Initial commit

internal/env/loader.go

@@ -0,0 +1,83 @@
+// Package env provides a minimal, dependency-free .env file loader.
+//
+// It reads KEY=VAL pairs from a file and sets them into the process
+// environment using os.Setenv, but only for variables that are NOT already
+// set. This gives the real environment (system env / shell) priority over
+// values in the .env file.
+package env
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strings"
+)
+
+// DefaultPath is the file LoadEnvDefault reads when no path is given.
+const DefaultPath = ".env"
+
+// LoadEnvDefault loads environment variables from the default ".env" file
+// in the current working directory.
+func LoadEnvDefault() error {
+	return LoadEnv(DefaultPath)
+}
+
+// LoadEnv reads the file at path line by line and sets each KEY=VALUE pair
+// into the process environment.
+//
+// Rules:
+//   - Blank lines and lines starting with '#' (comments) are ignored.
+//   - Values may be wrapped in single or double quotes, which are stripped.
+//   - A variable already present in the environment is never overridden
+//     (system env wins; .env is the lowest priority).
+func LoadEnv(path string) error {
+	f, err := os.Open(path)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	scanner := bufio.NewScanner(f)
+	for scanner.Scan() {
+		line := strings.TrimSpace(scanner.Text())
+		if line == "" || strings.HasPrefix(line, "#") {
+			continue
+		}
+
+		key, value, ok := strings.Cut(line, "=")
+		if !ok {
+			// Not KEY=VAL format; skip silently.
+			continue
+		}
+		key = strings.TrimSpace(key)
+		if key == "" {
+			continue
+		}
+		value = strings.TrimSpace(value)
+		value = unquote(value)
+
+		if _, exists := os.LookupEnv(key); exists {
+			// System environment wins over .env.
+			continue
+		}
+		if err := os.Setenv(key, value); err != nil {
+			return fmt.Errorf("failed to set env var %q: %w", key, err)
+		}
+	}
+	if err := scanner.Err(); err != nil {
+		return fmt.Errorf("failed to read %s: %w", path, err)
+	}
+	return nil
+}
+
+// unquote strips a single matching pair of surrounding single or double
+// quotes from value, if present. Any other value is returned unchanged.
+func unquote(value string) string {
+	if len(value) >= 2 {
+		first, last := value[0], value[len(value)-1]
+		if (first == '"' && last == '"') || (first == '\'' && last == '\'') {
+			return value[1 : len(value)-1]
+		}
+	}
+	return value
+}