NAME

       OSSL_STORE_CTX, OSSL_STORE_post_process_info_fn, OSSL_STORE_open, OSSL_STORE_ctrl,
       OSSL_STORE_load, OSSL_STORE_eof, OSSL_STORE_error, OSSL_STORE_close - Types and functions
       to read objects from a URI

SYNOPSIS

        #include <openssl/store.h>

        typedef struct ossl_store_ctx_st OSSL_STORE_CTX;

        typedef OSSL_STORE_INFO *(*OSSL_STORE_post_process_info_fn)(OSSL_STORE_INFO *,
                                                                    void *);

        OSSL_STORE_CTX *OSSL_STORE_open(const char *uri, const UI_METHOD *ui_method,
                                        void *ui_data,
                                        OSSL_STORE_post_process_info_fn post_process,
                                        void *post_process_data);
        int OSSL_STORE_ctrl(OSSL_STORE_CTX *ctx, int cmd, ... /* args */);
        OSSL_STORE_INFO *OSSL_STORE_load(OSSL_STORE_CTX *ctx);
        int OSSL_STORE_eof(OSSL_STORE_CTX *ctx);
        int OSSL_STORE_error(OSSL_STORE_CTX *ctx);
        int OSSL_STORE_close(OSSL_STORE_CTX *ctx);

DESCRIPTION

       These functions help the application to fetch supported objects (see "SUPPORTED OBJECTS"
       in OSSL_STORE_INFO(3) for information on which those are) from a given URI (see "SUPPORTED
       SCHEMES" for more information on the supported URI schemes).  The general method to do so
       is to "open" the URI using OSSL_STORE_open(), read each available and supported object
       using OSSL_STORE_load() as long as OSSL_STORE_eof() hasn't been reached, and finish it off
       with OSSL_STORE_close().

       The retrieved information is stored in a OSSL_STORE_INFO, which is further described in
       OSSL_STORE_INFO(3).

   Types
       OSSL_STORE_CTX is a context variable that holds all the internal information for
       OSSL_STORE_open(), OSSL_STORE_load(), OSSL_STORE_eof() and OSSL_STORE_close() to work
       together.

   Functions
       OSSL_STORE_open() takes a uri or path uri, password UI method ui_method with associated
       data ui_data, and post processing callback post_process with associated data
       post_process_data, opens a channel to the data located at that URI and returns a
       OSSL_STORE_CTX with all necessary internal information.  The given ui_method and
       ui_data_data will be reused by all functions that use OSSL_STORE_CTX when interaction is
       needed.  The given post_process and post_process_data will be reused by OSSL_STORE_load()
       to manipulate or drop the value to be returned.  The post_process function drops values by
       returning NULL, which will cause OSSL_STORE_load() to start its process over with loading
       the next object, until post_process returns something other than NULL, or the end of data
       is reached as indicated by OSSL_STORE_eof().

       OSSL_STORE_ctrl() takes a OSSL_STORE_CTX, and command number cmd and more arguments not
       specified here.  The available loader specific command numbers and arguments they each
       take depends on the loader that's used and is documented together with that loader.

       There are also global controls available:

       OSSL_STORE_C_USE_SECMEM
           Controls if the loader should attempt to use secure memory for any allocated
           OSSL_STORE_INFO and its contents.  This control expects one argument, a pointer to an
           int that is expected to have the value 1 (yes) or 0 (no).  Any other value is an
           error.

       OSSL_STORE_load() takes a OSSL_STORE_CTX, tries to load the next available object and
       return it wrapped with  OSSL_STORE_INFO.

       OSSL_STORE_eof() takes a OSSL_STORE_CTX and checks if we've reached the end of data.

       OSSL_STORE_error() takes a OSSL_STORE_CTX and checks if an error occurred in the last
       OSSL_STORE_load() call.  Note that it may still be meaningful to try and load more
       objects, unless OSSL_STORE_eof() shows that the end of data has been reached.

       OSSL_STORE_close() takes a OSSL_STORE_CTX, closes the channel that was opened by
       OSSL_STORE_open() and frees all other information that was stored in the OSSL_STORE_CTX,
       as well as the OSSL_STORE_CTX itself.

SUPPORTED SCHEMES

       The basic supported scheme is file:.  Any other scheme can be added dynamically, using
       OSSL_STORE_register_loader().

NOTES

       A string without a scheme prefix (that is, a non-URI string) is implicitly interpreted as
       using the file: scheme.

       There are some tools that can be used together with OSSL_STORE_open() to determine if any
       failure is caused by an unparsable URI, or if it's a different error (such as memory
       allocation failures); if the URI was parsable but the scheme unregistered, the top error
       will have the reason "OSSL_STORE_R_UNREGISTERED_SCHEME".

       These functions make no direct assumption regarding the pass phrase received from the
       password callback.  The loaders may make assumptions, however.  For example, the file:
       scheme loader inherits the assumptions made by OpenSSL functionality that handles the
       different file types; this is mostly relevant for PKCS#12 objects.  See
       passphrase-encoding(7) for further information.

RETURN VALUES

       OSSL_STORE_open() returns a pointer to a OSSL_STORE_CTX on success, or NULL on failure.

       OSSL_STORE_load() returns a pointer to a OSSL_STORE_INFO on success, or NULL on error or
       when end of data is reached.  Use OSSL_STORE_error() and OSSL_STORE_eof() to determine the
       meaning of a returned NULL.

       OSSL_STORE_eof() returns 1 if the end of data has been reached, otherwise 0.

       OSSL_STORE_error() returns 1 if an error occurred in an OSSL_STORE_load() call, otherwise
       0.

       OSSL_STORE_ctrl() and OSSL_STORE_close() returns 1 on success, or 0 on failure.

SEE ALSO

       ossl_store(7), OSSL_STORE_INFO(3), OSSL_STORE_register_loader(3), passphrase-encoding(7)

HISTORY

       OSSL_STORE_CTX(), OSSL_STORE_post_process_info_fn(), OSSL_STORE_open(), OSSL_STORE_ctrl(),
       OSSL_STORE_load(), OSSL_STORE_eof() and OSSL_STORE_close() were added to OpenSSL 1.1.1.

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 <https://www.openssl.org/source/license.html>.