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// Copyright 2018 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
package shed
import (
"encoding/json"
"errors"
"fmt"
)
var (
// LevelDB key value for storing the schema.
keySchema = []byte{0}
// LevelDB key prefix for all field type.
// LevelDB keys will be constructed by appending name values to this prefix.
keyPrefixFields byte = 1
// LevelDB key prefix from which indexing keys start.
// Every index has its own key prefix and this value defines the first one.
keyPrefixIndexStart byte = 2 // Q: or maybe a higher number like 7, to have more space for potential specific perfixes
)
// schema is used to serialize known database structure information.
type schema struct {
Fields map[string]fieldSpec `json:"fields"` // keys are field names
Indexes map[byte]indexSpec `json:"indexes"` // keys are index prefix bytes
}
// fieldSpec holds information about a particular field.
// It does not need Name field as it is contained in the
// schema.Field map key.
type fieldSpec struct {
Type string `json:"type"`
}
// indxSpec holds information about a particular index.
// It does not contain index type, as indexes do not have type.
type indexSpec struct {
Name string `json:"name"`
}
// schemaFieldKey retrieves the complete LevelDB key for
// a particular field form the schema definition.
func (db *DB) schemaFieldKey(name, fieldType string) (key []byte, err error) {
if name == "" {
return nil, errors.New("field name can not be blank")
}
if fieldType == "" {
return nil, errors.New("field type can not be blank")
}
s, err := db.getSchema()
if err != nil {
return nil, err
}
var found bool
for n, f := range s.Fields {
if n == name {
if f.Type != fieldType {
return nil, fmt.Errorf("field %q of type %q stored as %q in db", name, fieldType, f.Type)
}
break
}
}
if !found {
s.Fields[name] = fieldSpec{
Type: fieldType,
}
err := db.putSchema(s)
if err != nil {
return nil, err
}
}
return append([]byte{keyPrefixFields}, []byte(name)...), nil
}
// schemaIndexID retrieves the complete LevelDB prefix for
// a particular index.
func (db *DB) schemaIndexPrefix(name string) (id byte, err error) {
if name == "" {
return 0, errors.New("index name can not be blank")
}
s, err := db.getSchema()
if err != nil {
return 0, err
}
nextID := keyPrefixIndexStart
for i, f := range s.Indexes {
if i >= nextID {
nextID = i + 1
}
if f.Name == name {
return i, nil
}
}
id = nextID
s.Indexes[id] = indexSpec{
Name: name,
}
return id, db.putSchema(s)
}
// getSchema retrieves the complete schema from
// the database.
func (db *DB) getSchema() (s schema, err error) {
b, err := db.Get(keySchema)
if err != nil {
return s, err
}
err = json.Unmarshal(b, &s)
return s, err
}
// putSchema stores the complete schema to
// the database.
func (db *DB) putSchema(s schema) (err error) {
b, err := json.Marshal(s)
if err != nil {
return err
}
return db.Put(keySchema, b)
}
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