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WMS requests for group layers fail in some instances

Description

This problem concerns WMS, group layers and, apparently, images with transparency. I start by creating a group layer containing two layers. Each layer sources its data from a GeoTIFF image and the images have RGBA bands. I load the group layer in a client via WMS. I find that there is a range of requests which fail to draw. I have included some example requests below. The logged error is included below too.

If I replace the source GeoTIFFs with RGB (no transparency) the problem does not occur.

If I add the individual layers (ie the layers that are included in the group layer) separately to the client, the problem does not occur. But if I add the individual layers to the client in a single request (ie layers=layer-1,layer-2) the problem does occur.

I've uploaded the information that is logged when draws fail in

I've uploaded some sample data in

which I'll describe in a comment.

I have set the affects version to 2.15.2. I have tested the issue in previous versions of GeoServer and found that it does not occur in 2.14.0, but it does occur in 2.14.1 onward.

Environment

Oracle Corporation: 1.8.0_162 (Java HotSpot(TM) 64-Bit Server VM
Windows 10

Native JAI: false

Native JAI ImageIO: false

Status

Assignee

Unassigned

Reporter

James R

Triage

None

Fix versions

None

Affects versions

2.15.2

Components

Priority

Medium