=pod

=head1 NAME

ossl_store - Store retrieval functions

=head1 SYNOPSIS

=for comment generic

#include <openssl/store.h>

=head1 DESCRIPTION

=head2 General

A STORE is a layer of functionality to retrieve a number of supported
objects from a repository of any kind, addressable as a file name or
as a URI.

The functionality supports the pattern "open a channel to the
repository", "loop and retrieve one object at a time", and "finish up
by closing the channel".

The retrieved objects are returned as a wrapper type B<OSSL_STORE_INFO>,
from which an OpenSSL type can be retrieved.

=head2 URI schemes and loaders

Support for a URI scheme is called a STORE "loader", and can be added
dynamically from the calling application or from a loadable engine.

=head2 The 'file' scheme

Support for the 'file' scheme is already built into C<libcrypto>.
Since files come in all kinds of formats and content types, the 'file'
scheme has its own layer of functionality called "file handlers",
which are used to try to decode diverse types of file contents.

In case a file is formatted as PEM, each called file handler receives
the PEM name (everything following any 'C<-----BEGIN >') as well as
possible PEM headers, together with the decoded PEM body.  Since PEM
formatted files can contain more than one object, the file handlers
are called upon for each such object.

If the file isn't determined to be formatted as PEM, the content is
loaded in raw form in its entirety and passed to the available file
handlers as is, with no PEM name or headers.

Each file handler is expected to handle PEM and non-PEM content as
appropriate.  Some may refuse non-PEM content for the sake of
determinism (for example, there are keys out in the wild that are
represented as an ASN.1 OCTET STRING.  In raw form, it's not easily
possible to distinguish those from any other data coming as an ASN.1
OCTET STRING, so such keys would naturally be accepted as PEM files
only).

=head1 EXAMPLES

=head2 A generic call

 OSSL_STORE_CTX *ctx = OSSL_STORE_open("file:/foo/bar/data.pem");

 /*
  * OSSL_STORE_eof() simulates file semantics for any repository to signal
  * that no more data can be expected
  */
 while (!OSSL_STORE_eof(ctx)) {
     OSSL_STORE_INFO *info = OSSL_STORE_load(ctx);

     /*
      * Do whatever is necessary with the OSSL_STORE_INFO,
      * here just one example
      */
     switch (OSSL_STORE_INFO_get_type(info)) {
     case OSSL_STORE_INFO_X509:
         /* Print the X.509 certificate text */
         X509_print_fp(stdout, OSSL_STORE_INFO_get0_CERT(info));
         /* Print the X.509 certificate PEM output */
         PEM_write_X509(stdout, OSSL_STORE_INFO_get0_CERT(info));
         break;
     }
 }

 OSSL_STORE_close(ctx);

=head1 SEE ALSO

L<OSSL_STORE_INFO(3)>, L<OSSL_STORE_LOADER(3)>,
L<OSSL_STORE_open(3)>, L<OSSL_STORE_expect(3)>,
L<OSSL_STORE_SEARCH(3)>

=head1 COPYRIGHT

Copyright 2016-2018 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (the "License").  You may not use
this file except in compliance with the License.  You can obtain a copy
in the file LICENSE in the source distribution or at
L<https://www.openssl.org/source/license.html>.

=cut