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Bidirectional Communication

The Stepflow Protocol supports bidirectional communication, enabling component servers to make requests back to the runtime during component execution. This capability enables powerful patterns like blob storage, flow evaluation, and runtime introspection while maintaining the JSON-RPC request-response model.

Overview​

While the primary communication flow is Runtime → Component Server, the protocol enables Component Server → Runtime requests for:

  • Blob Storage: Store and retrieve persistent data using content-addressable storage
  • Flow Evaluation: Resolve workflow expressions in runtime context
  • Runtime Queries: Access workflow metadata and execution state (future)
  • Resource Access: Request additional resources or capabilities (future)

Communication Model​

Unidirectional vs Bidirectional​

Traditional Model (Unidirectional):

Stepflow Model (Bidirectional):

Available Methods​

Component servers can call these methods during execution:

Blob Storage Methods​

  • blobs/put: Store JSON data, receive content-addressable blob ID
  • blobs/get: Retrieve stored data by blob ID

See Blob Storage Methods for detailed specifications.

Flow Evaluation Methods​

  • flows/evaluate: Evaluate workflow expressions in runtime context

See Flow Methods for detailed specifications.