Computer Science Homework Help

a. As mentioned above, the URL to get will be given in a double-quoted string as argv[1]. Therefore, the first step is to remove the double-quotes.

b. Have your program ignore Ctrl-C (SIGINT). You do not have to do this, but Ctrl-C is the way to stop simpleHttpServer.

If you do not ignore it then when you press Ctrl-C to stop the webserver, it will also get passed along to your program too. That will stop it.

Then when the webserver sends:

{“command”:”quit”}

your program will not be around to read() it. This will make the webserver upset. It will say:

Fine! No input for you!

c. Execute the HTTP call to get the JSON. Keep the data.

d. Enter a loop where you will get instructions in JSON from its standard input.

1. If the instruction your program gets is

{“command”:”quit”}

then to its standard output it should write:

{“status”:”quitting”}

and then stop the program.

2. If the instruction your program gets is like:

{“command”:”plot”,”xAxis”:”pl_orbper”,”yAxis”:”pl_orbeccen”}

then to its standard output it should create the desired graph.

Get the values for JSON variables “xAxis” and “yAxis”. Make the corresponding graph.

how to do that?

Personally, I recommend that you use gnuplot because it is already loaded on my system.

 Open a data file (I called mine ./data.txt. To this data file write all x-axis and y-axis value pairs where both values are given. (If one or both values are null then do not bother writing them!)

 Write a file that is a small program for gnuplot. I called mine scatter.gnu and its contents where:

 set term png size 640,480

 set output “scatterPlot.png”

 set title “pl_orbeccen as a fnc of pl_orbper”

 plot “./data.txt” with points pt 1

 quit

 gnuplot seems to like the size width: 640, height: 480, but feel free to play with those dimensions if you have the time.

 Notice I have the x- and y-axis names in the title

 fork() a child process to run /usr/bin/gnuplot. Pass the name of your gnuplot program (for me it is “scatter.gnu”) as an argument. Of course, have the parent wait() for the child.

 Send JSON back to the webserver by writing to standard output. I found I had better results when I multiplied both the height and width by 3/4: {“status”:”success”,”imageFilename”:”scatterPlot.png”,”height”:360,”width”:480}