Inside Macintosh: Networking With Open Transport / Part 1 - Open Transport Essentials

Chapter 7 - Option Management

This chapter explains the use of options, values associated with an endpoint provider, which you can change to fine-tune or customize the data-transfer service offered by the endpoint. In general, the use of options degrades transport independence. Therefore, it is important to note that default option values are provided for every type of endpoint and that you can write applications that never need to specify any options. You need to read this chapter if

• you need to use services that must be specified using options

  For example, you are using a transaction-based endpoint and need to be able to send expedited data in order to forward an attention message.

• it is critical to your application that you fine-tune the data-transfer services offered by a protocol and you can only do this by using options

  For example, you need to manipulate the size of internal send and receive buffers to eliminate data backlog or buffer overflow problems.

• you need to create a debugging version of the application through the use of options

This chapter describes general options that can be specified by any protocol that supports them, explains how you construct an options buffer, how you get and set option values, and how you verify values. It also provides code samples that show how you

• construct option buffers

• parse buffers containing option information

• get, set, and display option values.

To understand this chapter, you should be familiar with endpoint providers and the endpoint functions used to transfer data. These topics are discussed in "Endpoints". For specific information about the options that are supported for a protocol implementation, you need to consult the documentation provided for that protocol.

In general, it is recommended that you set up your options using the OTOptionManagement function after creating your endpoint and before using it. The actual semantics of option negotiation are somewhat complicated and are covered in "XTI Option Summary".

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Chapter Contents

About Options and Option Negotiation

Explicit Use of Options and Portability of Code

Types of Options

The Format of Option Information

XTI-Level Options and General Options

Using Options

Determining Which Function to Use to Negotiate Options

Obtaining the Maximum Size of an Options Buffer

Setting Option Values

Specifying Option Values

Setting Default Values

Retrieving Option Values

Obtaining Current and Default Values

Parsing an Options Buffer

Verifying Option Values

Sample Code: Getting and Setting Options