fix(config): introduce maximum config size

core/entrypoint.go

@@ -32,7 +32,7 @@ func setupDebugging(opts state.NylonOptions) {
 	}
 }
 
-func readCentralConfig(centralPath, nodePath string) (*state.CentralCfg, error) {
+func readCentralConfig(centralPath, nodePath string, tunables *state.RouterTunables) (*state.CentralCfg, error) {
 	var centralCfg state.CentralCfg
 
 	file, err := os.ReadFile(centralPath)
@@ -58,7 +58,7 @@ func readCentralConfig(centralPath, nodePath string) (*state.CentralCfg, error)
 			return nil, fmt.Errorf("central.yaml not found and node.yaml has no dist config")
 		}
 
-		cfg, err := FetchConfig(nodeCfg.Dist.Url, nodeCfg.Dist.Key)
+		cfg, err := FetchConfig(nodeCfg.Dist.Url, nodeCfg.Dist.Key, tunables.MaxConfigSize)
 		if err != nil {
 			return nil, err
 		}
@@ -103,7 +103,8 @@ func Bootstrap(centralPath, nodePath, logPath string, verbose bool, opts state.N
 		level = slog.LevelDebug
 	}
 
-	centralCfg, err := readCentralConfig(centralPath, nodePath)
+	tunables := state.DefaultRouterTunables()
+	centralCfg, err := readCentralConfig(centralPath, nodePath, &tunables)
 	if err != nil {
 		panic(err)
 	}

core/nylon_distribution.go

@@ -16,7 +16,7 @@ import (
 )
 
 // fetches and unbundles central config from url
-func FetchConfig(repoStr string, key state.NyPublicKey) (*state.CentralCfg, error) {
+func FetchConfig(repoStr string, key state.NyPublicKey, maxSize int64) (*state.CentralCfg, error) {
 	repo, err := url.Parse(repoStr)
 	if err != nil {
 		return nil, fmt.Errorf("failed to parse repo URL %s: %w", repoStr, err)
@@ -56,7 +56,7 @@ func FetchConfig(repoStr string, key state.NyPublicKey) (*state.CentralCfg, erro
 		if err != nil {
 			return nil, fmt.Errorf("failed to fetch %s: %w", repo.String(), err)
 		}
-		cfgBody, err = io.ReadAll(res.Body)
+		cfgBody, err = io.ReadAll(io.LimitReader(res.Body, maxSize))
 		if err != nil {
 			res.Body.Close()
 			return nil, fmt.Errorf("failed to read response from %s: %w", repo.String(), err)
@@ -85,7 +85,7 @@ func checkForConfigUpdates(n *Nylon) error {
 	for _, repoStr := range repos {
 		go func(repo string) {
 			err := func() error {
-				config, err := FetchConfig(repo, key)
+				config, err := FetchConfig(repo, key, n.MaxConfigSize)
 				if err != nil {
 					return err
 				}

state/tunables.go

@@ -40,6 +40,8 @@ type RouterTunables struct {
 
 	EndpointResolveExpiry time.Duration
 	EndpointResolveDelay  time.Duration
+
+	MaxConfigSize int64
 }
 
 // NylonOptions contains runtime flags set at startup (typically from CLI flags).
@@ -87,6 +89,8 @@ func DefaultRouterTunables() RouterTunables {
 
 		EndpointResolveExpiry: time.Minute * 1,
 		EndpointResolveDelay:  time.Second * 15,
+
+		MaxConfigSize: 1 << 20, // 1 MB
 	}
 }