go-ethereum/ethdb/iterator.go

// 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 ethdb

// Iterator iterates over a database's key/value pairs in ascending key order.
//
// When it encounters an error any seek will return false and will yield no key/
// value pairs. The error can be queried by calling the Error method. Calling
// Release is still necessary.
//
// An iterator must be released after use, but it is not necessary to read an
// iterator until exhaustion. An iterator is not safe for concurrent use, but it
// is safe to use multiple iterators concurrently.
type Iterator interface {
	// Next moves the iterator to the next key/value pair. It returns whether the
	// iterator is exhausted.
	Next() bool

	// Error returns any accumulated error. Exhausting all the key/value pairs
	// is not considered to be an error.
	Error() error

	// Key returns the key of the current key/value pair, or nil if done. The caller
	// should not modify the contents of the returned slice, and its contents may
	// change on the next call to Next.
	Key() []byte

	// Value returns the value of the current key/value pair, or nil if done. The
	// caller should not modify the contents of the returned slice, and its contents
	// may change on the next call to Next.
	Value() []byte

	// Release releases associated resources. Release should always succeed and can
	// be called multiple times without causing error.
	Release()
}

// Iteratee wraps the NewIterator methods of a backing data store.
type Iteratee interface {
	// NewIterator creates a binary-alphabetical iterator over a subset
	// of database content with a particular key prefix, starting at a particular
	// initial key (or after, if it does not exist).
	//
	// Note: This method assumes that the prefix is NOT part of the start, so there's
	// no need for the caller to prepend the prefix to the start
	NewIterator(prefix []byte, start []byte) Iterator
}