mcp_host library

Kernel sub-barrel for the reference MCP host adapters.

Hosts that want a mcp_server + mcp_client backed surface import this barrel in addition to package:brain_kernel/brain_kernel.dart. The main barrel exposes only the KernelServerHost / KernelClientHost abstracts; this barrel surfaces the reference impls (ServerBootstrap aka McpServerKernelHost, McpClientKernelHost) plus the raw mcp_server / mcp_client types so hosts can reach out to wire-shape APIs (custom prompts, resource subscriptions, OAuth, etc).

Usage:

import 'package:brain_kernel/brain_kernel.dart';
import 'package:brain_kernel/mcp_host.dart';

final app = await KernelApp.boot(
  workspaceId: 'studio',
  kvStorage: kv,
  serverHostFactory: ServerBootstrap.factory,  // MCP server-backed
  clientHost: McpClientKernelHost(),           // outbound calls
);

Hosts that never expose a server transport omit serverHostFactory (kernel falls back to in-process). Hosts that never make outbound calls omit clientHost.

Classes

ApiKeyValidator: Simple API key validator
AudioContent: Audio content (spec 2025-03-26+).
AuthContext: Authorization context for MCP requests
AuthMiddleware: Authentication middleware for HTTP requests
AuthResult: Authentication result
CachedResource: Cached resource item for performance optimization
CallToolResult: Tool call result.
CancellationToken: Cancellation token for async operations
Client: Main MCP Client class that handles all client-side protocol operations
ClientSession: Client session information
CompletionsCapability: Completions capability — server advertises support for argument autocompletion via the completion/complete request (spec).
Content: Base class for all MCP content types (2025-03-26 compliant)
CreateMessageRequest: Create message request for sampling
CreateMessageResult: Create message result from sampling
DeprecationInfo: Deprecation information
ErrorCode: Error codes for standardized error handling
EventMessage: Event message with optional ID for SSE
Failure<T, E extends Object>: Represents a failed result
GetPromptResult: Get prompt result
ImageContent: Image content representation
JsonRpcMessage: JSON-RPC message
Level: Levels to control logging output. Logging can be enabled to include all levels above certain Level. Levels are ordered using an integer value Level.value. The predefined Level constants below are sorted as follows (in descending order): Level.SHOUT, Level.SEVERE, Level.WARNING, Level.INFO, Level.CONFIG, Level.FINE, Level.FINER, Level.FINEST, and Level.ALL.
Logger: Use a Logger to log debug messages.
LoggingCapability: Logging capability
LogRecord: A log entry representation used to propagate information from Logger to individual handlers.
McpClientKernelHost
McpErrorCodes: MCP Error codes as defined in the specification
McpMethodAuth: MCP method authorization configuration
McpMethods: Standard MCP methods that must be implemented
McpProtocol: MCP Protocol Version constants and definitions
McpServer: Modern MCP Server factory with enhanced configuration and error handling
McpServerConfig: Configuration for creating MCP servers
Message: Message model for prompt system
ModelHint: Model hint for sampling
ModelPreferences: Model preferences for sampling
OAuthTokenValidator: OAuth 2.1 token validator
PendingOperation: Pending operation for cancellation support
ProgressCapability: Progress capability
ProgressNotification: Progress notification data (2025-03-26)
Prompt: Prompt definition
PromptArgument: Prompt argument definition
PromptMessage: Prompt message (2025-03-26)
PromptsCapability: Prompts capability
ReadResourceResult: Resource read result
Resource: Resource definition
ResourceContent: Resource content representation
ResourceContentInfo: Resource content info (used in ReadResourceResult)
ResourceLinkContent: Resource link content (spec 2025-06-18+) — a tool result that points to a server resource by URI without inlining the content.
ResourcesCapability: Resources capability
ResourceTemplate: Resource template definition
ResourceUsage: Resource usage indicators
Result<T, E extends Object>: A sealed class representing the result of an operation that can succeed or fail
Results: Utility functions for working with Results
Root: Root definition for filesystem access
RootsCapability: Roots capability
SamplingCapability: Sampling capability
Server: Main MCP Server class that handles all server-side protocol operations
ServerBootstrap
ServerCapabilities: Server capabilities configuration for MCP 2025-03-26 protocol
ServerHealth: Server health information
ServerInterface: Interface for server to expose key functionality for testing
ServerTransport: Abstract base class for server transport implementations
SseClientTransport: Transport implementation using Server-Sent Events (SSE) over HTTP
SseServerTransport: Transport implementation using Server-Sent Events (SSE) over HTTP
SseStreamInfo: SSE stream information for request-specific streams
SseTransportConfig
StdioClientTransport: Transport implementation using standard input/output streams
StdioServerTransport: Transport implementation using standard input/output streams
StdioTransportConfig
StreamableHttpClientTransport: Streamable HTTP client transport for MCP
StreamableHttpServerConfig: Configuration for StreamableHTTP server transport
StreamableHttpServerTransport: MCP 2025-03-26 StreamableHTTP Server Transport Implementation Supports both JSON responses and SSE streaming according to MCP standard
StreamableHttpTransportConfig
Success<T, E extends Object>: Represents a successful result
TextContent: Text content representation
TokenValidator: Token validation interface
Tool: Tool definition (2025-03-26 compliant)
ToolAnnotationBuilder: Tool annotation builder for creating standard annotations
ToolAnnotationKeys: Standard tool annotation keys defined in MCP 2025-03-26
ToolAnnotationPresets: Common tool annotation presets
ToolAnnotationUtils: Utility functions for working with tool annotations
ToolsCapability: Tools capability
TransportConfig: Configuration for transport connections

Enums

MCPContentType
McpLogLevel: Log levels for MCP protocol
MessageRole: Base content type enum for MCP
PromptMessageRole: Prompt message roles
ToolPriority: Tool priority levels

Extensions

FutureResultExtensions on Future<Result<T, E>>: Extension methods for Future<Result>
LoggerExtensions on Logger
OAuthServerMethods on Server

Constants

defaultLevel → const Level: The default Level.
getStreamKey → const String

Properties

hierarchicalLoggingEnabled ↔ bool: Whether to allow fine-grain logging and configuration of loggers in a hierarchy.
getter/setter pair
recordStackTraceAtLevel ↔ Level: Automatically record stack traces for any message of this level or above.
getter/setter pair

Typedefs

CompletionHandler = Future<Map<String, dynamic>> Function(Map<String, dynamic> ref, Map<String, dynamic> argument, Map<String, dynamic>? context): Type definition for completion handler functions (spec completion/complete).
IsCancelledCheck = bool Function(): Callback type for checking if operation is cancelled
MCPServer = McpServer
ProgressCallback = void Function(double progress, String message): Callback type for tool execution progress updates
PromptHandler = Future Function(Map<String, dynamic> arguments): Type definition for prompt handler functions
ResourceHandler = Future Function(String uri, Map<String, dynamic> params): Type definition for resource handler functions
SseServerConfig = SseTransportConfig
ToolHandler = Future Function(Map<String, dynamic> arguments): Type definition for tool handler functions with cancellation and progress reporting

Exceptions / Errors

CancelledException: Exception thrown when an operation is cancelled
McpError: Error class for MCP-related errors

mcp_host library

Classes

Enums

Extensions

Constants

Properties

Typedefs

Exceptions / Errors

brain_kernel package

mcp_host library