fix: error checking prior to file writes

src/cmd/tools/compose.go

@@ -47,7 +47,13 @@ var composeCmd = &cobra.Command{
 			outputFile = GetDefaultOutputFile(composeOpts.InputFile)
 		}
 
-		err := Compose(composeOpts.InputFile, outputFile)
+		// Check if output file contains a valid OSCAL model
+		_, err := oscal.ValidOSCALModelAtPath(outputFile)
+		if err != nil {
+			message.Fatalf(err, "Output file %s is not a valid OSCAL model: %v", outputFile, err)
+		}
+
+		err = Compose(composeOpts.InputFile, outputFile)
 		if err != nil {
 			message.Fatalf(err, "Composition error: %s", err)
 		}

src/cmd/validate/validate.go

@@ -52,6 +52,12 @@ var validateCmd = &cobra.Command{
 			outputFile = getDefaultOutputFile(opts.InputFile)
 		}
 
+		// Check if output file contains a valid OSCAL model
+		_, err := oscal.ValidOSCALModelAtPath(outputFile)
+		if err != nil {
+			message.Fatalf(err, "Output file %s is not a valid OSCAL model: %v", outputFile, err)
+		}
+
 		if SaveResources {
 			ResourcesDir = filepath.Join(filepath.Dir(outputFile))
 		}
@@ -261,7 +267,7 @@ func ValidateOnControlImplementations(controlImplementations *[]oscalTypes_1_1_2
 	return findings, observations, nil
 }
 
-// GetDefaultOutputFile returns the default output file name
+// getDefaultOutputFile returns the default output file name and checks if the file already exists
 func getDefaultOutputFile(inputFile string) string {
 	dirPath := filepath.Dir(inputFile)
 	filename := "assessment-results" + filepath.Ext(inputFile)

src/pkg/common/oscal/complete-schema.go

@@ -52,16 +52,16 @@ func WriteOscalModel(filePath string, model *oscalTypes_1_1_2.OscalModels) error
 		// If the file exists - read the data into the model
 		existingFileBytes, err := os.ReadFile(filePath)
 		if err != nil {
-			return err
+			return fmt.Errorf("error reading file: %v", err)
 		}
 		existingModel, err := NewOscalModel(existingFileBytes)
 		if err != nil {
-			return err
+			return fmt.Errorf("error getting existing model: %v", err)
 		}
 
 		existingModelType, err := GetOscalModel(existingModel)
 		if err != nil {
-			return nil
+			return fmt.Errorf("error getting existing model type: %v", err)
 		}
 
 		if existingModelType != modelType {
@@ -224,6 +224,27 @@ func GetOscalModel(model *oscalTypes_1_1_2.OscalModels) (modelType string, err e
 
 }
 
+// ValidOSCALModelAtPath takes a path and returns a bool indicating if the model exists/is valid
+// bool = T/F that oscal model exists, error = if not nil OSCAL model is invalid
+func ValidOSCALModelAtPath(path string) (bool, error) {
+	_, err := os.Stat(path)
+	if err != nil {
+		return false, nil
+	}
+
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return true, err
+	}
+
+	_, err = NewOscalModel(data)
+	if err != nil {
+		return true, err
+	}
+
+	return true, nil
+}
+
 // InjectIntoOSCALModel takes a model target and a map[string]interface{} of values to inject into the model
 func InjectIntoOSCALModel(target *oscalTypes_1_1_2.OscalModels, values map[string]interface{}, path string) (*oscalTypes_1_1_2.OscalModels, error) {
 	// If the target is nil, return an error