contains a generator of frames that should be sent. The server
       assumes that all frames are sent to the client.

    error
       Indicates that an error occurred. Consumer should probably abort.

    runcommand
       Indicates that the consumer should run a wire protocol command. Details
       of the command to run are given in the data structure.

    wantframe
       Indicates that nothing of interest happened and the server is waiting on
       more frames from the client before anything interesting can be done.

    noop
       Indicates no additional action is required.

    Known Issues
    ------------

    There are no limits to the number of partially received commands or their
    size. A malicious client could stream command request data and exhaust the
    server's memory.

    Partially received commands are not acted upon when end of input is
    reached. Should the server error if it receives a partial request?
    Should the client send a message to abort a partially transmitted request
    to facilitate graceful shutdown?

    Active requests that haven't been responded to aren't tracked. This means
    that if we receive a command and instruct its dispatch, another command
    with its request ID can come in over the wire and there will be a race
    between who responds to what.
    c