Implement self-update recovery (T-403)

core/updater/transaction.go

@@ -0,0 +1,87 @@
+package updater
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"io"
+	"os"
+)
+
+type transactionPhase string
+
+const (
+	phasePrepared         transactionPhase = "prepared"
+	phaseTargetBackedUp   transactionPhase = "target_backed_up"
+	phaseStagingActivated transactionPhase = "staging_activated"
+	phaseLaunched         transactionPhase = "launched"
+	phaseCommitted        transactionPhase = "committed"
+)
+
+type transaction struct {
+	SchemaVersion int              `json:"schema_version"`
+	RequestID     string           `json:"request_id"`
+	Phase         transactionPhase `json:"phase"`
+}
+
+func (record transaction) validate() error {
+	if record.SchemaVersion != transactionSchemaVersion || !validRequestID(record.RequestID) {
+		return ErrTransactionCorrupt
+	}
+	switch record.Phase {
+	case phasePrepared, phaseTargetBackedUp, phaseStagingActivated, phaseLaunched, phaseCommitted:
+		return nil
+	default:
+		return ErrTransactionCorrupt
+	}
+}
+
+func writeTransaction(layout updateLayout, phase transactionPhase, syncer DirectorySyncer) error {
+	record := transaction{SchemaVersion: transactionSchemaVersion, RequestID: layout.requestID, Phase: phase}
+	if err := record.validate(); err != nil {
+		return err
+	}
+	data, err := json.Marshal(record)
+	if err != nil {
+		return fmt.Errorf("encode self-update transaction: %w", err)
+	}
+	data = append(data, '\n')
+	if err := replaceRegularFile(layout.root, layout.transaction, ".self-update-transaction-*.tmp", data, syncer); err != nil {
+		return fmt.Errorf("write self-update transaction: %w", err)
+	}
+	return nil
+}
+
+func loadTransaction(layout updateLayout) (transaction, bool, error) {
+	data, err := readRegularFile(layout.transaction)
+	if os.IsNotExist(err) {
+		return transaction{}, false, nil
+	}
+	if err != nil {
+		return transaction{}, false, fmt.Errorf("read self-update transaction: %w", err)
+	}
+	decoder := json.NewDecoder(bytes.NewReader(data))
+	decoder.DisallowUnknownFields()
+	var record transaction
+	if err := decoder.Decode(&record); err != nil {
+		return transaction{}, false, fmt.Errorf("%w: %v", ErrTransactionCorrupt, err)
+	}
+	var extra interface{}
+	if err := decoder.Decode(&extra); err != io.EOF {
+		if err == nil {
+			return transaction{}, false, fmt.Errorf("%w: trailing JSON value", ErrTransactionCorrupt)
+		}
+		return transaction{}, false, fmt.Errorf("%w: trailing data: %v", ErrTransactionCorrupt, err)
+	}
+	if err := record.validate(); err != nil {
+		return transaction{}, false, err
+	}
+	return record, true, nil
+}
+
+func removeTransaction(layout updateLayout, syncer DirectorySyncer) error {
+	if err := removeRegularFile(layout.transaction, layout.root, syncer); err != nil {
+		return fmt.Errorf("remove self-update transaction: %w", err)
+	}
+	return nil
+}