缩短 MQTT 主题过滤 function

Question

I wrote the following logic function, but I am sure it is possible to write it (way) shorter. In case you are unfamiliar with MQTT wildcards, you can read up on them here.

self is the topic we are "subscribed" to, containing zero or more wildcards. incoming is the topic we received something on, which must match the self topic either fully, or conforming to the wildcard rules.

All my tests on this function succeed, but I just don't like the lengthiness and "iffyness" of this Scala function.

def filterTopic(incoming: String, self: String): Boolean = {
  if (incoming == self || self == "#") {
    true
  } else if (self.startsWith("#") || (self.contains("#") && !self.endsWith("#")) || self.endsWith("+")) {
    false
  } else {
    var valid = true
    val selfSplit = self.split('/')
    var j = 0

    for (i <- selfSplit.indices) {
      if (selfSplit(i) != "+" && selfSplit(i) != "#" && selfSplit(i) != incoming.split('/')(i)) {
        valid = false
      }
      j += 1
    }

    if (j < selfSplit.length && selfSplit(j) == "#") {
      j += 1
    }

    j == selfSplit.length && valid
  }
}

Answer 1

Here's a shot at it assuming that '+' can be at the end and that the topics are otherwise well-structured

    def filterTopic(incoming: String, self: String): Boolean = {
        // helper function that works on lists of parts of the topics
        def go(incParts: List[String], sParts: List[String]): Boolean = (incParts, sParts) match {
            // if they're the same list, the topics match
            case (is, ss) if is == ss => true
            // if sParts is just a single "#", the topics match
            case (_, "#" :: Nil) => true
            // if sParts starts with '+', just check if the rest match
            case (_ :: is, s :: ss) if s == "+" =>
                go(is, ss)
            // otherwise the first parts have to match, and we check the rest
            case (i :: is, s :: ss) if i == s =>
                go(is, ss)
            // otherwise they don't match
            case _ => false
        }

        // split the topic strings into parts 
        go(incoming.split('/').toList, self.split('/').toList)
    }