cobalt/site/docs/reference/starboard/modules/storage.md

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# Starboard Module Reference: `storage.h`

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.

## Macros

### kSbStorageInvalidRecord

Well-defined value for an invalid storage record handle.

## Typedefs

### SbStorageRecord

A handle to an open storage record.

#### Definition

```
typedef SbStorageRecordPrivate* SbStorageRecord
```

## Functions

### SbStorageCloseRecord

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.

#### Declaration

```
bool SbStorageCloseRecord(SbStorageRecord record)
```

### SbStorageDeleteRecord

Deletes the `SbStorageRecord` for `user` 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 for the user, like what
would have been deleted with the previous version of SbStorageDeleteRecord.

This function must not be called while the user's storage record is open. This
function performs blocking I/O on the calling thread.

`user`: The user for whom the record will be deleted. `name`: The filesystem-
safe name of the record to open.

#### Declaration

```
bool SbStorageDeleteRecord(SbUser user, const char *name)
```

### SbStorageGetRecordSize

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.

#### Declaration

```
int64_t SbStorageGetRecordSize(SbStorageRecord record)
```

### SbStorageIsValidRecord

Returns whether the given storage record handle is valid.

#### Declaration

```
static bool SbStorageIsValidRecord(SbStorageRecord record)
```

### SbStorageOpenRecord

Opens and returns the SbStorageRecord for `user` named `name`, blocking I/O on
the calling thread until the open is completed. If `user` is not a valid
`SbUser`, the function returns `kSbStorageInvalidRecord`. 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 for the user, like what
would have been saved with the previous version of SbStorageOpenRecord.

`user`: The user for which the storage record will be opened. `name`: The
filesystem-safe name of the record to open.

#### Declaration

```
SbStorageRecord SbStorageOpenRecord(SbUser user, const char *name)
```

### SbStorageReadRecord

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.

#### Declaration

```
int64_t SbStorageReadRecord(SbStorageRecord record, char *out_data, int64_t data_size)
```

### SbStorageWriteRecord

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.

#### Declaration

```
bool SbStorageWriteRecord(SbStorageRecord record, const char *data, int64_t data_size)
```