Background - Keyman Core API
Namespace
All calls, types and enums are prefixed with the namespace identifier km_core_
API idioms
Error Handling
Error handling and success failure notification are communicated through a
general mechanism similar to COM’s HRESULT scheme (unlike COM, any non-zero
value is an error). Any functions that can fail will always return a status
value and all results are returned via outparams passed to the function.
Passing variable length data out
Almost all calls marshalling variable length aggregate data in or out of an API object take the form:
km_core_status fn_name(object_ref, buffer_ptr, size_ptr)where the buffer_ptr is nullable and all other arguments are required (will
result in an KM_CORE_STATUS_INVALID_ARGUMENT
status being returned if nulled). When buffer_ptr is nullptr or 0 the
function will place the size of the required buffer in the variable pointed to
by size_ptr.
Resource management
Calls which result in the allocation of resources, regardless of resulting ownership, are of the form:
km_core_status fn_name(object_ref, handle_out_ptr)where handle_out_ptr is a valid pointer to a caller allocated variable to hold
the resulting resource handle. This is often a reference to a created object.
Unless stated all arguments are required (will result in an
KM_CORE_STATUS_INVALID_ARGUMENT status being
returned if nulled).
All dispose calls are designed to accept nullptr or 0 as a valid value and
will do nothing in that event.
Fixed size attribute access
For accessors to fixed size attributes of an object these will take the form:
attr_value fn_name(object_ref)object_ref is required to be valid and will result in a nonsense value being returned if nullptr or 0.
Versioning scheme
This follows the libtool interface versioning scheme of current.age.revision:
current
The most recent interface number that the engine implements.
age
How many interface numbers back from current the library implements. E.g. 5.2.0 would mean the library provides interface versions 3-5 and 5.0.0 would mean just interface version 5 and nothing older.
revision
The implementation version of the current interface. This represents improvements to the code that don't change the intended behaviour of the interface such as bug fixes and optimisations.
For Linux and other OS which support this scheme the dynamic linker will automatically choose the most updated version if more than one implementation is available. For Windows or dynamic loaded shared objects on Linux you can use the km_core_get_engine_attrs call and Library version macros to check the loaded DLL supplies the correct interface.
Common functions, types, and macros
Basic types
Fundamental types for representing data passed across the API.
km_core_cp type
uint16_t/char16_t
Represents a UTF16 codepoint, most strings are passed as UTF16.
km_core_usv type
uint32_t/char32_t
An integral type capable of holding a single Unicode Scalar Value, a decoded UTF codepoint.
km_core_virtual_key type
uint16_t
An integral type capable of holding a platform specific virtual key code.
km_core_status type
uint32_t
An integral 32 bit wide type capable of holding any valid status code as defined
by the enum km_core_status_codes.
km_core_modifier_state type
uint16_t
An integral type bitmask representing the state of each modifier key.
Resource types
Opaque types for representing resources provided or created by the keyboard processor implementation.
km_core_keyboard struct
Represents a keyboard loaded from disk, that can be executed by the keyboard processor to consume events, update state associated with an insertion point and produce action items. A keyboard object may be referenced by any number of state objects but must be disposed of after all state objects referencing it have first been disposed of.
km_core_state struct
Represents all state associated with an insertion point using a keyboard. This tracks context, and current action items resulting from a processed keyboard event. There can be many state objects using the same keyboard. A state object may not live longer than the keyboard it manages state for.
km_core_options struct
Represents a set of option items for environmental state and keyboard state.
km_core_status_codes enum
Description
An error code mechanism similar to COM’s HRESULT scheme (unlike COM, any
non-zero value is an error).
Specification
enum km_core_status_codes {
KM_CORE_STATUS_OK = 0,
KM_CORE_STATUS_NO_MEM = 1,
KM_CORE_STATUS_IO_ERROR = 2,
KM_CORE_STATUS_INVALID_ARGUMENT = 3,
KM_CORE_STATUS_KEY_ERROR = 4,
KM_CORE_STATUS_INSUFFICENT_BUFFER = 5,
KM_CORE_STATUS_INVALID_UTF = 6,
KM_CORE_STATUS_INVALID_KEYBOARD = 7,
KM_CORE_STATUS_NOT_IMPLEMENTED = 8,
KM_CORE_STATUS_OS_ERROR = 0x80000000
};
Values
KM_CORE_STATUS_OKSuccess code. Call completed as documented.
KM_CORE_STATUS_NO_MEMThe call failed to allocate memory during its execution, causing it to fail.
KM_CORE_STATUS_IO_ERRORThe call performed an I/O operation which failed, causing it to fail.
KM_CORE_STATUS_INVALID_ARGUMENTThe call detected one of its parameters was invalid or unsafe.
KM_CORE_STATUS_KEY_ERRORThe provided key or index into a collection object was not present.
KM_CORE_STATUS_INSUFFICENT_BUFFERThe provided buffer did not contain enough space to fully encode or copy the result of this call.
KM_CORE_STATUS_INVALID_UTFA malformed or partial UTF sequence prevented complete decoding of a unicode string.
KM_CORE_STATUS_INVALID_KEYBOARDAn attempt to decode a keyboard file failed.
KM_CORE_STATUS_OS_ERRORThis allows encapsulating a platform error code: the remaining 31 low bits are the error code returned by the OS for cases where the failure mode is platform specific. For HRESULT codes this only permits failure codes to be passed and not success codes.
km_core_attr struct
Description
A structure describing information about Keyman Core implementing this API.
Specification
typedef struct {
size_t max_context;
uint16_t current;
uint16_t revision;
uint16_t age;
uint16_t technology;
char const *vendor;
} km_core_attr;
Members
max_context- Maximum context size supported by processor.
current- Current API number supported.
revision- Implementation number of current API.
age- current - age == Oldest API number supported.
technology- A bit field of [km_core_tech_value] values, specifiying which Keyboard technologies the engine supports.
vendor- A UTF-8 encoded string identifying the implementer of the processor.
km_core_tech_value enum
Description
Values for a bit field indicating which keyboarding technologies a keyboard processor supports.
Specification
enum km_core_tech_value {
KM_CORE_TECH_UNSPECIFIED = 0,
KM_CORE_TECH_MOCK = 1 << 0,
KM_CORE_TECH_KMX = 1 << 1,
KM_CORE_TECH_LDML = 1 << 2
};
Values
KM_CORE_TECH_UNSPECIFIED- The keyboard processor implementation does not disclose which technologies it implements.
KM_CORE_TECH_MOCK- The keyboard processor implements a simple en-US keyboard for the purposes of testing the API.
KM_CORE_TECH_UNSPECIFIED- The keyboard processor implements a Keyman KMX compatible engine.
KM_CORE_TECH_UNSPECIFIED- The keyboard processor implements a LDML capable processing engine.
km_core_get_engine_attrs()
Description
Get access processors attributes describing version and technology implemented.
Specification
KMN_API
km_core_attr const *
km_core_get_engine_attrs(km_core_state const *state);
Parameters
state- An opaque pointer to a [km_core_state].
Returns
A pointer to a [km_core_attr] structure. Do not modify the contents of this structure.
km_core_bool enum
Description
Defines a boolean state.
Specification
typedef enum { KM_CORE_FALSE = 0, KM_CORE_TRUE = 1 } km_core_bool;
