Description:
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If PHP has been compiled with the --disable-ipv6 option, the constant STREAM_PF_INET6 should not exist. It could be useful to detect whether IPv6 has been enabled. To ensure BC, it would be better to set STREAM_PF_INET6 to -1 (or 0, false…).

We could already detect if IPv6 has been disabled with the AF_INET6 constant, declared in ext/sockets/sockets.c with #if HAVE_IPV6, but this solution is worthless if PHP has been compiled with the --disable-socket option. We could use IPv6 with stream_* functions, not only with socket_* functions.

Test script:
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$ php -r "var_dump(defined('STREAM_PF_INET6'), STREAM_PF_INET6);"
$ php -i | grep "IPv6"

Expected result:
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bool(true)
int(-1)
IPv6 Support => disabled

Actual result:
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bool(true)
int(30)
IPv6 Support => disabled