create a websocket game server

game-server/internal/config/config.go

@@ -0,0 +1,82 @@
+// Package config loads the game server configuration from environment
+// variables.
+package config
+
+import (
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+	"time"
+)
+
+type Config struct {
+	// ListenAddr is the address the websocket HTTP server binds to
+	// (e.g. ":8081"). The server may sit behind a reverse proxy.
+	ListenAddr string
+	// PublicAddr is the public endpoint address of this server
+	// (e.g. "ws://example.com:8081/ws"). It is used only to identify this
+	// server: the "game_server" claim of a game token must match it
+	// strictly. The main server must be configured to put exactly this
+	// string into the tokens it issues.
+	PublicAddr string
+	// JWTSecret is the HS256 secret shared with the main server; both the
+	// game token and the user token are verified with it.
+	JWTSecret []byte
+	// JoinTimeout is how long the first player waits for the second one
+	// before the match is cancelled.
+	JoinTimeout time.Duration
+	// AllowedOrigins restricts the Origin header of websocket upgrade
+	// requests; ["*"] disables the check.
+	AllowedOrigins []string
+}
+
+func Load() (Config, error) {
+	var cfg Config
+
+	cfg.ListenAddr = getenv("LISTEN_ADDR", ":8081")
+
+	cfg.PublicAddr = os.Getenv("PUBLIC_ADDR")
+	if cfg.PublicAddr == "" {
+		return cfg, fmt.Errorf("PUBLIC_ADDR is required (public endpoint address, e.g. ws://example.com:8081/ws)")
+	}
+
+	secret := os.Getenv("JWT_SECRET")
+	if secret == "" {
+		return cfg, fmt.Errorf("JWT_SECRET is required (HS256 secret shared with the main server)")
+	}
+	cfg.JWTSecret = []byte(secret)
+
+	joinTimeout, err := parseDuration(getenv("JOIN_TIMEOUT", "2m"))
+	if err != nil {
+		return cfg, fmt.Errorf("invalid JOIN_TIMEOUT: %w", err)
+	}
+	cfg.JoinTimeout = joinTimeout
+
+	origins := getenv("ALLOWED_ORIGINS", "*")
+	cfg.AllowedOrigins = strings.Split(origins, ",")
+	for i := range cfg.AllowedOrigins {
+		cfg.AllowedOrigins[i] = strings.TrimSpace(cfg.AllowedOrigins[i])
+	}
+
+	return cfg, nil
+}
+
+func getenv(key, fallback string) string {
+	if v := os.Getenv(key); v != "" {
+		return v
+	}
+	return fallback
+}
+
+// parseDuration accepts either a Go duration string ("90s", "2m") or a plain
+// number of seconds ("120").
+func parseDuration(s string) (time.Duration, error) {
+	if d, err := time.ParseDuration(s); err == nil {
+		return d, nil
+	}
+	if secs, err := strconv.Atoi(s); err == nil {
+		return time.Duration(secs) * time.Second, nil
+	}
+	return 0, fmt.Errorf("not a duration: %q", s)
+}