I have been looking at the Ktor-client source code on github trying to understand it before making contributions when I came across this file. I see java syntax but I do not understand why it has the extension (.api), plus what it is used for. Any answers of ref links will be appreciated.

CodePudding user response：

It is because of the following line in Gradle configuration https://github.com/ktorio/ktor/blob/290cd60fc1ee4c78ae84fcba4c76d590ab0af18f/gradle/compatibility.gradle#L1

Quoting from README of Binary compatibility validator on GitHub

The tool allows to dump binary API of a Kotlin library that is public in sense of Kotlin visibilities and ensures that the public binary API wasn't changed in a way that make this change binary incompatible.

You can read more about this at https://github.com/Kotlin/binary-compatibility-validator.