fix(copilot): implement official transactional hook contract

cmd/elydora/plugins/transaction_precondition.go

@@ -0,0 +1,95 @@
+package plugins
+
+import (
+	"bytes"
+	"fmt"
+	"os"
+)
+
+type filePrecondition struct {
+	filePath    string
+	label       string
+	snapshot    *managedFileSnapshot
+	maximumSize int64
+}
+
+func prepareSnapshotSourceChange(
+	filePath, label string,
+	original *managedFileSnapshot,
+	next []byte,
+	mode os.FileMode,
+	remove bool,
+) (*fileChange, error) {
+	if !remove && int64(len(next)) > maxManagedSourceBytes {
+		return nil, fmt.Errorf(
+			"%s exceeds %d bytes: %s",
+			label,
+			maxManagedSourceBytes,
+			filePath,
+		)
+	}
+	current, err := readManagedFile(filePath, label, maxManagedSourceBytes)
+	if err != nil {
+		return nil, err
+	}
+	if !sameManagedSnapshot(current, original) {
+		return nil, fmt.Errorf("%s changed before update: %s", label, filePath)
+	}
+	if original == nil && (remove || next == nil) {
+		return nil, nil
+	}
+	if original != nil && !remove && bytes.Equal(original.contents, next) {
+		return nil, nil
+	}
+	change := &fileChange{
+		filePath: filePath,
+		label:    label,
+		next:     append([]byte(nil), next...),
+		mode:     mode,
+		remove:   remove,
+	}
+	if original != nil {
+		change.original = append([]byte(nil), original.contents...)
+		change.originalInfo = original.info
+		change.originalMode = original.mode
+		change.existed = true
+	}
+	return change, nil
+}
+
+func sameManagedSnapshot(current, expected *managedFileSnapshot) bool {
+	if current == nil || expected == nil {
+		return current == expected
+	}
+	return bytes.Equal(current.contents, expected.contents) &&
+		os.SameFile(current.info, expected.info)
+}
+
+func assertFilePreconditions(
+	preconditions []filePrecondition,
+	operation string,
+) error {
+	for _, condition := range preconditions {
+		maximumSize := condition.maximumSize
+		if maximumSize <= 0 {
+			maximumSize = maxManagedSourceBytes
+		}
+		current, err := readManagedFile(
+			condition.filePath,
+			condition.label,
+			maximumSize,
+		)
+		if err != nil {
+			return err
+		}
+		if !sameManagedSnapshot(current, condition.snapshot) {
+			return fmt.Errorf(
+				"%s changed during %s: %s",
+				condition.label,
+				operation,
+				condition.filePath,
+			)
+		}
+	}
+	return nil
+}