fix(get_file_contents): keep modern-protocol results under 1 MiB

Author: severus0044

pkg/github/repositories.go

@@ -12,6 +12,7 @@ import (
 	"strings"
 	"time"
 
+	ghcontext "github.com/github/github-mcp-server/v2/pkg/context"
 	ghErrors "github.com/github/github-mcp-server/v2/pkg/errors"
 	"github.com/github/github-mcp-server/v2/pkg/ifc"
 	"github.com/github/github-mcp-server/v2/pkg/inventory"
@@ -1103,6 +1104,16 @@ func GetFileContents(t translations.TranslationHelperFunc) inventory.ServerTool
 				}
 				const maxContentSize = 1024 * 1024 // 1MB
 
+				// From protocol 2026-07-28 on, the MCP SDK mirrors the file body in
+				// structuredContent, so an inlined file takes roughly twice its size
+				// in the encoded result. Halve the inline budget there so a file that
+				// fits the old limit does not push the whole result past common 1 MiB
+				// transport limits.
+				inlineContentLimit := maxContentSize
+				if info, ok := ghcontext.MCPMethod(ctx); ok && info.ProtocolVersion >= inventory.ProtocolVersionMultiRoundTrip {
+					inlineContentLimit = maxContentSize / 2
+				}
+
 				read, respInspect, err := inspectRepositoryFile(ctx, client, owner, repo, ref, path, fileContent)
 				if err != nil {
 					if respInspect != nil {
@@ -1134,7 +1145,7 @@ func GetFileContents(t translations.TranslationHelperFunc) inventory.ServerTool
 				}
 
 				// For files >= 1MB, return a ResourceLink instead of content
-				if fileSize >= maxContentSize {
+				if fileSize >= inlineContentLimit {
 					size := int64(fileSize)
 					resourceLink := &mcp.ResourceLink{
 						URI:   resourceURI,

pkg/github/repositories_test.go

@@ -13,6 +13,7 @@ import (
 	"github.com/github/github-mcp-server/v2/internal/githubv4mock"
 	"github.com/github/github-mcp-server/v2/internal/requeststate"
 	"github.com/github/github-mcp-server/v2/internal/toolsnaps"
+	ghcontext "github.com/github/github-mcp-server/v2/pkg/context"
 	"github.com/github/github-mcp-server/v2/pkg/inventory"
 	"github.com/github/github-mcp-server/v2/pkg/raw"
 	"github.com/github/github-mcp-server/v2/pkg/translations"
@@ -40,6 +41,7 @@ type repositoryReadFixture struct {
 	blobs    map[string][]byte
 	trees    map[string]*github.Tree
 	inspect  func(*http.Request)
+	ctx      context.Context
 }
 
 func runRepositoryReadFixture(t *testing.T, fixture repositoryReadFixture, args map[string]any) (*mcp.CallToolResult, int) {
@@ -73,7 +75,11 @@ func runRepositoryReadFixture(t *testing.T, fixture repositoryReadFixture, args
 	tool := GetFileContents(translations.NullTranslationHelper)
 	handler := tool.Handler(deps)
 	request := createMCPRequest(args)
-	result, err := handler(ContextWithDeps(context.Background(), deps), &request)
+	ctx := fixture.ctx
+	if ctx == nil {
+		ctx = context.Background()
+	}
+	result, err := handler(ContextWithDeps(ctx, deps), &request)
 	require.NoError(t, err)
 	return result, counter.count
 }
@@ -772,6 +778,39 @@ func Test_GetFileContents_SymlinkDisclosure(t *testing.T) {
 	})
 }
 
+func Test_GetFileContents_ModernProtocolInlineLimit(t *testing.T) {
+	commitSHA := strings.Repeat("c", 40)
+	content := strings.Repeat("a", 600*1024)
+	encoded := base64.StdEncoding.EncodeToString([]byte(content))
+	fileSHA := gitBlobSHA([]byte(content))
+	args := map[string]any{"owner": "owner", "repo": "repo", "path": "medium.txt", "sha": commitSHA}
+
+	fixture := repositoryReadFixture{
+		contents: &github.RepositoryContent{
+			Type: new("file"), Path: new("medium.txt"), SHA: new(fileSHA), Size: new(len(content)),
+			Content: new(encoded), Encoding: new("base64"),
+		},
+	}
+
+	t.Run("legacy protocol inlines the file", func(t *testing.T) {
+		result, _ := runRepositoryReadFixture(t, fixture, args)
+		require.False(t, result.IsError)
+		_, ok := result.Content[1].(*mcp.EmbeddedResource)
+		require.True(t, ok, "expected an inline resource on the legacy protocol")
+	})
+
+	t.Run("modern protocol returns a ResourceLink", func(t *testing.T) {
+		modern := fixture
+		modern.ctx = ghcontext.WithMCPMethodInfo(context.Background(), &ghcontext.MCPMethodInfo{
+			ProtocolVersion: inventory.ProtocolVersionMultiRoundTrip,
+		})
+		result, _ := runRepositoryReadFixture(t, modern, args)
+		require.False(t, result.IsError)
+		_, ok := result.Content[1].(*mcp.ResourceLink)
+		require.True(t, ok, "expected a ResourceLink on the modern protocol")
+	})
+}
+
 func Test_GetFileContents_ContentlessRequestCounts(t *testing.T) {
 	commitSHA := strings.Repeat("c", 40)
 	fileSHA := strings.Repeat("a", 40)