Set the request-body limit to 5 MiB at both layers

Bounds the total HTTP request, so allow modest headroom over the MCP
SDK's 4 MiB default for JSON-RPC and tool-call envelope overhead rather
than spending the whole budget on tool content.

Because the limit now exceeds the SDK default, passing it to
StreamableHTTPOptions is load-bearing: without it the SDK would cap
requests at 4 MiB and the headroom would not exist. Covered by a test
that sends a request between the two limits.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Author: SamMorrowDrums

pkg/http/handler.go

@@ -250,8 +250,8 @@ func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		return ghServer
 	}, &mcp.StreamableHTTPOptions{
 		Stateless: true,
-		// Keep the SDK's own guard in step with the middleware, otherwise its
-		// default would silently cap a larger configured limit.
+		// Required, not just belt-and-braces: the effective limit exceeds the
+		// SDK's own default, which would otherwise cap it.
 		MaxRequestBodyBytes: h.maxRequestBodyBytes(),
 	})
 

pkg/http/handler_test.go

@@ -15,6 +15,7 @@ import (
 	ghcontext "github.com/github/github-mcp-server/pkg/context"
 	"github.com/github/github-mcp-server/pkg/github"
 	"github.com/github/github-mcp-server/pkg/http/headers"
+	"github.com/github/github-mcp-server/pkg/http/middleware"
 	"github.com/github/github-mcp-server/pkg/inventory"
 	"github.com/github/github-mcp-server/pkg/scopes"
 	"github.com/github/github-mcp-server/pkg/translations"
@@ -1289,12 +1290,16 @@ func TestUIMetaStrippedWhenClientLacksCapability(t *testing.T) {
 	require.NotNil(t, unknown[0].Tool.Meta["ui"], "_meta.ui should be preserved when capability is unknown and FF is on")
 }
 
-// TestMaxRequestBodyBytes checks the effective limit tracks the MCP SDK
-// default and honours an operator override.
+// TestMaxRequestBodyBytes checks the effective limit and, critically, that it
+// sits above the MCP SDK default — which is why it must also be passed to
+// StreamableHTTPOptions rather than left to the SDK.
 func TestMaxRequestBodyBytes(t *testing.T) {
-	t.Run("defaults to the MCP SDK limit", func(t *testing.T) {
+	t.Run("default leaves headroom above the MCP SDK limit", func(t *testing.T) {
 		h := &Handler{config: &ServerConfig{}}
-		assert.Equal(t, int64(mcp.DefaultMaxRequestBodyBytes), h.maxRequestBodyBytes())
+
+		assert.Equal(t, int64(5<<20), h.maxRequestBodyBytes())
+		assert.Greater(t, h.maxRequestBodyBytes(), int64(mcp.DefaultMaxRequestBodyBytes),
+			"the default intentionally exceeds the SDK limit, so the SDK must be told about it")
 	})
 
 	t.Run("configured value overrides the default", func(t *testing.T) {
@@ -1320,11 +1325,11 @@ func TestMaxRequestBodySizeEnforcement(t *testing.T) {
 		return strings.Replace(payload, "PADDING", "PADDING"+pad, 1)
 	}
 
-	newHandler := func(t *testing.T, mcpServerFactoryCalled *bool) *Handler {
+	newHandler := func(t *testing.T, maxBytes int64, mcpServerFactoryCalled *bool) *Handler {
 		t.Helper()
 		return NewHTTPMcpHandler(
 			context.Background(),
-			&ServerConfig{Version: "test", MaxRequestBodyBytes: limit},
+			&ServerConfig{Version: "test", MaxRequestBodyBytes: maxBytes},
 			nil,
 			translations.NullTranslationHelper,
 			slog.Default(),
@@ -1359,7 +1364,7 @@ func TestMaxRequestBodySizeEnforcement(t *testing.T) {
 
 	t.Run("middleware rejects an oversized request before the MCP server is built", func(t *testing.T) {
 		var mcpServerFactoryCalled bool
-		r := newRouter(newHandler(t, &mcpServerFactoryCalled))
+		r := newRouter(newHandler(t, limit, &mcpServerFactoryCalled))
 
 		body := buildBody(limit + 1)
 		require.Greater(t, len(body), limit)
@@ -1374,7 +1379,7 @@ func TestMaxRequestBodySizeEnforcement(t *testing.T) {
 
 	t.Run("request at the configured limit succeeds", func(t *testing.T) {
 		var mcpServerFactoryCalled bool
-		r := newRouter(newHandler(t, &mcpServerFactoryCalled))
+		r := newRouter(newHandler(t, limit, &mcpServerFactoryCalled))
 
 		body := buildBody(limit)
 		require.Len(t, body, limit)
@@ -1387,7 +1392,7 @@ func TestMaxRequestBodySizeEnforcement(t *testing.T) {
 	})
 
 	t.Run("SDK handler enforces the configured limit when the middleware is bypassed", func(t *testing.T) {
-		h := newHandler(t, nil)
+		h := newHandler(t, limit, nil)
 
 		body := buildBody(limit + 1)
 		require.Greater(t, len(body), limit)
@@ -1399,4 +1404,21 @@ func TestMaxRequestBodySizeEnforcement(t *testing.T) {
 		assert.Contains(t, rr.Body.String(), fmt.Sprintf("request body exceeds %d bytes", limit),
 			"the SDK should report the configured limit, not its own default")
 	})
+
+	// The default headroom only exists if it reaches the SDK as well; leaving
+	// the SDK on its own default would silently reject this request.
+	t.Run("unconfigured handler accepts a request above the MCP SDK limit", func(t *testing.T) {
+		var mcpServerFactoryCalled bool
+		r := newRouter(newHandler(t, 0, &mcpServerFactoryCalled))
+
+		body := buildBody(mcp.DefaultMaxRequestBodyBytes + 1024)
+		require.Greater(t, int64(len(body)), int64(mcp.DefaultMaxRequestBodyBytes))
+		require.Less(t, int64(len(body)), middleware.DefaultMaxRequestBodyBytes)
+
+		rr := httptest.NewRecorder()
+		r.ServeHTTP(rr, newRequest(body))
+
+		assert.Equal(t, http.StatusOK, rr.Code, "response body: %s", rr.Body.String())
+		assert.True(t, mcpServerFactoryCalled, "the MCP server should be constructed for an allowed request")
+	})
 }

pkg/http/middleware/body_limit.go

@@ -3,13 +3,13 @@ package middleware
 import (
 	"errors"
 	"net/http"
-
-	"github.com/modelcontextprotocol/go-sdk/mcp"
 )
 
-// DefaultMaxRequestBodyBytes tracks the MCP SDK's own request-body limit, so
-// enforcing it earlier in the chain does not change which requests are accepted.
-const DefaultMaxRequestBodyBytes int64 = mcp.DefaultMaxRequestBodyBytes
+// DefaultMaxRequestBodyBytes bounds the total HTTP request, not just the tool
+// payload within it. It sits modestly above the MCP SDK's own default to leave
+// room for JSON-RPC and tool-call envelope overhead; because it is the larger
+// of the two, callers must also pass it to the SDK or the SDK would cap it.
+const DefaultMaxRequestBodyBytes int64 = 5 << 20 // 5 MiB
 
 // WithMaxBodySize bounds the size of the request body. It must be registered
 // before any middleware that reads or buffers the body (WithMCPParse,