client.go

package mcp

import (
	"context"
	"errors"
	"fmt"
	"log/slog"

	"github.com/agent-api/jsonrpc2"
)

type Client struct {
	// conn is a JSON RPC 2.0 connection
	conn               *jsonrpc2.Conn
	supportedVersions  []string
	serverVersion      string
	serverCapabilities *ServerCapabilities
	serverInfo         *ServerInfo
	initialized        bool

	// logger is a slog logger
	logger *slog.Logger
}

type ClientOpts struct {
	Conn              *jsonrpc2.Conn
	SupportedVersions []string
	Logger            *slog.Logger
}

func NewClient(opts *ClientOpts) *Client {
	return &Client{
		conn:              opts.Conn,
		supportedVersions: opts.SupportedVersions,
		logger:            opts.Logger,
	}
}

func (c *Client) Initialize(ctx context.Context, clientInfo ClientInfo, clientCapabilities ClientCapabilities) error {
	c.logger.Debug("client checking if already initialized")
	if c.initialized {
		return errors.New("already initialized")
	}

	c.logger.Debug("client checking if supported versions provided")
	if len(c.supportedVersions) == 0 {
		return errors.New("no supported protocol versions")
	}

	params := InitializeParams{
		ProtocolVersion: c.supportedVersions[0],
		Capabilities:    clientCapabilities,
		ClientInfo:      clientInfo,
	}
	c.logger.Debug("using mcp protocol version", "protocol version", params.ProtocolVersion)
	c.logger.Debug("using capabilities", "capabilities", params.Capabilities)
	c.logger.Debug("using client info", "client info", params.ClientInfo)

	c.logger.Debug("client calling server initialization method")
	var result InitializeResult
	if err := c.conn.Call(ctx, "initialize", params, &result); err != nil {
		return fmt.Errorf("initialize request failed: %w", err)
	}

	supported := false
	for _, v := range c.supportedVersions {
		c.logger.Debug("client comparing server supported versions", "client version", v, "server version", result.ProtocolVersion)
		if v == result.ProtocolVersion {
			supported = true
			break
		}
	}
	if !supported {
		return fmt.Errorf("unsupported server protocol version: %s", result.ProtocolVersion)
	}

	c.serverVersion = result.ProtocolVersion
	c.logger.Debug("client set server mcp version", "server version", c.serverVersion)

	c.serverCapabilities = result.Capabilities
	c.logger.Debug("client set server mcp capabilities", "server capabilities", c.serverCapabilities)

	c.serverInfo = result.ServerInfo
	c.logger.Debug("client set server mcp server info", "server info", c.serverInfo)

	c.logger.Debug("client notifying server initialization complete")
	if err := c.conn.Notify(ctx, "notifications/initialized", nil); err != nil {
		return fmt.Errorf("failed to send initialized notification: %w", err)
	}

	c.initialized = true
	return nil
}