Exchanging Data During a PPC Session

After a session begins, each application can send data to and receive data from

the other using a sequence of message blocks. The PPC Toolbox treats each

message block as a byte stream and does not interpret the contents of the

message block. The size of a message block can be between 0 and (232-1)

bytes. The PPC Toolbox treats the buffer size as an unsigned long integer.

The PPC Toolbox delivers the message blocks in the same sequence as they

are sent and without duplicates. In the following picture, an application

transmits message blocks during a session.

Transmitting message blocks

For each message block, you specify a block creator, block type, and

user data. The first PPCWrite function that you use to create a new message

block sets the attributes for the block. The PPCRead function returns the

block creator, block type, and user data attributes for the current message

block when the call completes.

Although the PPC Toolbox does not interpret these attributes, they can give

the receiving application information about how to process the contents of the

message block. For example, a database application may specify a counter to

indicate the block number (block number 20 of 30 total blocks) in the block

creator field. This application could also specify a code, such as 'DREC', in the

block type field to indicate that the information it contains is a database record.

In addition, this application could specify the length of the message block in the

user data field.