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Migrate MCP Apps support from insiders mode to feature flag with insiders opt-in #2335
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Apr 16, 2026
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -1,7 +1,56 @@ | ||
| package github | ||
|
|
||
| // MCPAppsFeatureFlag is the feature flag name for MCP Apps (interactive UI forms). | ||
| const MCPAppsFeatureFlag = "remote_mcp_ui_apps" | ||
|
|
||
| // AllowedFeatureFlags is the allowlist of feature flags that can be enabled | ||
| // by users via --features CLI flag or X-MCP-Features HTTP header. | ||
| // Only flags in this list are accepted; unknown flags are silently ignored. | ||
| // This is the single source of truth for which flags are user-controllable. | ||
| var AllowedFeatureFlags = []string{ | ||
| MCPAppsFeatureFlag, | ||
| FeatureFlagIssuesGranular, | ||
| FeatureFlagPullRequestsGranular, | ||
| } | ||
|
|
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| // InsidersFeatureFlags is the list of feature flags that insiders mode enables. | ||
| // When insiders mode is active, all flags in this list are treated as enabled. | ||
| // This is the single source of truth for what "insiders" means in terms of | ||
| // feature flag expansion. | ||
| var InsidersFeatureFlags = []string{ | ||
| MCPAppsFeatureFlag, | ||
| } | ||
|
|
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| // FeatureFlags defines runtime feature toggles that adjust tool behavior. | ||
| type FeatureFlags struct { | ||
| LockdownMode bool | ||
| InsidersMode bool | ||
| } | ||
|
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| // ResolveFeatureFlags computes the effective set of enabled feature flags by: | ||
| // 1. Taking explicitly enabled features (from CLI flags or HTTP headers) | ||
| // 2. Adding insiders-expanded features when insiders mode is active | ||
| // 3. Validating all features against the AllowedFeatureFlags allowlist | ||
| // | ||
| // Returns a set (map) for O(1) lookup by the feature checker. | ||
| func ResolveFeatureFlags(enabledFeatures []string, insidersMode bool) map[string]bool { | ||
| allowed := make(map[string]bool, len(AllowedFeatureFlags)) | ||
| for _, f := range AllowedFeatureFlags { | ||
| allowed[f] = true | ||
| } | ||
|
|
||
| effective := make(map[string]bool) | ||
| for _, f := range enabledFeatures { | ||
| if allowed[f] { | ||
| effective[f] = true | ||
| } | ||
| } | ||
| if insidersMode { | ||
| for _, f := range InsidersFeatureFlags { | ||
| if allowed[f] { | ||
| effective[f] = true | ||
| } | ||
| } | ||
| } | ||
| return effective | ||
| } | ||
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
|
|
@@ -8,7 +8,6 @@ import ( | |
| "net/http" | ||
| "os" | ||
| "os/signal" | ||
| "slices" | ||
| "syscall" | ||
| "time" | ||
|
|
||
|
|
@@ -25,10 +24,6 @@ import ( | |
| "github.com/go-chi/chi/v5" | ||
| ) | ||
|
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| // knownFeatureFlags are the feature flags that can be enabled via X-MCP-Features header. | ||
| // Only these flags are accepted from headers. | ||
| var knownFeatureFlags = github.HeaderAllowedFeatureFlags() | ||
|
|
||
| type ServerConfig struct { | ||
| // Version of the server | ||
| Version string | ||
|
|
@@ -233,19 +228,14 @@ func initGlobalToolScopeMap(t translations.TranslationHelperFunc) error { | |
| return nil | ||
| } | ||
|
|
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| // createHTTPFeatureChecker creates a feature checker that reads header features from context | ||
| // and validates them against the knownFeatureFlags whitelist | ||
| // createHTTPFeatureChecker creates a feature checker that resolves features | ||
| // per-request by reading header features and insiders mode from context, | ||
| // then validating against the centralized AllowedFeatureFlags allowlist. | ||
| func createHTTPFeatureChecker() inventory.FeatureFlagChecker { | ||
| // Pre-compute whitelist as set for O(1) lookup | ||
| knownSet := make(map[string]bool, len(knownFeatureFlags)) | ||
| for _, f := range knownFeatureFlags { | ||
| knownSet[f] = true | ||
| } | ||
|
|
||
| return func(ctx context.Context, flag string) (bool, error) { | ||
| if knownSet[flag] && slices.Contains(ghcontext.GetHeaderFeatures(ctx), flag) { | ||
| return true, nil | ||
| } | ||
| return false, nil | ||
| headerFeatures := ghcontext.GetHeaderFeatures(ctx) | ||
| insidersMode := ghcontext.IsInsidersMode(ctx) | ||
| effective := github.ResolveFeatureFlags(headerFeatures, insidersMode) | ||
| return effective[flag], nil | ||
| } | ||
|
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| } | ||
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AllowedFeatureFlags is exported as a mutable slice variable. External callers can accidentally append/modify it, which can lead to hard-to-debug behavior changes and potential data races in concurrent programs. Consider making the underlying allowlist unexported and exposing an exported function that returns a cloned slice (similar to HeaderAllowedFeatureFlags), or otherwise ensuring callers cannot mutate the shared backing array.