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