The RFCs say that the CN must not be checked if a subjectAltName extension
of type dNSName is present. IOW, if subjectAltName extension is present,
but there are no dNSNames, we can still check the CN.
Alexey Klyukin
This patch makes libpq check the server's hostname against DNS names listed
in the X509 subjectAltName extension field in the server certificate. This
allows the same certificate to be used for multiple domain names. If there
are no SANs in the certificate, the Common Name field is used, like before
this patch. If both are given, the Common Name is ignored. That is a bit
surprising, but that's the behavior mandated by the relevant RFCs, and it's
also what the common web browsers do.
This also adds a libpq_ngettext helper macro to allow plural messages to be
translated in libpq. Apparently this happened to be the first plural message
in libpq, so it was not needed before.
Alexey Klyukin, with some kibitzing by me.
This refactoring is in preparation for adding support for other SSL
implementations, with no user-visible effects. There are now two #defines,
USE_OPENSSL which is defined when building with OpenSSL, and USE_SSL which
is defined when building with any SSL implementation. Currently, OpenSSL is
the only implementation so the two #defines go together, but USE_SSL is
supposed to be used for implementation-independent code.
The libpq SSL code is changed to use a custom BIO, which does all the raw
I/O, like we've been doing in the backend for a long time. That makes it
possible to use MSG_NOSIGNAL to block SIGPIPE when using SSL, which avoids
a couple of syscall for each send(). Probably doesn't make much performance
difference in practice - the SSL encryption is expensive enough to mask the
effect - but it was a natural result of this refactoring.
Based on a patch by Martijn van Oosterhout from 2006. Briefly reviewed by
Alvaro Herrera, Andreas Karlsson, Jeff Janes.
