<> <> The publish / subscribe model is a very flexible communication paradigm, but its many-to-many one-way transport is not appropriate for RPC request / reply interactions, which are often required in a distributed system. Request / reply is done via a ''Service,'' which is defined by a pair of [[Messages|messages]]: one for the request and one for the reply. A providing ROS [[Nodes|node]] offers a service under a string [[Names|name]], and a client calls the service by sending the request message and awaiting the reply. Client libraries usually present this interaction to the programmer as if it were a remote procedure call. Services are defined using [[srv]] files, which are compiled into source code by a ROS client library. A client can make a ''persistent connection'' to a service, which enables higher performance at the cost of less robustness to service provider changes. == Service Types == Like [[Topics|topics]], services have an associated ''service type'' that is the [[Names|package resource name]] of the `.srv` file. As with other ROS filesystem-based types, the service type is the package name + the name of the `.srv` file. For example, `my_srvs/srv/PolledImage.srv` has the service type `my_srvs/PolledImage`. In addition to the service type, services are versioned by an MD5 sum of the `.srv` file. Nodes can only make service calls if both the service type and MD5 sum match. This ensures that the client and server code were built from a consistent codebase. == Service Tools == * [[rossrv]]: displays information about `.srv` data structures. See [[rossrv]] for documentation on how to use this tool. * [[rosservice]]: lists and queries ROS Services == Client Library Support == === Python === See the [[rospy/Overview/Services| rospy overview]]. === C++ === See the [[roscpp/Overview/Services| roscpp overview]]. == Additional Resources == Here are some additional resources contributed by the community: === Video Tutorial === The following video presents a small tutorial explaining the concept of ROS Service <>