src/cobalt/site/docs/reference/starboard/modules/4/storage.md

---
layout: doc
title: "Starboard Module Reference: storage.h"
---

Defines a user-based Storage API. This is a simple, all-at-once BLOB storage and
retrieval API that is intended for robust long-term, per-user 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 per user and, thus, a maximum of
one open storage record can exist for each user. Attempting to open a second
record for a user 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 default `SbStorageRecord` for the `user`. 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`.

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.

#### Declaration ####

```
bool SbStorageDeleteRecord(SbUser user)
```

### 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 default SbStorageRecord for `user`, 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.

`user`: The user for which the storage record will be opened.

#### Declaration ####

```
SbStorageRecord SbStorageOpenRecord(SbUser user)
```

### 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. Thus, if
`data_size` is smaller than the total size of `data`, only part of `data` is
written to the record.

#### Declaration ####

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