cpp-mcp/include/mcp_protocol.h

/**
 * @file mcp_protocol.h
 * @brief Core definitions for the Model Context Protocol (MCP) framework
 * 
 * This file contains the core structures, enums, and definitions for the MCP protocol.
 * MCP connects AI models with data sources and tools in a standardized way.
 */

#ifndef MCP_PROTOCOL_H
#define MCP_PROTOCOL_H

#include <string>
#include <vector>
#include <map>
#include <functional>
#include <memory>
#include <stdexcept>

// Include the JSON library for parsing and generating JSON
#include "json.hpp"

namespace mcp {

// Use the nlohmann json library
using json = nlohmann::ordered_json;

// MCP version
constexpr const char* MCP_VERSION = "1.0.0";

// MCP error codes
enum class error_code {
    none = 0,
    invalid_request = 400,
    unauthorized = 401,
    forbidden = 403,
    not_found = 404,
    method_not_allowed = 405,
    conflict = 409,
    payload_too_large = 413,
    unsupported_media_type = 415,
    internal_server_error = 500,
    service_unavailable = 503
};

// MCP exception class
class mcp_exception : public std::runtime_error {
public:
    mcp_exception(error_code code, const std::string& message)
        : std::runtime_error(message), code_(code) {}

    error_code code() const { return code_; }

private:
    error_code code_;
};

// Resource Types
enum class resource_type {
    file,           // File resource
    directory,      // Directory/folder resource
    database,       // Database resource
    api,            // API endpoints
    document,       // Document resource
    image,          // Image resource
    custom          // Custom resource type
};

// Content Types
struct content_type {
    static constexpr const char* json = "application/json";
    static constexpr const char* text = "text/plain"; 
    static constexpr const char* octet_stream = "application/octet-stream";
    static constexpr const char* form = "application/x-www-form-urlencoded";
    static constexpr const char* multipart = "multipart/form-data";
    static constexpr const char* image_jpeg = "image/jpeg";
    static constexpr const char* image_png = "image/png";
};

// HTTP Methods
enum class http_method {
    get,
    post,
    put,
    delete_,
    patch,
    options,
    head
};

// Convert HTTP method to string
inline std::string http_method_to_string(http_method method) {
    switch (method) {
        case http_method::get: return "GET";
        case http_method::post: return "POST";
        case http_method::put: return "PUT";
        case http_method::delete_: return "DELETE";
        case http_method::patch: return "PATCH";
        case http_method::options: return "OPTIONS";
        case http_method::head: return "HEAD";
        default: return "UNKNOWN";
    }
}

// Convert string to HTTP method
inline http_method string_to_http_method(const std::string& method_str) {
    if (method_str == "GET") return http_method::get;
    if (method_str == "POST") return http_method::post;
    if (method_str == "PUT") return http_method::put;
    if (method_str == "DELETE") return http_method::delete_;
    if (method_str == "PATCH") return http_method::patch;
    if (method_str == "OPTIONS") return http_method::options;
    if (method_str == "HEAD") return http_method::head;
    throw mcp_exception(error_code::method_not_allowed, "Unsupported HTTP method: " + method_str);
}

// MCP Request structure
struct request {
    http_method method;
    std::string path;
    std::map<std::string, std::string> headers;
    std::map<std::string, std::string> query_params;
    std::string body;
    
    // Parse JSON body
    json json_body() const {
        if (body.empty()) {
            return json::object();
        }
        try {
            return json::parse(body);
        } catch (const json::exception& e) {
            throw mcp_exception(error_code::invalid_request, "Invalid JSON in request body: " + std::string(e.what()));
        }
    }
};

// MCP Response structure
struct response {
    int status_code = 200;
    std::map<std::string, std::string> headers;
    std::string body;
    
    // Set JSON body
    void set_json_body(const json& data) {
        body = data.dump();
        headers["Content-Type"] = content_type::json;
    }
    
    // Set error response
    void set_error(error_code code, const std::string& message) {
        status_code = static_cast<int>(code);
        json error = {
            {"error", {
                {"code", status_code},
                {"message", message}
            }}
        };
        set_json_body(error);
    }
};

// Base class for MCP resources
class resource {
public:
    virtual ~resource() = default;
    
    // Get resource type
    virtual resource_type type() const = 0;
    
    // Get resource metadata
    virtual json metadata() const = 0;
    
    // Handle request
    virtual response handle_request(const request& req) = 0;
    
    // Get resource schema
    virtual json schema() const {
        return json::object();  // Default empty schema
    }
};

// MCP Tool definition
struct tool {
    std::string name;
    std::string description;
    json parameters_schema;
    
    // Convert to JSON for API documentation
    json to_json() const {
        return {
            {"name", name},
            {"description", description},
            {"parameters", parameters_schema}
        };
    }
};

// Tool handler function type
using tool_handler = std::function<json(const json&)>;

} // namespace mcp

#endif // MCP_PROTOCOL_H