Implement safepoints

reader/enhanced_reader.go

@@ -4,26 +4,28 @@ import (
 	"context"
 	"database/sql"
 
+	_ "github.com/localhots/mysql" // MySQL driver
+
 	"github.com/juju/errors"
 	"github.com/localhots/bocadillo/binlog"
 	"github.com/localhots/bocadillo/mysql"
 	"github.com/localhots/bocadillo/reader/schema"
 	"github.com/localhots/bocadillo/reader/slave"
-	_ "github.com/localhots/mysql" // MySQL driver
 )
 
 // EnhancedReader is an extended version of the reader that maintains schema
 // details to add column names and signed integers support.
 type EnhancedReader struct {
 	reader    *Reader
+	safepoint binlog.Position
 	schemaMgr *schema.Manager
 }
 
 // EnhancedRowsEvent ...
 type EnhancedRowsEvent struct {
-	Type  binlog.EventType
-	Table binlog.TableDescription
-	Rows  []map[string]interface{}
+	Header binlog.EventHeader
+	Table  binlog.TableDescription
+	Rows   []map[string]interface{}
 }
 
 // NewEnhanced creates a new enhanced binary log reader.
@@ -41,6 +43,7 @@ func NewEnhanced(dsn string, sc slave.Config) (*EnhancedReader, error) {
 	return &EnhancedReader{
 		reader:    r,
 		schemaMgr: schema.NewManager(conn),
+		safepoint: r.state,
 	}, nil
 }
 
@@ -121,9 +124,9 @@ func (r *EnhancedReader) nextRowsEvent() (*EnhancedRowsEvent, error) {
 		}
 
 		ere := EnhancedRowsEvent{
-			Type:  re.Type,
-			Table: *evt.Table,
-			Rows:  make([]map[string]interface{}, len(re.Rows)),
+			Header: evt.Header,
+			Table:  *evt.Table,
+			Rows:   make([]map[string]interface{}, len(re.Rows)),
 		}
 		for i, row := range re.Rows {
 			erow := make(map[string]interface{}, len(row))
@@ -145,11 +148,26 @@ func (r *EnhancedReader) nextRowsEvent() (*EnhancedRowsEvent, error) {
 	}
 }
 
+func (r *EnhancedReader) processEvent(evt Event) {
+	switch evt.Header.Type {
+	case binlog.EventTypeFormatDescription, binlog.EventTypeTableMap, binlog.EventTypeXID:
+		r.safepoint.Offset = evt.Offset
+	case binlog.EventTypeRotate:
+		r.safepoint = r.reader.state
+	}
+}
+
 // State returns current position in the binary log.
 func (r *EnhancedReader) State() binlog.Position {
 	return r.reader.state
 }
 
+// Safepoint returns last encountered position that is considered safe to start
+// with.
+func (r *EnhancedReader) Safepoint() binlog.Position {
+	return r.safepoint
+}
+
 // Close underlying database connection.
 func (r *EnhancedReader) Close() error {
 	return r.reader.Close()

reader/reader.go

@@ -19,11 +19,18 @@ type Event struct {
 	Format binlog.FormatDescription
 	Header binlog.EventHeader
 	Buffer []byte
+	Offset uint64
 
 	// Table is not empty for rows events
 	Table *binlog.TableDescription
 }
 
+var (
+	// ErrUnknownTableID is returned when a table ID from a rows event is
+	// missing in the table map index.
+	ErrUnknownTableID = errors.New("Unknown table ID")
+)
+
 // New creates a new binary log reader.
 func New(dsn string, sc slave.Config) (*Reader, error) {
 	conn, err := slave.Connect(dsn, sc)
@@ -112,7 +119,7 @@ func (r *Reader) ReadEvent() (*Event, error) {
 		tableID, flags := re.PeekTableIDAndFlags(evt.Buffer, r.format)
 		td, ok := r.tableMap[tableID]
 		if !ok {
-			return nil, errors.New("Unknown table ID")
+			return nil, ErrUnknownTableID
 		}
 		evt.Table = &td