feat: transaction implement

internal/transaction/errors.go

@@ -0,0 +1,26 @@
+package transaction
+
+import (
+	"errors"
+	"fmt"
+)
+
+var (
+	ErrNotFound       = errors.New("transaction record not found")
+	ErrActiveExists   = errors.New("an unfinished transaction already exists")
+	ErrStepConflict   = errors.New("step key already refers to different intent")
+	ErrStepNotPending = errors.New("step is not waiting for an execution result")
+)
+
+// ActiveTransactionError 告知调用方当前阻塞新请求的事务。
+type ActiveTransactionError struct {
+	TransactionID string
+}
+
+func (e *ActiveTransactionError) Error() string {
+	return fmt.Sprintf("%s: %s", ErrActiveExists, e.TransactionID)
+}
+
+func (e *ActiveTransactionError) Unwrap() error {
+	return ErrActiveExists
+}