Add in memory cache for lockdown mode (#1416)

* Apply lockdown mode to issues and pull requests

* Add cache

* Unlock in defer

* Add muesli/cache2go

* [WIP] Replace custom cache in lockdown.go with cache2go struct (#1425)

* Initial plan

* Replace custom cache with cache2go library

- Added github.com/muesli/cache2go dependency
- Replaced custom map-based cache with cache2go.CacheTable
- Removed manual timer management (scheduleExpiry, ensureEntry methods)
- Removed timer field from repoAccessCacheEntry struct
- Updated GetRepoAccessInfo to use cache2go's Value() and Add() methods
- Updated SetTTL to flush and re-add entries with new TTL
- Used unique cache names per instance to avoid test interference
- All existing tests pass with the new implementation

Co-authored-by: JoannaaKL <[email protected]>

* Final verification complete

Co-authored-by: JoannaaKL <[email protected]>

---------

Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: JoannaaKL <[email protected]>

* Use muesli for cache

* Make RepoAccessCache a singleton (#1426)

* Initial plan

* Implement RepoAccessCache as a singleton pattern

Co-authored-by: JoannaaKL <[email protected]>

* Complete singleton implementation and verification

Co-authored-by: JoannaaKL <[email protected]>

* Remove cacheIDCounter as requested

Co-authored-by: JoannaaKL <[email protected]>

---------

Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: JoannaaKL <[email protected]>

* Update mutexes

* .

* Reuse cache

* .

* .

* Fix logic after vibe coding

* Update docs

* .

* Refactoring to make the code pretty

* Hide lockdown logic behind shouldFilter function

* .

* Tests

---------

Co-authored-by: Copilot <[email protected]>

Author: JoannaaKL

README.md

@@ -1264,7 +1264,7 @@ docker run -i --rm \
 
 ## Lockdown Mode
 
-Lockdown mode limits the content that the server will surface from public repositories. When enabled, requests that fetch issue details will return an error if the issue was created by someone who does not have push access to the repository. Private repositories are unaffected, and collaborators can still access their own issues.
+Lockdown mode limits the content that the server will surface from public repositories. When enabled, the server checks whether the author of each item has push access to the repository. Private repositories are unaffected, and collaborators keep full access to their own content.
 
 ```bash
 ./github-mcp-server --lockdown-mode
@@ -1279,7 +1279,20 @@ docker run -i --rm \
   ghcr.io/github/github-mcp-server
 ```
 
-At the moment lockdown mode applies to the issue read toolset, but it is designed to extend to additional data surfaces over time.
+The behavior of lockdown mode depends on the tool invoked.
+
+Following tools will return an error when the author lacks the push access:
+
+- `issue_read:get`
+- `pull_request_read:get`
+
+Following tools will filter out content from users lacking the push access:
+
+- `issue_read:get_comments`
+- `issue_read:get_sub_issues`
+- `pull_request_read:get_comments`
+- `pull_request_read:get_review_comments`
+- `pull_request_read:get_reviews`
 
 ## i18n / Overriding Descriptions
 

cmd/github-mcp-server/generate_docs.go

@@ -10,6 +10,7 @@ import (
 	"strings"
 
 	"github.com/github/github-mcp-server/pkg/github"
+	"github.com/github/github-mcp-server/pkg/lockdown"
 	"github.com/github/github-mcp-server/pkg/raw"
 	"github.com/github/github-mcp-server/pkg/toolsets"
 	"github.com/github/github-mcp-server/pkg/translations"
@@ -64,7 +65,8 @@ func generateReadmeDocs(readmePath string) error {
 	t, _ := translations.TranslationHelper()
 
 	// Create toolset group with mock clients
-	tsg := github.DefaultToolsetGroup(false, mockGetClient, mockGetGQLClient, mockGetRawClient, t, 5000, github.FeatureFlags{})
+	repoAccessCache := lockdown.GetInstance(nil)
+	tsg := github.DefaultToolsetGroup(false, mockGetClient, mockGetGQLClient, mockGetRawClient, t, 5000, github.FeatureFlags{}, repoAccessCache)
 
 	// Generate toolsets documentation
 	toolsetsDoc := generateToolsetsDoc(tsg)
@@ -302,7 +304,8 @@ func generateRemoteToolsetsDoc() string {
 	t, _ := translations.TranslationHelper()
 
 	// Create toolset group with mock clients
-	tsg := github.DefaultToolsetGroup(false, mockGetClient, mockGetGQLClient, mockGetRawClient, t, 5000, github.FeatureFlags{})
+	repoAccessCache := lockdown.GetInstance(nil)
+	tsg := github.DefaultToolsetGroup(false, mockGetClient, mockGetGQLClient, mockGetRawClient, t, 5000, github.FeatureFlags{}, repoAccessCache)
 
 	// Generate table header
 	buf.WriteString("| Name           | Description                                      | API URL                                               | 1-Click Install (VS Code)                                                                                                                                                                                                 | Read-only Link                                                                                                 | 1-Click Read-only Install (VS Code)                                                                                                                                                                                                 |\n")

cmd/github-mcp-server/main.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"os"
 	"strings"
+	"time"
 
 	"github.com/github/github-mcp-server/internal/ghmcp"
 	"github.com/github/github-mcp-server/pkg/github"
@@ -50,6 +51,7 @@ var (
 				enabledToolsets = []string{github.ToolsetMetadataDefault.ID}
 			}
 
+			ttl := viper.GetDuration("repo-access-cache-ttl")
 			stdioServerConfig := ghmcp.StdioServerConfig{
 				Version:              version,
 				Host:                 viper.GetString("host"),
@@ -62,6 +64,7 @@ var (
 				LogFilePath:          viper.GetString("log-file"),
 				ContentWindowSize:    viper.GetInt("content-window-size"),
 				LockdownMode:         viper.GetBool("lockdown-mode"),
+				RepoAccessCacheTTL:   &ttl,
 			}
 			return ghmcp.RunStdioServer(stdioServerConfig)
 		},
@@ -84,6 +87,7 @@ func init() {
 	rootCmd.PersistentFlags().String("gh-host", "", "Specify the GitHub hostname (for GitHub Enterprise etc.)")
 	rootCmd.PersistentFlags().Int("content-window-size", 5000, "Specify the content window size")
 	rootCmd.PersistentFlags().Bool("lockdown-mode", false, "Enable lockdown mode")
+	rootCmd.PersistentFlags().Duration("repo-access-cache-ttl", 5*time.Minute, "Override the repo access cache TTL (e.g. 1m, 0s to disable)")
 
 	// Bind flag to viper
 	_ = viper.BindPFlag("toolsets", rootCmd.PersistentFlags().Lookup("toolsets"))
@@ -95,6 +99,7 @@ func init() {
 	_ = viper.BindPFlag("host", rootCmd.PersistentFlags().Lookup("gh-host"))
 	_ = viper.BindPFlag("content-window-size", rootCmd.PersistentFlags().Lookup("content-window-size"))
 	_ = viper.BindPFlag("lockdown-mode", rootCmd.PersistentFlags().Lookup("lockdown-mode"))
+	_ = viper.BindPFlag("repo-access-cache-ttl", rootCmd.PersistentFlags().Lookup("repo-access-cache-ttl"))
 
 	// Add subcommands
 	rootCmd.AddCommand(stdioCmd)

go.mod

@@ -8,6 +8,7 @@ require (
 	github.com/mark3labs/mcp-go v0.36.0
 	github.com/microcosm-cc/bluemonday v1.0.27
 	github.com/migueleliasweb/go-github-mock v1.3.0
+	github.com/muesli/cache2go v0.0.0-20221011235721-518229cd8021
 	github.com/spf13/cobra v1.10.1
 	github.com/spf13/viper v1.21.0
 	github.com/stretchr/testify v1.11.1
@@ -37,7 +38,7 @@ require (
 	github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc // indirect
 	github.com/fsnotify/fsnotify v1.9.0 // indirect
 	github.com/go-viper/mapstructure/v2 v2.4.0
-	github.com/google/go-querystring v1.1.0
+	github.com/google/go-querystring v1.1.0 // indirect
 	github.com/google/uuid v1.6.0 // indirect
 	github.com/inconshreveable/mousetrap v1.1.0 // indirect
 	github.com/pelletier/go-toml/v2 v2.2.4 // indirect

go.sum

@@ -63,6 +63,8 @@ github.com/microcosm-cc/bluemonday v1.0.27 h1:MpEUotklkwCSLeH+Qdx1VJgNqLlpY2KXwX
 github.com/microcosm-cc/bluemonday v1.0.27/go.mod h1:jFi9vgW+H7c3V0lb6nR74Ib/DIB5OBs92Dimizgw2cA=
 github.com/migueleliasweb/go-github-mock v1.3.0 h1:2sVP9JEMB2ubQw1IKto3/fzF51oFC6eVWOOFDgQoq88=
 github.com/migueleliasweb/go-github-mock v1.3.0/go.mod h1:ipQhV8fTcj/G6m7BKzin08GaJ/3B5/SonRAkgrk0zCY=
+github.com/muesli/cache2go v0.0.0-20221011235721-518229cd8021 h1:31Y+Yu373ymebRdJN1cWLLooHH8xAr0MhKTEJGV/87g=
+github.com/muesli/cache2go v0.0.0-20221011235721-518229cd8021/go.mod h1:WERUkUryfUWlrHnFSO/BEUZ+7Ns8aZy7iVOGewxKzcc=
 github.com/niemeyer/pretty v0.0.0-20200227124842-a10e7caefd8e/go.mod h1:zD1mROLANZcx1PVRCS0qkT7pwLkGfwJo4zjcN/Tysno=
 github.com/pelletier/go-toml/v2 v2.2.4 h1:mye9XuhQ6gvn5h28+VilKrrPoQVanw5PMw/TB0t5Ec4=
 github.com/pelletier/go-toml/v2 v2.2.4/go.mod h1:2gIqNv+qfxSVS7cM2xJQKtLSTLUE9V8t9Stt+h56mCY=

internal/ghmcp/server.go

@@ -16,6 +16,7 @@ import (
 
 	"github.com/github/github-mcp-server/pkg/errors"
 	"github.com/github/github-mcp-server/pkg/github"
+	"github.com/github/github-mcp-server/pkg/lockdown"
 	mcplog "github.com/github/github-mcp-server/pkg/log"
 	"github.com/github/github-mcp-server/pkg/raw"
 	"github.com/github/github-mcp-server/pkg/translations"
@@ -54,6 +55,9 @@ type MCPServerConfig struct {
 
 	// LockdownMode indicates if we should enable lockdown mode
 	LockdownMode bool
+
+	// RepoAccessTTL overrides the default TTL for repository access cache entries.
+	RepoAccessTTL *time.Duration
 }
 
 const stdioServerLogPrefix = "stdioserver"
@@ -80,6 +84,14 @@ func NewMCPServer(cfg MCPServerConfig) (*server.MCPServer, error) {
 		},
 	} // We're going to wrap the Transport later in beforeInit
 	gqlClient := githubv4.NewEnterpriseClient(apiHost.graphqlURL.String(), gqlHTTPClient)
+	repoAccessOpts := []lockdown.RepoAccessOption{}
+	if cfg.RepoAccessTTL != nil {
+		repoAccessOpts = append(repoAccessOpts, lockdown.WithTTL(*cfg.RepoAccessTTL))
+	}
+	var repoAccessCache *lockdown.RepoAccessCache
+	if cfg.LockdownMode {
+		repoAccessCache = lockdown.GetInstance(gqlClient, repoAccessOpts...)
+	}
 
 	// When a client send an initialize request, update the user agent to include the client info.
 	beforeInit := func(_ context.Context, _ any, message *mcp.InitializeRequest) {
@@ -165,6 +177,7 @@ func NewMCPServer(cfg MCPServerConfig) (*server.MCPServer, error) {
 		cfg.Translator,
 		cfg.ContentWindowSize,
 		github.FeatureFlags{LockdownMode: cfg.LockdownMode},
+		repoAccessCache,
 	)
 	err = tsg.EnableToolsets(enabledToolsets, nil)
 
@@ -219,6 +232,9 @@ type StdioServerConfig struct {
 
 	// LockdownMode indicates if we should enable lockdown mode
 	LockdownMode bool
+
+	// RepoAccessCacheTTL overrides the default TTL for repository access cache entries.
+	RepoAccessCacheTTL *time.Duration
 }
 
 // RunStdioServer is not concurrent safe.
@@ -229,23 +245,6 @@ func RunStdioServer(cfg StdioServerConfig) error {
 
 	t, dumpTranslations := translations.TranslationHelper()
 
-	ghServer, err := NewMCPServer(MCPServerConfig{
-		Version:           cfg.Version,
-		Host:              cfg.Host,
-		Token:             cfg.Token,
-		EnabledToolsets:   cfg.EnabledToolsets,
-		DynamicToolsets:   cfg.DynamicToolsets,
-		ReadOnly:          cfg.ReadOnly,
-		Translator:        t,
-		ContentWindowSize: cfg.ContentWindowSize,
-		LockdownMode:      cfg.LockdownMode,
-	})
-	if err != nil {
-		return fmt.Errorf("failed to create MCP server: %w", err)
-	}
-
-	stdioServer := server.NewStdioServer(ghServer)
-
 	var slogHandler slog.Handler
 	var logOutput io.Writer
 	if cfg.LogFilePath != "" {
@@ -262,6 +261,24 @@ func RunStdioServer(cfg StdioServerConfig) error {
 	logger := slog.New(slogHandler)
 	logger.Info("starting server", "version", cfg.Version, "host", cfg.Host, "dynamicToolsets", cfg.DynamicToolsets, "readOnly", cfg.ReadOnly, "lockdownEnabled", cfg.LockdownMode)
 	stdLogger := log.New(logOutput, stdioServerLogPrefix, 0)
+
+	ghServer, err := NewMCPServer(MCPServerConfig{
+		Version:           cfg.Version,
+		Host:              cfg.Host,
+		Token:             cfg.Token,
+		EnabledToolsets:   cfg.EnabledToolsets,
+		DynamicToolsets:   cfg.DynamicToolsets,
+		ReadOnly:          cfg.ReadOnly,
+		Translator:        t,
+		ContentWindowSize: cfg.ContentWindowSize,
+		LockdownMode:      cfg.LockdownMode,
+		RepoAccessTTL:     cfg.RepoAccessCacheTTL,
+	})
+	if err != nil {
+		return fmt.Errorf("failed to create MCP server: %w", err)
+	}
+
+	stdioServer := server.NewStdioServer(ghServer)
 	stdioServer.SetErrorLogger(stdLogger)
 
 	if cfg.ExportTranslations {

pkg/github/issues.go

@@ -228,7 +228,7 @@ func fragmentToIssue(fragment IssueFragment) *github.Issue {
 }
 
 // GetIssue creates a tool to get details of a specific issue in a GitHub repository.
-func IssueRead(getClient GetClientFn, getGQLClient GetGQLClientFn, t translations.TranslationHelperFunc, flags FeatureFlags) (tool mcp.Tool, handler server.ToolHandlerFunc) {
+func IssueRead(getClient GetClientFn, getGQLClient GetGQLClientFn, cache *lockdown.RepoAccessCache, t translations.TranslationHelperFunc, flags FeatureFlags) (tool mcp.Tool, handler server.ToolHandlerFunc) {
 	return mcp.NewTool("issue_read",
 			mcp.WithDescription(t("TOOL_ISSUE_READ_DESCRIPTION", "Get information about a specific issue in a GitHub repository.")),
 			mcp.WithToolAnnotation(mcp.ToolAnnotation{
@@ -297,20 +297,20 @@ Options are:
 
 			switch method {
 			case "get":
-				return GetIssue(ctx, client, gqlClient, owner, repo, issueNumber, flags)
+				return GetIssue(ctx, client, cache, owner, repo, issueNumber, flags)
 			case "get_comments":
-				return GetIssueComments(ctx, client, owner, repo, issueNumber, pagination, flags)
+				return GetIssueComments(ctx, client, cache, owner, repo, issueNumber, pagination, flags)
 			case "get_sub_issues":
-				return GetSubIssues(ctx, client, owner, repo, issueNumber, pagination, flags)
+				return GetSubIssues(ctx, client, cache, owner, repo, issueNumber, pagination, flags)
 			case "get_labels":
-				return GetIssueLabels(ctx, gqlClient, owner, repo, issueNumber, flags)
+				return GetIssueLabels(ctx, gqlClient, owner, repo, issueNumber)
 			default:
 				return mcp.NewToolResultError(fmt.Sprintf("unknown method: %s", method)), nil
 			}
 		}
 }
 
-func GetIssue(ctx context.Context, client *github.Client, gqlClient *githubv4.Client, owner string, repo string, issueNumber int, flags FeatureFlags) (*mcp.CallToolResult, error) {
+func GetIssue(ctx context.Context, client *github.Client, cache *lockdown.RepoAccessCache, owner string, repo string, issueNumber int, flags FeatureFlags) (*mcp.CallToolResult, error) {
 	issue, resp, err := client.Issues.Get(ctx, owner, repo, issueNumber)
 	if err != nil {
 		return nil, fmt.Errorf("failed to get issue: %w", err)
@@ -326,12 +326,16 @@ func GetIssue(ctx context.Context, client *github.Client, gqlClient *githubv4.Cl
 	}
 
 	if flags.LockdownMode {
-		if issue.User != nil {
-			shouldRemoveContent, err := lockdown.ShouldRemoveContent(ctx, gqlClient, *issue.User.Login, owner, repo)
+		if cache == nil {
+			return nil, fmt.Errorf("lockdown cache is not configured")
+		}
+		login := issue.GetUser().GetLogin()
+		if login != "" {
+			isSafeContent, err := cache.IsSafeContent(ctx, login, owner, repo)
 			if err != nil {
 				return mcp.NewToolResultError(fmt.Sprintf("failed to check lockdown mode: %v", err)), nil
 			}
-			if shouldRemoveContent {
+			if !isSafeContent {
 				return mcp.NewToolResultError("access to issue details is restricted by lockdown mode"), nil
 			}
 		}
@@ -355,7 +359,7 @@ func GetIssue(ctx context.Context, client *github.Client, gqlClient *githubv4.Cl
 	return mcp.NewToolResultText(string(r)), nil
 }
 
-func GetIssueComments(ctx context.Context, client *github.Client, owner string, repo string, issueNumber int, pagination PaginationParams, _ FeatureFlags) (*mcp.CallToolResult, error) {
+func GetIssueComments(ctx context.Context, client *github.Client, cache *lockdown.RepoAccessCache, owner string, repo string, issueNumber int, pagination PaginationParams, flags FeatureFlags) (*mcp.CallToolResult, error) {
 	opts := &github.IssueListCommentsOptions{
 		ListOptions: github.ListOptions{
 			Page:    pagination.Page,
@@ -376,6 +380,30 @@ func GetIssueComments(ctx context.Context, client *github.Client, owner string,
 		}
 		return mcp.NewToolResultError(fmt.Sprintf("failed to get issue comments: %s", string(body))), nil
 	}
+	if flags.LockdownMode {
+		if cache == nil {
+			return nil, fmt.Errorf("lockdown cache is not configured")
+		}
+		filteredComments := make([]*github.IssueComment, 0, len(comments))
+		for _, comment := range comments {
+			user := comment.User
+			if user == nil {
+				continue
+			}
+			login := user.GetLogin()
+			if login == "" {
+				continue
+			}
+			isSafeContent, err := cache.IsSafeContent(ctx, login, owner, repo)
+			if err != nil {
+				return mcp.NewToolResultError(fmt.Sprintf("failed to check lockdown mode: %v", err)), nil
+			}
+			if isSafeContent {
+				filteredComments = append(filteredComments, comment)
+			}
+		}
+		comments = filteredComments
+	}
 
 	r, err := json.Marshal(comments)
 	if err != nil {
@@ -385,7 +413,7 @@ func GetIssueComments(ctx context.Context, client *github.Client, owner string,
 	return mcp.NewToolResultText(string(r)), nil
 }
 
-func GetSubIssues(ctx context.Context, client *github.Client, owner string, repo string, issueNumber int, pagination PaginationParams, _ FeatureFlags) (*mcp.CallToolResult, error) {
+func GetSubIssues(ctx context.Context, client *github.Client, cache *lockdown.RepoAccessCache, owner string, repo string, issueNumber int, pagination PaginationParams, featureFlags FeatureFlags) (*mcp.CallToolResult, error) {
 	opts := &github.IssueListOptions{
 		ListOptions: github.ListOptions{
 			Page:    pagination.Page,
@@ -412,6 +440,31 @@ func GetSubIssues(ctx context.Context, client *github.Client, owner string, repo
 		return mcp.NewToolResultError(fmt.Sprintf("failed to list sub-issues: %s", string(body))), nil
 	}
 
+	if featureFlags.LockdownMode {
+		if cache == nil {
+			return nil, fmt.Errorf("lockdown cache is not configured")
+		}
+		filteredSubIssues := make([]*github.SubIssue, 0, len(subIssues))
+		for _, subIssue := range subIssues {
+			user := subIssue.User
+			if user == nil {
+				continue
+			}
+			login := user.GetLogin()
+			if login == "" {
+				continue
+			}
+			isSafeContent, err := cache.IsSafeContent(ctx, login, owner, repo)
+			if err != nil {
+				return mcp.NewToolResultError(fmt.Sprintf("failed to check lockdown mode: %v", err)), nil
+			}
+			if isSafeContent {
+				filteredSubIssues = append(filteredSubIssues, subIssue)
+			}
+		}
+		subIssues = filteredSubIssues
+	}
+
 	r, err := json.Marshal(subIssues)
 	if err != nil {
 		return nil, fmt.Errorf("failed to marshal response: %w", err)
@@ -420,7 +473,7 @@ func GetSubIssues(ctx context.Context, client *github.Client, owner string, repo
 	return mcp.NewToolResultText(string(r)), nil
 }
 
-func GetIssueLabels(ctx context.Context, client *githubv4.Client, owner string, repo string, issueNumber int, _ FeatureFlags) (*mcp.CallToolResult, error) {
+func GetIssueLabels(ctx context.Context, client *githubv4.Client, owner string, repo string, issueNumber int) (*mcp.CallToolResult, error) {
 	// Get current labels on the issue using GraphQL
 	var query struct {
 		Repository struct {