phase3: HTTP server with converter, one-shot preview store, and middleware

internal/server/config.go

@@ -0,0 +1,94 @@
+package server
+
+import (
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+	"time"
+)
+
+const (
+	defaultAddr             = ":8080"
+	defaultMaxMarkdownBytes = int64(1_048_576)
+	defaultMaxRequestBytes  = int64(1_200_000)
+	defaultPreviewTTL       = time.Hour
+	defaultShutdownTimeout  = 10 * time.Second
+)
+
+type Config struct {
+	Addr             string
+	MaxMarkdownBytes int64
+	MaxRequestBytes  int64
+	PreviewTTL       time.Duration
+	ShutdownTimeout  time.Duration
+}
+
+func LoadConfig() (Config, error) {
+	maxMarkdownBytes, err := loadPositiveInt64("MAX_MARKDOWN_BYTES", defaultMaxMarkdownBytes)
+	if err != nil {
+		return Config{}, err
+	}
+
+	maxRequestBytes, err := loadPositiveInt64("MAX_REQUEST_BYTES", defaultMaxRequestBytes)
+	if err != nil {
+		return Config{}, err
+	}
+
+	previewTTL, err := loadDuration("PREVIEW_TTL", defaultPreviewTTL)
+	if err != nil {
+		return Config{}, err
+	}
+
+	shutdownTimeout, err := loadDuration("SHUTDOWN_TIMEOUT", defaultShutdownTimeout)
+	if err != nil {
+		return Config{}, err
+	}
+
+	addr := strings.TrimSpace(os.Getenv("ADDR"))
+	if addr == "" {
+		addr = defaultAddr
+	}
+
+	return Config{
+		Addr:             addr,
+		MaxMarkdownBytes: maxMarkdownBytes,
+		MaxRequestBytes:  maxRequestBytes,
+		PreviewTTL:       previewTTL,
+		ShutdownTimeout:  shutdownTimeout,
+	}, nil
+}
+
+func loadPositiveInt64(name string, fallback int64) (int64, error) {
+	raw := strings.TrimSpace(os.Getenv(name))
+	if raw == "" {
+		return fallback, nil
+	}
+
+	value, err := strconv.ParseInt(raw, 10, 64)
+	if err != nil {
+		return 0, fmt.Errorf("%s must be an integer: %w", name, err)
+	}
+	if value <= 0 {
+		return 0, fmt.Errorf("%s must be positive", name)
+	}
+
+	return value, nil
+}
+
+func loadDuration(name string, fallback time.Duration) (time.Duration, error) {
+	raw := strings.TrimSpace(os.Getenv(name))
+	if raw == "" {
+		return fallback, nil
+	}
+
+	value, err := time.ParseDuration(raw)
+	if err != nil {
+		return 0, fmt.Errorf("%s must be a valid duration: %w", name, err)
+	}
+	if value <= 0 {
+		return 0, fmt.Errorf("%s must be positive", name)
+	}
+
+	return value, nil
+}