Add concurrency limits and configuration options for SteamCache

- Introduced maxConcurrentRequests and maxRequestsPerClient fields in the Config struct to manage request limits.
- Updated the SteamCache implementation to utilize these new configuration options for controlling concurrent requests.
- Enhanced the ServeHTTP method to enforce global and per-client rate limiting using semaphores.
- Modified the root command to accept new flags for configuring concurrency limits via command-line arguments.
- Updated tests to reflect changes in the SteamCache initialization and request handling logic.

cmd/root.go

@@ -19,6 +19,9 @@ var (
 
 	logLevel  string
 	logFormat string
+
+	maxConcurrentRequests int64
+	maxRequestsPerClient  int64
 )
 
 var rootCmd = &cobra.Command{
@@ -94,6 +97,17 @@ var rootCmd = &cobra.Command{
 			Str("config_path", configPath).
 			Msg("Configuration loaded successfully")
 
+		// Use command-line flags if provided, otherwise use config values
+		finalMaxConcurrentRequests := cfg.MaxConcurrentRequests
+		if maxConcurrentRequests > 0 {
+			finalMaxConcurrentRequests = maxConcurrentRequests
+		}
+
+		finalMaxRequestsPerClient := cfg.MaxRequestsPerClient
+		if maxRequestsPerClient > 0 {
+			finalMaxRequestsPerClient = maxRequestsPerClient
+		}
+
 		sc := steamcache.New(
 			cfg.ListenAddress,
 			cfg.Cache.Memory.Size,
@@ -102,6 +116,8 @@ var rootCmd = &cobra.Command{
 			cfg.Upstream,
 			cfg.Cache.Memory.GCAlgorithm,
 			cfg.Cache.Disk.GCAlgorithm,
+			finalMaxConcurrentRequests,
+			finalMaxRequestsPerClient,
 		)
 
 		logger.Logger.Info().
@@ -128,4 +144,7 @@ func init() {
 
 	rootCmd.Flags().StringVarP(&logLevel, "log-level", "l", "info", "Logging level: debug, info, error")
 	rootCmd.Flags().StringVarP(&logFormat, "log-format", "f", "console", "Logging format: json, console")
+
+	rootCmd.Flags().Int64Var(&maxConcurrentRequests, "max-concurrent-requests", 0, "Maximum concurrent requests (0 = use config file value)")
+	rootCmd.Flags().Int64Var(&maxRequestsPerClient, "max-requests-per-client", 0, "Maximum concurrent requests per client IP (0 = use config file value)")
 }