[Mapserver-users] Sending image to stdout under Apache

[Joe Bussell]

I like the idea, but I have not been able to reproduce your results.  I 
currently produce maps for TrafficDodger using the two-step temp file 
technique.  I would like to rip the image right to Apache.  The 
filehandle OUT is not defined in my system.  I wonder what you have set, 
or exported to get this to produce useful results.  Have you declared an 
output file?

If I write to STDOUT I get complaints  "Use of uninitialized value in 
null operation".  It appears that $img->saveImage( undef, 
$mapscript::MS_PNG, 1, 1, 95 ); is not returning anything useful for the 
print call.  Any ideas?

Is this dependent on the latest rev of Mapserver?

Cordially,

Joe Bussell


Lowell Filak wrote:
> Doh!
> That's what I get for being in a hurry.
> From what I've read:
> 1) You don't need binmode on *n*x.
> 2) You need to print to OUT as opposed to STDOUT or the content is shipped before the content-type.
> print OUT $ref_img->saveImage(undef, $mapscript::MS_PNG, $map->{transparent}, $map->{interlace}, 0);
> HTH
> Lowell F.
> 
> The following message was sent by Eric Bridger <eric at gomoos.org> on 05 Mar 2003 10:57:23 +0000.
> 
> 
>>Thanks Lowell,
>>
>>Yes, that was the work-around I mentioned.  But avoiding the write to
>>disk is what I am after.  I have found that using /cgi-bin/mapserv as an
>>image engine results in significant performance improvements for our
>>mapscript application.  But constructing the proper query strings to
>>manipulate the map is cumbersome and seems to have certain limitations. 
>>I'd prefer to manipulate the map using mapscript and then print it to
>>the stdout. But somehow, using $img->saveImage(undef, ...) which spends
>>some time doing something, never sends the image to the stdout when run
>>as a CGI.  From the command line, it works.
>>
>>We don't have this problem with a graphing application in the same
>>environment which uses GD.pm.
>>
>>
>>On Wed, 2003-03-05 at 15:27, Lowell Filak wrote:
>>
>>>Hmmm...
>>>I thought I replied back concerning that.?
>>>Just do a:
>>>print "Content-type: image/png\n\n";
>>>system("cat junk.png");
>>>and that will send the image to stdout/the browser.
>>>HTH
>>>Lowell F.
>>>
>>>The following message was sent by Eric Bridger <eric at gomoos.org> on 05 Mar 2003 08:59:12 +0000.
>>>
>>>
>>>>
>>>>The list archives show that this came up last Dec.
>>>>(http://mapserver.gis.umn.edu/data2/wilma/mapserver-users/0212/msg00265.html) and while a work around was suggested there was no solution to the problem given, so I was wondering if anyone else had run into this problem. 
>>>>
>>>>I'm having a problem using Perl mapscript $img->saveImage(undef, ...),
>>>>to send an image, PNG and/or JPEG, to the standard output under Apache. 
>>>>Running in /cgi-bin I have the following script: 
>>>>
>>>>my $map = new mapscript::mapObj($ms_dir . "/test.map"); 
>>>>
>>>>my $ref_img = $map->drawReferenceMap(); 
>>>>
>>>># This works fine: 
>>>>#$ref_img->saveImage("junk.png", $mapscript::MS_PNG,  
>>>>$map->{transparent}, $map->{interlace}, 0); 
>>>>
>>>>print "HTTP/1.0 200 OK\n"; 
>>>>print "Content-type: image/png\r\n\r\n"; 
>>>>binmode STDOUT; 
>>>>
>>>># this produces no output on Apache's STDOUT 
>>>>$ref_img->saveImage("", $mapscript::MS_PNG, $map->{transparent},
>>>>$map->{interlace}, 0); 
>>>>
>>>>$ref_img->free(); 
>>>>exit; 
>>>>
>>>>
>>>>>From the command line this script works as expected.  But when run under
>>>>Apache/mod_perl  it's as if the C msSaveImage() stdout stream is
>>>>pointing somewhere other than the Apache stdout (i.e. the client
>>>>browser). 
>>>>
>>>>The work around of course is to save a disk file and then print it, but
>>>>the whole point of this is to avoid the temp. disk files.  I've noticed
>>>>a significant increase in performance when using mapserv as an image
>>>>engine rather then using temp disk files. 
>>>>
>>>>Thanks. 
>>>>Eric 
>>>>
>>>>
>>>>Setup: 
>>>>
>>>>Apache/1.3.26 (Unix) 
>>>>Mapserv 3.6.4 
>>>>mod_perl 1.22 
>>>>
>>>>
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>>>
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>>
>>
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