You can generate a URL-encoded string either from a List of Pairs of Strings or a Parameters instance:
fun List<Pair<String, String?>>.formUrlEncode(): String
fun List<Pair<String, String?>>.formUrlEncodeTo(out: Appendable)
fun Parameters.formUrlEncode(): String
fun Parameters.formUrlEncodeTo(out: Appendable)
You can construct a URL-encoded string from List<Pair<String, String>> like this:
listOf(
"error" to "invalid_request",
"error_description" to "client_id is missing"
).formUrlEncode()
You can also construct it from a Parameters instance that you can instantiate by using the Parameters.build builder and then calling the formUrlEncode extension, or with the parametersOf() builder method:
Parameters.build {
append("error", "invalid_request")
append("error_description", "client_id is missing")
}.formUrlEncode()
The parametersOf builder has several signatures, and there is Parameters operator overloading (+) to join two Parameters instances:
parametersOf("a" to "b1", "a" to "b2").formUrlEncode()
(parametersOf("a", "b1") + parametersOf("a", "b2")).formUrlEncode()
parametersOf("a", listOf("b1", "b2")).formUrlEncode()
From a normal Map<String, String> you can also construct a URL-encoded string, but first you will have to create a List from it:
mapOf(
"error" to "invalid_request",
"error_description" to "client_id is missing"
).toList().formUrlEncode()
You can also construct it from a Map<String, List<String>> by flatMapping it first:
mapOf(
"error" to listOf("invalid_request"),
"error_descriptions" to listOf("client_id is missing", "server error")
).flatMap { map -> map.value.map { map.key to it } }.formUrlEncode()
In case you want to avoid constructing a whole String with the content and instead want to write to somewhere directly, you can use the formUrlEncodeTo method.
Responding URL-encoded
You can do something like:
call.respondUrlEncoded("hello" to listOf("world"))
by adding the following extension methods to your project:
suspend fun ApplicationCall.respondUrlEncoded(vararg keys: Pair<String, List<String>>) =
respondUrlEncoded(parametersOf(*keys))
suspend fun ApplicationCall.respondUrlEncoded(parameters: Parameters) =
respondTextWriter(ContentType.Application.FormUrlEncoded) {
parameters.formUrlEncodeTo(this)
}