storage.h

// Copyright 2016 The Cobalt Authors. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// Module Overview: Starboard Storage module
//
// Defines a Storage API. This is a simple, all-at-once BLOB storage
// and retrieval API that is intended for robust long-term storage.
// Some platforms have different mechanisms for this kind of storage, so this
// API exists to allow a client application to access this kind of storage.
//
// Note that there can be only one storage record and, thus, a maximum
// of one open storage record can exist. Attempting to open a second record
// will result in undefined behavior.
//
// These APIs are NOT expected to be thread-safe, so either call them from a
// single thread, or perform proper synchronization around all calls.

#ifndef STARBOARD_STORAGE_H_
#define STARBOARD_STORAGE_H_

#include "starboard/export.h"
#include "starboard/types.h"

#ifdef __cplusplus
extern "C" {
#endif

// Private structure representing a single storage record.
typedef struct SbStorageRecordPrivate SbStorageRecordPrivate;

// A handle to an open storage record.
typedef SbStorageRecordPrivate* SbStorageRecord;

// Well-defined value for an invalid storage record handle.
#define kSbStorageInvalidRecord (SbStorageRecord) NULL

// Returns whether the given storage record handle is valid.
static inline bool SbStorageIsValidRecord(SbStorageRecord record) {
  return record != kSbStorageInvalidRecord;
}

// Opens and returns the SbStorageRecord named |name|, blocking I/O
// on the calling thread until the open is completed. Will return an
// |SbStorageRecord| of size zero if the record does not yet exist. Opening an
// already-open |SbStorageRecord| has undefined behavior.
//
// If |name| is NULL, opens the default storage record, like what
// would have been saved with the previous version of SbStorageOpenRecord.
//
// |name|: The filesystem-safe name of the record to open.
SB_EXPORT SbStorageRecord SbStorageOpenRecord(const char* name);

// Closes |record|, synchronously ensuring that all written data is flushed.
// This function performs blocking I/O on the calling thread.
//
// The return value indicates whether the operation succeeded. Storage writes
// should be as atomic as possible, so the record should either be fully
// written or deleted (or, even better, untouched).
//
// |record|: The storage record to close. |record| is invalid after this point,
// and subsequent calls referring to |record| will fail.
SB_EXPORT bool SbStorageCloseRecord(SbStorageRecord record);

// Returns the size of |record|, or |-1| if there is an error. This function
// performs blocking I/O on the calling thread.
//
// |record|: The record to retrieve the size of.
SB_EXPORT int64_t SbStorageGetRecordSize(SbStorageRecord record);

// Reads up to |data_size| bytes from |record|, starting at the beginning of
// the record. The function returns the actual number of bytes read, which
// must be <= |data_size|. The function returns |-1| in the event of an error.
// This function makes a best-effort to read the entire record, and it performs
// blocking I/O on the calling thread until the entire record is read or an
// error is encountered.
//
// |record|: The record to be read.
// |out_data|: The data read from the record.
// |data_size|: The amount of data, in bytes, to read.
SB_EXPORT int64_t SbStorageReadRecord(SbStorageRecord record,
                                      char* out_data,
                                      int64_t data_size);

// Replaces the data in |record| with |data_size| bytes from |data|. This
// function always deletes any previous data in that record. The return value
// indicates whether the write succeeded. This function makes a best-effort to
// write the entire record, and it may perform blocking I/O on the calling
// thread until the entire record is written or an error is encountered.
//
// While |SbStorageWriteRecord()| may defer the persistence,
// |SbStorageReadRecord()| is expected to work as expected immediately
// afterwards, even without a call to |SbStorageCloseRecord()|. The data should
// be persisted after a short time, even if there is an unexpected process
// termination before |SbStorageCloseRecord()| is called.
//
// |record|: The record to be written to.
// |data|: The data to write to the record.
// |data_size|: The amount of |data|, in bytes, to write to the record.
SB_EXPORT bool SbStorageWriteRecord(SbStorageRecord record,
                                    const char* data,
                                    int64_t data_size);

// Deletes the |SbStorageRecord| named |name|. The return value
// indicates whether the record existed and was successfully deleted. If the
// record did not exist or could not be deleted, the function returns |false|.
//
// If |name| is NULL, deletes the default storage record, like what
// would have been deleted with the previous version of SbStorageDeleteRecord.
//
// This function must not be called while the storage record is open.
// This function performs blocking I/O on the calling thread.
//
// |name|: The filesystem-safe name of the record to open.
SB_EXPORT bool SbStorageDeleteRecord(const char* name);

#ifdef __cplusplus
}  // extern "C"
#endif

#endif  // STARBOARD_STORAGE_H_