/* Generated with cbindgen:0.16.0 */

/* Warning, this file is autogenerated by cbindgen. Don't modify this manually. */

#include <stdarg.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdlib.h>

/**
 * Return value upon success
 */
#define OK 0

/**
 * NULL pointer argument
 */
#define ERR_NULLPTR 1

/**
 * Invalid coordinator URL
 */
#define ERR_INVALID_URL 2

/**
 * Invalid settings: coordinator URL is not set
 */
#define ERR_SETTINGS_URL 3

/**
 * Invalid settings: signing keys are not set
 */
#define ERR_SETTINGS_KEYS 4

/**
 * Failed to set the local model: invalid model
 */
#define ERR_SETMODEL_MODEL 5

/**
 * Failed to set the local model: invalid data type
 */
#define ERR_SETMODEL_DATATYPE 6

/**
 * Failed to initialized the crypto library
 */
#define ERR_CRYPTO_INIT 7

/**
 * Invalid secret signing key
 */
#define ERR_CRYPTO_SECRET_KEY 8

/**
 * Invalid public signing key
 */
#define ERR_CRYPTO_PUBLIC_KEY 9

/**
 * No global model is currently available
 */
#define GLOBALMODEL_NONE 10

/**
 * Failed to get the global model: communication with the coordinator failed
 */
#define ERR_GLOBALMODEL_IO 11

/**
 * Failed to get the global model: invalid data type
 */
#define ERR_GLOBALMODEL_DATATYPE 12

/**
 * Failed to get the global model: invalid buffer length
 */
#define ERR_GLOBALMODEL_LEN 13

/**
 * Failed to get the global model: invalid model
 */
#define ERR_GLOBALMODEL_CONVERT 14

/**
 * The participant is not taking part in the sum or update task
 */
#define PARTICIPANT_TASK_NONE 1

/**
 * The participant is not taking part in the sum task
 */
#define PARTICIPANT_TASK_SUM (1 << 1)

/**
 * The participant is not taking part in the update task
 */
#define PARTICIPANT_TASK_UPDATE (1 << 2)

/**
 * The participant is expected to set the model it trained
 */
#define PARTICIPANT_SHOULD_SET_MODEL (1 << 3)

/**
 * The participant is expected to set the model it trained
 */
#define PARTICIPANT_MADE_PROGRESS (1 << 4)

/**
 * A new global model is available
 */
#define PARTICIPANT_NEW_GLOBALMODEL (1 << 5)

/**
 * The original primitive data type of the numerical values to be masked.
 */
enum ModelDataType {
  /**
   * Numbers of type f32.
   */
  MODEL_DATA_TYPE_F32 = 0,
  /**
   * Numbers of type f64.
   */
  MODEL_DATA_TYPE_F64 = 1,
  /**
   * Numbers of type i32.
   */
  MODEL_DATA_TYPE_I32 = 2,
  /**
   * Numbers of type i64.
   */
  MODEL_DATA_TYPE_I64 = 3,
};
typedef uint8_t ModelDataType;

/**
 * A signing key pair
 */
typedef struct KeyPair KeyPair;

/**
 * A participant. It embeds an internal state machine that executes the PET
 * protocol. However, it is the caller's responsibility to drive this state machine by
 * calling [`Participant::tick()`], and to take action when the participant state
 * changes.
 */
typedef struct Participant Participant;

/**
 * A participant settings
 */
typedef struct Settings Settings;

/**
 * ByteBuffer is a struct that represents an array of bytes to be sent over the FFI boundaries.
 * There are several cases when you might want to use this, but the primary one for us
 * is for returning protobuf-encoded data to Swift and Java. The type is currently rather
 * limited (implementing almost no functionality), however in the future it may be
 * more expanded.
 *
 * ## Caveats
 *
 * Note that the order of the fields is `len` (an i64) then `data` (a `*mut u8`), getting
 * this wrong on the other side of the FFI will cause memory corruption and crashes.
 * `i64` is used for the length instead of `u64` and `usize` because JNA has interop
 * issues with both these types.
 *
 * ### `Drop` is not implemented
 *
 * ByteBuffer does not implement Drop. This is intentional. Memory passed into it will
 * be leaked if it is not explicitly destroyed by calling [`ByteBuffer::destroy`], or
 * [`ByteBuffer::destroy_into_vec`]. This is for two reasons:
 *
 * 1. In the future, we may allow it to be used for data that is not managed by
 *    the Rust allocator\*, and `ByteBuffer` assuming it's okay to automatically
 *    deallocate this data with the Rust allocator.
 *
 * 2. Automatically running destructors in unsafe code is a
 *    [frequent footgun](https://without.boats/blog/two-memory-bugs-from-ringbahn/)
 *    (among many similar issues across many crates).
 *
 * Note that calling `destroy` manually is often not needed, as usually you should
 * be passing these to the function defined by [`define_bytebuffer_destructor!`] from
 * the other side of the FFI.
 *
 * Because this type is essentially *only* useful in unsafe or FFI code (and because
 * the most common usage pattern does not require manually managing the memory), it
 * does not implement `Drop`.
 *
 * \* Note: in the case of multiple Rust shared libraries loaded at the same time,
 * there may be multiple instances of "the Rust allocator" (one per shared library),
 * in which case we're referring to whichever instance is active for the code using
 * the `ByteBuffer`. Note that this doesn't occur on all platforms or build
 * configurations, but treating allocators in different shared libraries as fully
 * independent is always safe.
 *
 * ## Layout/fields
 *
 * This struct's field are not `pub` (mostly so that we can soundly implement `Send`, but also so
 * that we can verify rust users are constructing them appropriately), the fields, their types, and
 * their order are *very much* a part of the public API of this type. Consumers on the other side
 * of the FFI will need to know its layout.
 *
 * If this were a C struct, it would look like
 *
 * ```c,no_run
 * struct ByteBuffer {
 *     // Note: This should never be negative, but values above
 *     // INT64_MAX / i64::MAX are not allowed.
 *     int64_t len;
 *     // Note: nullable!
 *     uint8_t *data;
 * };
 * ```
 *
 * In rust, there are two fields, in this order: `len: i64`, and `data: *mut u8`.
 *
 * For clarity, the fact that the data pointer is nullable means that `Option<ByteBuffer>` is not
 * the same size as ByteBuffer, and additionally is not FFI-safe (the latter point is not
 * currently guaranteed anyway as of the time of writing this comment).
 *
 * ### Description of fields
 *
 * `data` is a pointer to an array of `len` bytes. Note that data can be a null pointer and therefore
 * should be checked.
 *
 * The bytes array is allocated on the heap and must be freed on it as well. Critically, if there
 * are multiple rust shared libraries using being used in the same application, it *must be freed
 * on the same heap that allocated it*, or you will corrupt both heaps.
 *
 * Typically, this object is managed on the other side of the FFI (on the "FFI consumer"), which
 * means you must expose a function to release the resources of `data` which can be done easily
 * using the [`define_bytebuffer_destructor!`] macro provided by this crate.
 */
typedef struct ByteBuffer {
  int64_t len;
  uint8_t *data;
} ByteBuffer;

/**
 * `FfiStr<'a>` is a safe (`#[repr(transparent)]`) wrapper around a
 * nul-terminated `*const c_char` (e.g. a C string). Conceptually, it is
 * similar to [`std::ffi::CStr`], except that it may be used in the signatures
 * of extern "C" functions.
 *
 * Functions accepting strings should use this instead of accepting a C string
 * directly. This allows us to write those functions using safe code without
 * allowing safe Rust to cause memory unsafety.
 *
 * A single function for constructing these from Rust ([`FfiStr::from_raw`])
 * has been provided. Most of the time, this should not be necessary, and users
 * should accept `FfiStr` in the parameter list directly.
 *
 * ## Caveats
 *
 * An effort has been made to make this struct hard to misuse, however it is
 * still possible, if the `'static` lifetime is manually specified in the
 * struct. E.g.
 *
 * ```rust,no_run
 * # use ffi_support::FfiStr;
 * // NEVER DO THIS
 * #[no_mangle]
 * extern "C" fn never_do_this(s: FfiStr<'static>) {
 *     // save `s` somewhere, and access it after this
 *     // function returns.
 * }
 * ```
 *
 * Instead, one of the following patterns should be used:
 *
 * ```
 * # use ffi_support::FfiStr;
 * #[no_mangle]
 * extern "C" fn valid_use_1(s: FfiStr<'_>) {
 *     // Use of `s` after this function returns is impossible
 * }
 * // Alternative:
 * #[no_mangle]
 * extern "C" fn valid_use_2(s: FfiStr) {
 *     // Use of `s` after this function returns is impossible
 * }
 * ```
 */
typedef const char *FfiStr;

/**
 * The model configuration of the model that is expected in [`xaynet_ffi_participant_set_model()`].
 *
 * [`xaynet_ffi_participant_set_model()`]: crate::ffi::xaynet_ffi_participant_set_model
 */
typedef struct LocalModelConfig {
  /**
   * The expected data type of the model.
   */
  ModelDataType data_type;
  /**
   * the expected length of the model.
   */
  uint64_t len;
} LocalModelConfig;

/**
 * Destroy the given `ByteBuffer` and free its memory. This function must only be
 * called on `ByteBuffer`s that have been created on the Rust side of the FFI. If you
 * have created a `ByteBuffer` on the other side of the FFI, do not use this function,
 * use `free()` instead.
 *
 * # Return value
 *
 * - [`OK`] on success
 * - [`ERR_NULLPTR`] if `buf` is NULL
 *
 * # Safety
 *
 * 1. When calling this method, you have to ensure that *either* the pointer is NULL
 * *or* all of the following is true:
 *  - The pointer must be properly [aligned].
 *  - It must be "dereferencable" in the sense defined in the [`std::ptr`] module
 *    documentation.
 * 2. After destroying the `ByteBuffer` the pointer becomes invalid and must not be
 *    used.
 * 3. Calling this function on a `ByteBuffer` that has not been created on the Rust
 *    side of the FFI is UB.
 *
 * [`std::ptr`]: https://doc.rust-lang.org/std/ptr/index.html#safety
 * [aligned]: https://doc.rust-lang.org/std/ptr/index.html#alignment
 */
int xaynet_ffi_byte_buffer_destroy(const struct ByteBuffer *buf);

/**
 * Initialize the crypto library. This method must be called before instantiating a
 * participant with [`xaynet_ffi_participant_new()`] or before generating new keys with
 * [`xaynet_ffi_generate_key_pair()`].
 *
 * # Return value
 *
 * - [`OK`] if the initialization succeeded
 * - -[`ERR_CRYPTO_INIT`] if the initialization failed
 *
 * # Safety
 *
 * This function is safe to call
 */
int xaynet_ffi_crypto_init(void);

/**
 * Destroy the participant created by [`xaynet_ffi_participant_new()`] or
 * [`xaynet_ffi_participant_restore()`].
 *
 * # Return value
 *
 * - [`OK`] on success
 * - [`ERR_NULLPTR`] if `participant` is NULL
 *
 * # Safety
 *
 * 1. When calling this method, you have to ensure that *either* the pointer is NULL
 *    *or* all of the following is true:
 *    - The pointer must be properly [aligned].
 *    - It must be "dereferencable" in the sense defined in the [`std::ptr`] module
 *      documentation.
 * 2. After destroying the `Participant`, the pointer becomes invalid and must not be
 *    used.
 * 3. This function should only be called on a pointer that has been created by
 *    [`xaynet_ffi_participant_new()`] or [`xaynet_ffi_participant_restore()`]
 *
 * [`std::ptr`]: https://doc.rust-lang.org/std/ptr/index.html#safety
 * [aligned]: https://doc.rust-lang.org/std/ptr/index.html#alignment
 */
int xaynet_ffi_participant_destroy(struct Participant *participant);

/**
 * Instantiate a new participant with the given settings. The participant must be
 * destroyed with [`xaynet_ffi_participant_destroy`].
 *
 * # Return value
 *
 * - a NULL pointer if `settings` is NULL or if the participant creation failed
 * - a valid pointer to a [`Participant`] otherwise
 *
 * # Safety
 *
 * When calling this method, you have to ensure that *either* the pointer is NULL *or*
 * all of the following is true:
 *
 * - The pointer must be properly [aligned].
 * - It must be "dereferencable" in the sense defined in the [`std::ptr`] module
 *   documentation.
 *
 * After destroying the participant with [`xaynet_ffi_participant_destroy`] becomes
 * invalid and must not be used.
 *
 * [`std::ptr`]: https://doc.rust-lang.org/std/ptr/index.html#safety
 * [aligned]: https://doc.rust-lang.org/std/ptr/index.html#alignment
 */
struct Participant *xaynet_ffi_participant_new(const struct Settings *settings);

/**
 * Drive the participant internal state machine. Every tick, the state machine
 * attempts to perform a small work unit.
 *
 * # Return value
 *
 * - [`ERR_NULLPTR`] is `participant` is NULL
 * - a bitflag otherwise, with the following flags:
 *   - [`PARTICIPANT_MADE_PROGRESS`]: if set, this flag indicates that the participant
 *     internal state machine was able to make some progress, and that the participant
 *     state changed. This information can be used as an indication for saving the
 *     participant state for instance. If the flag is not set, the state machine was
 *     not able to make progress. There are many potential causes for this, including:
 *       - the participant is not taking part to the current training round and is just
 *         waiting for a new one to start
 *       - the Xaynet coordinator is not reachable or has not published some
 *         information the participant is waiting for
 *       - the state machine is waiting for the model to be set (see
 *         [`xaynet_ffi_participant_set_model()`])
 *   - [`PARTICIPANT_TASK_NONE`], [`PARTICIPANT_TASK_SUM`] and
 *     [`PARTICIPANT_TASK_UPDATE`]: these flags are mutually exclusive, and indicate
 *     which task the participant has been selected for, for the current round. If
 *     [`PARTICIPANT_TASK_NONE`] is set, then the participant will just wait for a new
 *     round to start. If [`PARTICIPANT_TASK_UPDATE`] is set, then the participant has
 *     been selected to update the global model, and should prepare to provide a new
 *     model once the [`PARTICIPANT_SHOULD_SET_MODEL`] flag is set.
 *   - [`PARTICIPANT_SHOULD_SET_MODEL`]: if set, then the participant should set its
 *     model, by calling [`xaynet_ffi_participant_set_model()`]
 *   - [`PARTICIPANT_NEW_GLOBALMODEL`]: if set, the participant can fetch the new global
 *     model, by calling [`xaynet_ffi_participant_global_model()`]
 *
 * # Safety
 *
 * When calling this method, you have to ensure that *either* the pointer is NULL *or*
 * all of the following is true:
 *
 * - The pointer must be properly [aligned].
 * - It must be "dereferencable" in the sense defined in the [`std::ptr`] module
 *   documentation.
 *
 * After destroying the participant with [`xaynet_ffi_participant_destroy`] becomes
 * invalid and must not be used.
 *
 * [`std::ptr`]: https://doc.rust-lang.org/std/ptr/index.html#safety
 * [aligned]: https://doc.rust-lang.org/std/ptr/index.html#alignment
 */
int xaynet_ffi_participant_tick(struct Participant *participant);

/**
 * Serialize the participant state and return a buffer that contains the serialized
 * participant.
 *
 * # Safety
 *
 * 1. When calling this method, you have to ensure that *either* the pointer is NULL
 *    *or* all of the following is true:
 *    - The pointer must be properly [aligned].
 *    - It must be "dereferencable" in the sense defined in the [`std::ptr`] module
 *      documentation.
 * 2. the `ByteBuffer` created by this function must be destroyed with
 *    [`xaynet_ffi_participant_destroy`]. Attempting to free the memory from the other
 *    side of the FFI is UB.
 * 3. This function destroys the participant. Therefore, **the pointer becomes invalid
 *    and must not be used anymore**. Instead, a new participant should be created,
 *    either with [`xaynet_ffi_participant_new()`] or
 *    [`xaynet_ffi_participant_restore()`]
 *
 * [`std::ptr`]: https://doc.rust-lang.org/std/ptr/index.html#safety
 * [aligned]: https://doc.rust-lang.org/std/ptr/index.html#alignment
 *
 * # Example
 *
 * To save the participant into a file:
 *
 * ```c
 *  const ByteBuffer *save_buf = xaynet_ffi_participant_save(participant);
 *  assert(save_buf);
 *
 *  char *path = "./participant.bin";
 *  FILE *f = fopen(path, "w");
 *  fwrite(save_buf->data, 1, save_buf->len, f);
 *  fclose(f);
 * ```
 */
const struct ByteBuffer *xaynet_ffi_participant_save(struct Participant *participant);

/**
 * Restore the participant from a buffer that contained its serialized state.
 *
 * # Return value
 *
 * - a NULL pointer on failure
 * - a pointer to the restored participant on success
 *
 * # Safety
 *
 * When calling this method, you have to ensure that *either* the pointers are NULL
 * *or* all of the following is true:
 * - The pointers must be properly [aligned].
 * - They must be "dereferencable" in the sense defined in the [`std::ptr`] module
 *   documentation.
 *
 * [`std::ptr`]: https://doc.rust-lang.org/std/ptr/index.html#safety
 * [aligned]: https://doc.rust-lang.org/std/ptr/index.html#alignment
 *
 * # Example
 *
 * To restore a participant from a file:
 *
 * ```c
 * f = fopen("./participant.bin", "r");
 * fseek(f, 0L, SEEK_END);
 * int fsize = ftell(f);
 * fseek(f, 0L, SEEK_SET);
 * ByteBuffer buf = {
 *     .len = fsize,
 *     .data = (uint8_t *)malloc(fsize),
 * };
 * int n_read = fread(buf.data, 1, fsize, f);
 * assert(n_read == fsize);
 * fclose(f);
 * Participant *restored =
 *     xaynet_ffi_participant_restore("http://localhost:8081", &buf);
 * free(buf.data);
 * ```
 */
struct Participant *xaynet_ffi_participant_restore(FfiStr url, const struct ByteBuffer *buffer);

/**
 * Set the participant's model. Usually this should be called when the value returned
 * by [`xaynet_ffi_participant_tick()`] contains the [`PARTICIPANT_SHOULD_SET_MODEL`]
 * flag, but it can be called anytime. The model just won't be sent to the coordinator
 * until it's time.
 *
 * - `buffer` should be a pointer to a buffer that contains the model
 * - `data_type` specifies the type of the model weights (see [`DataType`]). The C header
 *   file generated by this crate provides an enum corresponding to the parameters: `DataType`.
 * - `len` is the number of weights the model has
 *
 * # Return value
 *
 * - [`OK`] if the model is set successfully
 * - [`ERR_NULLPTR`] if `participant` is NULL
 * - [`ERR_SETMODEL_DATATYPE`] if the datatype is invalid
 * - [`ERR_SETMODEL_MODEL`] if the model is invalid
 *
 * # Safety
 *
 * 1. When calling this method, you have to ensure that *either* the pointer is NULL
 *    *or* all of the following is true:
 *    - The pointer must be properly [aligned].
 *    - It must be "dereferencable" in the sense defined in the [`std::ptr`] module
 *      documentation.
 * 2. If `len` or `data_type` do not match the model in `buffer`, this method will
 *    result in a buffer over-read.
 *
 * [`std::ptr`]: https://doc.rust-lang.org/std/ptr/index.html#safety
 * [aligned]: https://doc.rust-lang.org/std/ptr/index.html#alignment
 */
int xaynet_ffi_participant_set_model(struct Participant *participant,
                                     const void *buffer,
                                     unsigned char data_type,
                                     unsigned int len);

/**
 * Return the latest global model from the coordinator.
 *
 * - `buffer` is the array in which the global model should be copied.
 * - `data_type` specifies the type of the model weights (see [`DataType`]). The C header
 *   file generated by this crate provides an enum corresponding to the parameters: `DataType`.
 * - `len` is the number of weights the model has
 *
 * # Return Value
 *
 * - [`OK`] if the model is set successfully
 * - [`ERR_NULLPTR`] if `participant` or the `buffer` is NULL
 * - [`GLOBALMODEL_NONE`] if no model exists
 * - [`ERR_GLOBALMODEL_IO`] if the communication with the coordinator failed
 * - [`ERR_GLOBALMODEL_DATATYPE`] if the datatype is invalid
 * - [`ERR_GLOBALMODEL_LEN`] if the length of the buffer does not match the length of the model
 * - [`ERR_GLOBALMODEL_CONVERT`] if the conversion of the model failed
 *
 * # Note
 *
 *   It is **not** guaranteed, that the model configuration returned by
 *   [`xaynet_ffi_participant_local_model_config`] corresponds to the configuration of
 *   the global model. This means that the global model can have a different length / data type
 *   than it is defined in model configuration. That both model configurations are the same is
 *   only guaranteed if the model config **never** changes on the coordinator side.
 *
 * # Safety
 *
 * 1. When calling this method, you have to ensure that *either* the pointer is NULL
 *    *or* all of the following is true:
 *    - The pointer must be properly [aligned].
 *    - It must be "dereferencable" in the sense defined in the [`std::ptr`] module
 *      documentation.
 * 2. If `len` or `data_type` do not match the model in `buffer`, this method will
 *    result in a buffer over-read.
 *
 * [aligned]: https://doc.rust-lang.org/std/ptr/index.html#alignment
 */
int xaynet_ffi_participant_global_model(struct Participant *participant,
                                        void *buffer,
                                        unsigned char data_type,
                                        unsigned int len);

/**
 * Return the local model configuration of the model that is expected in the
 * [`xaynet_ffi_participant_set_model()`] function.
 *
 * # Safety
 *
 * 1. When calling this method, you have to ensure that *either* the pointer is NULL
 *    *or* all of the following is true:
 *    - The pointer must be properly [aligned].
 *    - It must be "dereferencable" in the sense defined in the [`std::ptr`] module
 *      documentation.
 *
 * [aligned]: https://doc.rust-lang.org/std/ptr/index.html#alignment
 */
struct LocalModelConfig *xaynet_ffi_participant_local_model_config(const struct Participant *participant);

/**
 * Destroy the settings created by [`xaynet_ffi_settings_new()`].
 *
 * # Return value
 *
 * - [`OK`] on success
 * - [`ERR_NULLPTR`] if `buf` is NULL
 *
 * # Safety
 *
 * 1. When calling this method, you have to ensure that *either* the pointer is NULL
 *    *or* all of the following is true:
 *    - The pointer must be properly [aligned].
 *    - It must be "dereferencable" in the sense defined in the [`std::ptr`] module
 *      documentation.
 * 2. After destroying the `Settings`, the pointer becomes invalid and must not be
 *    used.
 * 3. This function should only be called on a pointer that has been created by
 *    [`xaynet_ffi_settings_new`].
 *
 * [`std::ptr`]: https://doc.rust-lang.org/std/ptr/index.html#safety
 * [aligned]: https://doc.rust-lang.org/std/ptr/index.html#alignment
 */
int xaynet_ffi_settings_destroy(struct Settings *settings);

/**
 * Create new [`Settings`] and return a pointer to it.
 *
 * # Safety
 *
 * The `Settings` created by this function must be destroyed with
 * [`xaynet_ffi_settings_destroy()`]. Attempting to free the memory from the other side
 * of the FFI is UB.
 */
struct Settings *xaynet_ffi_settings_new(void);

/**
 * Set scalar setting.
 *
 * # Return value
 *
 * - [`OK`] if successful
 * - [`ERR_NULLPTR`] if `settings` is `NULL`
 *
 * # Safety
 *
 * When calling this method, you have to ensure that *either* the pointer is NULL *or*
 * all of the following is true:
 * - The pointer must be properly [aligned].
 * - It must be "dereferencable" in the sense defined in the [`std::ptr`] module
 *   documentation.
 *
 * [`std::ptr`]: https://doc.rust-lang.org/std/ptr/index.html#safety
 * [aligned]: https://doc.rust-lang.org/std/ptr/index.html#alignment
 */
int xaynet_ffi_settings_set_scalar(struct Settings *settings, double scalar);

/**
 * Set coordinator URL.
 *
 * # Return value
 *
 * - [`OK`] if successful
 * - [`ERR_INVALID_URL`] if `url` is not a valid string
 * - [`ERR_NULLPTR`] if `settings` is `NULL`
 *
 * # Safety
 *
 * When calling this method, you have to ensure that *either* the pointers are NULL
 * *or* all of the following is true:
 * - The pointers must be properly [aligned].
 * - They must be "dereferencable" in the sense defined in the [`std::ptr`] module
 *   documentation.
 *
 * [`std::ptr`]: https://doc.rust-lang.org/std/ptr/index.html#safety
 * [aligned]: https://doc.rust-lang.org/std/ptr/index.html#alignment
 */
int xaynet_ffi_settings_set_url(struct Settings *settings, FfiStr url);

/**
 * Generate a new signing key pair that can be used in the [`Settings`]. **Before
 * calling this function you must initialize the crypto library with
 * [`xaynet_ffi_crypto_init()`]**.
 *
 * The returned value contains a pointer to the secret key. For security reasons, you
 * must make sure that this buffer life is a short as possible, and call
 * [`xaynet_ffi_forget_key_pair`] to destroy it.
 *
 * [`xaynet_ffi_crypto_init()`]: crate::ffi::xaynet_ffi_crypto_init
 *
 * # Safety
 *
 * This function is safe to call
 */
const struct KeyPair *xaynet_ffi_generate_key_pair(void);

/**
 * De-allocate the buffers that contain the signing keys, and zero out the content of
 * the buffer that contains the secret key.
 *
 * # Return value
 *
 * - [`ERR_NULLPTR`] is `key_pair` is NULL
 * - [`OK`] otherwise
 *
 * # Safety
 *
 * When calling this method, you have to ensure that *either* the pointer is NULL *or*
 * all of the following is true:
 * - The pointer must be properly [aligned].
 * - It must be "dereferencable" in the sense defined in the [`std::ptr`] module
 *   documentation.
 *
 * [`std::ptr`]: https://doc.rust-lang.org/std/ptr/index.html#safety
 * [aligned]: https://doc.rust-lang.org/std/ptr/index.html#alignment
 */
int xaynet_ffi_forget_key_pair(const struct KeyPair *key_pair);

/**
 * Set participant signing keys.
 *
 * # Return value
 *
 * - [`OK`] if successful
 * - [`ERR_NULLPTR`] if `settings` or `key_pair` is `NULL`
 * - [`ERR_CRYPTO_PUBLIC_KEY`] if the given `key_pair` contains an invalid public key
 * - [`ERR_CRYPTO_SECRET_KEY`] if the given `key_pair` contains an invalid secret key
 *
 * # Safety
 *
 * When calling this method, you have to ensure that *either* the pointers are NULL
 * *or* all of the following is true:
 * - The pointers must be properly [aligned].
 * - They must be "dereferencable" in the sense defined in the [`std::ptr`] module
 *   documentation.
 *
 * [`std::ptr`]: https://doc.rust-lang.org/std/ptr/index.html#safety
 * [aligned]: https://doc.rust-lang.org/std/ptr/index.html#alignment
 */
int xaynet_ffi_settings_set_keys(struct Settings *settings, const struct KeyPair *key_pair);

/**
 * Check whether the given settings are valid and can be used to instantiate a
 * participant (see [`xaynet_ffi_participant_new()`]).
 *
 * # Return value
 *
 * - [`OK`] on success
 * - [`ERR_SETTINGS_URL`] if the URL has not been set
 * - [`ERR_SETTINGS_KEYS`] if the signing keys have not been set
 *
 * # Safety
 *
 * When calling this method, you have to ensure that *either* the pointer is NULL *or*
 * all of the following is true:
 *
 * - The pointer must be properly [aligned].
 * - It must be "dereferencable" in the sense defined in the [`std::ptr`] module
 *   documentation.
 *
 * [`xaynet_ffi_participant_new()`]: crate::ffi::xaynet_ffi_participant_new
 * [`std::ptr`]: https://doc.rust-lang.org/std/ptr/index.html#safety
 * [aligned]: https://doc.rust-lang.org/std/ptr/index.html#alignment
 */
int xaynet_ffi_check_settings(const struct Settings *settings);

/**
 * Destroy the model configuration created by [`xaynet_ffi_participant_local_model_config()`].
 *
 * # Return value
 *
 * - [`OK`] on success
 * - [`ERR_NULLPTR`] if `local_model_config` is NULL
 *
 * # Safety
 *
 * 1. When calling this method, you have to ensure that *either* the pointer is NULL
 *    *or* all of the following is true:
 *    - The pointer must be properly [aligned].
 *    - It must be "dereferencable" in the sense defined in the [`std::ptr`] module
 *      documentation.
 * 2. After destroying the `LocalModelConfig`, the pointer becomes invalid and must not be
 *    used.
 * 3. This function should only be called on a pointer that has been created by
 *    [`xaynet_ffi_participant_local_model_config()`].
 *
 * [`std::ptr`]: https://doc.rust-lang.org/std/ptr/index.html#safety
 * [aligned]: https://doc.rust-lang.org/std/ptr/index.html#alignment
 * [`xaynet_ffi_participant_local_model_config()`]: crate::ffi::xaynet_ffi_participant_local_model_config
 */
int xaynet_ffi_local_model_config_destroy(struct LocalModelConfig *local_model_config);