Moving from JSON to non-JSON input filter

[ZillaG]

I've been sending our application logs via UDP wrapped in a JSON format, so the log looks something like this

{
  "key1" : "value1",
  "key2" : "value2",
  "message" : "2017-03-02 INFO com.company.app Hello world!"
}

and my Logstash input filter looks like tis

input {
  udp {
    port => 1234
    codec => json
  }
}

However Logstash gives me _jsonparsefailure when the message contains a long stack dump or an XML file. (See Help with _jsonparsefailure)

So I want to try sending my logs in a non-JSON format, and I have two questions.

Question 1:

Should I send them like this, i.e., single line

key1: value1 key2: value2 message: 2017-03-02 INFO com.company.app Hello world!

...or should I send them like this, that is, multi-lines

key1: value1 key2: value2 message: 2017-03-02 INFO com.company.app Hello world!

Question 2:
In either case, how should my input filter look like so I can separate logs from each other?

This is the main reason I wrapped the logs in JSON in the first place since they were naturally separated.

I hope that makes sense. Thanks!