Re: [Mingw-cross-env-list] libpng 1.2.39 is no longer available for download

[Volker Grabsch]

Aleksandr Tishin <address@hidden> schrieb:
> 1.2.40 is stable now.
> I have fix it by replacing two lines in libpng.mk:
> 
> > $(PKG)_VERSION := 1.2.40
> > $(PKG)_CHECKSUM := 776cf18a799af58303590f6996f6d3aa5a7908ff

Upgrading libpng fights the symptoms, but we also need to fight
the cause.

[ CC to the current libpng maintainer:
    Glenn, you are welcome to take part on this discussion.
    It would be great if you could fix the libpng URI scheme. ]

Some time ago, the arrangement of file releases on SourceForge
was completely revised. That forced many projects including
libpng to change their URI scheme as well. [1]  Most changes
were for the better, but some made it worse.

Libpng is an example for the latter. When a new stable version
is released, it is assigned the following URI:

http:// (sf_mirror) 
/project/libpng/00-libpng-stable/X.Y.ZZ/libpng-X.Y.ZZ.tar.bz2

However, after a next release, the very same version is no longer
available at that URI. Instead, it is moved to:

http:// (sf_mirror) /project/libpng/libpng-stable/X.Y.ZZ/libpng-X.Y.ZZ.tar.bz2

So a libpng package URI is not persistent until it's outdated.
This is a really annoying URI design mistake. I remember that
GDAL did something similar in the past. Luckily, they corrected
it later. I strongly recommend everyone to read the excellent
W3C article on that topic: http://www.w3.org/Provider/Style/URI

FWIW, the other libpng download site ftp.simplesystems.org has
the same design problem. A new release gets the URI:

ftp:// ftp.simplesystems.org /pub/libpng/png/src/libpng-X.Y.ZZ.tar.bz2

but is later moved to:

ftp:// ftp.simplesystems.org /pub/libpng/png/src/history/libpng-X.Y.ZZ.tar.bz2

For now, I fixed mingw-cross-env to simply try both URIs. That
mechanism already exists for selecting an alternative site in
case the first download site is down. I'd rather use it to
switch between "sourceforge.net" and "ftp.simplesystems.org", but
until libpng's URI scheme is fixed, I'll have to use it to switch
between "00-libpng-stable" and "libpng-stable".

http://hg.savannah.gnu.org/hgweb/mingw-cross-env/rev/99ec72400ffe


Greets,

    Volker



[1] SourceForge also installed HTTP redirects, so their old URI scheme
    still worked. However, those redirects caused an unlucky automatic
    switch of the selected mirror, bypassing mingw-cross-env's
    SOURCEFORGE_MIRROR setting and making the package downloads stall
    on slow mirrors. So I had no chance but to adapt mingw-cross-env
    to their new URI scheme:
    http://hg.savannah.gnu.org/hgweb/mingw-cross-env/rev/c6984a01ecbb
    http://hg.savannah.gnu.org/hgweb/mingw-cross-env/rev/8e93be50e66f

-- 
Volker Grabsch
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