Stepping off end of collection when desired key is not in the payload but other ignored keys are present

[rubixhacker]

• Version: 0.5.2
• All platforms

When decoding a nested structure if the desired key is not present in the structure and ignoreUnknownKeys is set to true, MsgPackDecoder will step outside the bounds of the nested structure and continue searching for the key in the parent structure until it hits the end of the payload. Causing Kotlin Serialization to report required keys are missing in the parent structure.

As an example, take the given json encoded payload:

{
    "a": 1,
    "b": {
        "d": 2,
        "e": 3
     },
     "f":4
}

And the following Kotlin serializable class

@Serializable
data class Example(val a: Int, val b: Example.Child, val f: Int) {
     
     @Serializable
     data class Child(val c: String? = null)
}

ClassMsgPackDecoder when trying to find "c" will start a recursive call to BasicMsgPackDecoder.decodeElementIndex which if ignoreUnknownKeys is true will continue recursively calling BasicMsgPackDecoder.decodeElementIndex until it either finds "c" or in this case hits the end of the payload. Kotlin serialization will report that it could not find the required key "f"

ClassMsgPackDecoder needs to get the result of BasicMsgPackDecoder.decodeElementIndex so that it can properly increment decodedElements

[esensar]

Thank you for reporting this and thank you for taking your time to investigate the issue.

Feel free to open a PR if you wish to fix this yourself. If not, I will take it on as soon as I have the time.