=pod

=head1 NAME

OSSL_STORE_LOADER, OSSL_STORE_LOADER_CTX, OSSL_STORE_LOADER_new,
OSSL_STORE_LOADER_get0_engine, OSSL_STORE_LOADER_get0_scheme,
OSSL_STORE_LOADER_set_open, OSSL_STORE_LOADER_set_ctrl,
OSSL_STORE_LOADER_set_expect, OSSL_STORE_LOADER_set_find,
OSSL_STORE_LOADER_set_load, OSSL_STORE_LOADER_set_eof,
OSSL_STORE_LOADER_set_error, OSSL_STORE_LOADER_set_close,
OSSL_STORE_LOADER_free, OSSL_STORE_register_loader,
OSSL_STORE_unregister_loader, OSSL_STORE_open_fn, OSSL_STORE_ctrl_fn,
OSSL_STORE_expect_fn, OSSL_STORE_find_fn,
OSSL_STORE_load_fn, OSSL_STORE_eof_fn, OSSL_STORE_error_fn,
OSSL_STORE_close_fn - Types and functions to manipulate, register and
unregister STORE loaders for different URI schemes

=head1 SYNOPSIS

 #include <openssl/store.h>

 typedef struct ossl_store_loader_st OSSL_STORE_LOADER;

 OSSL_STORE_LOADER *OSSL_STORE_LOADER_new(ENGINE *e, const char *scheme);
 const ENGINE *OSSL_STORE_LOADER_get0_engine(const OSSL_STORE_LOADER
                                             *store_loader);
 const char *OSSL_STORE_LOADER_get0_scheme(const OSSL_STORE_LOADER
                                           *store_loader);

 /* struct ossl_store_loader_ctx_st is defined differently by each loader */
 typedef struct ossl_store_loader_ctx_st OSSL_STORE_LOADER_CTX;

 typedef OSSL_STORE_LOADER_CTX *(*OSSL_STORE_open_fn)(const char *uri,
                                                      const UI_METHOD *ui_method,
                                                      void *ui_data);
 int OSSL_STORE_LOADER_set_open(OSSL_STORE_LOADER *store_loader,
                                OSSL_STORE_open_fn store_open_function);
 typedef int (*OSSL_STORE_ctrl_fn)(OSSL_STORE_LOADER_CTX *ctx, int cmd,
                                   va_list args);
 int OSSL_STORE_LOADER_set_ctrl(OSSL_STORE_LOADER *store_loader,
                                OSSL_STORE_ctrl_fn store_ctrl_function);
 typedef int (*OSSL_STORE_expect_fn)(OSSL_STORE_LOADER_CTX *ctx, int expected);
 int OSSL_STORE_LOADER_set_expect(OSSL_STORE_LOADER *loader,
                                  OSSL_STORE_expect_fn expect_function);
 typedef int (*OSSL_STORE_find_fn)(OSSL_STORE_LOADER_CTX *ctx,
                                   OSSL_STORE_SEARCH *criteria);
 int OSSL_STORE_LOADER_set_find(OSSL_STORE_LOADER *loader,
                                OSSL_STORE_find_fn find_function);
 typedef OSSL_STORE_INFO *(*OSSL_STORE_load_fn)(OSSL_STORE_LOADER_CTX *ctx,
                                                UI_METHOD *ui_method,
                                                void *ui_data);
 int OSSL_STORE_LOADER_set_load(OSSL_STORE_LOADER *store_loader,
                                OSSL_STORE_load_fn store_load_function);
 typedef int (*OSSL_STORE_eof_fn)(OSSL_STORE_LOADER_CTX *ctx);
 int OSSL_STORE_LOADER_set_eof(OSSL_STORE_LOADER *store_loader,
                               OSSL_STORE_eof_fn store_eof_function);
 typedef int (*OSSL_STORE_error_fn)(OSSL_STORE_LOADER_CTX *ctx);
 int OSSL_STORE_LOADER_set_error(OSSL_STORE_LOADER *store_loader,
                                 OSSL_STORE_error_fn store_error_function);
 typedef int (*OSSL_STORE_close_fn)(OSSL_STORE_LOADER_CTX *ctx);
 int OSSL_STORE_LOADER_set_close(OSSL_STORE_LOADER *store_loader,
                                 OSSL_STORE_close_fn store_close_function);
 void OSSL_STORE_LOADER_free(OSSL_STORE_LOADER *store_loader);

 int OSSL_STORE_register_loader(OSSL_STORE_LOADER *loader);
 OSSL_STORE_LOADER *OSSL_STORE_unregister_loader(const char *scheme);

=head1 DESCRIPTION

These functions help applications and engines to create loaders for
schemes they support.

=head2 Types

B<OSSL_STORE_LOADER> is the type to hold a loader.
It contains a scheme and the functions needed to implement
OSSL_STORE_open(), OSSL_STORE_load(), OSSL_STORE_eof(), OSSL_STORE_error() and
OSSL_STORE_close() for this scheme.

B<OSSL_STORE_LOADER_CTX> is a type template, to be defined by each loader
using B<struct ossl_store_loader_ctx_st { ... }>.

B<OSSL_STORE_open_fn>, B<OSSL_STORE_ctrl_fn>, B<OSSL_STORE_expect_fn>,
B<OSSL_STORE_find_fn>, B<OSSL_STORE_load_fn>, B<OSSL_STORE_eof_fn>,
and B<OSSL_STORE_close_fn>
are the function pointer types used within a STORE loader.
The functions pointed at define the functionality of the given loader.

=over 4

=item B<OSSL_STORE_open_fn>

This function takes a URI and is expected to interpret it in the best
manner possible according to the scheme the loader implements, it also
takes a B<UI_METHOD> and associated data, to be used any time
something needs to be prompted for.
Furthermore, this function is expected to initialize what needs to be
initialized, to create a privata data store (B<OSSL_STORE_LOADER_CTX>, see
above), and to return it.
If something goes wrong, this function is expected to return NULL.

=item B<OSSL_STORE_ctrl_fn>

This function takes a B<OSSL_STORE_LOADER_CTX> pointer, a command number
B<cmd> and a B<va_list> B<args> and is used to manipulate loader
specific parameters.

=begin comment

Globally known command numbers are documented in L<OSSL_STORE_ctrl(3)>,
along with what B<args> are expected with each of them.

=end comment

Loader specific command numbers must begin at B<OSSL_STORE_C_CUSTOM_START>.
Any number below that is reserved for future globally known command
numbers.

This function is expected to return 1 on success, 0 on error.

=item B<OSSL_STORE_expect_fn>

This function takes a B<OSSL_STORE_LOADER_CTX> pointer and a B<OSSL_STORE_INFO>
identity B<expected>, and is used to tell the loader what object type is
expected.
B<expected> may be zero to signify that no specific object type is expected.

This function is expected to return 1 on success, 0 on error.

=item B<OSSL_STORE_find_fn>

This function takes a B<OSSL_STORE_LOADER_CTX> pointer and a
B<OSSL_STORE_SEARCH> search criterion, and is used to tell the loader what
to search for.

When called with the loader context being B<NULL>, this function is expected
to return 1 if the loader supports the criterion, otherwise 0.

When called with the loader context being something other than B<NULL>, this
function is expected to return 1 on success, 0 on error.

=item B<OSSL_STORE_load_fn>

This function takes a B<OSSL_STORE_LOADER_CTX> pointer and a B<UI_METHOD>
with associated data.
It's expected to load the next available data, mold it into a data
structure that can be wrapped in a B<OSSL_STORE_INFO> using one of the
L<OSSL_STORE_INFO(3)> functions.
If no more data is available or an error occurs, this function is
expected to return NULL.
The B<OSSL_STORE_eof_fn> and B<OSSL_STORE_error_fn> functions must indicate if
it was in fact the end of data or if an error occurred.

Note that this function retrieves I<one> data item only.

=item B<OSSL_STORE_eof_fn>

This function takes a B<OSSL_STORE_LOADER_CTX> pointer and is expected to
return 1 to indicate that the end of available data has been reached.
It is otherwise expected to return 0.

=item B<OSSL_STORE_error_fn>

This function takes a B<OSSL_STORE_LOADER_CTX> pointer and is expected to
return 1 to indicate that an error occurred in a previous call to the
B<OSSL_STORE_load_fn> function.
It is otherwise expected to return 0.

=item B<OSSL_STORE_close_fn>

This function takes a B<OSSL_STORE_LOADER_CTX> pointer and is expected to
close or shut down what needs to be closed, and finally free the
contents of the B<OSSL_STORE_LOADER_CTX> pointer.
It returns 1 on success and 0 on error.

=back

=head2 Functions

OSSL_STORE_LOADER_new() creates a new B<OSSL_STORE_LOADER>.
It takes an B<ENGINE> B<e> and a string B<scheme>.
B<scheme> must I<always> be set.
Both B<e> and B<scheme> are used as is and must therefore be alive as
long as the created loader is.

OSSL_STORE_LOADER_get0_engine() returns the engine of the B<store_loader>.
OSSL_STORE_LOADER_get0_scheme() returns the scheme of the B<store_loader>.

OSSL_STORE_LOADER_set_open() sets the opener function for the
B<store_loader>.

OSSL_STORE_LOADER_set_ctrl() sets the control function for the
B<store_loader>.

OSSL_STORE_LOADER_set_expect() sets the expect function for the
B<store_loader>.

OSSL_STORE_LOADER_set_load() sets the loader function for the
B<store_loader>.

OSSL_STORE_LOADER_set_eof() sets the end of file checker function for the
B<store_loader>.

OSSL_STORE_LOADER_set_close() sets the closing function for the
B<store_loader>.

OSSL_STORE_LOADER_free() frees the given B<store_loader>.

OSSL_STORE_register_loader() register the given B<store_loader> and thereby
makes it available for use with OSSL_STORE_open(), OSSL_STORE_load(),
OSSL_STORE_eof() and OSSL_STORE_close().

OSSL_STORE_unregister_loader() unregister the store loader for the given
B<scheme>.

=head1 NOTES

The B<file:> scheme has built in support.

=head1 RETURN VALUES

The functions with the types B<OSSL_STORE_open_fn>, B<OSSL_STORE_ctrl_fn>,
B<OSSL_STORE_expect_fn>,
B<OSSL_STORE_load_fn>, B<OSSL_STORE_eof_fn> and B<OSSL_STORE_close_fn> have the
same return values as OSSL_STORE_open(), OSSL_STORE_ctrl(), OSSL_STORE_expect(),
OSSL_STORE_load(), OSSL_STORE_eof() and OSSL_STORE_close(), respectively.

OSSL_STORE_LOADER_new() returns a pointer to a B<OSSL_STORE_LOADER> on success,
or B<NULL> on failure.

OSSL_STORE_LOADER_set_open(), OSSL_STORE_LOADER_set_ctrl(),
OSSL_STORE_LOADER_set_load(), OSSL_STORE_LOADER_set_eof() and
OSSL_STORE_LOADER_set_close() return 1 on success, or 0 on failure.

OSSL_STORE_register_loader() returns 1 on success, or 0 on failure.

OSSL_STORE_unregister_loader() returns the unregistered loader on success,
or B<NULL> on failure.

=head1 SEE ALSO

L<ossl_store(7)>, L<OSSL_STORE_open(3)>

=head1 HISTORY

OSSL_STORE_LOADER(), OSSL_STORE_LOADER_CTX(), OSSL_STORE_LOADER_new(),
OSSL_STORE_LOADER_set0_scheme(), OSSL_STORE_LOADER_set_open(),
OSSL_STORE_LOADER_set_ctrl(), OSSL_STORE_LOADER_set_load(),
OSSL_STORE_LOADER_set_eof(), OSSL_STORE_LOADER_set_close(),
OSSL_STORE_LOADER_free(), OSSL_STORE_register_loader(),
OSSL_STORE_unregister_loader(), OSSL_STORE_open_fn(), OSSL_STORE_ctrl_fn(),
OSSL_STORE_load_fn(), OSSL_STORE_eof_fn() and OSSL_STORE_close_fn()
were added in OpenSSL 1.1.1.

=head1 COPYRIGHT

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

Licensed under the Apache License 2.0 (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
