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Support MCP protocol negotiation for 2025-06-18 and 2025-03-26 #7

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1 change: 0 additions & 1 deletion src/main.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -78,7 +78,6 @@ int main(int argc, char* argv[])
json response;
if(msg.is_array())
{
// JSON-RPC batch
if(msg.empty())
{
json errorResp;
Expand Down
68 changes: 50 additions & 18 deletions src/mcp/mcp_server.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -50,7 +50,7 @@ json McpServer::makeError(const json& id, int code, const std::string& message)
return resp;
}

json McpServer::makeToolResult(const json& data, bool isError)
json McpServer::makeToolResult(const json& data, bool isError) const
{
json result;
json content;
Expand All @@ -62,11 +62,39 @@ json McpServer::makeToolResult(const json& data, bool isError)
content["text"] = data.dump();

result["content"] = json::array({content});
if(m_protocolVersion == ProtocolVersion::V2025_06_18 && !isError && data.is_object())
result["structuredContent"] = data;
if(isError)
result["isError"] = true;
return result;
}

ProtocolVersion McpServer::negotiateProtocolVersion(const json& params)
{
if(params.contains("protocolVersion"))
{
const auto clientVersion = params["protocolVersion"].get<std::string>();
if(clientVersion == kProtocolVersion2025_03_26)
return ProtocolVersion::V2025_03_26;
if(clientVersion == kProtocolVersion2025_06_18)
return ProtocolVersion::V2025_06_18;
}

return ProtocolVersion::V2025_06_18;
}

const char* McpServer::protocolVersionString(ProtocolVersion version)
{
switch(version)
{
case ProtocolVersion::V2025_03_26:
return kProtocolVersion2025_03_26;
case ProtocolVersion::V2025_06_18:
return kProtocolVersion2025_06_18;
}
return kProtocolVersion;
}

// ── Message dispatch ────────────────────────────────────────────────────────

json McpServer::handleMessage(const json& msg)
Expand All @@ -80,9 +108,13 @@ json McpServer::handleMessage(const json& msg)
json id = msg.value("id", json(nullptr));

// Route methods
if(method == "initialize")
if(method == "ping")
{
if(m_initialized)
return makeResponse(id, json::object());
}
else if(method == "initialize")
{
if(m_initializeSeen)
return makeError(id, -32600, "Server already initialized");
return handleInitialize(msg);
}
Expand Down Expand Up @@ -112,11 +144,10 @@ json McpServer::handleMessage(const json& msg)

json McpServer::handleBatch(const json& arr)
{
// Check for initialize in batch (forbidden by MCP spec)
for(const auto& msg : arr)
if(!m_initializeSeen || m_protocolVersion == ProtocolVersion::V2025_06_18)
{
if(msg.is_object() && msg.value("method", "") == "initialize")
return makeError(nullptr, -32600, "Invalid Request: initialize must not appear in a JSON-RPC batch");
return makeError(nullptr, -32600,
"Invalid Request: JSON-RPC batching is not supported by the negotiated MCP protocol");
}

json responses = json::array();
Expand All @@ -127,12 +158,12 @@ json McpServer::handleBatch(const json& arr)
responses.push_back(makeError(nullptr, -32600, "Invalid Request: batch element is not an object"));
continue;
}

json resp = handleMessage(msg);
if(!resp.is_null())
responses.push_back(resp);
}

// If all were notifications, return nothing
if(responses.empty())
return nullptr;

Expand All @@ -145,24 +176,25 @@ json McpServer::handleInitialize(const json& msg)
{
json id = msg.value("id", json(nullptr));

// Validate client protocol version for compatibility
static constexpr const char* kSupportedProtocolVersion = "2025-03-26";
json params = msg.value("params", json::object());
if (params.contains("protocolVersion")) {
std::string clientVersion = params["protocolVersion"].get<std::string>();
if (clientVersion != kSupportedProtocolVersion) {
return makeError(id, -32602,
"Unsupported protocol version: " + clientVersion +
" (server supports " + kSupportedProtocolVersion + ")");
}
if(!params.is_object())
{
return makeError(id, -32602, "Invalid params: initialize params must be an object");
}
if(params.contains("protocolVersion") && !params["protocolVersion"].is_string())
{
return makeError(id, -32602, "Invalid params: protocolVersion must be a string");
}

m_protocolVersion = negotiateProtocolVersion(params);

json result;
result["protocolVersion"] = kSupportedProtocolVersion;
result["protocolVersion"] = protocolVersionString(m_protocolVersion);
result["capabilities"]["tools"] = json::object();
result["serverInfo"]["name"] = "renderdoc-mcp";
result["serverInfo"]["version"] = "1.0.0";

m_initializeSeen = true;
return makeResponse(id, result);
}

Expand Down
18 changes: 16 additions & 2 deletions src/mcp/mcp_server.h
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Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,16 @@ namespace renderdoc::core { class DiffSession; }

namespace renderdoc::mcp {

inline constexpr const char* kProtocolVersion2025_03_26 = "2025-03-26";
inline constexpr const char* kProtocolVersion2025_06_18 = "2025-06-18";
inline constexpr const char* kProtocolVersion = kProtocolVersion2025_06_18;

enum class ProtocolVersion
{
V2025_03_26,
V2025_06_18,
};

class McpServer
{
public:
Expand All @@ -21,7 +31,7 @@ class McpServer
// Process a single JSON-RPC message. Returns response JSON, or nullptr for notifications.
nlohmann::json handleMessage(const nlohmann::json& msg);

// Process a JSON-RPC batch (array). Returns response array.
// Process a JSON-RPC batch. Supported only after negotiating a batch-capable protocol.
nlohmann::json handleBatch(const nlohmann::json& arr);

void shutdown();
Expand All @@ -35,14 +45,18 @@ class McpServer
// JSON-RPC response helpers
static nlohmann::json makeResponse(const nlohmann::json& id, const nlohmann::json& result);
static nlohmann::json makeError(const nlohmann::json& id, int code, const std::string& message);
static nlohmann::json makeToolResult(const nlohmann::json& data, bool isError = false);
nlohmann::json makeToolResult(const nlohmann::json& data, bool isError = false) const;
static ProtocolVersion negotiateProtocolVersion(const nlohmann::json& params);
static const char* protocolVersionString(ProtocolVersion version);

std::unique_ptr<core::Session> m_ownedSession; // owned, only set by default ctor
core::Session* m_session = nullptr; // always valid (points to owned or injected)
std::unique_ptr<core::DiffSession> m_ownedDiffSession; // owned, only set by default ctor
core::DiffSession* m_diffSession = nullptr; // always valid (points to owned or injected)
std::unique_ptr<ToolRegistry> m_ownedRegistry; // owned, only set by default ctor
ToolRegistry* m_registry = nullptr; // always valid (points to owned or injected)
ProtocolVersion m_protocolVersion = ProtocolVersion::V2025_06_18;
bool m_initializeSeen = false;
bool m_initialized = false;
};

Expand Down
35 changes: 17 additions & 18 deletions tests/integration/test_protocol.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,8 @@
#include <chrono>
#include <thread>

#include "mcp/mcp_server.h"

#ifdef _WIN32
#include <windows.h>
#endif
Expand Down Expand Up @@ -250,7 +252,7 @@ class ProtocolTest : public ::testing::Test {
initReq["jsonrpc"] = "2.0";
initReq["id"] = 0;
initReq["method"] = "initialize";
initReq["params"]["protocolVersion"] = "2025-03-26";
initReq["params"]["protocolVersion"] = renderdoc::mcp::kProtocolVersion;
initReq["params"]["clientInfo"]["name"] = "test-runner";
initReq["params"]["clientInfo"]["version"] = "1.0.0";
initReq["params"]["capabilities"] = json::object();
Expand Down Expand Up @@ -326,6 +328,7 @@ TEST_F(ProtocolTest, InitializeHandshake)
auto& result = s_initResponse["result"];

EXPECT_TRUE(result.contains("protocolVersion"));
EXPECT_EQ(result["protocolVersion"], renderdoc::mcp::kProtocolVersion);
EXPECT_TRUE(result.contains("serverInfo"));
EXPECT_TRUE(result["serverInfo"].contains("name"));
EXPECT_EQ(result["serverInfo"]["name"], "renderdoc-mcp");
Expand Down Expand Up @@ -408,30 +411,26 @@ TEST_F(ProtocolTest, MethodNotFound_UnknownMethod)
EXPECT_EQ((*resp)["error"]["code"].get<int>(), -32601);
}

TEST_F(ProtocolTest, BatchRequest_ArrayResponse)
TEST_F(ProtocolTest, Ping_ReturnsEmptyResult)
{
auto req = makeRequest("ping");
auto resp = send(req);
ASSERT_TRUE(resp.has_value());
ASSERT_TRUE(resp->contains("result"));
EXPECT_TRUE((*resp)["result"].is_object());
EXPECT_TRUE((*resp)["result"].empty());
}

TEST_F(ProtocolTest, BatchRequest_Rejected)
{
json batch = json::array();
batch.push_back(makeRequest("tools/list", json::object(), 1));
batch.push_back(makeRequest("nonexistent/method", json::object(), 2));

auto resp = send(batch);
ASSERT_TRUE(resp.has_value());
ASSERT_TRUE(resp->is_array());
EXPECT_EQ(resp->size(), 2u);

// Find responses by id
bool foundToolsList = false;
bool foundMethodNotFound = false;
for (auto& r : *resp) {
if (r.contains("id")) {
if (r["id"] == 1 && r.contains("result"))
foundToolsList = true;
if (r["id"] == 2 && r.contains("error") && r["error"]["code"] == -32601)
foundMethodNotFound = true;
}
}
EXPECT_TRUE(foundToolsList) << "Batch should contain tools/list result";
EXPECT_TRUE(foundMethodNotFound) << "Batch should contain method-not-found error";
ASSERT_TRUE(resp->contains("error"));
EXPECT_EQ((*resp)["error"]["code"].get<int>(), -32600);
}

TEST_F(ProtocolTest, ProcessStable_MultipleRequests)
Expand Down
4 changes: 3 additions & 1 deletion tests/integration/test_workflow.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,8 @@
#include <optional>
#include <chrono>

#include "mcp/mcp_server.h"

#ifdef _WIN32
#include <windows.h>
#endif
Expand Down Expand Up @@ -218,7 +220,7 @@ class WorkflowTest : public ::testing::Test {
initReq["jsonrpc"] = "2.0";
initReq["id"] = 0;
initReq["method"] = "initialize";
initReq["params"]["protocolVersion"] = "2025-03-26";
initReq["params"]["protocolVersion"] = renderdoc::mcp::kProtocolVersion;
initReq["params"]["clientInfo"]["name"] = "test-runner";
initReq["params"]["clientInfo"]["version"] = "1.0.0";
initReq["params"]["capabilities"] = json::object();
Expand Down
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