Preflight comparison transaction names

internal/comparison/publish.go

@@ -24,6 +24,11 @@ const (
 	DestinationNotEmpty         DestinationErrorKind = "not_empty"
 	DestinationUnrecognized     DestinationErrorKind = "unrecognized"
 	DestinationInspection       DestinationErrorKind = "inspection"
+
+	maxComparisonComponentBytes = 255
+	temporaryRandomBytes        = 10
+	stagingDirectoryPattern     = ".weatherreporter-staging-*"
+	backupDirectoryPattern      = ".weatherreporter-backup-*"
 )
 
 // DestinationError provides inspectable context without making filesystem
@@ -82,6 +87,9 @@ func PlanDestination(workingDirectory, target string, replace bool) (Destination
 	if target == workingDirectory {
 		return DestinationPlan{}, newDestinationError(DestinationWorkingDirectory, target, nil)
 	}
+	if err := validateTransactionSiblingNames(target); err != nil {
+		return DestinationPlan{}, newDestinationError(DestinationInvalidPath, target, err)
+	}
 
 	plan := DestinationPlan{WorkingDirectory: workingDirectory, Target: target, Replace: replace}
 	info, err := os.Lstat(target)
@@ -119,6 +127,22 @@ func PlanDestination(workingDirectory, target string, replace bool) (Destination
 	return plan, nil
 }
 
+func validateTransactionSiblingNames(target string) error {
+	if len(filepath.Base(target)) > maxComparisonComponentBytes {
+		return fmt.Errorf("destination name exceeds the %d-byte limit", maxComparisonComponentBytes)
+	}
+	for _, pattern := range []string{stagingDirectoryPattern, backupDirectoryPattern} {
+		if !temporaryPatternFitsComponentLimit(pattern) {
+			return fmt.Errorf("comparison transaction sibling pattern exceeds the %d-byte limit", maxComparisonComponentBytes)
+		}
+	}
+	return nil
+}
+
+func temporaryPatternFitsComponentLimit(pattern string) bool {
+	return len(strings.Replace(pattern, "*", strings.Repeat("0", temporaryRandomBytes), 1)) <= maxComparisonComponentBytes
+}
+
 func absoluteCleanPath(value string) (string, error) {
 	if strings.TrimSpace(value) == "" {
 		return "", fmt.Errorf("path is required")
@@ -480,7 +504,7 @@ func publish(ctx context.Context, plan DestinationPlan, bundle LogicalBundle, op
 	if err := os.MkdirAll(filepath.Dir(plan.Target), 0o755); err != nil {
 		return PublicationResult{}, fmt.Errorf("create comparison destination parent %q: %w", filepath.Dir(plan.Target), err)
 	}
-	temporaryDirectory, err := os.MkdirTemp(filepath.Dir(plan.Target), "."+filepath.Base(plan.Target)+".staging-")
+	temporaryDirectory, err := os.MkdirTemp(filepath.Dir(plan.Target), stagingDirectoryPattern)
 	if err != nil {
 		return PublicationResult{}, fmt.Errorf("create comparison staging directory: %w", err)
 	}
@@ -516,7 +540,7 @@ func publish(ctx context.Context, plan DestinationPlan, bundle LogicalBundle, op
 		return PublicationResult{Committed: true}, nil
 	}
 
-	backupDirectory, err := uniqueSiblingPath(filepath.Dir(currentPlan.Target), "."+filepath.Base(currentPlan.Target)+".backup-")
+	backupDirectory, err := uniqueSiblingPath(filepath.Dir(currentPlan.Target), backupDirectoryPattern)
 	if err != nil {
 		return PublicationResult{}, err
 	}