UI stands for User Interface, and is general purpose set of routines to prompt the user for text-based
information. Through user-written methods (see UI_create_method(3)), prompting can be done in any way
imaginable, be it plain text prompting, through dialog boxes or from a cell phone.
All the functions work through a context of the type UI. This context contains all the information
needed to prompt correctly as well as a reference to a UI_METHOD, which is an ordered vector of functions
that carry out the actual prompting.
The first thing to do is to create a UI with UI_new() or UI_new_method(), then add information to it with
the UI_add or UI_dup functions. Also, user-defined random data can be passed down to the underlying
method through calls to UI_add_user_data() or UI_dup_user_data(). The default UI method doesn't care
about these data, but other methods might. Finally, use UI_process() to actually perform the prompting
and UI_get0_result() and UI_get_result_length() to find the result to the prompt and its length.
A UI can contain more than one prompt, which are performed in the given sequence. Each prompt gets an
index number which is returned by the UI_add and UI_dup functions, and has to be used to get the
corresponding result with UI_get0_result() and UI_get_result_length().
UI_process() can be called more than once on the same UI, thereby allowing a UI to have a long lifetime,
but can just as well have a short lifetime.
The functions are as follows:
UI_new() creates a new UI using the default UI method. When done with this UI, it should be freed using
UI_free().
UI_new_method() creates a new UI using the given UI method. When done with this UI, it should be freed
using UI_free().
UI_OpenSSL() returns the built-in UI method (note: not necessarily the default one, since the default can
be changed. See further on). This method is the most machine/OS dependent part of OpenSSL and normally
generates the most problems when porting.
UI_null() returns a UI method that does nothing. Its use is to avoid getting internal defaults for
passed UI_METHOD pointers.
UI_free() removes a UI from memory, along with all other pieces of memory that's connected to it, like
duplicated input strings, results and others. If ui is NULL nothing is done.
UI_add_input_string() and UI_add_verify_string() add a prompt to the UI, as well as flags and a result
buffer and the desired minimum and maximum sizes of the result, not counting the final NUL character.
The given information is used to prompt for information, for example a password, and to verify a password
(i.e. having the user enter it twice and check that the same string was entered twice).
UI_add_verify_string() takes and extra argument that should be a pointer to the result buffer of the
input string that it's supposed to verify, or verification will fail.
UI_add_input_boolean() adds a prompt to the UI that's supposed to be answered in a boolean way, with a
single character for yes and a different character for no. A set of characters that can be used to
cancel the prompt is given as well. The prompt itself is divided in two, one part being the descriptive
text (given through the prompt argument) and one describing the possible answers (given through the
action_desc argument).
UI_add_info_string() and UI_add_error_string() add strings that are shown at the same time as the prompt
for extra information or to show an error string. The difference between the two is only conceptual.
With the built-in method, there's no technical difference between them. Other methods may make a
difference between them, however.
The flags currently supported are UI_INPUT_FLAG_ECHO, which is relevant for UI_add_input_string() and
will have the users response be echoed (when prompting for a password, this flag should obviously not be
used, and UI_INPUT_FLAG_DEFAULT_PWD, which means that a default password of some sort will be used
(completely depending on the application and the UI method).
UI_dup_input_string(), UI_dup_verify_string(), UI_dup_input_boolean(), UI_dup_info_string() and
UI_dup_error_string() are basically the same as their UI_add counterparts, except that they make their
own copies of all strings.
UI_construct_prompt() is a helper function that can be used to create a prompt from two pieces of
information: a phrase description phrase_desc and an object name object_name, where the latter may be
NULL. The default constructor (if there is none provided by the method used) creates a string "Enter
phrase_desc for object_name:" where the " for object_name" part is left out if object_name is NULL. With
the description "pass phrase" and the filename "foo.key", that becomes "Enter pass phrase for foo.key:".
Other methods may create whatever string and may include encodings that will be processed by the other
method functions.
UI_add_user_data() adds a user data pointer for the method to use at any time. The built-in UI method
doesn't care about this info. Note that several calls to this function doesn't add data, it replaces the
previous blob with the one given as argument.
UI_dup_user_data() duplicates the user data and works as an alternative to UI_add_user_data() when the
user data needs to be preserved for a longer duration, perhaps even the lifetime of the application. The
UI object takes ownership of this duplicate and will free it whenever it gets replaced or the UI is
destroyed. UI_dup_user_data() returns 0 on success, or -1 on memory allocation failure or if the method
doesn't have a duplicator function.
UI_get0_user_data() retrieves the data that has last been given to the UI with UI_add_user_data() or
UI_dup_user_data.
UI_get0_result() returns a pointer to the result buffer associated with the information indexed by i.
UI_get_result_length() returns the length of the result buffer associated with the information indexed by
i.
UI_process() goes through the information given so far, does all the printing and prompting and returns
the final status, which is -2 on out-of-band events (Interrupt, Cancel, ...), -1 on error and 0 on
success.
UI_ctrl() adds extra control for the application author. For now, it understands two commands:
UI_CTRL_PRINT_ERRORS, which makes UI_process() print the OpenSSL error stack as part of processing the
UI, and UI_CTRL_IS_REDOABLE, which returns a flag saying if the used UI can be used again or not.
UI_set_default_method() changes the default UI method to the one given. This function is not thread-safe
and should not be called at the same time as other OpenSSL functions.
UI_get_default_method() returns a pointer to the current default UI method.
UI_get_method() returns the UI method associated with a given UI.
UI_set_method() changes the UI method associated with a given UI.
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