Parse nginx rewrite rules to extract from and to - scala

Question

If I have, say, a list of nginx-esque config rewrite statement as such:
val rewritesList : List[String] = List(
"rewrite (?i)^/first$ http://www.firstredirect.com redirect;",
"rewrite (?i)^/second$ http://www.seconredirect.com redirect;"
)
And I would like to extract from and to from that list. I am not worried about the final structure as long as I extract the info, but for sake of demonstration:
val rewritesMap : Map[String, String] = Map(
"first" -> "http://www.firstredirect.com",
"second" -> "http://www.seconredirect.com"
)

Answer 1

You can use regular expressions with Scala's pattern matching:
val rewritesList : List[String] = List(
"rewrite (?i)^/first$ http://www.firstredirect.com redirect;",
"rewrite (?i)^/second$ http://www.seconredirect.com redirect;"
)
val Regex = """^rewrite \(\?i\)\^/(\w+)\$ ([^ ]+) redirect;$""".r
val rewritesMap = (for {
Regex(from, to) <- rewritesList
} yield (from -> to)).toMap
println(rewritesMap)
You could also use the more explicit findFirstMatchIn to extract a single match:
val rewritesMap = (for {
str <- rewritesList
} yield {
val m = Regex.findFirstMatchIn(str).get
(m.group(1), m.group(2))
}).toMap
Both versions print (up to indentation):
Map(
first -> http://www.firstredirect.com,
second -> http://www.seconredirect.com
)
Note that the latter variant will throw a NoSuchElementException if the input data is not of the format defined by the regex. I don't know what you want to do if the data does not match the regex: you can raise exceptions, but you can also simply skip the cases that aren't parsed correctly.