mcp.js

var _mcp_messages = [];
var _mcp_buffer = "";

function clear_content_length(r) {
    delete r.headersOut['Content-Length'];
}

function filter(r, data, flags) {
    _mcp_buffer += data;
    r.sendBuffer(data, flags);

    if (_mcp_messages.length === 0) {
        var sse_messages = _mcp_buffer.split(/\\n\\n/);
        for (var i = 0; i < sse_messages.length; i++) {
            var msg = sse_messages[i];
            r.log("Processing SSE message: " + msg);
            if (msg.startsWith("data: ")) {
                var json_str = msg.substring(6); // "data: ".length
                try {
                    var json_obj = JSON.parse(json_str);
                    _mcp_messages.push(json_obj);
                    r.done();
                    return;
                } catch (e) {
                }
            }
        }
    }
}

function getPath(r, json_obj, path) {
    if (!json_obj) {
        return undefined;
    }

    var parts = path.split('.');
    var current = json_obj;
    for (var i = 0; i < parts.length; i++) {
        var part = parts[i];
        if (typeof current !== 'object' || current === null || !current.hasOwnProperty(part)) {
            return undefined;
        }

        current = current[part];
    }

    return current;
}

function has_error(r) {
    if (_mcp_messages.length === 0) {
        r.log("No MCP messages parsed yet, cannot determine error status");
        return false; // No message parsed yet, assume no error
    }

    var first_message = _mcp_messages[0];
    r.log("Checking for errors in message: " + JSON.stringify(first_message));

    // JSON-RPC2 error response
    if (getPath(r, first_message, "error")) {
        r.log("Error found in JSON-RPC2 response");
        return true;
    }

    // Tool error (IsError: true in result)
    if (getPath(r, first_message, "result.isError")) {
        r.log("Error found in tool execution result");
        return true;
    }

    return false;
}

function mcp_tool_name(r) {
    var body = JSON.parse(r.requestText || '{}');
    var method = body.method;
    if (method == 'tools/call') {
        return body.params.name;
    }

    return '';
}

function mcp_tool_status(r) {
    if (has_error(r)) {
        return 'error';
    }

    return 'ok';
}

export default { filter, clear_content_length, mcp_tool_name, mcp_tool_status };