libutil: add C bindings

src/libutil/nix_api_util.h

@@ -0,0 +1,223 @@
+#ifndef NIX_API_UTIL_H
+#define NIX_API_UTIL_H
+
+/** @file
+ * @brief Main entry for the libutil C bindings
+ *
+ * Also contains error handling utilities
+ */
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+// cffi start
+
+// Error codes
+/**
+ * @brief Type for error codes in the NIX system
+ *
+ * This type can have one of several predefined constants:
+ * - NIX_OK: No error occurred (0)
+ * - NIX_ERR_UNKNOWN: An unknown error occurred (-1)
+ * - NIX_ERR_OVERFLOW: An overflow error occurred (-2)
+ * - NIX_ERR_KEY: A key error occurred (-3)
+ * - NIX_ERR_NIX_ERROR: A generic Nix error occurred (-4)
+ */
+typedef int nix_err;
+
+/**
+ * @brief No error occurred.
+ *
+ * This error code is returned when no error has occurred during the function
+ * execution.
+ */
+#define NIX_OK 0
+
+/**
+ * @brief An unknown error occurred.
+ *
+ * This error code is returned when an unknown error occurred during the
+ * function execution.
+ */
+#define NIX_ERR_UNKNOWN -1
+
+/**
+ * @brief An overflow error occurred.
+ *
+ * This error code is returned when an overflow error occurred during the
+ * function execution.
+ */
+#define NIX_ERR_OVERFLOW -2
+
+/**
+ * @brief A key error occurred.
+ *
+ * This error code is returned when a key error occurred during the function
+ * execution.
+ */
+#define NIX_ERR_KEY -3
+
+/**
+ * @brief A generic Nix error occurred.
+ *
+ * This error code is returned when a generic Nix error occurred during the
+ * function execution.
+ */
+#define NIX_ERR_NIX_ERROR -4
+
+/**
+ * @brief This object stores error state.
+ *
+ * Passed as a first parameter to C functions that can fail, will store error
+ * information. Optional wherever it is used, passing NULL will throw a C++
+ * exception instead. The first field is a nix_err, that can be read directly to
+ * check for errors.
+ * @note These can be reused between different function calls,
+ *  but make sure not to use them for multiple calls simultaneously (which can
+ * happen in callbacks).
+ */
+typedef struct nix_c_context nix_c_context;
+
+// Function prototypes
+
+/**
+ * @brief Allocate a new nix_c_context.
+ * @throws std::bad_alloc
+ * @return allocated nix_c_context, owned by the caller. Free using
+ * `nix_c_context_free`.
+ */
+nix_c_context *nix_c_context_create();
+/**
+ * @brief Free a nix_c_context. Does not fail.
+ * @param[out] context The context to free, mandatory.
+ */
+void nix_c_context_free(nix_c_context *context);
+
+/**
+ * @brief Initializes nix_libutil and its dependencies.
+ *
+ * This function can be called multiple times, but should be called at least
+ * once prior to any other nix function.
+ *
+ * @param[out] context Optional, stores error information
+ * @return NIX_OK if the initialization is successful, or an error code
+ * otherwise.
+ */
+nix_err nix_libutil_init(nix_c_context *context);
+
+/**
+ * @brief Retrieves a setting from the nix global configuration.
+ *
+ * This function requires nix_libutil_init() to be called at least once prior to
+ * its use.
+ *
+ * @param[out] context optional, Stores error information
+ * @param[in] key The key of the setting to retrieve.
+ * @param[out] value A pointer to a buffer where the value of the setting will
+ * be stored.
+ * @param[in] n The size of the buffer pointed to by value.
+ * @return NIX_ERR_KEY if the setting is unknown, NIX_ERR_OVERFLOW if the
+ * provided buffer is too short, or NIX_OK if the setting was retrieved
+ * successfully.
+ */
+nix_err nix_setting_get(nix_c_context *context, const char *key, char *value,
+                        int n);
+
+/**
+ * @brief Sets a setting in the nix global configuration.
+ *
+ * Use "extra-<setting name>" to append to the setting's value.
+ *
+ * Settings only apply for new States. Call nix_plugins_init() when you are done
+ * with the settings to load any plugins.
+ *
+ * @param[out] context optional, Stores error information
+ * @param[in] key The key of the setting to set.
+ * @param[in] value The value to set for the setting.
+ * @return NIX_ERR_KEY if the setting is unknown, or NIX_OK if the setting was
+ * set successfully.
+ */
+nix_err nix_setting_set(nix_c_context *context, const char *key,
+                        const char *value);
+
+// todo: nix_plugins_init()
+
+/**
+ * @brief Retrieves the nix library version.
+ *
+ * Does not fail.
+ * @return A static string representing the version of the nix library.
+ */
+const char *nix_version_get();
+
+/**
+ * @brief Retrieves the most recent error message from a context.
+ *
+ * @pre This function should only be called after a previous nix function has
+ * returned an error.
+ *
+ * @param[out] context optional, the context to store errors in if this function
+ * fails
+ * @param[in] ctx the context to retrieve the error message from
+ * @param[out] n optional: a pointer to an unsigned int that is set to the
+ * length of the error.
+ * @return nullptr if no error message was ever set,
+ *         a borrowed pointer to the error message otherwise.
+ */
+const char *nix_err_msg(nix_c_context *context, const nix_c_context *ctx,
+                        unsigned int *n);
+
+/**
+ * @brief Retrieves the error message from errorInfo in a context.
+ *
+ * Used to inspect nix Error messages.
+ *
+ * @pre This function should only be called after a previous nix function has
+ * returned a NIX_ERR_NIX_ERROR
+ *
+ * @param[out] context optional, the context to store errors in if this function
+ * fails
+ * @param[in] read_context the context to retrieve the error message from
+ * @param[out] value The allocated area to write the error string to.
+ * @param[in] n Maximum size of the returned string.
+ * @return NIX_OK if there were no errors, an error code otherwise.
+ */
+nix_err nix_err_info_msg(nix_c_context *context,
+                         const nix_c_context *read_context, char *value, int n);
+
+/**
+ * @brief Retrieves the error name from a context.
+ *
+ * Used to inspect nix Error messages.
+ *
+ * @pre This function should only be called after a previous nix function has
+ * returned a NIX_ERR_NIX_ERROR
+ *
+ * @param context optional, the context to store errors in if this function
+ * fails
+ * @param[in] read_context the context to retrieve the error message from
+ * @param[out] value The allocated area to write the error string to.
+ * @param[in] n Maximum size of the returned string.
+ * @return NIX_OK if there were no errors, an error code otherwise.
+ */
+nix_err nix_err_name(nix_c_context *context, const nix_c_context *read_context,
+                     char *value, int n);
+
+/**
+ * @brief Retrieves the most recent error code from a nix_c_context
+ *
+ * Equivalent to reading the first field of the context.
+ *
+ * @param[out] context optional, the context to store errors in if this function
+ * fails
+ * @param[in] read_context the context to retrieve the error message from
+ * @return most recent error code stored in the context.
+ */
+nix_err nix_err_code(nix_c_context *context, const nix_c_context *read_context);
+
+// cffi end
+#ifdef __cplusplus
+}
+#endif
+
+#endif // NIX_API_UTIL_H