io.modelcontextprotocol.client.transport

Class StdioClientTransport

java.lang.Object

io.modelcontextprotocol.client.transport.StdioClientTransport

All Implemented Interfaces:

McpClientTransport, McpTransport

public class StdioClientTransport
extends Object
implements McpClientTransport

Implementation of the MCP Stdio transport that communicates with a server process using standard input/output streams. Messages are exchanged as newline-delimited JSON-RPC messages over stdin/stdout, with errors and debug information sent to stderr.

Author:

Christian Tzolov, Dariusz Jędrzejczyk

Constructor Summary

Constructors

Constructor and Description
StdioClientTransport(ServerParameters params) Creates a new StdioClientTransport with the specified parameters and default ObjectMapper.
StdioClientTransport(ServerParameters params, com.fasterxml.jackson.databind.ObjectMapper objectMapper) Creates a new StdioClientTransport with the specified parameters and ObjectMapper.

Method Summary

Modifier and Type	Method and Description
void	awaitForExit() Waits for the server process to exit.
reactor.core.publisher.Mono<Void>	closeGracefully() Gracefully closes the transport by destroying the process and disposing of the schedulers.
reactor.core.publisher.Mono<Void>	connect(Function<reactor.core.publisher.Mono<McpSchema.JSONRPCMessage>,reactor.core.publisher.Mono<McpSchema.JSONRPCMessage>> handler) Starts the server process and initializes the message processing streams.
reactor.core.publisher.Sinks.Many<String>	getErrorSink()
protected ProcessBuilder	getProcessBuilder() Creates and returns a new ProcessBuilder instance.
protected void	handleOutbound(Function<reactor.core.publisher.Flux<McpSchema.JSONRPCMessage>,reactor.core.publisher.Flux<McpSchema.JSONRPCMessage>> outboundConsumer)
reactor.core.publisher.Mono<Void>	sendMessage(McpSchema.JSONRPCMessage message) Sends a message to the peer asynchronously.
void	setStdErrorHandler(Consumer<String> errorHandler) Sets the handler for processing transport-level errors.
<T> T	unmarshalFrom(Object data, com.fasterxml.jackson.core.type.TypeReference<T> typeRef) Unmarshals the given data into an object of the specified type.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface io.modelcontextprotocol.spec.McpClientTransport

setExceptionHandler

Methods inherited from interface io.modelcontextprotocol.spec.McpTransport

close, protocolVersions

Constructor Detail

StdioClientTransport

public StdioClientTransport(ServerParameters params)

Creates a new StdioClientTransport with the specified parameters and default ObjectMapper.

Parameters:

params - The parameters for configuring the server process

StdioClientTransport

public StdioClientTransport(ServerParameters params,
                            com.fasterxml.jackson.databind.ObjectMapper objectMapper)

Creates a new StdioClientTransport with the specified parameters and ObjectMapper.

Parameters:

params - The parameters for configuring the server process

objectMapper - The ObjectMapper to use for JSON serialization/deserialization

Method Detail

connect

public reactor.core.publisher.Mono<Void> connect(Function<reactor.core.publisher.Mono<McpSchema.JSONRPCMessage>,reactor.core.publisher.Mono<McpSchema.JSONRPCMessage>> handler)

Starts the server process and initializes the message processing streams. This method sets up the process with the configured command, arguments, and environment, then starts the inbound, outbound, and error processing threads.

Specified by:

connect in interface McpClientTransport

Parameters:

handler - a transformer for incoming messages

Returns:

a Mono that terminates upon successful client setup. It can mean establishing a connection (which can be later disposed) but it doesn't have to, depending on the transport type. The successful termination of the returned Mono simply means the client can now be used. An error can be retried according to the application requirements.

Throws:

RuntimeException - if the process fails to start or if the process streams are null

getProcessBuilder

protected ProcessBuilder getProcessBuilder()

Creates and returns a new ProcessBuilder instance. Protected to allow overriding in tests.

Returns:

A new ProcessBuilder instance

setStdErrorHandler

public void setStdErrorHandler(Consumer<String> errorHandler)

Sets the handler for processing transport-level errors.

The provided handler will be called when errors occur during transport operations, such as connection failures or protocol violations.

Parameters:

errorHandler - a consumer that processes error messages

awaitForExit

public void awaitForExit()

Waits for the server process to exit.

Throws:

RuntimeException - if the process is interrupted while waiting

sendMessage

public reactor.core.publisher.Mono<Void> sendMessage(McpSchema.JSONRPCMessage message)

Description copied from interface: McpTransport

Sends a message to the peer asynchronously.

This method handles the transmission of messages to the server in an asynchronous manner. Messages are sent in JSON-RPC format as specified by the MCP protocol.

Specified by:

sendMessage in interface McpTransport

Parameters:

message - the McpSchema.JSONRPCMessage to be sent to the server

Returns:

a Mono that completes when the message has been sent

handleOutbound

protected void handleOutbound(Function<reactor.core.publisher.Flux<McpSchema.JSONRPCMessage>,reactor.core.publisher.Flux<McpSchema.JSONRPCMessage>> outboundConsumer)

closeGracefully

public reactor.core.publisher.Mono<Void> closeGracefully()

Gracefully closes the transport by destroying the process and disposing of the schedulers. This method sends a TERM signal to the process and waits for it to exit before cleaning up resources.

Specified by:

closeGracefully in interface McpTransport

Returns:

A Mono that completes when the transport is closed

getErrorSink

public reactor.core.publisher.Sinks.Many<String> getErrorSink()

unmarshalFrom

public <T> T unmarshalFrom(Object data,
                           com.fasterxml.jackson.core.type.TypeReference<T> typeRef)

Description copied from interface: McpTransport

Unmarshals the given data into an object of the specified type.

Specified by:

unmarshalFrom in interface McpTransport

Type Parameters:

T - the type of the object to unmarshal

Parameters:

data - the data to unmarshal

typeRef - the type reference for the object to unmarshal

Returns:

the unmarshalled object