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Id: 87397
Status: resolved
Priority: 0/
Queue: IPC-Run

Owner: Nobody in particular
Requestors: larry.knibb [...]

Bug Information
Severity: (no value)
Broken in: (no value)
Fixed in: (no value)

Subject: No STDIN to subprocess under mod_cgi on Windows
Date: Mon, 29 Jul 2013 07:47:22 +0000
To: <bug-IPC-Run [...]>
From: <larry.knibb [...]>
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As per the discussion on I'm trying to get GraphViz2 (which uses IPC::Run) to work in a CGI script under Apache (mod_cgi) on Windows. In a command line context it Just Works and I get the expected SVG output. In the CGI context it gets as far as an IPC::Run::run call to fdp.exe (, which never returns. Apache eventually times-out and gives up trying to serve the page. The fdp.exe process runs forever (or until I kill it). When `fdp -T svg` is called manually with no input (i.e. nothing piped to STDIN), that similarly waits forever for input; so my hypothesis is that the data that should be passed to fdp.exe's STDIN is not being sent in the mod_cgi context. With IPC::Run debugging on (IPCRUNDEBUG=gory) I ran the script once on the command line (which works) and again as a CGI (which doesn't) to compare the debug output. There are no error messages or warnings and except for the PIDs, about the only difference I can see is that as a CGI, all the paths (temp file, path to executable) contain double backslashes, whereas from the command line invocation the debug output has only single backslashes: [CGI] IPC::Run 0008 01234567890123 [#1(5888)]: cmd line: "C:\\Program Files (x86)\\Graphviz2.30\\bin\\fdp.exe" -Tsvg [CLI] IPC::Run 0008 01234567890123 [#1(5472)]: cmd line: "C:\Program Files (x86)\Graphviz2.30\bin\fdp.exe" -Tsvg The input to fdp.exe is successfully written to a temp file in both cases and the fdp.exe process is successfully started in both cases. Let me know if you need any more info to debug the issue. Cheers, Larry
Ticket migrated to github as

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