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[web] CGI Wait Screen?

Started by 31337 Sep 25, 2004 at 9:52 PM 14 replies 2.4k views

Original Post

Sep 25, 2004 at 9:52 PM

I wrote a CGI web service in C++ and I want to add in some sort of intermediate waiting page. How do I do this? I'm sort of stuck, this is an esoteric topic. Thanks in advance.

C-Junkie

139

C-Junkie

Sep 25, 2004 at 9:55 PM

explain slightly more about whaqt you want to do.

pjcast

Sep 25, 2004 at 10:04 PM

You could probably either a) send a mete-refresh with a certain wait time out, or b) have an html file that has the meta-refresh

C-Junkie

139

C-Junkie

Sep 25, 2004 at 10:43 PM

i'm sure he knows about refresh, and since its an cgi page, he can just send an http one, rather than a meta one.

The devil is in the details, do you want to wait a few seconds? or wait until some complicated transaction completes?

31337

Author

31337

Sep 26, 2004 at 8:50 PM

I was thinking of something where they click submit and then a new page pops up that says their request is being processed. It could take anywhere from 20 seconds to a day and so I think I might put in time estimates, but that would be preferable. What is a meta refresh? Thanks

igni ferroque

Sep 27, 2004 at 11:16 AM

Will the application finish writing the output before the submitted data has been processed? If so, output the intermediate page and set a refresh for 5-10 seconds (or however long you need) and keep outputting that page until the script detects that the submitted data has been processed. Otherwise, use DHTML/javascript to display the wait message and disable the form.

31337

Author

31337

Sep 29, 2004 at 12:26 AM

Currently my program doesn't output anything until after the data has been processed. How does refreshing work? How does that interface with my C++ program? Thanks

pjcast

Oct 1, 2004 at 1:50 AM

Check out here for a little info on either the http refresh or meta refresh: scroll down to client pull
http://wp.netscape.com/assist/net_sites/pushpull.html

You can also google for more info.

As far as how it integrates into you c++ cgi program, no differently then how you send any http headers or html text. You send it down the stream.

31337

Author

31337

Oct 4, 2004 at 12:21 PM

Alright, this is enough to make me bash my head through a wall. I read that document (and many others) and I can't figure out why my program doesn't work. The problem is that instead of processing the data as multipart/mixed it is outputting at the top of my data:

--PageBorder
Content-Type: text/html

At the start I output:

Content-type: multipart/x-mixed-replace;boundary=PageBorder\n\n

Then:

--pageBorder\nContent-Type: text/html\n\n

Followed by my HTML data and ended by:

\n--PageBorder--\n

Now what on earth is wrong? Why is it sticking my pageborder into the output page? I am really stuck and getting frustrated. Thank you.

Kylotan

Mod

3,487

Kylotan

Oct 4, 2004 at 6:19 PM

I've never seen that sort of thing used by HTTP before. I don't think it's a good idea to rely on it. Client pull is probably the way to go.

31337

Author

31337

Oct 4, 2004 at 7:03 PM

Client pull wouldn't work for me because I don't know how long it will take for my document to be ready.

pjcast

Oct 5, 2004 at 1:17 AM

Do this then, have your cgi write an entry to a file or database with the a user_id session with a flag of some sort that it is working and set a complete flag when done... Send the clients browser with a refresh rate of (depending on your average completion time) 5-10 (or more) seconds. But, also put a hidden form on the page with some kindof flag (such as task=check_status) or just have it go to status_check.cgi or whatever.

When the page gets refreshed, it will initiate a new cgi process app on your server, but the first thing this app does is check the flag in the database or file to see if the process is done, if not, resend refresh and try again. If it is do whatever else you were trying to do.

Sounds reasonable to me.

fractoid

$fractoid$

fractoid

Oct 5, 2004 at 2:25 AM

In the past, I've always just had a page that displays the 'loading...' message, and then immediately forwarded to the new, takes-ages-to-load page. As long as no actual data is sent by the server until the time-consuming bit is complete, most browsers seem to just wait while displaying the previous page (in this case, your loading page).

pjcast

Oct 5, 2004 at 4:39 PM

fractoid, I never thought of that, sounds like it would work prety good.

I just thought of another benifit in refreshing though, you could also modify my suggestion and have an entry in the data base for a percentage of work done, an a time count down based on that. This could be updated by the cgi script still working, and then cgi script that gets invoked during refresh would just read the database and update the screen with new info (such as a completion bar graph)

31337

Author

31337

Oct 6, 2004 at 12:48 AM

How about I do this:

Create a temporary html output file where I copy a generic waiting message. Forward the user to that temporary html file. That temporary html file refreshes every 15 seconds (or whatever). When my process is done, I open that temporary html file and replace it with my output data and then close the file.

Only one question, what if I open the file right when the client is trying to refresh? What would happen? Is it safe?

31337

Author

31337

Oct 6, 2004 at 11:17 PM

Alright so I made it so that my program does the following:

Reads the waiting screen html file and copies it to a temporary HTML file.

It then forwards the user to the temporary HTML file.

The temporary HTML files meta-refresh with CONTENT set to 10.

At the end of the program execution, it overwrites the wait screen with the output.

The problem I'm having is that when I send Location:waiting.html\n\n, the browser keeps pausing until the entire program is complete. How do I tell it to close the connection and go to the waiting screen?

Thanks

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