## page was renamed from Implementing_Client_Libraries
= Implementing Client Libraries =

NOTE: this page is just a collection of notes right now. Apologies.

It is ''highly recommended'' that you read the [[ROS/Technical Overview|ROS Technical Overview]] first. It describes the general interaction of these APIs.


At a minimum, a client library MUST:
 * implement the slave side of the [[ROS/Master_Slave_APIs|master/slave API]].  This involves managing an XML/RPC server, and issuing and responding to XML/RPC requests. 
 * handle node-to-node transport negotiation and connection setup.  A client library may only support a subset of the possible transport mechanisms, most likely [[ROS/TCPROS]]
 * handle transport-specific serialization and deserialization of messages.

A client library SHOULD also:

 * parse command-line [[Remapping Arguments]]. A node that cannot do this will not be reconfigurable.
 * Subscribe to a simulated [[Clock]]
 * publish debugging messages to [[rosout]]
 * depend on the [[roslang]] package, which allows [[rosbuild]] and other tools to perform appropriate actions, such as msg- and srv-based code generation

In addition, client libraries generally offer other features, such as:
 * object representation of message types
 * event loop for connection servicing
 * user callback invocation on message receipt

== Message generation ==

Message generators commonly include two fields within the generated source code that is required during Topic/Service connection:
 * md5sum: this is computed by `roslib/scripts/gendeps --md5 msg-file`
 * Message definition: this is computed by `roslib/scripts/gendeps --cat msg-file`

== Topic/Service Connection ==

Nodes usually spin up a TCP/IP server socket to receive both TCPROS-based Topic connections as well as all Service connections. The client will send the server a [[ROS/Connection_Header]], which can be used the route the inbound connection to the appropriate Topic/Service handler. For more information on these fields, see the [[ROS/Connection_Header]] documentation.