telodendria/include/Cytoplasm/Db.h
2024-08-11 12:46:49 +02:00

199 lines
6.7 KiB
C

/*
* Copyright (C) 2022-2024 Jordan Bancino <@jordan:bancino.net>
*
* Permission is hereby granted, free of charge, to any person
* obtaining a copy of this software and associated documentation files
* (the "Software"), to deal in the Software without restriction,
* including without limitation the rights to use, copy, modify, merge,
* publish, distribute, sublicense, and/or sell copies of the Software,
* and to permit persons to whom the Software is furnished to do so,
* subject to the following conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
#ifndef CYTOPLASM_DB_H
#define CYTOPLASM_DB_H
/***
* @Nm Db
* @Nd A minimal flat-file database with mutex locking and cache.
* @Dd April 27 2023
* @Xr Json
*
* Cytoplasm operates on a flat-file database instead of a
* traditional relational database. This greatly simplifies the
* persistent storage code, and creates a relatively basic API,
* described here.
*/
#include <stddef.h>
#include <stdbool.h>
#include "HashMap.h"
#include "Array.h"
/**
* All functions in this API operate on a database structure that is
* opaque to the caller.
*/
typedef struct Db Db;
/**
* Some "hints" for the database backend for operations.
* Hints are a way for the program to declare what to except of it
* (and the program MUST adhere to these hints, but the backend
* MAY adhere).
*/
typedef enum DbHint {
DB_HINT_READONLY, /* The database reference is treated as read-only */
DB_HINT_WRITE /* The database reference is treated as read/write */
} DbHint;
/**
* When an object is locked, a reference is returned. This reference
* is owned by the current thread, and the database is inaccessible to
* other threads until all references have been returned to the
* database.
* .Pp
* This reference is opaque, but can be manipulated by the functions
* defined here.
*/
typedef struct DbRef DbRef;
/**
* Open a data directory. This function takes a path to open, and a
* cache size in bytes. If the cache size is 0, then caching is
* disabled and objects are loaded off the disk every time they are
* locked. Otherwise, objects are stored in the cache, and they are
* evicted in a least-recently-used manner.
*/
extern Db * DbOpen(char *, size_t);
/**
* Open a LMDB data directory. This function is similar to
* .Fn DbOpen ,
* but works with a LMDB-based backend, with the second argument
* being the maximum filesize. This function fails with NULL if ever
* called without LMDB enabled at compiletime.
*/
extern Db * DbOpenLMDB(char *, size_t);
/**
* Close the database. This function will flush anything in the cache
* to the disk, and then close the data directory. It assumes that
* all references have been unlocked. If a reference has not been
* unlocked, undefined behavior results.
*/
extern void DbClose(Db *);
/**
* Set the maximum cache size allowed before
* .Nm
* starts evicting old objects. If this is set to 0, everything in the
* cache is immediately evicted and caching is disabled. If the
* database was opened with a cache size of 0, setting this will
* initialize the cache, and subsequent calls to
* .Fn DbLock
* will begin caching objects.
*/
extern void DbMaxCacheSet(Db *, size_t);
/**
* Create a new object in the database with the specified name. This
* function will fail if the object already exists in the database. It
* takes a variable number of C strings, with the exact number being
* specified by the second parameter. These C strings are used to
* generate a filesystem path at which to store the object. These paths
* ensure each object is uniquely identifiable, and provides semantic
* meaning to an object.
*/
extern DbRef * DbCreate(Db *, size_t,...);
/**
* Lock an existing object in the database. This function will fail
* if the object does not exist. It takes a variable number of C
* strings, with the exact number being specified by the second
* parameter. These C strings are used to generate the filesystem path
* at which to load the object. These paths ensure each object is
* uniquely identifiable, and provides semantic meaning to an object.
*/
extern DbRef * DbLock(Db *, size_t,...);
/**
* Behaves like
* .Fn DbLock ,
* but with hints on the reference itself, as
* .Fn DbLock
* itself is read/write.
*/
extern DbRef * DbLockIntent(Db *, DbHint, size_t,...);
/**
* Immediately and permanently remove an object from the database.
* This function assumes the object is not locked, otherwise undefined
* behavior will result.
*/
extern bool DbDelete(Db *, size_t,...);
/**
* Unlock an object and return it back to the database. This function
* immediately syncs the object to the filesystem. The cache is a
* read cache; writes are always immediate to ensure data integrity in
* the event of a system failure.
*/
extern bool DbUnlock(Db *, DbRef *);
/**
* Check the existence of the given database object in a more efficient
* manner than attempting to lock it with
* .Fn DbLock .
* This function does not lock the object, nor does it load it into
* memory if it exists.
*/
extern bool DbExists(Db *, size_t,...);
/**
* List all of the objects at a given path. Unlike the other varargs
* functions, this one does not take a path to a specific object; it
* takes a directory to be iterated, where each path part is its own
* C string. Note that the resulting list only contains the objects
* in the specified directory, it does not list any subdirectories.
* .Pp
* The array returned is an array of C strings containing the object
* name.
*/
extern Array * DbList(Db *, size_t,...);
/**
* Free the list returned by
* .Fn DbListFree .
*/
extern void DbListFree(Array *);
/**
* Convert a database reference into JSON that can be manipulated.
* At this time, the database actually stores objects as JSON on the
* disk, so this function just returns an internal pointer, but in the
* future it may have to be generated by decompressing a binary blob,
* or something of that nature.
*/
extern HashMap * DbJson(DbRef *);
/**
* Free the existing JSON associated with the given reference, and
* replace it with new JSON. This is more efficient than duplicating
* a separate object into the database reference.
*/
extern bool DbJsonSet(DbRef *, HashMap *);
#endif