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CallToolResult

pub(all) struct CallToolResult {
  content : Array[@colmugx/mcp/protocol/types.ContentItem
ContentItem]
  is_error : Bool
} derive(Eq, @moonbitlang/core/debug.Debug
Debug)

ClientBackend

source

pub enum ClientBackend {
  Modern
  Legacy(@colmugx/mcp/client/legacy.LegacyClient
LegacyClient)
}

Backend selected after era probing. Modern clients speak the stateless 2026-07-28 protocol; Legacy clients wrap the 2025-11-25 session client.

CompletionResult

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pub(all) struct CompletionResult {
  values : Array[String]
  total : Int?
  has_more : Bool?
} derive(Eq, @moonbitlang/core/debug.Debug
Debug)

ListPromptsResult

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pub(all) struct ListPromptsResult {
  prompts : Array[@colmugx/mcp/protocol/prompt.PromptDefinition
PromptDefinition]
  next_cursor : String?
} derive(Eq, @moonbitlang/core/debug.Debug
Debug)

ListResourceTemplatesResult

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pub(all) struct ListResourceTemplatesResult {
  resource_templates : Array[ResourceTemplate]
  next_cursor : String?
} derive(Eq, @moonbitlang/core/debug.Debug
Debug)

ListResourcesResult

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pub(all) struct ListResourcesResult {
  resources : Array[@colmugx/mcp/protocol/resource.ResourceDefinition
ResourceDefinition]
  next_cursor : String?
} derive(Eq, @moonbitlang/core/debug.Debug
Debug)

ListToolsResult

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pub(all) struct ListToolsResult {
  tools : Array[@colmugx/mcp/protocol/types.ToolDefinition
ToolDefinition]
  next_cursor : String?
} derive(Eq, @moonbitlang/core/debug.Debug
Debug)

ListenFilter

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pub(all) struct ListenFilter {
  tools_list_changed : Bool
  prompts_list_changed : Bool
  resources_list_changed : Bool
  resource_subscriptions : Array[String]
} derive(Eq, @moonbitlang/core/debug.Debug
Debug)

Filter for a subscriptions/listen request. Controls which server notification channels the client wants multiplexed onto this single long-lived request.

ListenFilter::default

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fn ListenFilter::default() -> ListenFilter

Default filter: subscribe only to list-change notifications, with no per-resource subscriptions.

MCPClient

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pub struct MCPClient {
  client_name : String
  client_version : String
  capabilities : @colmugx/mcp/protocol/types.ClientCapabilities
ClientCapabilities
  transport : @colmugx/mcp/transport.AnyTransport
AnyTransport
  id_counter : RequestIdCounter
  server_capabilities : @colmugx/mcp/protocol/types.ServerCapabilities
ServerCapabilities?
  server_info : @colmugx/mcp/protocol/types.ServerInfo
ServerInfo?
  notification_handlers : NotificationHandlers
  subscription_handlers : Map[String, (Json) -> Unit]
  sampling_handler : (Json) -> Result[@colmugx/mcp/protocol/types.CreateMessageResult
CreateMessageResult, @colmugx/mcp/protocol/types.MCPError
MCPError]?
  roots_handler : () -> Result[Array[@colmugx/mcp/protocol/types.Root
Root], @colmugx/mcp/protocol/types.MCPError
MCPError]?
  elicitation_handler : (Json) -> Result[@colmugx/mcp/protocol/types.ElicitationResult
ElicitationResult, @colmugx/mcp/protocol/types.MCPError
MCPError]?
  response_map : Map[Int, @moonbitlang/async/aqueue.Queue
Queue[String]]
  event_loop_started : Bool
  legacy_mode : Bool
  backend : ClientBackend
}

MCPClient::call_tool

source

async fn MCPClient::call_tool(self : MCPClient, name : String, arguments? : String) -> Result[CallToolResult, @colmugx/mcp/protocol/types.MCPError
MCPError]

MCPClient::cancel_listen

source

async fn MCPClient::cancel_listen(self : MCPClient, subscription_id : String) -> Result[Unit, @colmugx/mcp/protocol/types.MCPError
MCPError]

Cancel a running subscriptions/listen subscription. For stdio transports this sends a notifications/cancelled notification. HTTP transports do not currently support per-stream cancellation in this SDK, so this returns an error explaining that limitation.

MCPClient::cancel_request

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async fn MCPClient::cancel_request(self : MCPClient, request_id : String, reason? : String) -> Result[Unit, @colmugx/mcp/protocol/types.MCPError
MCPError]

Cancel an in-flight request. Per the 2026-07-28 spec (transports/streamable-http), the core protocol defines no client→server notification on Streamable HTTP: cancellation there is signalled by closing the SSE response stream. So only stdio client transports send notifications/cancelled; HTTP and other transports return a clear error instead (same style as cancel_listen).

MCPClient::close

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async fn MCPClient::close(self : MCPClient) -> Unit

MCPClient::complete

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async fn MCPClient::complete(self : MCPClient, ref_type~ : String, ref_name~ : String, argument_name~ : String, argument_value~ : String) -> Result[CompletionResult, @colmugx/mcp/protocol/types.MCPError
MCPError]

MCPClient::connect_http

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async fn MCPClient::connect_http(url~ : String, name~ : String, version~ : String, auth_token? : String, extra_headers? : Array[(String, String)], era? : ProtocolEra) -> Result[MCPClient, @colmugx/mcp/protocol/types.MCPError
MCPError]

Connect to a remote MCP server over HTTP.

era constrains how the protocol era is negotiated:

era	server/discover probe	legacy fallback
Auto	yes (default)	allowed
Legacy	skipped	direct connect
Modern	yes	forbidden (Err)

extra_headers are appended to every request this transport issues, after the built-in headers. Same-name entries override the built-ins (including the spec-mandated MCP-Protocol-Version/Mcp-Method/Mcp-Name and the auth_token-derived Authorization — extra wins), so pass reserved headers only deliberately. The same set is applied on the legacy-era fallback path, so header-gated servers (bearer, routing, session-context) see identical headers on both protocol eras.

MCPClient::connect_stdio

source

async fn MCPClient::connect_stdio(cmd~ : String, args? : Array[String], name~ : String, version~ : String, extra_env? : Map[String, String], group~ : @moonbitlang/async.TaskGroup
TaskGroup[Unit], era? : ProtocolEra) -> Result[MCPClient, @colmugx/mcp/protocol/types.MCPError
MCPError]

Connect to a local MCP server by spawning it as a child process.

era constrains era negotiation exactly like connect_http:

era	server/discover probe	legacy fallback
Auto	yes (default)	allowed
Legacy	skipped	direct connect
Modern	yes	forbidden (Err)

MCPClient::discover

source

async fn MCPClient::discover(self : MCPClient) -> Result[@colmugx/mcp/protocol/types.ServerCapabilities
ServerCapabilities, @colmugx/mcp/protocol/types.MCPError
MCPError]

Query the server's supported versions, capabilities, and identity via server/discover (required by the 2026-07-28 spec). Stores the results in server_capabilities and server_info for later use. Optional for clients per spec, but recommended — and the primary era probe for legacy fallback.

MCPClient::get_prompt

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async fn MCPClient::get_prompt(self : MCPClient, name : String, arguments? : String) -> Result[@colmugx/mcp/protocol/types.GetPromptResult
GetPromptResult, @colmugx/mcp/protocol/types.MCPError
MCPError]

MCPClient::list_prompts

source

async fn MCPClient::list_prompts(self : MCPClient, cursor? : String) -> Result[ListPromptsResult, @colmugx/mcp/protocol/types.MCPError
MCPError]

MCPClient::list_resource_templates

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async fn MCPClient::list_resource_templates(self : MCPClient, cursor? : String) -> Result[ListResourceTemplatesResult, @colmugx/mcp/protocol/types.MCPError
MCPError]

MCPClient::list_resources

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async fn MCPClient::list_resources(self : MCPClient, cursor? : String) -> Result[ListResourcesResult, @colmugx/mcp/protocol/types.MCPError
MCPError]

MCPClient::list_tools

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async fn MCPClient::list_tools(self : MCPClient, cursor? : String) -> Result[ListToolsResult, @colmugx/mcp/protocol/types.MCPError
MCPError]

MCPClient::listen

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fn MCPClient::listen(self : MCPClient, filter? : ListenFilter, handler~ : (Json) -> Unit, group~ : @moonbitlang/async.TaskGroup
TaskGroup[Unit]) -> Result[String, @colmugx/mcp/protocol/types.MCPError
MCPError]

Start a subscriptions/listen request. Returns the subscription id string on success. The caller must already have started the event loop via run; otherwise a clear error is returned. Notifications carrying the subscription id in params._meta are routed to handler until the server closes the subscription (the final JSON-RPC response causes a background cleanup task to unregister the handler).

MCPClient::next_request_id

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fn MCPClient::next_request_id(self : MCPClient) -> Int

MCPClient::on_elicitation

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fn MCPClient::on_elicitation(self : MCPClient, handler : (Json) -> Result[@colmugx/mcp/protocol/types.ElicitationResult
ElicitationResult, @colmugx/mcp/protocol/types.MCPError
MCPError]) -> MCPClient

MCPClient::on_notification

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fn MCPClient::on_notification(self : MCPClient, handlers : NotificationHandlers) -> MCPClient

MCPClient::on_roots

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fn MCPClient::on_roots(self : MCPClient, handler : () -> Result[Array[@colmugx/mcp/protocol/types.Root
Root], @colmugx/mcp/protocol/types.MCPError
MCPError]) -> MCPClient

MCPClient::on_sampling

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fn MCPClient::on_sampling(self : MCPClient, handler : (Json) -> Result[@colmugx/mcp/protocol/types.CreateMessageResult
CreateMessageResult, @colmugx/mcp/protocol/types.MCPError
MCPError]) -> MCPClient

MCPClient::read_resource

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async fn MCPClient::read_resource(self : MCPClient, uri : String) -> Result[ReadResourceResult, @colmugx/mcp/protocol/types.MCPError
MCPError]

MCPClient::run

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async fn MCPClient::run(self : MCPClient, group : @moonbitlang/async.TaskGroup
TaskGroup[Unit]) -> Unit

MCPClient::set_legacy_mode

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fn MCPClient::set_legacy_mode(self : MCPClient, enabled : Bool) -> MCPClient

Enable or disable legacy mode. When enabled, the event loop accepts server-initiated requests (2025-11-25 behavior); when disabled (the default), such requests are rejected with -32601 per the 2026-07-28 spec.

MCPHost

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pub struct MCPHost {
  name : String
  version : String
  connections : Map[String, MCPClient]
}

MCPHost::MCPHost

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fn MCPHost::MCPHost(name~ : String, version~ : String) -> MCPHost

MCPHost::call_tool

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async fn MCPHost::call_tool(self : MCPHost, qualified_name : String, arguments? : String) -> Result[CallToolResult, @colmugx/mcp/protocol/types.MCPError
MCPError]

MCPHost::close_all

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async fn MCPHost::close_all(self : MCPHost) -> Unit

MCPHost::connect_http

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async fn MCPHost::connect_http(self : MCPHost, name~ : String, url~ : String, auth_token? : String, era? : ProtocolEra) -> Result[Unit, @colmugx/mcp/protocol/types.MCPError
MCPError]

era	server/discover probe	legacy fallback
Auto	yes (default)	allowed
Legacy	skipped	direct connect
Modern	yes	forbidden (Err)

MCPHost::connect_stdio

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async fn MCPHost::connect_stdio(self : MCPHost, name~ : String, cmd~ : String, args? : Array[String], extra_env? : Map[String, String], group~ : @moonbitlang/async.TaskGroup
TaskGroup[Unit], era? : ProtocolEra) -> Result[Unit, @colmugx/mcp/protocol/types.MCPError
MCPError]

Register a named connection to a spawned MCP server. era is passed through to MCPClient::connect_stdio (same semantics table as MCPHost::connect_http).

MCPHost::list_tools

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async fn MCPHost::list_tools(self : MCPHost) -> Result[ListToolsResult, @colmugx/mcp/protocol/types.MCPError
MCPError]

NotificationHandlers

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pub(all) struct NotificationHandlers {
  on_tools_changed : () -> Unit?
  on_resources_changed : () -> Unit?
  on_prompts_changed : () -> Unit?
  on_progress : (@colmugx/mcp/protocol/types.ProgressNotification
ProgressNotification) -> Unit?
  on_cancelled : (@colmugx/mcp/protocol/types.CancelledNotification
CancelledNotification) -> Unit?
  on_resource_updated : (@colmugx/mcp/protocol/types.ResourceUpdatedNotification
ResourceUpdatedNotification) -> Unit?
  on_message : (String, Json?) -> Unit?
}

NotificationHandlers::empty

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fn NotificationHandlers::empty() -> NotificationHandlers

ProtocolEra

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pub(all) enum ProtocolEra {
  Auto
  Legacy
  Modern
} derive(Eq)

Protocol era a client should assume when connecting.

ReadResourceResult

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pub(all) struct ReadResourceResult {
  contents : Array[@colmugx/mcp/protocol/resource.ResourceReadResult
ResourceReadResult]
} derive(Eq, @moonbitlang/core/debug.Debug
Debug)

RequestIdCounter

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type RequestIdCounter

ResourceTemplate

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pub(all) struct ResourceTemplate {
  uri_template : String
  name : String
  description : String?
  mime_type : String?
} derive(Eq, @moonbitlang/core/debug.Debug
Debug)

Source Files

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#CallToolResult

#ClientBackend

#CompletionResult

#ListPromptsResult

#ListResourceTemplatesResult

#ListResourcesResult

#ListToolsResult

#ListenFilter

#ListenFilter::default

#MCPClient

#MCPClient::call_tool

#MCPClient::cancel_listen

#MCPClient::cancel_request

#MCPClient::close

#MCPClient::complete

#MCPClient::connect_http

#MCPClient::connect_stdio

#MCPClient::discover

#MCPClient::get_prompt

#MCPClient::list_prompts

#MCPClient::list_resource_templates

#MCPClient::list_resources

#MCPClient::list_tools

#MCPClient::listen

#MCPClient::next_request_id

#MCPClient::on_elicitation

#MCPClient::on_notification

#MCPClient::on_roots

#MCPClient::on_sampling

#MCPClient::read_resource

#MCPClient::run

#MCPClient::set_legacy_mode

#MCPHost

#MCPHost::MCPHost

#MCPHost::call_tool

#MCPHost::close_all

#MCPHost::connect_http

#MCPHost::connect_stdio

#MCPHost::list_tools

#NotificationHandlers

#NotificationHandlers::empty

#ProtocolEra

#ReadResourceResult

#RequestIdCounter

#ResourceTemplate

Source Files

CallToolResult

ClientBackend

CompletionResult

ListPromptsResult

ListResourceTemplatesResult

ListResourcesResult

ListToolsResult

ListenFilter

ListenFilter::default

MCPClient

MCPClient::call_tool

MCPClient::cancel_listen

MCPClient::cancel_request

MCPClient::close

MCPClient::complete

MCPClient::connect_http

MCPClient::connect_stdio

MCPClient::discover

MCPClient::get_prompt

MCPClient::list_prompts

MCPClient::list_resource_templates

MCPClient::list_resources

MCPClient::list_tools

MCPClient::listen

MCPClient::next_request_id

MCPClient::on_elicitation

MCPClient::on_notification

MCPClient::on_roots

MCPClient::on_sampling

MCPClient::read_resource

MCPClient::run

MCPClient::set_legacy_mode

MCPHost

MCPHost::MCPHost

MCPHost::call_tool

MCPHost::close_all

MCPHost::connect_http

MCPHost::connect_stdio

MCPHost::list_tools

NotificationHandlers

NotificationHandlers::empty

ProtocolEra

ReadResourceResult

RequestIdCounter

ResourceTemplate