Transport Interface

Using the Transport Interface

Some transports may ignore the

ReceiveRequest

message, since they receive

data continuously. Others may use this message as a trigger to initiate a connection.

You can choose to comply with or ignore any request to receive, depending on the
communication resources available and their status. If you choose to comply, the

ReceiveRequest

method should establish a connection and begin receiving by

whatever means the transport uses to communicate. For example, many transports
use the Endpoint interface to establish and operate a connection. After receiving the
item, you should call the transport method

NewFromItem

to copy it into a

standard item frame used by the In/Out Box. Finally, you must call

ItemCompleted

to write the item to the In Box.

If your transport creates virtual binary objects, you must use the method

GetDefaultOwnerStore

to determine on which store to create them.

The

body

slot within every received item must have a

class

slot

to identify its data class. Data objects received from other Newton
devices always have a

class

slot. For data received from other

systems, your transport must assign a meaningful class to the

item.body

object.

Some transports might want to download just part of an item initially, such as its
title, then download the actual item data when a user requests it. For example, upon
connection an e-mail transport might download just the titles of messages or other
data objects. When the user attempts to view one of these items in the In Box, the
transport then downloads the body of the item from the remote host.

This feature is accomplished by the use of the

cause

slot in the parameter passed

to the

ReceiveRequest

method, and by the use of a

remote

slot in the item frame.

If a transport initially downloads just a part of each item, such as its title, it must
insert a slot called

remote

, whose value is

true

in the item frame of those items.

This slot serves as a flag to tell the In/Out Box that the body of the item is stored
remotely and has not yet been downloaded.

When the user attempts to view one of these items in the In Box, the In Box sees
the

remote

slot, and sends the transport the

ReceiveRequest

message with the

'remote

cause. This alerts the transport to download the body of the item from

the remote host. If the user selected multiple remote items for downloading, you
must use the

ItemRequest

method to retrieve subsequent requested items and

download them. Keep calling

ItemRequest

until it returns

nil

, which signals

that there are no more items to retrieve.