Followed by previous post covering message in ROS, this one introduce service in ROS. Service is another information exchange mechanism provided in ROS which provides RPC (remote procedure call) style request-response pattern. The service is defined by .srv file, which can be treated as a combination of two message representing service request and service reply, respectively. Most of information in this post is refer to Services page in ROS wiki, srv page in ROS wiki and source code for ROS core module.

Messages are spread across the whole system of a ROS instance, which are the essence and physical base of communication and coordination in ROS system. The message is a serializable and platform agnostic (in the perspective of OS, programming language, etc) specification of structured data. Most of information in this post is refer to msg page in ROS wiki and source code for ROS core module. A directly connected concept in ROS is Topic, which is named bus for message exchange, which will be covered in later post. The Service is also based on the infrastructure of message, which will be illustrated in next post.

ROS, the robot operation system, is a flexible environment for writing robot software. It is not a traditional operating system but a software development framework including a collection of tools, libraries, and conventions to manage and reduce the complexity of robotic systems. The following configurations are based on the following environment. base: raw Ubuntu 16.04.2 amd64 ROS release: Kinetic (to be installed)