Initial DDC release

internal/config/env.go

@@ -0,0 +1,78 @@
+package config
+
+import (
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+)
+
+type envReader struct {
+	err error
+}
+
+func (reader *envReader) fail(name string, err error) {
+	if reader.err == nil {
+		reader.err = fmt.Errorf("%s: %w", name, err)
+	}
+}
+
+func (reader *envReader) text(name, fallback string) string {
+	value := strings.TrimSpace(os.Getenv(name))
+	if value == "" {
+		return fallback
+	}
+	return value
+}
+
+func (reader *envReader) boolean(name string, fallback bool) bool {
+	raw := reader.text(name, "")
+	if raw == "" {
+		return fallback
+	}
+	value, err := strconv.ParseBool(raw)
+	if err != nil {
+		reader.fail(name, err)
+		return fallback
+	}
+	return value
+}
+
+func (reader *envReader) integer(name string, fallback int) int {
+	raw := reader.text(name, "")
+	if raw == "" {
+		return fallback
+	}
+	value, err := strconv.Atoi(raw)
+	if err != nil {
+		reader.fail(name, err)
+		return fallback
+	}
+	return value
+}
+
+func (reader *envReader) ports(name, fallback string) []uint16 {
+	raw := reader.text(name, fallback)
+	if raw == "*" {
+		return nil
+	}
+
+	var ports []uint16
+	for _, part := range strings.Split(raw, ",") {
+		part = strings.TrimSpace(part)
+		if part == "" {
+			continue
+		}
+		value, err := strconv.ParseUint(part, 10, 16)
+		if err != nil || value == 0 {
+			reader.fail(name, fmt.Errorf("invalid port %q", part))
+			return nil
+		}
+		ports = append(ports, uint16(value))
+	}
+
+	if len(ports) == 0 {
+		reader.fail(name, fmt.Errorf("no ports listed, use * to allow any port"))
+	}
+	return ports
+}