[mapserver-users] Corrupted PNG issue

[John Huotari]

I'm attempting to upgrade from MapServer 7.6.1 to 7.6.4 via compiled packages obtained from GISInternals.  I'm running it on Windows/IIS and whereas 7.6.1 was generating .PNG tiles perfectly for me, after upgrading to 7.6.4, the .PNGs being created appear to be corrupt.  I can replace the 7.6.4 exe and dlls with 7.6.1 versions and the PNG images generate fine again, so while there are quite a few places that could introduce an issue, with the exception of a change to MapServer everything would be identical in my stack between having the issue in 7.6.4 and not in 7.6.1.

The good headers from 7.6.1 look like this

89 50 4e 47 0d 0a 1a 0a  00 00 00 0d 49 48 44 52

and the corrupted ones from 7.6.4 look like this

89 50 4e 47 0d 0d 0a 1a 0d 0a 00 00 00 0d 49 48 44 52

It appears that the 0a values from the valid header are being converted to 0d 0a.  I might be wrong here, but it appears to me that something is interpreting the 0a as a line feed and given the code is running on Windows, is converting that LF into a CR LF.  The replacement doesn't seem to be limited to the file header as I see the 7.6.4 version of the file is slightly larger (18,571 bytes instead of 18,407 bytes) and in spot checking, I've verified some additional 0d's exist precede 0a within the data blocks of the .PNG.  Has anyone experienced anything like this or know of any fixes?

PNG Images produced on the server with shp2img are just fine, it's only images produced by making a WMS request to mapserv.exe that have the issue.  An example WMS request would be

https://<Server Name Removed>/mapserv.exe?map=dynamic\5708d96b-c606-4c35-95e7-085fedc1dcce.map&SERVICE=WMS&VERSION=1.3.0&REQUEST=GetMap&FORMAT=image%2Fpng&TRANSPARENT=true&LAYERS=MAP&TILED=true&WIDTH=512&HEIGHT=512&CRS=EPSG%3A3857&STYLES=&BBOX=-10877294.873093722%2C5536486.832751887%2C-10876071.880641159%2C5537709.82520445

Maybe I'm completely misdiagnosing the problem as these PNG image files just show up as corrupted within a browser - for example FireFox reports "The image <full URL here> cannot be displayed because it contains errors."  The way I obtained the actual .PNG images to view in a binary editor was to use PostMan and save the body of the results.  Perhaps PostMan introduced the extra bytes when saving an unrecognizable format file to disk whereas it did not when saving a file it recognized as a valid PNG.  I can't find anything different between the valid and invalid files beyond the extra 0d's that have been added though, so I don't think PostMan or anything else in the chain introduced them.

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