Creating new method ReadConfigFS which allows users to pass use fs.FS for loading files

cleanenv.go

@@ -6,6 +6,7 @@ import (
 	"flag"
 	"fmt"
 	"io"
+	"io/fs"
 	"net/url"
 	"os"
 	"path/filepath"
@@ -53,6 +54,9 @@ const (
 	TagEnvPrefix = "env-prefix"
 )
 
+// ParseFunc defines the type signature that parser functions follow
+type ParseFunc func(io.Reader, interface{}) error
+
 // Setter is an interface for a custom value setter.
 //
 // To implement a custom value setter you need to add a SetValue function to your type that will receive a string raw value:
@@ -95,7 +99,57 @@ type Updater interface {
 //	    ...
 //	}
 func ReadConfig(path string, cfg interface{}) error {
-	err := parseFile(path, cfg)
+	parseFunc, err := getParseFunc(strings.ToLower(filepath.Ext(path)))
+	if err != nil {
+		return err
+	}
+
+	f, err := os.OpenFile(path, os.O_RDONLY|os.O_SYNC, 0)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	err = parseFunc(f, cfg)
+	if err != nil {
+		return err
+	}
+
+	return readEnvVars(cfg, false)
+}
+
+// ReadConfigFS reads configuration file from provided filesystem and parses it depending on tags in structure provided.
+//
+// Example:
+//
+//		type ConfigDatabase struct {
+//			Port     string `yaml:"port" env:"PORT" env-default:"5432"`
+//			Host     string `yaml:"host" env:"HOST" env-default:"localhost"`
+//			Name     string `yaml:"name" env:"NAME" env-default:"postgres"`
+//			User     string `yaml:"user" env:"USER" env-default:"user"`
+//			Password string `yaml:"password" env:"PASSWORD"`
+//		}
+//
+//		var cfg ConfigDatabase
+//
+//		fsys := os.DirFS("/example/config/folder")
+//	 	err := cleanenv.ReadConfigFS(fsys, "config.yml", &cfg)
+//		if err != nil {
+//			...
+//		}
+func ReadConfigFS(fsys fs.FS, fname string, cfg interface{}) error {
+	parseFunc, err := getParseFunc(strings.ToLower(filepath.Ext(fname)))
+	if err != nil {
+		return err
+	}
+
+	f, err := fsys.Open(fname)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	err = parseFunc(f, cfg)
 	if err != nil {
 		return err
 	}
@@ -113,7 +167,7 @@ func UpdateEnv(cfg interface{}) error {
 	return readEnvVars(cfg, true)
 }
 
-// parseFile parses configuration file according to it's extension
+// getParseFunc returns the parsing function based on the file extension passed in.
 //
 // Currently following file extensions are supported:
 //
@@ -126,33 +180,21 @@ func UpdateEnv(cfg interface{}) error {
 // - env
 //
 // - edn
-func parseFile(path string, cfg interface{}) error {
-	// open the configuration file
-	f, err := os.OpenFile(path, os.O_RDONLY|os.O_SYNC, 0)
-	if err != nil {
-		return err
-	}
-	defer f.Close()
-
-	// parse the file depending on the file type
-	switch ext := strings.ToLower(filepath.Ext(path)); ext {
+func getParseFunc(ext string) (ParseFunc, error) {
+	switch ext {
 	case ".yaml", ".yml":
-		err = ParseYAML(f, cfg)
+		return ParseYAML, nil
 	case ".json":
-		err = ParseJSON(f, cfg)
+		return ParseJSON, nil
 	case ".toml":
-		err = ParseTOML(f, cfg)
+		return ParseTOML, nil
 	case ".edn":
-		err = parseEDN(f, cfg)
+		return parseEDN, nil
 	case ".env":
-		err = parseENV(f, cfg)
+		return parseENV, nil
 	default:
-		return fmt.Errorf("file format '%s' doesn't supported by the parser", ext)
+		return nil, fmt.Errorf("file format '%s' is not supported by the parser", ext)
 	}
-	if err != nil {
-		return fmt.Errorf("config file parsing error: %s", err.Error())
-	}
-	return nil
 }
 
 // ParseYAML parses YAML from reader to data structure