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[lldb] Move the generic MCP server code into Protocol/MCP (NFC) #152396

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Merged
merged 2 commits into from
Aug 7, 2025
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[lldb] Move the generic MCP server code into Protocol/MCP (NFC) #152396

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10a3e90
[lldb] Move the generic MCP server code into Protocol/MCP (NFC)
JDevlieghere Aug 6, 2025
691c49f
Include mutex
JDevlieghere Aug 6, 2025
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2 changes: 1 addition & 1 deletion lldb/include/lldb/Protocol/MCP/Protocol.h
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Original file line number Diff line number Diff line change
Expand Up @@ -21,7 +21,7 @@

namespace lldb_protocol::mcp {

static llvm::StringLiteral kVersion = "2024-11-05";
static llvm::StringLiteral kProtocolVersion = "2024-11-05";

/// A request that expects a response.
struct Request {
Expand Down
70 changes: 70 additions & 0 deletions lldb/include/lldb/Protocol/MCP/Server.h
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Original file line number Diff line number Diff line change
@@ -0,0 +1,70 @@
//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#ifndef LLDB_PROTOCOL_MCP_SERVER_H
#define LLDB_PROTOCOL_MCP_SERVER_H

#include "lldb/Protocol/MCP/Protocol.h"
#include "lldb/Protocol/MCP/Resource.h"
#include "lldb/Protocol/MCP/Tool.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/Support/Error.h"
#include <mutex>

namespace lldb_protocol::mcp {

class Server {
public:
Server(std::string name, std::string version);
virtual ~Server() = default;

void AddTool(std::unique_ptr<Tool> tool);
void AddResourceProvider(std::unique_ptr<ResourceProvider> resource_provider);

protected:
virtual Capabilities GetCapabilities() = 0;

using RequestHandler =
std::function<llvm::Expected<Response>(const Request &)>;
using NotificationHandler = std::function<void(const Notification &)>;

void AddRequestHandlers();

void AddRequestHandler(llvm::StringRef method, RequestHandler handler);
void AddNotificationHandler(llvm::StringRef method,
NotificationHandler handler);

llvm::Expected<std::optional<Message>> HandleData(llvm::StringRef data);

llvm::Expected<Response> Handle(Request request);
void Handle(Notification notification);

llvm::Expected<Response> InitializeHandler(const Request &);

llvm::Expected<Response> ToolsListHandler(const Request &);
llvm::Expected<Response> ToolsCallHandler(const Request &);

llvm::Expected<Response> ResourcesListHandler(const Request &);
llvm::Expected<Response> ResourcesReadHandler(const Request &);

std::mutex m_mutex;

private:
const std::string m_name;
const std::string m_version;

llvm::StringMap<std::unique_ptr<Tool>> m_tools;
std::vector<std::unique_ptr<ResourceProvider>> m_resource_providers;

llvm::StringMap<RequestHandler> m_request_handlers;
llvm::StringMap<NotificationHandler> m_notification_handlers;
};

} // namespace lldb_protocol::mcp

#endif
252 changes: 8 additions & 244 deletions lldb/source/Plugins/Protocol/MCP/ProtocolServerMCP.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -27,25 +27,12 @@ using namespace llvm;
LLDB_PLUGIN_DEFINE(ProtocolServerMCP)

static constexpr size_t kChunkSize = 1024;
static constexpr llvm::StringLiteral kName = "lldb-mcp";
static constexpr llvm::StringLiteral kVersion = "0.1.0";

ProtocolServerMCP::ProtocolServerMCP() : ProtocolServer() {
AddRequestHandler("initialize",
std::bind(&ProtocolServerMCP::InitializeHandler, this,
std::placeholders::_1));

AddRequestHandler("tools/list",
std::bind(&ProtocolServerMCP::ToolsListHandler, this,
std::placeholders::_1));
AddRequestHandler("tools/call",
std::bind(&ProtocolServerMCP::ToolsCallHandler, this,
std::placeholders::_1));

AddRequestHandler("resources/list",
std::bind(&ProtocolServerMCP::ResourcesListHandler, this,
std::placeholders::_1));
AddRequestHandler("resources/read",
std::bind(&ProtocolServerMCP::ResourcesReadHandler, this,
std::placeholders::_1));
ProtocolServerMCP::ProtocolServerMCP()
: ProtocolServer(),
lldb_protocol::mcp::Server(std::string(kName), std::string(kVersion)) {
AddNotificationHandler("notifications/initialized",
[](const lldb_protocol::mcp::Notification &) {
LLDB_LOG(GetLog(LLDBLog::Host),
Expand Down Expand Up @@ -77,32 +64,6 @@ llvm::StringRef ProtocolServerMCP::GetPluginDescriptionStatic() {
return "MCP Server.";
}

llvm::Expected<lldb_protocol::mcp::Response>
ProtocolServerMCP::Handle(lldb_protocol::mcp::Request request) {
auto it = m_request_handlers.find(request.method);
if (it != m_request_handlers.end()) {
llvm::Expected<lldb_protocol::mcp::Response> response = it->second(request);
if (!response)
return response;
response->id = request.id;
return *response;
}

return make_error<MCPError>(
llvm::formatv("no handler for request: {0}", request.method).str());
}

void ProtocolServerMCP::Handle(lldb_protocol::mcp::Notification notification) {
auto it = m_notification_handlers.find(notification.method);
if (it != m_notification_handlers.end()) {
it->second(notification);
return;
}

LLDB_LOG(GetLog(LLDBLog::Host), "MPC notification: {0} ({1})",
notification.method, notification.params);
}

void ProtocolServerMCP::AcceptCallback(std::unique_ptr<Socket> socket) {
LLDB_LOG(GetLog(LLDBLog::Host), "New MCP client ({0}) connected",
m_clients.size() + 1);
Expand Down Expand Up @@ -157,7 +118,7 @@ llvm::Error ProtocolServerMCP::ReadCallback(Client &client) {
}

llvm::Error ProtocolServerMCP::Start(ProtocolServer::Connection connection) {
std::lock_guard<std::mutex> guard(m_server_mutex);
std::lock_guard<std::mutex> guard(m_mutex);

if (m_running)
return llvm::createStringError("the MCP server is already running");
Expand Down Expand Up @@ -189,7 +150,7 @@ llvm::Error ProtocolServerMCP::Start(ProtocolServer::Connection connection) {

llvm::Error ProtocolServerMCP::Stop() {
{
std::lock_guard<std::mutex> guard(m_server_mutex);
std::lock_guard<std::mutex> guard(m_mutex);
if (!m_running)
return createStringError("the MCP sever is not running");
m_running = false;
Expand All @@ -204,7 +165,7 @@ llvm::Error ProtocolServerMCP::Stop() {
m_loop_thread.join();

{
std::lock_guard<std::mutex> guard(m_server_mutex);
std::lock_guard<std::mutex> guard(m_mutex);
m_listener.reset();
m_listen_handlers.clear();
m_clients.clear();
Expand All @@ -213,48 +174,6 @@ llvm::Error ProtocolServerMCP::Stop() {
return llvm::Error::success();
}

llvm::Expected<std::optional<lldb_protocol::mcp::Message>>
ProtocolServerMCP::HandleData(llvm::StringRef data) {
auto message = llvm::json::parse<lldb_protocol::mcp::Message>(/*JSON=*/data);
if (!message)
return message.takeError();

if (const lldb_protocol::mcp::Request *request =
std::get_if<lldb_protocol::mcp::Request>(&(*message))) {
llvm::Expected<lldb_protocol::mcp::Response> response = Handle(*request);

// Handle failures by converting them into an Error message.
if (!response) {
lldb_protocol::mcp::Error protocol_error;
llvm::handleAllErrors(
response.takeError(),
[&](const MCPError &err) { protocol_error = err.toProtcolError(); },
[&](const llvm::ErrorInfoBase &err) {
protocol_error.error.code = MCPError::kInternalError;
protocol_error.error.message = err.message();
});
protocol_error.id = request->id;
return protocol_error;
}

return *response;
}

if (const lldb_protocol::mcp::Notification *notification =
std::get_if<lldb_protocol::mcp::Notification>(&(*message))) {
Handle(*notification);
return std::nullopt;
}

if (std::get_if<lldb_protocol::mcp::Error>(&(*message)))
return llvm::createStringError("unexpected MCP message: error");

if (std::get_if<lldb_protocol::mcp::Response>(&(*message)))
return llvm::createStringError("unexpected MCP message: response");

llvm_unreachable("all message types handled");
}

lldb_protocol::mcp::Capabilities ProtocolServerMCP::GetCapabilities() {
lldb_protocol::mcp::Capabilities capabilities;
capabilities.tools.listChanged = true;
Expand All @@ -263,158 +182,3 @@ lldb_protocol::mcp::Capabilities ProtocolServerMCP::GetCapabilities() {
capabilities.resources.listChanged = false;
return capabilities;
}

void ProtocolServerMCP::AddTool(std::unique_ptr<Tool> tool) {
std::lock_guard<std::mutex> guard(m_server_mutex);

if (!tool)
return;
m_tools[tool->GetName()] = std::move(tool);
}

void ProtocolServerMCP::AddResourceProvider(
std::unique_ptr<ResourceProvider> resource_provider) {
std::lock_guard<std::mutex> guard(m_server_mutex);

if (!resource_provider)
return;
m_resource_providers.push_back(std::move(resource_provider));
}

void ProtocolServerMCP::AddRequestHandler(llvm::StringRef method,
RequestHandler handler) {
std::lock_guard<std::mutex> guard(m_server_mutex);
m_request_handlers[method] = std::move(handler);
}

void ProtocolServerMCP::AddNotificationHandler(llvm::StringRef method,
NotificationHandler handler) {
std::lock_guard<std::mutex> guard(m_server_mutex);
m_notification_handlers[method] = std::move(handler);
}

llvm::Expected<lldb_protocol::mcp::Response>
ProtocolServerMCP::InitializeHandler(
const lldb_protocol::mcp::Request &request) {
lldb_protocol::mcp::Response response;
response.result.emplace(llvm::json::Object{
{"protocolVersion", lldb_protocol::mcp::kVersion},
{"capabilities", GetCapabilities()},
{"serverInfo",
llvm::json::Object{{"name", kName}, {"version", kVersion}}}});
return response;
}

llvm::Expected<lldb_protocol::mcp::Response>
ProtocolServerMCP::ToolsListHandler(
const lldb_protocol::mcp::Request &request) {
lldb_protocol::mcp::Response response;

llvm::json::Array tools;
for (const auto &tool : m_tools)
tools.emplace_back(toJSON(tool.second->GetDefinition()));

response.result.emplace(llvm::json::Object{{"tools", std::move(tools)}});

return response;
}

llvm::Expected<lldb_protocol::mcp::Response>
ProtocolServerMCP::ToolsCallHandler(
const lldb_protocol::mcp::Request &request) {
lldb_protocol::mcp::Response response;

if (!request.params)
return llvm::createStringError("no tool parameters");

const json::Object *param_obj = request.params->getAsObject();
if (!param_obj)
return llvm::createStringError("no tool parameters");

const json::Value *name = param_obj->get("name");
if (!name)
return llvm::createStringError("no tool name");

llvm::StringRef tool_name = name->getAsString().value_or("");
if (tool_name.empty())
return llvm::createStringError("no tool name");

auto it = m_tools.find(tool_name);
if (it == m_tools.end())
return llvm::createStringError(llvm::formatv("no tool \"{0}\"", tool_name));

lldb_protocol::mcp::ToolArguments tool_args;
if (const json::Value *args = param_obj->get("arguments"))
tool_args = *args;

llvm::Expected<lldb_protocol::mcp::TextResult> text_result =
it->second->Call(tool_args);
if (!text_result)
return text_result.takeError();

response.result.emplace(toJSON(*text_result));

return response;
}

llvm::Expected<lldb_protocol::mcp::Response>
ProtocolServerMCP::ResourcesListHandler(
const lldb_protocol::mcp::Request &request) {
lldb_protocol::mcp::Response response;

llvm::json::Array resources;

std::lock_guard<std::mutex> guard(m_server_mutex);
for (std::unique_ptr<ResourceProvider> &resource_provider_up :
m_resource_providers) {
for (const lldb_protocol::mcp::Resource &resource :
resource_provider_up->GetResources())
resources.push_back(resource);
}
response.result.emplace(
llvm::json::Object{{"resources", std::move(resources)}});

return response;
}

llvm::Expected<lldb_protocol::mcp::Response>
ProtocolServerMCP::ResourcesReadHandler(
const lldb_protocol::mcp::Request &request) {
lldb_protocol::mcp::Response response;

if (!request.params)
return llvm::createStringError("no resource parameters");

const json::Object *param_obj = request.params->getAsObject();
if (!param_obj)
return llvm::createStringError("no resource parameters");

const json::Value *uri = param_obj->get("uri");
if (!uri)
return llvm::createStringError("no resource uri");

llvm::StringRef uri_str = uri->getAsString().value_or("");
if (uri_str.empty())
return llvm::createStringError("no resource uri");

std::lock_guard<std::mutex> guard(m_server_mutex);
for (std::unique_ptr<ResourceProvider> &resource_provider_up :
m_resource_providers) {
llvm::Expected<lldb_protocol::mcp::ResourceResult> result =
resource_provider_up->ReadResource(uri_str);
if (result.errorIsA<UnsupportedURI>()) {
llvm::consumeError(result.takeError());
continue;
}
if (!result)
return result.takeError();

lldb_protocol::mcp::Response response;
response.result.emplace(std::move(*result));
return response;
}

return make_error<MCPError>(
llvm::formatv("no resource handler for uri: {0}", uri_str).str(),
MCPError::kResourceNotFound);
}
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