Incoming response

Receiving an incoming response

An invoker returns an incoming response asynchronously. This incoming response is created by the connection when it receives the response from the peer.

An incoming response holds:

• a status code
• an error message, set only when the status code is not Ok
• response fields
• the payload of the response

Status code

The status code represents the status of the dispatch by the peer. It can be Ok or an error. StatusCode is an enumeration defined in Slice:

unchecked enum StatusCode : varuint62 {
    Ok = 0
    ApplicationError
    NotFound
    NotImplemented
    ... more errors ...
}

The caller that consumes the response uses this status code to figure out the content of the response payload. For example when the caller is code generated by the Slice compiler, it interprets Ok as meaning the response payload holds a Slice-encoded return value.

Response fields

The response fields represent out-of-band information carried by a response. These fields are usually read and written by middleware and interceptors in an effort to coordinate the processing of the same response in the server and in the client.

A field is an entry in a dictionary ResponseFieldKey to sequence of bytes, where ResponseFieldKey is an enumeration defined in Slice.

unchecked enum ResponseFieldKey : varuint62 {
    CompressionFormat = 2
    ...
}

For example, when the compressor middleware compresses the payload of an outgoing response, it sets the response field CompressionFormat. This tells the compressor interceptor on the other side of the connection "this payload is compressed with brotli"; the compressor interceptor can then decompress this (incoming) response payload.

Response payload

The payload of an incoming response is a stream of bytes that represents the return value of an operation. As far as IceRPC is concerned, the number of bytes in this stream is unknown.