include/git2/odb.h

/*
 * Copyright (C) the libgit2 contributors. All rights reserved.
 *
 * This file is part of libgit2, distributed under the GNU GPL v2 with
 * a Linking Exception. For full terms see the included COPYING file.
 */
#ifndef INCLUDE_git_odb_h__
#define INCLUDE_git_odb_h__

#include "common.h"
#include "types.h"
#include "oid.h"
#include "oidarray.h"
#include "indexer.h"

/**
 * @file git2/odb.h
 * @brief Git object database routines
 * @defgroup git_odb Git object database routines
 * @ingroup Git
 * @{
 */
GIT_BEGIN_DECL

/**
 * Function type for callbacks from git_odb_foreach.
 */
typedef int GIT_CALLBACK(git_odb_foreach_cb)(const git_oid *id, void *payload);

/**
 * Create a new object database with no backends.
 *
 * Before the ODB can be used for read/writing, a custom database
 * backend must be manually added using `git_odb_add_backend()`
 *
 * @param out location to store the database pointer, if opened.
 *			Set to NULL if the open failed.
 * @return 0 or an error code
 */
GIT_EXTERN(int) git_odb_new(git_odb **out);

/**
 * Create a new object database and automatically add
 * the two default backends:
 *
 *	- git_odb_backend_loose: read and write loose object files
 *		from disk, assuming `objects_dir` as the Objects folder
 *
 *	- git_odb_backend_pack: read objects from packfiles,
 *		assuming `objects_dir` as the Objects folder which
 *		contains a 'pack/' folder with the corresponding data
 *
 * @param out location to store the database pointer, if opened.
 *			Set to NULL if the open failed.
 * @param objects_dir path of the backends' "objects" directory.
 * @return 0 or an error code
 */
GIT_EXTERN(int) git_odb_open(git_odb **out, const char *objects_dir);

/**
 * Add an on-disk alternate to an existing Object DB.
 *
 * Note that the added path must point to an `objects`, not
 * to a full repository, to use it as an alternate store.
 *
 * Alternate backends are always checked for objects *after*
 * all the main backends have been exhausted.
 *
 * Writing is disabled on alternate backends.
 *
 * @param odb database to add the backend to
 * @param path path to the objects folder for the alternate
 * @return 0 on success; error code otherwise
 */
GIT_EXTERN(int) git_odb_add_disk_alternate(git_odb *odb, const char *path);

/**
 * Close an open object database.
 *
 * @param db database pointer to close. If NULL no action is taken.
 */
GIT_EXTERN(void) git_odb_free(git_odb *db);

/**
 * Read an object from the database.
 *
 * This method queries all available ODB backends
 * trying to read the given OID.
 *
 * The returned object is reference counted and
 * internally cached, so it should be closed
 * by the user once it's no longer in use.
 *
 * @param out pointer where to store the read object
 * @param db database to search for the object in.
 * @param id identity of the object to read.
 * @return
 * - 0 if the object was read;
 * - GIT_ENOTFOUND if the object is not in the database.
 */
GIT_EXTERN(int) git_odb_read(git_odb_object **out, git_odb *db, const git_oid *id);

/**
 * Read an object from the database, given a prefix
 * of its identifier.
 *
 * This method queries all available ODB backends
 * trying to match the 'len' first hexadecimal
 * characters of the 'short_id'.
 * The remaining (GIT_OID_HEXSZ-len)*4 bits of
 * 'short_id' must be 0s.
 * 'len' must be at least GIT_OID_MINPREFIXLEN,
 * and the prefix must be long enough to identify
 * a unique object in all the backends; the
 * method will fail otherwise.
 *
 * The returned object is reference counted and
 * internally cached, so it should be closed
 * by the user once it's no longer in use.
 *
 * @param out pointer where to store the read object
 * @param db database to search for the object in.
 * @param short_id a prefix of the id of the object to read.
 * @param len the length of the prefix
 * @return
 * - 0 if the object was read;
 * - GIT_ENOTFOUND if the object is not in the database.
 * - GIT_EAMBIGUOUS if the prefix is ambiguous (several objects match the prefix)
 */
GIT_EXTERN(int) git_odb_read_prefix(git_odb_object **out, git_odb *db, const git_oid *short_id, size_t len);

/**
 * Read the header of an object from the database, without
 * reading its full contents.
 *
 * The header includes the length and the type of an object.
 *
 * Note that most backends do not support reading only the header
 * of an object, so the whole object will be read and then the
 * header will be returned.
 *
 * @param len_out pointer where to store the length
 * @param type_out pointer where to store the type
 * @param db database to search for the object in.
 * @param id identity of the object to read.
 * @return
 * - 0 if the object was read;
 * - GIT_ENOTFOUND if the object is not in the database.
 */
GIT_EXTERN(int) git_odb_read_header(size_t *len_out, git_object_t *type_out, git_odb *db, const git_oid *id);

/**
 * Determine if the given object can be found in the object database.
 *
 * @param db database to be searched for the given object.
 * @param id the object to search for.
 * @return
 * - 1, if the object was found
 * - 0, otherwise
 */
GIT_EXTERN(int) git_odb_exists(git_odb *db, const git_oid *id);

/**
 * Determine if an object can be found in the object database by an
 * abbreviated object ID.
 *
 * @param out The full OID of the found object if just one is found.
 * @param db The database to be searched for the given object.
 * @param short_id A prefix of the id of the object to read.
 * @param len The length of the prefix.
 * @return 0 if found, GIT_ENOTFOUND if not found, GIT_EAMBIGUOUS if multiple
 *         matches were found, other value < 0 if there was a read error.
 */
GIT_EXTERN(int) git_odb_exists_prefix(
	git_oid *out, git_odb *db, const git_oid *short_id, size_t len);

/**
 * The information about object IDs to query in `git_odb_expand_ids`,
 * which will be populated upon return.
 */
typedef struct git_odb_expand_id {
	/** The object ID to expand */
	git_oid id;

	/**
	 * The length of the object ID (in nibbles, or packets of 4 bits; the
	 * number of hex characters)
	 * */
	unsigned short length;

	/**
	 * The (optional) type of the object to search for; leave as `0` or set
	 * to `GIT_OBJECT_ANY` to query for any object matching the ID.
	 */
	git_object_t type;
} git_odb_expand_id;

/**
 * Determine if one or more objects can be found in the object database
 * by their abbreviated object ID and type.  The given array will be
 * updated in place:  for each abbreviated ID that is unique in the
 * database, and of the given type (if specified), the full object ID,
 * object ID length (`GIT_OID_HEXSZ`) and type will be written back to
 * the array.  For IDs that are not found (or are ambiguous), the
 * array entry will be zeroed.
 *
 * Note that since this function operates on multiple objects, the
 * underlying database will not be asked to be reloaded if an object is
 * not found (which is unlike other object database operations.)
 *
 * @param db The database to be searched for the given objects.
 * @param ids An array of short object IDs to search for
 * @param count The length of the `ids` array
 * @return 0 on success or an error code on failure
 */
GIT_EXTERN(int) git_odb_expand_ids(
	git_odb *db,
	git_odb_expand_id *ids,
	size_t count);

/**
 * Refresh the object database to load newly added files.
 *
 * If the object databases have changed on disk while the library
 * is running, this function will force a reload of the underlying
 * indexes.
 *
 * Use this function when you're confident that an external
 * application has tampered with the ODB.
 *
 * NOTE that it is not necessary to call this function at all. The
 * library will automatically attempt to refresh the ODB
 * when a lookup fails, to see if the looked up object exists
 * on disk but hasn't been loaded yet.
 *
 * @param db database to refresh
 * @return 0 on success, error code otherwise
 */
GIT_EXTERN(int) git_odb_refresh(struct git_odb *db);

/**
 * List all objects available in the database
 *
 * The callback will be called for each object available in the
 * database. Note that the objects are likely to be returned in the index
 * order, which would make accessing the objects in that order inefficient.
 * Return a non-zero value from the callback to stop looping.
 *
 * @param db database to use
 * @param cb the callback to call for each object
 * @param payload data to pass to the callback
 * @return 0 on success, non-zero callback return value, or error code
 */
GIT_EXTERN(int) git_odb_foreach(git_odb *db, git_odb_foreach_cb cb, void *payload);

/**
 * Write an object directly into the ODB
 *
 * This method writes a full object straight into the ODB.
 * For most cases, it is preferred to write objects through a write
 * stream, which is both faster and less memory intensive, specially
 * for big objects.
 *
 * This method is provided for compatibility with custom backends
 * which are not able to support streaming writes
 *
 * @param out pointer to store the OID result of the write
 * @param odb object database where to store the object
 * @param data buffer with the data to store
 * @param len size of the buffer
 * @param type type of the data to store
 * @return 0 or an error code
 */
GIT_EXTERN(int) git_odb_write(git_oid *out, git_odb *odb, const void *data, size_t len, git_object_t type);

/**
 * Open a stream to write an object into the ODB
 *
 * The type and final length of the object must be specified
 * when opening the stream.
 *
 * The returned stream will be of type `GIT_STREAM_WRONLY`, and it
 * won't be effective until `git_odb_stream_finalize_write` is called
 * and returns without an error
 *
 * The stream must always be freed when done with `git_odb_stream_free` or
 * will leak memory.
 *
 * @see git_odb_stream
 *
 * @param out pointer where to store the stream
 * @param db object database where the stream will write
 * @param size final size of the object that will be written
 * @param type type of the object that will be written
 * @return 0 if the stream was created; error code otherwise
 */
GIT_EXTERN(int) git_odb_open_wstream(git_odb_stream **out, git_odb *db, git_object_size_t size, git_object_t type);

/**
 * Write to an odb stream
 *
 * This method will fail if the total number of received bytes exceeds the
 * size declared with `git_odb_open_wstream()`
 *
 * @param stream the stream
 * @param buffer the data to write
 * @param len the buffer's length
 * @return 0 if the write succeeded; error code otherwise
 */
GIT_EXTERN(int) git_odb_stream_write(git_odb_stream *stream, const char *buffer, size_t len);

/**
 * Finish writing to an odb stream
 *
 * The object will take its final name and will be available to the
 * odb.
 *
 * This method will fail if the total number of received bytes
 * differs from the size declared with `git_odb_open_wstream()`
 *
 * @param out pointer to store the resulting object's id
 * @param stream the stream
 * @return 0 on success; an error code otherwise
 */
GIT_EXTERN(int) git_odb_stream_finalize_write(git_oid *out, git_odb_stream *stream);

/**
 * Read from an odb stream
 *
 * Most backends don't implement streaming reads
 */
GIT_EXTERN(int) git_odb_stream_read(git_odb_stream *stream, char *buffer, size_t len);

/**
 * Free an odb stream
 *
 * @param stream the stream to free
 */
GIT_EXTERN(void) git_odb_stream_free(git_odb_stream *stream);

/**
 * Open a stream to read an object from the ODB
 *
 * Note that most backends do *not* support streaming reads
 * because they store their objects as compressed/delta'ed blobs.
 *
 * It's recommended to use `git_odb_read` instead, which is
 * assured to work on all backends.
 *
 * The returned stream will be of type `GIT_STREAM_RDONLY` and
 * will have the following methods:
 *
 *		- stream->read: read `n` bytes from the stream
 *		- stream->free: free the stream
 *
 * The stream must always be free'd or will leak memory.
 *
 * @see git_odb_stream
 *
 * @param out pointer where to store the stream
 * @param len pointer where to store the length of the object
 * @param type pointer where to store the type of the object
 * @param db object database where the stream will read from
 * @param oid oid of the object the stream will read from
 * @return 0 if the stream was created; error code otherwise
 */
GIT_EXTERN(int) git_odb_open_rstream(
	git_odb_stream **out,
	size_t *len,
	git_object_t *type,
	git_odb *db,
	const git_oid *oid);

/**
 * Open a stream for writing a pack file to the ODB.
 *
 * If the ODB layer understands pack files, then the given
 * packfile will likely be streamed directly to disk (and a
 * corresponding index created).  If the ODB layer does not
 * understand pack files, the objects will be stored in whatever
 * format the ODB layer uses.
 *
 * @see git_odb_writepack
 *
 * @param out pointer to the writepack functions
 * @param db object database where the stream will read from
 * @param progress_cb function to call with progress information.
 * Be aware that this is called inline with network and indexing operations,
 * so performance may be affected.
 * @param progress_payload payload for the progress callback
 */
GIT_EXTERN(int) git_odb_write_pack(
	git_odb_writepack **out,
	git_odb *db,
	git_indexer_progress_cb progress_cb,
	void *progress_payload);

/**
 * Determine the object-ID (sha1 hash) of a data buffer
 *
 * The resulting SHA-1 OID will be the identifier for the data
 * buffer as if the data buffer it were to written to the ODB.
 *
 * @param out the resulting object-ID.
 * @param data data to hash
 * @param len size of the data
 * @param type of the data to hash
 * @return 0 or an error code
 */
GIT_EXTERN(int) git_odb_hash(git_oid *out, const void *data, size_t len, git_object_t type);

/**
 * Read a file from disk and fill a git_oid with the object id
 * that the file would have if it were written to the Object
 * Database as an object of the given type (w/o applying filters).
 * Similar functionality to git.git's `git hash-object` without
 * the `-w` flag, however, with the --no-filters flag.
 * If you need filters, see git_repository_hashfile.
 *
 * @param out oid structure the result is written into.
 * @param path file to read and determine object id for
 * @param type the type of the object that will be hashed
 * @return 0 or an error code
 */
GIT_EXTERN(int) git_odb_hashfile(git_oid *out, const char *path, git_object_t type);

/**
 * Create a copy of an odb_object
 *
 * The returned copy must be manually freed with `git_odb_object_free`.
 * Note that because of an implementation detail, the returned copy will be
 * the same pointer as `source`: the object is internally refcounted, so the
 * copy still needs to be freed twice.
 *
 * @param dest pointer where to store the copy
 * @param source object to copy
 * @return 0 or an error code
 */
GIT_EXTERN(int) git_odb_object_dup(git_odb_object **dest, git_odb_object *source);

/**
 * Close an ODB object
 *
 * This method must always be called once a `git_odb_object` is no
 * longer needed, otherwise memory will leak.
 *
 * @param object object to close
 */
GIT_EXTERN(void) git_odb_object_free(git_odb_object *object);

/**
 * Return the OID of an ODB object
 *
 * This is the OID from which the object was read from
 *
 * @param object the object
 * @return a pointer to the OID
 */
GIT_EXTERN(const git_oid *) git_odb_object_id(git_odb_object *object);

/**
 * Return the data of an ODB object
 *
 * This is the uncompressed, raw data as read from the ODB,
 * without the leading header.
 *
 * This pointer is owned by the object and shall not be free'd.
 *
 * @param object the object
 * @return a pointer to the data
 */
GIT_EXTERN(const void *) git_odb_object_data(git_odb_object *object);

/**
 * Return the size of an ODB object
 *
 * This is the real size of the `data` buffer, not the
 * actual size of the object.
 *
 * @param object the object
 * @return the size
 */
GIT_EXTERN(size_t) git_odb_object_size(git_odb_object *object);

/**
 * Return the type of an ODB object
 *
 * @param object the object
 * @return the type
 */
GIT_EXTERN(git_object_t) git_odb_object_type(git_odb_object *object);

/**
 * Add a custom backend to an existing Object DB
 *
 * The backends are checked in relative ordering, based on the
 * value of the `priority` parameter.
 *
 * Read <sys/odb_backend.h> for more information.
 *
 * @param odb database to add the backend to
 * @param backend pointer to a git_odb_backend instance
 * @param priority Value for ordering the backends queue
 * @return 0 on success; error code otherwise
 */
GIT_EXTERN(int) git_odb_add_backend(git_odb *odb, git_odb_backend *backend, int priority);

/**
 * Add a custom backend to an existing Object DB; this
 * backend will work as an alternate.
 *
 * Alternate backends are always checked for objects *after*
 * all the main backends have been exhausted.
 *
 * The backends are checked in relative ordering, based on the
 * value of the `priority` parameter.
 *
 * Writing is disabled on alternate backends.
 *
 * Read <sys/odb_backend.h> for more information.
 *
 * @param odb database to add the backend to
 * @param backend pointer to a git_odb_backend instance
 * @param priority Value for ordering the backends queue
 * @return 0 on success; error code otherwise
 */
GIT_EXTERN(int) git_odb_add_alternate(git_odb *odb, git_odb_backend *backend, int priority);

/**
 * Get the number of ODB backend objects
 *
 * @param odb object database
 * @return number of backends in the ODB
 */
GIT_EXTERN(size_t) git_odb_num_backends(git_odb *odb);

/**
 * Lookup an ODB backend object by index
 *
 * @param out output pointer to ODB backend at pos
 * @param odb object database
 * @param pos index into object database backend list
 * @return 0 on success; GIT_ENOTFOUND if pos is invalid; other errors < 0
 */
GIT_EXTERN(int) git_odb_get_backend(git_odb_backend **out, git_odb *odb, size_t pos);

/** @} */
GIT_END_DECL
#endif