Transport Interface

Using the Transport Interface

the routing slip is not closed. If

TransportChanged

returns

nil

, then the

transport is changed and operations continue normally.

You can use the function

GetGroupTransport

to determine the name of the

current (last-used for sending by the user) transport in a group. Note that when you
install a grouped transport, it becomes the current transport for that group.

Transports that are part of a group are individually selectable on the Send, Receive,
and Preferences pickers in the In/Out Box.

Sending Data

22

The Out Box sends the

SendRequest

message to your transport when data needs

to be sent. If your transport supports sending data, you must define this method to
actually send the data. For a complete description of the

SendRequest

method,

see "SendRequest" (page 19-33) in Newton Programmer's Reference.

The Out Box puts its own query information in the request frame argument to

SendRequest

. Your

SendRequest

method must pass this frame to the

ItemRequest

message to get the item (or next item) to send. In your

SendRequest

method, keep calling

ItemRequest

until it returns

nil

,

signalling no more items to send. For a complete description of the

ItemRequest

method, see "ItemRequest" (page 19-26) in Newton Programmer's Reference.

If the

body

slot of an item originally contained an alias, the alias is automatically

resolved by

ItemRequest

. That is, items returned by

ItemRequest

always

contain a

body

slot that is not an alias.

Note that you can save entry aliases to items returned by

ItemRequest

, if you

want. Later, when using them, make sure that

ResolveEntryAlias

returns a

non-

nil

value, and that the item

state

slot is set as expected.

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

SendRequest

method must obtain one or more items from the Out Box by using

the

ItemRequest

method, and send them by whatever means the transport uses

to communicate. For example, most transports use the Endpoint interface to
establish and operate a connection.

If request.

cause

is

'submit

, the item is queued in the Out Box for later sending,

but the Out Box still notifies the transport by sending it this

SendRequest

message so that the transport knows there are items waiting to be sent. Typically, a
transport doesn't need to take any immediate action on items where request.

cause

is

'submit

, so you can use code like this to simply return:

If request.cause = 'submit then return nil;

The

item.connect

slot contains a Boolean value indicating if the user chose to

send the item now (

true

) or later (

nil

).