Re^2: Creating a "Progress" page with CGI

Hi Randal,

The "Lines 1 through 3 begin nearly every CGI program I write: enabling taint checking, compiler restrictions, and disabling the buffering of standard output." in your article doesn't hold true any more for Apache 2. Specifically the "$|++;" which does disable the buffering at the perl level but not within Apache v2. :(

The method to use now is forking the process in the background and providing updates. Roy Johnson provides the link to the redirection discussion.

Update: I remembered my tests wrong. My apologies to Merlyn.

Jason L. Froebe

Team Sybase member

No one has seen what you have seen, and until that happens, we're all going to think that you're nuts. - Jack O'Neil, Stargate SG-1

Comment on Re^2: Creating a "Progress" page with CGI

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Re^3: Creating a "Progress" page with CGI by merlyn (Sage) on Dec 06, 2005 at 19:11 UTC
The "Lines 1 through 3 begin nearly every CGI program I write: enabling taint checking, compiler restrictions, and disabling the buffering of standard output." in your article doesn't hold true any more for Apache 2. Specifically the "$\|++;" which does disable the buffering at the perl level but not within Apache v2. :( Uh, you're apparently confused. I'm unbuffering the connection between the forked Perl process and Apache. That doesn't matter whether it's Apache 1 or Apache 2. That's to keep unbuffered and buffered output from intermixing badly to STDOUT, so that the header doesn't appear after some of the body content, for example. The method to use now is forking the process in the background and providing updates. Roy Johnson provides the link to the redirection discussion. And the technique shown is indeed "fork and continue the process in the background". Did you read the article? -- Randal L. Schwartz, Perl hacker Be sure to read my standard disclaimer if this is a reply.	[reply]
Re^4: Creating a "Progress" page with CGI by jfroebe (Parson) on Dec 06, 2005 at 19:15 UTC
Hi Randal, Actually I did many times both on the web and also in the book. Anyways, I didn't explain myself clearly enough. Sorry about that. With Apache 2, the unbuffering at the perl level doesn't seem to make any difference (atleast with my testing). update: nevermind. I remembered my test wrong. ugh.. must be too close to monday Jason L. Froebe Team Sybase member No one has seen what you have seen, and until that happens, we're all going to think that you're nuts. - Jack O'Neil, Stargate SG-1	[reply]
Re^5: Creating a "Progress" page with CGI by merlyn (Sage) on Dec 06, 2005 at 19:18 UTC
The difference is for programs like this: `#!/usr/bin/perl ## uncomment this: ## $\|++; print "content-type: text/plain\n\n"; system "date";` [download] When left commented, this fails (under both apache 1 and 2) because the system date comes out before the header, causing a 500 error. When uncommented, it works correctly. This is what I'm talking about. You were probably testing something else, like whether you could see it all the way through to the browser. That's a different problem, and was never related to my use of `$\|++`. -- Randal L. Schwartz, Perl hacker Be sure to read my standard disclaimer if this is a reply.	[reply] [d/l] [select]