Apple Newton Utilities User's Guide download pdf (Page 848)

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101

CHAPTER 23

Endpoint Interface

23-20 Using the Endpoint Interface

IMPORTANT

Do not call the Input or Partial methods in a polling loop to

look for incoming data. The Newton communications architecture

requires a return to the main event loop in order to process

incoming data from the endpoint’s underlying communication

tool. These methods are included as an alternate way of retrieving

data from the incoming data buffer, not as a way to implement

synchronous data receives.

▲

To ﬂush data from the input buffer, you can use the methods FlushInput and

FlushPartial. The FlushInput method discards all data in the input buffer,

and

FlushPartial discards all data read by the last call to the Partial method.

Streaming Data In and Out 23

Besides protoBasicEndpoint, there is another type of endpoint proto called

protoStreamingEndpoint. The purpose of this streaming endpoint is to

provide a way to send and receive large frames without having ﬁrst to ﬂatten or

unﬂatten them.

Flattening refers to the process of converting a frame object into a stream of bytes.

Unﬂattening refers to the process of converting those bytes back into a frame object.

With the streaming endpoint, frame data is ﬂattened or unﬂattened in chunks as it is

sent or received. This allows large objects to be sent and received without causing

the NewtonScript heap to overﬂow as a result of having to convert an entire object

at once.

The

protoStreamingEndpoint proto is based on protoBasicEndpoint

and includes a method,

StreamIn, that allows you to receive streamed data. This

method automatically unﬂattens received data into a frame object in memory, and

can place embedded virtual binary objects directly on a store. Another method,

StreamOut, allows you to send frame data as a byte stream. Note that these two

methods are synchronous; that is, they don’t return until the operation is complete.

However, they do provide progress information during the operation by means of a

periodic callback.

Working With Binary Data 23

For receiving binary data, the data is returned as a raw byte stream. The data is not

converted and is block-moved directly into a binary object that you have

preallocated and speciﬁed as the target for the input.

To create this target object, specify a

target frame in your input spec. This frame

contains a

data slot and optionally an offset slot. The data slot contains the

preallocated binary (or virtual binary) object, while the

offset slot is the offset

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