31.2.3 Using transport agents via system calls

Once transport agents have been configured and applications attached, applications can use transport services via the following system calls. These calls can be invoked at either OTcl or C++ level, thereby allowing applications to be coded in either C++ or OTcl. These functions have been implemented as virtual functions in the base class Agent, and can be redefined as needed by derived Agents.

• send(int nbytes)--Send nbytes of data to peer. For TCP agents, if nbytes == -1, this corresponds to an ``infinite'' send; i.e., the TCP agent will act as if its send buffer is continually replenished by the application.
• sendmsg(int nbytes, const char* flags = 0)--Identical to send(int nbytes), except that it passes an additional string flags. Currently one flag value, ``MSG_EOF,'' is defined; MSG_EOF specifies that this is the last batch of data that the application will submit, and serves as an implied close (so that TCP can send FIN with data).
• close()--Requests the agent to close the connection (only applicable for TCP).
• listen()--Requests the agent to listen for new connections (only applicable for Full TCP).
• set_pkttype(int pkttype)--This function sets the type_ variable in the agent to pkttype. Packet types are defined in packet.h. This function is used to override the transport layer packet type for tracing purposes.

Note that certain calls are not applicable for certain agents; e.g., a call to []close a UDP connection results in a no-op. Additional calls can be implemented in specialized agents, provided that they are made public member functions.