[mapserver-users] Corrupted PNG issue

[Steve Lime]

Hmmm... I've not run into or heard of this before although I'm not a
windows user. I did a quick sanity check with a mapfile here and the latest
7.4 and 7.6 versions. While not exactly the same setup you have in terms of
versions, they produce the exact same png image.

What do you get for output if you use mapserv.exe at the command line? So
something like:

  mapserv.exe -nh "QUERY_STRING=
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"
> test.png

That would take PostMan and the web server out of the picture. Is there any
chance different versions of libpng are being used? What are you using to
manage the tiles?

--Steve

On Wed, Nov 17, 2021 at 4:57 PM John Huotari via MapServer-users <
mapserver-users at lists.osgeo.org> wrote:

> 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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