Inside Macintosh: Open Transport /

Chapter 2 - Providers / Providers Reference

Constants and Data Types

The TNetbuf Structure

You use a TNetbuf structure to specify the location and size of a buffer that contains an address, option information, or user data. Provider functions use TNetbuf structures both as input parameters and output parameters. If you are using a TNetbuf structure as an input parameter, you use it to specify the location and size of a buffer containing information you want to send. If you are using a TNetbuf structure as an output parameter, you use it to specify the location and the maximum size of the buffer used to hold information when the function returns.

The TNetbuf structure is defined by the TNetbuf data type.

struct TNetbuf {
   UInt32   maxlen;
   UInt32   len;
   UInt8*   buf;
};

Field Description

maxlen

The size (in bytes) of the buffer to which the buf field points. You must set the maxlen field before passing a TNetbuf structure to a provider function as an output parameter. Open Transport ignores this field if you pass the TNetbuf structure as an input parameter.

len

The actual length (in bytes) of the information in the buffer to which the buf field points. If you are using the TNetbuf structure as an input parameter, you must set this field.

If you pass the TNetbuf structure as an output parameter, on return, the provider function sets this field to the number of bytes the function has actually placed in the buffer referenced by the buf field.

buf

A pointer to a buffer. You must make sure that the buf field points to a valid buffer and that the buffer is large enough to store the information for which it is intended.