init

gonfig.go

@@ -0,0 +1,74 @@
+// Package gonfig provides utilities for reading, unmarshaling, and validating
+// configuration files.
+package gonfig
+
+import (
+	"errors"
+	"fmt"
+	"os"
+)
+
+// Validator defines an interface for validating a configuration of type T. It
+// ensures that the provided configuration meets required constraints.
+type Validator[T any] interface {
+	// Validate checks the provided configuration and returns an error if it is
+	// invalid.
+	Validate(config T) []error
+}
+
+// ReadConfig reads a configuration file, unmarshals its content into the given
+// configuration object, and validates it using the provided validator. If the
+// primary path is empty, it searches for the configuration file in the
+// fallback paths. The function returns the resolved path to the configuration
+// file or a list of errors if the file cannot be located, read, unmarshaled,
+// or validated.
+func ReadConfig[T any](path string, paths []string, c *T, unmarshal func([]byte, *T) error, validator Validator[T]) (string, []error) {
+	var err error
+
+	path, err = findConfig(path, paths)
+	if err != nil {
+		return "", []error{err}
+	}
+
+	content, err := os.ReadFile(path)
+	if err != nil {
+		return "", []error{fmt.Errorf("unable to read configuration file %s: %w", path, err)}
+	}
+
+	err = unmarshal(content, c)
+	if err != nil {
+		return "", []error{fmt.Errorf("unable to unmarshal configuration file %s: %w", path, err)}
+	}
+
+	return path, validator.Validate(*c)
+}
+
+// findConfig determines the path to the configuration file by using the
+// provided primary path or searching through a list of fallback paths if the
+// primary path is empty. If no valid file is found, or if the specified file is
+// inaccessible, an error is returned.
+func findConfig(path string, paths []string) (string, error) {
+	var err error
+
+	if path == "" {
+		for _, p := range paths {
+			_, err = os.Stat(p)
+			if err != nil {
+				continue
+			}
+
+			path = p
+		}
+
+		if path == "" {
+			return "", errors.New("could not locate configuration file")
+		}
+	} else {
+		_, err = os.Stat(path)
+		if err != nil {
+			return "", fmt.Errorf("could not stat configuration file %s: %w", path, err)
+		}
+	}
+
+	return path, nil
+}