c++/src/capnp/stream.capnp

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@0x86c366a91393f3f8;
# Defines placeholder types used to provide backwards-compatibility while introducing streaming
# to the language. The goal is that old code generators that don't know about streaming can still
# generate code that functions, leaving it up to the application to implement flow control
# manually.

$import "/capnp/c++.capnp".namespace("capnp");

struct StreamResult @0x995f9a3377c0b16e {
  # Empty struct that serves as the return type for "streaming" methods.
  #
  # Defining a method like:
  #
  #     write @0 (bytes :Data) -> stream;
  #
  # Is equivalent to:
  #
  #     write @0 (bytes :Data) -> import "/capnp/stream.capnp".StreamResult;
  #
  # However, implementations that recognize streaming will elide the reference to StreamResult
  # and instead give write() a different signature appropriate for streaming.
  #
  # Streaming methods do not return a result -- that is, they return Promise<void>. This promise
  # resolves not to indicate that the call was actually delivered, but instead to provide
  # backpressure. When the previous call's promise resolves, it is time to make another call. On
  # the client side, the RPC system will resolve promises immediately until an appropriate number
  # of requests are in-flight, and then will delay promise resolution to apply back-pressure.
  # On the server side, the RPC system will deliver one call at a time.
}