replication.go

package replication

import (
	"encoding/json"
	"fmt"
	"strings"
)

const (
	// MaximumPositionSize is the maximum size of a
	// replication position. It is used as the maximum column size in the _vt.reparent_journal and
	// other related tables. A row has a maximum size of 65535 bytes. So
	// we want to stay under that. We use VARBINARY so the
	// character set doesn't matter, we only store ascii
	// characters anyway.
	MaximumPositionSize = 64000
)

// Position represents the information necessary to describe which
// transactions a server has seen, so that it can request a replication stream
// from a new master that picks up where it left off.
//
// This must be a concrete struct because custom Unmarshalers can't be
// registered on an interface.
//
// The == operator should not be used with Position, because the
// underlying GTIDSet might use slices, which are not comparable. Using == in
// those cases will result in a run-time panic.
type Position struct {
	// This is a zero byte compile-time check that no one is trying to
	// use == or != with Position. Without this, we won't know there's
	// a problem until the runtime panic. Note that this must not be
	// the last field of the struct, or else the Go compiler will add
	// padding to prevent pointers to this field from becoming invalid.
	_ [0]struct{ notComparable []byte }

	// GTIDSet is the underlying GTID set. It must not be anonymous,
	// or else Position would itself also implement the GTIDSet interface.
	GTIDSet GTIDSet
}

// Equal returns true if this position is equal to another.
func (rp Position) Equal(other Position) bool {
	if rp.GTIDSet == nil {
		return other.GTIDSet == nil
	}
	return rp.GTIDSet.Equal(other.GTIDSet)
}

// AtLeast returns true if this position is equal to or after another.
func (rp Position) AtLeast(other Position) bool {
	if rp.GTIDSet == nil {
		return other.GTIDSet == nil
	}
	return rp.GTIDSet.Contains(other.GTIDSet)
}

// String returns a string representation of the underlying GTIDSet.
// If the set is nil, it returns "<nil>" in the style of Sprintf("%v", nil).
func (rp Position) String() string {
	if rp.GTIDSet == nil {
		return "<nil>"
	}
	return rp.GTIDSet.String()
}

// IsZero returns true if this is the zero value, Position{}.
func (rp Position) IsZero() bool {
	return rp.GTIDSet == nil
}

// AppendGTID returns a new Position that represents the position
// after the given GTID is replicated.
func AppendGTID(rp Position, gtid GTID) Position {
	if gtid == nil {
		return rp
	}
	if rp.GTIDSet == nil {
		return Position{GTIDSet: gtid.GTIDSet()}
	}
	return Position{GTIDSet: rp.GTIDSet.AddGTID(gtid)}
}

// MustParsePosition calls ParsePosition and panics
// on error.
func MustParsePosition(flavor, value string) Position {
	rp, err := ParsePosition(flavor, value)
	if err != nil {
		panic(err)
	}
	return rp
}

// EncodePosition returns a string that contains both the flavor
// and value of the Position, so that the correct parser can be
// selected when that string is passed to DecodePosition.
func EncodePosition(rp Position) string {
	if rp.GTIDSet == nil {
		return ""
	}
	return fmt.Sprintf("%s/%s", rp.GTIDSet.Flavor(), rp.GTIDSet.String())
}

// DecodePosition converts a string in the format returned by
// EncodePosition back into a Position value with the
// correct underlying flavor.
func DecodePosition(s string) (rp Position, err error) {
	if s == "" {
		return rp, nil
	}

	parts := strings.SplitN(s, "/", 2)
	if len(parts) != 2 {
		// There is no flavor. Try looking for a default parser.
		return ParsePosition("", s)
	}
	return ParsePosition(parts[0], parts[1])
}

// ParsePosition calls the parser for the specified flavor.
func ParsePosition(flavor, value string) (rp Position, err error) {
	parser := gtidSetParsers[flavor]
	if parser == nil {
		return rp, fmt.Errorf("parse error: unknown GTIDSet flavor %#v", flavor)
	}
	gtidSet, err := parser(value)
	if err != nil {
		return rp, err
	}
	rp.GTIDSet = gtidSet
	return rp, err
}

// MarshalJSON implements encoding/json.Marshaler.
func (rp Position) MarshalJSON() ([]byte, error) {
	return json.Marshal(EncodePosition(rp))
}

// UnmarshalJSON implements encoding/json.Unmarshaler.
func (rp *Position) UnmarshalJSON(buf []byte) error {
	var s string
	err := json.Unmarshal(buf, &s)
	if err != nil {
		return err
	}

	*rp, err = DecodePosition(s)
	if err != nil {
		return err
	}
	return nil
}