Execute HTTP Post in a loop in Groovy (Jenkins) - rest

Question

I'm developing a shared library in Jenkins to help with interacting with an internal API. I can make single call which starts a long running process to create an object. I have to continue to query the API to check for the process' completion.
I'm trying to get this done in using a simple loop, but I keep getting stuck. Here's my function to query the API until it's completed:
def url = new URL("http://myapi/endpoint")
HttpURLConnection = http = (HttpURLConnection) url.openConnection()
http.setDoOutput(true)
http.setRequestMethod('POST')
http.setRequestProperty("Content-Type", "application/x-www-form-urlencoded")
def body = ["string", "anotherstring"].join('=')
OutputStreamWriter osw = new OutputStreamWriter(http.outStream)
osw.write(body)
osw.flush()
osw.close()
for(int i = 0; i < 30; i++) {
Integer counter = 0
http.connect()
response = http.content.text
def status = new JsonSlurperClassic().parseText(response)
// Code to check values here
}
When I run this through a pipeline, the first iteration through the loop works fine. The next iteration bombs with this error:
Caused: java.io.NotSerializableException: sun.net.www.protocol.http.HttpURLConnection
I just started in Groovy, so I feel like I'm trying to do this wrong. I've looked all over trying to find answers and tried several things without any luck.
Thanks in advance.

Answer 1

When running a pipeline job, Jenkins will constantly save the state of the execution so it can be paused and later on resumed, this means that Jenkins must be able to serialize the state of the script and therefore all of the objects that you create in your pipeline must be serializable.
If an object is not serializable you will get the NotSerializableException whenever Jenkins will attempt to serialize your un-serializable object when it save the state.
To overcome this issue you can use the #NonCPS annotation, which will cause Jenkins to execute the function without trying to serialize it. Read more info on this issue at pipeline-best-practice.
While normal Pipeline is restricted to serializable local variables (see appendix at bottom), #NonCPS functions can use more complex, nonserializable types internally (for example regex matchers, etc). Parameters and return types should still be Serializable, however.
There are however some limitations so read the documentation carefully, for example the return value types from #NonCPS methods must be serializable and you can't use any pipeline steps or CPS transformed methods inside a #NonCPS annotated function. Additional info can be found here.
One last thing, to overcome all these issues you can also use the Jenkins HTTP Plugin which includes all the HTTP abilities you will probably need wrapped in an easy to use build in interface.