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-rw-r--r--erts/doc/src/zlib.xml9
1 files changed, 9 insertions, 0 deletions
diff --git a/erts/doc/src/zlib.xml b/erts/doc/src/zlib.xml
index e1924fffee..04fcc4285d 100644
--- a/erts/doc/src/zlib.xml
+++ b/erts/doc/src/zlib.xml
@@ -315,6 +315,15 @@ list_to_binary([B1,B2])</pre>
<c><anno>WindowBits</anno></c> value suppresses the zlib header
(and checksum) from the stream. Notice that the zlib source
mentions this only as a undocumented feature.</p>
+ <warning>
+ <p>Due to a known bug in the underlying zlib library, <c>WindowBits</c> values 8 and -8
+ do not work as expected. In zlib versions before 1.2.9 values
+ 8 and -8 are automatically changed to 9 and -9. <em>From zlib version 1.2.9
+ value -8 is rejected</em> causing <c>zlib:deflateInit/6</c> to fail
+ (8 is still changed to 9). It also seem possible that future versions
+ of zlib may fix this bug and start accepting 8 and -8 as is.</p>
+ <p>Conclusion: Avoid values 8 and -8 unless you know your zlib version supports them.</p>
+ </warning>
</item>
<tag><c><anno>MemLevel</anno></c></tag>
<item>