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STDIO Transport

The STDIO transport provides process-based communication between the Stepflow runtime and component servers using standard input and output streams. This transport is ideal for local component servers that can be executed as subprocesses.

Overview​

STDIO transport creates a subprocess for each component server and communicates via:

  • stdin: Stepflow runtime sends JSON-RPC messages to the component server
  • stdout: Component server sends JSON-RPC responses and bidirectional requests
  • stderr: Component server sends logs and diagnostic information (not part of protocol)
warning

Relying on stderr for logging is discouraged, since it is not supported by other transports. It may be useful in development or when accessing the component-server logs is easy, but in general a structrued logging mechanism (e.g., tracing) is preferred.

Process Lifecycle​

The main benefit of the STDIO transport for local development is that the Stepflow runtime manages the component server processes.

Process Creation​

The Stepflow runtime spawns component server processes using the configured command and arguments:

See Configuration Documentation for complete plugin configuration options.

Process Management​

  • Startup: Runtime spawns process and waits for initialization
  • Health monitoring: Runtime monitors process status and stdio streams
  • Graceful shutdown: Runtime closes stdin and waits for process termination
  • Forced termination: Runtime kills process after timeout if needed

Process Environment​

Process environment, working directory, and resource limits are configured via the runtime configuration. See Configuration - STDIO Transport for details.