427698 - system libpng should not save unknown PNG chunk data

Status: RESOLVED INVALID

(Core :: Graphics: ImageLib, defect)

Description

[Glenn Randers-Pehrson]

When an unknown PNG chunk type is encountered by the system libpng, it saves the chunk data for possible later use.  Mozilla/Firefox will never use that data, so memory allocation and other CPU resources are wasted (The embedded libpng does not support unknown chunk handling and does not waste resources).  The test PNG in the URL above contains several unknown chunk types.  It is possible to avoid ever saving unknown chunk data by means of a one-line patch to the PNG decoder, similar to the lines already present to avoid saving unused known chunks.

Comment 1

[Glenn Randers-Pehrson]

Attachment: Always ignore unknown PNG chunk types

This patch does not affect the embedded libpng.  It will cause the system libpng to always ignore any unknown PNG chunk types that it encounters, thereby saving memory and other resources.

Comment 2

[Glenn Randers-Pehrson]

I have been studying this situation and now believe that the system libpng also already always ignores unknown chunks, so this patch is not necessary.  I suggest marking this WONTFIX.

Comment 3

[Glenn Randers-Pehrson]

Comment on attachment 314263 [details] [diff] [review]
Always ignore unknown PNG chunk types

Request for sr cancelled per comment #2.

Comment 4

[Glenn Randers-Pehrson]

Resolving INVALID.