Read From Environment Variable Even If Parse File Failed

cleanenv.go

@@ -68,7 +68,7 @@ type Updater interface {
 }
 
 // ReadConfig reads configuration file and parses it depending on tags in structure provided.
-// Then it reads and parses
+// Then it reads and parses configuration from environment variable
 //
 // Example:
 //
@@ -87,12 +87,17 @@ type Updater interface {
 //	     ...
 //	 }
 func ReadConfig(path string, cfg interface{}) error {
+	readDefaults(cfg)
+
 	err := parseFile(path, cfg)
-	if err != nil {
-		return err
+
+	if envErr := readEnvVars(cfg, false); envErr != nil {
+		if err != nil {
+			return fmt.Errorf("%s: %w", envErr.Error(), err)
+		}
 	}
 
-	return readEnvVars(cfg, false)
+	return nil
 }
 
 // ReadEnv reads environment variables into the structure.
@@ -328,6 +333,29 @@ func readStructMetadata(cfgRoot interface{}) ([]structMeta, error) {
 	return metas, nil
 }
 
+// readDefaults reads default values to the provided configuration structure
+//
+// Note: this method will overwrite existing values in the configuration structure
+func readDefaults(cfg interface{}) error {
+	metaInfo, err := readStructMetadata(cfg)
+	if err != nil {
+		return err
+	}
+
+	for _, meta := range metaInfo {
+		rawValue := meta.defValue
+		if rawValue == nil {
+			continue
+		}
+
+		if err := parseValue(meta.fieldValue, *rawValue, meta.separator, meta.layout); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
 // readEnvVars reads environment variables to the provided configuration structure
 func readEnvVars(cfg interface{}, update bool) error {
 	metaInfo, err := readStructMetadata(cfg)

cleanenv_test.go

@@ -1119,20 +1119,68 @@ no-env: this
 		},
 
 		{
-			name:    "unknown",
-			file:    "-",
-			ext:     "",
-			want:    nil,
-			wantErr: true,
+			name: "unknown filetype fallback to env",
+			file: "-",
+			ext:  "",
+			env: map[string]string{
+				"TEST_NUMBER": "3",
+				"TEST_STRING": "fromEnv",
+			},
+			want: &config{
+				Number:    3,
+				String:    "fromEnv",
+				NoDefault: "",
+				NoEnv:     "default",
+			},
+			wantErr: false,
 		},
-
 		{
-			name:    "parsing error",
-			file:    "-",
-			ext:     "json",
+			name: "parsing error fallback to env",
+			file: "-",
+			ext:  "json",
+			env: map[string]string{
+				"TEST_NUMBER": "3",
+				"TEST_STRING": "fromEnv",
+			},
+			want: &config{
+				Number:    3,
+				String:    "fromEnv",
+				NoDefault: "",
+				NoEnv:     "default",
+			},
+			wantErr: false,
+		},
+		{
+			name: "file and env parse error",
+			file: "-",
+			ext:  "json",
+			env: map[string]string{
+				"TEST_NUMBER": "five hundred",
+				"TEST_STRING": "fromEnv",
+			},
 			want:    nil,
 			wantErr: true,
 		},
+		{
+			name: "parsed file and failed to parse env",
+			file: `
+number: 2
+string: test
+no-default: NoDefault
+`,
+			ext: "yaml",
+			env: map[string]string{
+				"TEST_NUMBER": "five hundred",
+				"TEST_STRING": "fromEnv",
+			},
+			want: &config{
+				Number:    2,
+				String:    "test",
+				NoDefault: "NoDefault",
+				NoEnv:     "default",
+			},
+			wantErr: false,
+		},
 	}
 
 	for _, tt := range tests {
@@ -1163,3 +1211,48 @@ no-env: this
 		})
 	}
 }
+
+func TestReadDefaults(t *testing.T) {
+	type goodMetadataConfig struct {
+		Number    int64  `env-default:"1"`
+		String    string `env-default:"default"`
+		NoDefault string
+	}
+	type badMetadataConfig struct {
+		Number int64 `env-default:"one"`
+	}
+
+	tests := []struct {
+		name    string
+		want    interface{}
+		cfg     interface{}
+		wantErr bool
+	}{
+		{
+			name: "successfully reads default values",
+			want: &goodMetadataConfig{
+				Number:    1,
+				String:    "default",
+				NoDefault: "",
+			},
+			cfg:     &goodMetadataConfig{},
+			wantErr: false,
+		},
+		{
+			name:    "fails to read default values due to bad type",
+			want:    nil,
+			cfg:     &badMetadataConfig{},
+			wantErr: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if err := readDefaults(tt.cfg); (err != nil) != tt.wantErr {
+				t.Errorf("wrong error behavior %v, wantErr %v", err, tt.wantErr)
+			} else if err == nil && !reflect.DeepEqual(tt.cfg, tt.want) {
+				t.Errorf("wrong data %v, want %v", tt.cfg, tt.want)
+			}
+		})
+	}
+}