Stub (distributed computing)
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distributed computing Distributed computing is a field of computer science that studies distributed systems, defined as computer systems whose inter-communicating components are located on different networked computers. The components of a distributed system commu ...
, a stub is a program that acts as a temporary replacement for a remote service or object. It allows the client application to access a service as if it were local, while hiding the details of the underlying network communication. This can simplify the development process, as the client application does not need to be aware of the complexities of distributed computing. Instead, it can rely on the stub to handle the remote communication, while providing a familiar interface for the developer to work with.


Application

The stub represents a remote object or service on a local system. It acts as a proxy for the remote service and allows the client program to make method calls on the remote object as if it were local. The process of generating stubs involves creating a client-side proxy object that provides the same interface as the remote service, but routes method calls to the actual remote object. In
distributed computing Distributed computing is a field of computer science that studies distributed systems, defined as computer systems whose inter-communicating components are located on different networked computers. The components of a distributed system commu ...
, a stub is a piece of code that converts parameters passed between the client and server during a remote procedure call (RPC). The main purpose of an
RPC RPC may refer to: Science and technology * Rational polynomial coefficient * Reactive Plastic Curtain, a carbon-dioxide-absorbing device used in some rebreather breathing sets * Regional Playback Control, a regional lockout technology for DVDs ...
is to allow a local computer (
client Client(s) or The Client may refer to: * Client (business) * Client (computing), hardware or software that accesses a remote service on another computer * Customer or client, a recipient of goods or services in return for monetary or other valuable ...
) to invoke procedures on a remote computer (
server Server may refer to: Computing *Server (computing), a computer program or a device that provides requested information for other programs or devices, called clients. Role * Waiting staff, those who work at a restaurant or a bar attending custome ...
). Since the client and server have different address spaces, the parameters used in a function call must be converted. Otherwise, the parameter values would be unusable because pointers to parameters in one computer's memory would reference different data on the other computer. Also, the client and server can have different data representations, even for simple parameters like integers (e.g.,
big-endian '' Jonathan_Swift.html" ;"title="Gulliver's Travels'' by Jonathan Swift">Gulliver's Travels'' by Jonathan Swift, the novel from which the term was coined In computing, endianness is the order in which bytes within a word (data type), word of d ...
versus
little-endian '' Jonathan_Swift.html" ;"title="Gulliver's Travels'' by Jonathan Swift">Gulliver's Travels'' by Jonathan Swift, the novel from which the term was coined In computing, endianness is the order in which bytes within a word (data type), word of d ...
). Stubs handle parameter conversion, making a remote procedure call look like a local function call to the remote computer. Stub libraries are crucial in distributed computing, as they allow for local procedure calls to be made to remote objects or services. The client-side stub or proxy is responsible for converting the parameters used in a function call and deconverting the results returned by the server after executing the function, a process known as marshalling. The stub libraries must be installed on both the client and server, with the server-side stub, or server skeleton, being responsible for deconverting the parameters passed by the client and converting the results after executing the function. In virtual testing environments, stubs are used to simulate distributed computing, allowing for more efficient and effective verification of software updates in variant-rich automotive systems. /sup>


Steps to writing tests with stubs

To write tests with stubs, follow these steps: # Identify the external components or services that the component being tested relies on to function correctly. /sup> or manually create stubs versions of the dependencies that return predefined values or responses when called by the component under test. # Write test cases for the component, using the stubs instead of the actual dependencies. /sup> # Set up the test environment by initializing the component under test and its stubs. # Run the tests and analyze the results. If the tests fail, review the code and stubs to determine the cause of the issue. /sup> # Refactor the code and stubs as necessary to improve the quality of the tests and the component. /sup> It's crucial to use stubs only when needed, as they may introduce additional complexity and maintenance overhead. Furthermore, the stubs should accurately mimic the behavior of the actual dependencies to avoid introducing false positives or negatives in the tests. /sup>


References

{{reflist Distributed computing architecture