struct StreamOptions
    // The max size of unconsumed data allowed at remote side.
    // If |max_buf_size| <= 0, there's no limit of buf size
    // default: 2097152 (2M)
    int max_buf_size;

    // Notify user when there's no data for at least |idle_timeout_ms|
    // milliseconds since the last time that on_received_messages or on_idle_timeout
    // finished.
    // default: -1
    long idle_timeout_ms;

    // Maximum messages in batch passed to handler->on_received_messages
    // default: 128
    size_t messages_in_batch;

    // Handle input message, if handler is NULL, the remote side is not allowd to
    // write any message, who will get EBADF on writting
    // default: NULL
    StreamInputHandler* handler;
};

// [Called at the client side]
// Create a Stream at client-side along with the |cntl|, which will be connected
// when receiving the response with a Stream from server-side. If |options| is
// NULL, the Stream will be created with default options
// Return 0 on success, -1 otherwise
int StreamCreate(StreamId* request_stream, Controller &cntl, const StreamOptions* options);

// [Called at the server side]
// Accept the Stream. If client didn't create a Stream with the request
// (cntl.has_remote_stream() returns false), this method would fail.
// Return 0 on success, -1 otherwise.
int StreamAccept(StreamId* response_stream, Controller &cntl, const StreamOptions* options);

class StreamInputHandler {
public:
    // Callback when stream receives data
    virtual int on_received_messages(StreamId id, butil::IOBuf *const messages[], size_t size) = 0;

    // Callback when there is no data for a long time on the stream
    virtual void on_idle_timeout(StreamId id) = 0;

    // Callback when stream is closed by the other end
    virtual void on_closed(StreamId id) = 0;
};

// Write |message| into |stream_id|. The remote-side handler will received the
// message by the written order
// Returns 0 on success, errno otherwise
// Errno:
//  - EAGAIN: |stream_id| is created with positive |max_buf_size| and buf size
//            which the remote side hasn't consumed yet excceeds the number.
//  - EINVAL: |stream_id| is invalied or has been closed
int StreamWrite(StreamId stream_id, const butil::IOBuf &message);

// Wait util the pending buffer size is less than |max_buf_size| or error occurs
// Returns 0 on success, errno otherwise
// Errno:
//  - ETIMEDOUT: when |due_time| is not NULL and time expired this
//  - EINVAL: the Stream was close during waiting
int StreamWait(StreamId stream_id, const timespec* due_time);

// Async wait
void StreamWait(StreamId stream_id, const timespec *due_time,
                void (*on_writable)(StreamId stream_id, void* arg, int error_code),
                void *arg);

// Close |stream_id|, after this function is called:
//  - All the following |StreamWrite| would fail
//  - |StreamWait| wakes up immediately.
//  - Both sides |on_closed| would be notifed after all the pending buffers have
//    been received
// This function could be called multiple times without side-effects
int StreamClose(StreamId stream_id);