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meta.go
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meta.go
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package channeldb
import (
"github.com/coreos/bbolt"
)
var (
// metaBucket stores all the meta information concerning the state of
// the database.
metaBucket = []byte("metadata")
// dbVersionKey is a boltdb key and it's used for storing/retrieving
// current database version.
dbVersionKey = []byte("dbp")
)
// Meta structure holds the database meta information.
type Meta struct {
// DbVersionNumber is the current schema version of the database.
DbVersionNumber uint32
}
// FetchMeta fetches the meta data from boltdb and returns filled meta
// structure.
func (d *DB) FetchMeta(tx *bolt.Tx) (*Meta, error) {
meta := &Meta{}
err := d.View(func(tx *bolt.Tx) error {
return fetchMeta(meta, tx)
})
if err != nil {
return nil, err
}
return meta, nil
}
// fetchMeta is an internal helper function used in order to allow callers to
// re-use a database transaction. See the publicly exported FetchMeta method
// for more information.
func fetchMeta(meta *Meta, tx *bolt.Tx) error {
metaBucket := tx.Bucket(metaBucket)
if metaBucket == nil {
return ErrMetaNotFound
}
data := metaBucket.Get(dbVersionKey)
if data == nil {
meta.DbVersionNumber = getLatestDBVersion(dbVersions)
} else {
meta.DbVersionNumber = byteOrder.Uint32(data)
}
return nil
}
// PutMeta writes the passed instance of the database met-data struct to disk.
func (d *DB) PutMeta(meta *Meta) error {
return d.Update(func(tx *bolt.Tx) error {
return putMeta(meta, tx)
})
}
// putMeta is an internal helper function used in order to allow callers to
// re-use a database transaction. See the publicly exported PutMeta method for
// more information.
func putMeta(meta *Meta, tx *bolt.Tx) error {
metaBucket, err := tx.CreateBucketIfNotExists(metaBucket)
if err != nil {
return err
}
return putDbVersion(metaBucket, meta)
}
func putDbVersion(metaBucket *bolt.Bucket, meta *Meta) error {
scratch := make([]byte, 4)
byteOrder.PutUint32(scratch, meta.DbVersionNumber)
return metaBucket.Put(dbVersionKey, scratch)
}