This issue is coming from a discussion between @urso, @kvch and @ph

Recently we have refactored the interface used by prospectors to input, but we should do a bit more refactoring on the usage of the inputs especially between the interaction with each other.

• Currently, we have the Docker and the Log input coupled.
• We will have the Syslog and the UDP/TCP input coupled.

We think that An input must not use another inputs, inputs should be isolated and mostly deal
with configuration. Instead, the TCP/UDP/Log should be refactored to be reusable components for the
inputs. They could become InputReader or InputStream, that defined in their package.

We could have the following:

• A UDP Server
• A TCP Server
• A FileWatcher for files/log

This change is necessary with the planning of adding more inputs to Filebeat and making sure the code stay testable and isolated.

This issue is created to discuss implementation details and interface required for this change.