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=head1 NAME
nbdkit_strdup_intern, nbdkit_strndup_intern, nbdkit_printf_intern,
nbdkit_vprintf_intern - create a string with limited lifetime for nbdkit
=head1 SYNOPSIS
#include <nbdkit-plugin.h>
const char *nbdkit_strdup_intern (const char *str);
const char *nbdkit_strndup_intern (const char *str, size_t n);
const char *nbdkit_printf_intern (const char *fmt, ...);
const char *nbdkit_vprintf_intern (const char *fmt, va_list ap);
=head1 DESCRIPTION
Some callbacks are specified to return C<const char *>, even when a
plugin may not have a suitable compile-time constant to return.
Returning dynamically-allocated memory for such a callback would
induce a memory leak or otherwise complicate the plugin to perform
additional bookkeeping. For these cases, nbdkit provides several
convenience functions for creating a copy of a string for better
lifetime management.
=head2 nbdkit_strdup_intern
=head2 nbdkit_strndup_intern
Returns a copy of C<str>, possibly limited to a maximum of C<n> bytes.
After calling this, the plugin may free C<str> and use this copy in
its place.
If the copy is created outside the scope of a connection (such as
during C<.load> or C<.config>), the lifetime of the copy will last at
least through C<.unload>.
If the copy is created after a client has triggered a connection (such
as during C<.preconnect> or C<.open>), the lifetime will last at least
through C<.close>, but the copy is not safe to share with other
connections.
=head2 C<nbdkit_printf_intern>
=head2 C<nbdkit_vprintf_intern>
Return a string created from a format template, with a lifetime longer
than the current connection. These are shorthand for passing C<fmt>
to L<asprintf(3)> on a temporary string, then passing that result to
C<nbdkit_strdup_intern>.
=head1 RETURN VALUE
These functions return a string. This returned string I<must not> be
freed by the caller. It will be freed by nbdkit.
If there is an error they call L<nbdkit_error(3)> and return C<-1>.
=head1 HISTORY
The intern functions were added in nbdkit 1.24.
=head1 SEE ALSO
L<nbdkit(1)>,
L<nbdkit-plugin(3)>,
L<nbdkit-filter(3)>.
=head1 AUTHORS
Eric Blake
=head1 COPYRIGHT
Copyright Red Hat
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