store.go

package client

import (
	"context"
	"database/sql"
	"fmt"
	"io/ioutil"
	"os"
	"strings"
	"sync"

	"github.com/ghodss/yaml"
	"github.com/pkg/errors"

	"github.com/ardhipoetra/go-dqlite/protocol"
	_ "github.com/mattn/go-sqlite3" // Go SQLite bindings
)

// NodeStore is used by a dqlite client to get an initial list of candidate
// dqlite nodes that it can dial in order to find a leader dqlite node to use.
type NodeStore = protocol.NodeStore

// NodeRole identifies the role of a node.
type NodeRole = protocol.NodeRole

// NodeInfo holds information about a single server.
type NodeInfo = protocol.NodeInfo

// InmemNodeStore keeps the list of target dqlite nodes in memory.
type InmemNodeStore = protocol.InmemNodeStore

// NewInmemNodeStore creates NodeStore which stores its data in-memory.
var NewInmemNodeStore = protocol.NewInmemNodeStore

// DatabaseNodeStore persists a list addresses of dqlite nodes in a SQL table.
type DatabaseNodeStore struct {
	db     *sql.DB // Database handle to use.
	schema string  // Name of the schema holding the servers table.
	table  string  // Name of the servers table.
	column string  // Column name in the servers table holding the server address.
	where  string  // Optional WHERE filter
}

// DefaultNodeStore creates a new NodeStore using the given filename.
//
// If the filename ends with ".yaml" then the YamlNodeStore implementation will
// be used. Otherwise the SQLite-based one will be picked, with default names
// for the schema, table and column parameters.
//
// It also creates the table if it doesn't exist yet.
func DefaultNodeStore(filename string) (NodeStore, error) {
	if strings.HasSuffix(filename, ".yaml") {
		return NewYamlNodeStore(filename)
	}

	// Open the database.
	db, err := sql.Open("sqlite3", filename)
	if err != nil {
		return nil, errors.Wrap(err, "failed to open database")
	}

	// Since we're setting SQLite single-thread mode, we need to have one
	// connection at most.
	db.SetMaxOpenConns(1)

	// Create the servers table if it does not exist yet.
	_, err = db.Exec("CREATE TABLE IF NOT EXISTS servers (address TEXT, UNIQUE(address))")
	if err != nil {
		return nil, errors.Wrap(err, "failed to create servers table")
	}

	store := NewNodeStore(db, "main", "servers", "address")

	return store, nil
}

// Option that can be used to tweak node store parameters.
type NodeStoreOption func(*nodeStoreOptions)

type nodeStoreOptions struct {
	Where string
}

// WithNodeStoreWhereClause configures the node store to append the given
// hard-coded where clause to the SELECT query used to fetch nodes. Only the
// clause itself must be given, without the "WHERE" prefix.
func WithNodeStoreWhereClause(where string) NodeStoreOption {
	return func(options *nodeStoreOptions) {
		options.Where = where
	}
}

// NewNodeStore creates a new NodeStore.
func NewNodeStore(db *sql.DB, schema, table, column string, options ...NodeStoreOption) *DatabaseNodeStore {
	o := &nodeStoreOptions{}
	for _, option := range options {
		option(o)
	}

	return &DatabaseNodeStore{
		db:     db,
		schema: schema,
		table:  table,
		column: column,
		where:  o.Where,
	}
}

// Get the current servers.
func (d *DatabaseNodeStore) Get(ctx context.Context) ([]NodeInfo, error) {
	tx, err := d.db.Begin()
	if err != nil {
		return nil, errors.Wrap(err, "failed to begin transaction")
	}
	defer tx.Rollback()

	query := fmt.Sprintf("SELECT %s FROM %s.%s", d.column, d.schema, d.table)
	if d.where != "" {
		query += " WHERE " + d.where
	}
	rows, err := tx.QueryContext(ctx, query)
	if err != nil {
		return nil, errors.Wrap(err, "failed to query servers table")
	}
	defer rows.Close()

	servers := make([]NodeInfo, 0)
	for rows.Next() {
		var address string
		err := rows.Scan(&address)
		if err != nil {
			return nil, errors.Wrap(err, "failed to fetch server address")
		}
		servers = append(servers, NodeInfo{ID: 1, Address: address})
	}
	if err := rows.Err(); err != nil {
		return nil, errors.Wrap(err, "result set failure")
	}

	return servers, nil
}

// Set the servers addresses.
func (d *DatabaseNodeStore) Set(ctx context.Context, servers []NodeInfo) error {
	tx, err := d.db.Begin()
	if err != nil {
		return errors.Wrap(err, "failed to begin transaction")
	}

	query := fmt.Sprintf("DELETE FROM %s.%s", d.schema, d.table)
	if _, err := tx.ExecContext(ctx, query); err != nil {
		tx.Rollback()
		return errors.Wrap(err, "failed to delete existing servers rows")
	}

	query = fmt.Sprintf("INSERT INTO %s.%s(%s) VALUES (?)", d.schema, d.table, d.column)
	stmt, err := tx.PrepareContext(ctx, query)
	if err != nil {
		tx.Rollback()
		return errors.Wrap(err, "failed to prepare insert statement")
	}
	defer stmt.Close()

	for _, server := range servers {
		if _, err := stmt.ExecContext(ctx, server.Address); err != nil {
			tx.Rollback()
			return errors.Wrapf(err, "failed to insert server %s", server.Address)
		}
	}

	if err := tx.Commit(); err != nil {
		return errors.Wrap(err, "failed to commit transaction")
	}

	return nil
}

// Persists a list addresses of dqlite nodes in a YAML file.
type YamlNodeStore struct {
	path    string
	servers []NodeInfo
	mu      sync.RWMutex
}

// NewYamlNodeStore creates a new YamlNodeStore backed by the given YAML file.
func NewYamlNodeStore(path string) (*YamlNodeStore, error) {
	servers := []NodeInfo{}

	_, err := os.Stat(path)
	if err != nil {
		if !os.IsNotExist(err) {
			return nil, err
		}
	} else {
		data, err := ioutil.ReadFile(path)
		if err != nil {
			return nil, err
		}

		if err := yaml.Unmarshal(data, &servers); err != nil {
			return nil, err
		}
	}

	store := &YamlNodeStore{
		path:    path,
		servers: servers,
	}

	return store, nil
}

// Get the current servers.
func (s *YamlNodeStore) Get(ctx context.Context) ([]NodeInfo, error) {
	s.mu.RLock()
	defer s.mu.RUnlock()

	return s.servers, nil
}

// Set the servers addresses.
func (s *YamlNodeStore) Set(ctx context.Context, servers []NodeInfo) error {
	s.mu.Lock()
	defer s.mu.Unlock()

	data, err := yaml.Marshal(servers)
	if err != nil {
		return err
	}

	if err := ioutil.WriteFile(s.path, data, 0600); err != nil {
		return err
	}

	s.servers = servers

	return nil
}