sends must be able to access the text loaded into memory from the file, the positions of newline characters and many other variables. Because signal handlers do not have hooks for any data, and that data is most likely initialized in the main() function, these variables must be filescoped.
• Once it has set up signal handling, read and loaded files, initialized all data structures and so on, the main() function does very little other than detecting when the user enters one of the two keyboard sequences. It just needs to make sure that it detects these key presses and always keeps the cursor parked in the lower left corner. The main() function should use the sigwait() system call with suitable processing when it returns. Read its man page.
LIMITATIONS
• There is no limit on the size of a file to be displayed, up to your computer’s own limits on memory and disk storage. The program should be able to open any text file that other applications can open.
• The file can have lines that are longer than the width of the terminal window, but your program can assume that no line is longer than 4KB.
• The program can assume that the file’s last character is a newline. Alternatively, it can allows files that do not end in a newline and it can add a newline at the end. You might find it is easier when it always ends in a newline.
ERROR HANDLING
If the required file argument is missing, it is an error that must be handled with a suitable usage message. If an option is supplied but is anything other than -s followed by a positive integer less than 60, it is an error. The program should report all errors on standard error along with the correct form of usage.
SEE ALSO alarm(2), ioctl(3), sigwait(3), console_codes(7)
Hints
Debugging a program that has signal handlers and screen manipulation can be challenging. You should use a debugger such as gdb, and also use valgrind. You can also print to a second terminal window — open a second window, enter the command tty, record the output (such as /dev/pts/2) and in your program, write diagnostics to that file.
Code Re-Use and Program Structure
You are free to use any of the code in the class’s repository. There are a few demo programs in Chapter 9 that will be useful. All of them have GNU General Public Licenses. If you do use any of that code, the documentation should indicate which parts are not written by you. The program should be a single source code file. All functions other than main() should precede main() in the file.
Instructions for Submitting the Assignment
1. Use the submithwk_cs49366 program to submit your program. To submit, if your file is ~/autoscroll.c, you’d enter
$ cd ~
$ submithwk_cs49366 -t 5 autoscroll.c
The program will copy autoscroll.c into the directory
/data/biocs/b/student.accounts/cs493.66/hwks/hwk5/
and if it is successful, it will display the message, “File hwk5_username.c successfully submitted.” where username is your username. You will not be able to read this file, nor will anyone else except for me. But you can double-check that the command succeeded by typing the command ls -l /data/biocs/b/student.accounts/cs493.66/hwks/hwk5
2. You can do step 1 as many times as you want. Newer versions of the file will overwrite older ones.
Grading Rubric
This assignment is 18% of your final grade. The output must be correct and the program must conform to the rules written in the Programming Rules document on the class’s webpage. It must be thoroughly documented.