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Newton Technology Journal June 1996

configuration of your links, and a communications tool that you use with

your endpoints to perform communications on the Internet.

Figure 1 shows the relationship of the Newton Internet Enabler

components.

Figure 1 Newton Internet Enabler components

The Newton Internet Enabler application programming interface

provides two kinds of functions: domain name service functions and link

controller functions. You use the domain name service functions to translate

between Internet domain names and their corresponding IP addresses. You

use the link controller functions to establish, release, and find the status of

your Internet links.

The domain name service and link controller functions are global

functions in the Newton system software. These functions provide an

interface between Newton communications endpoints and the Inet tool,

which is the underlying communications tool that performs the actual work

of establishing, maintaining, and communicating over the links.

The Inet communications tool provides a configurable stack of protocols

at and below the TCP/IP level. The Inet tool is a standard Newton

communications tool, which means that it provides all of the endpoint

services that are provided by other built-in communications tools, such as

the built-in modem tool and the built-in serial tool. Like the other

communications tools, you can control the configuration of the Inet tool

with communications options.

The Inet tool can establish physical links using various low-level

communications services. Each communications service is provided by a

Newton communications tool such as the built-in modem tool. The Inet

tool can run various link-level protocols that are provided with the Newton

system software, including PPP and SLIP.

Your application can use several endpoints with the same Newton

Internet Enabler link. Each endpoint, however, requires a significant amount

of memory. The total number (for all applications) of endpoints that can be

active is restricted by a combination of the user’s hardware configuration and

which software is currently in use on the device.

The remainder of this article describes the Newton Internet Enabler

application programming interface. The November, 1995 issue of Newton

Technology Journal (Volume 1, Number 5) provides an overview of Newton

communications technology, including a discussion of endpoints and

communications tools.

NEWTON INTERNET ENABLER AND CALLBACK FUNCTIONS

Many of the Newton Internet Enabler functions require you to provide a

callback function, which is a function that the Inet tool calls during and/or

after the performance of the operation that you requested. The callback

function receives status and error information.

For example, the InetCancelLink function calls the callback

function that you provide after it finishes its operation. Your callback

function for InetCancelLink can determine if an error occurred and

can determine the current status of the link that you wanted canceled.

Some operations call your callback function more than once. For

example, the InetGrabLink function calls the callback function you

provide many times during its operations. You can use your

InetGrabLink callback function to monitor the progress of the grab,

since each call to it provides you with the current status.

When a function requires that you specify a callback function, you do

so by providing a context frame and the symbol of the function defined in

that frame that you want to use as the callback function. For example,

the InetGrabLink function takes three parameters and is declared

as follows:

InetGrabLink(linkID, clientContext, clientCallback);

When you call InetGrabLink, you must specify a frame (or your

application frame) as the value of

clientContext

, and you must specify a

function defined in the frame as the value of

clientCallback

You might create a callback function for your InetGrabLink calls

that looks like the following:

myApp.GrabLinkCallback := func(linkID, stat, err)

begin

if err=nil and stat.linkStatus <> 'connected then

; // display status

if err then

; //handle the error

// link established, so resolve the address

end;

Lower-level Newton comm tool

(e.g. the b uilt-in modem tool)

Link

Controller

requests

SLIP

PPP

configuration info

host names,

IP numbers

endpoint

comm scripting

messages

Inet tool

function calls

Inet tool

option requests

physical link requests

comm tool requests, e.g.

connect, get, put

data indata out

Setup

application

NewtonScript

client applications

Link Controller

Domain

Name

Server

Inet tool

TCP

UDP

serial stub driver

transport services

link-level protocols

communications stack

continued from page 1

Newton Internet Enabler

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