How to construct URIs and query parameters?

//> using toolkit latest

//> using dep com.softwaremill.sttp.client4::core:4.0.0-M1

lazy val example = project.in(file("example"))
  .settings(
    scalaVersion := "3.2.2",
    libraryDependencies += "org.scala-lang" %% "toolkit" % "0.1.7"
  )

libraryDependencies += "com.softwaremill.sttp.client4" %% "core" % "4.0.0-M1"

object example extends ScalaModule {
  def scalaVersion = "3.2.2"
  def ivyDeps =
    Agg(
      ivy"org.scala-lang::toolkit:0.1.7"
    )
}

ivy"com.softwaremill.sttp.client4::core:4.0.0-M1"

The uri interpolator

uri is a custom string interpolator that allows you to create valid web addresses, also called URIs. For example, you can write uri"https://example.com/".

You can insert any variable or expression in your URI with the usual $ or ${} syntax. For instance uri"https://example.com/$name", interpolates the value of the variable name into an URI. If name contains "peter", the result is https://example.com/peter.

uri escapes special characters automatically, as seen in this example:

import sttp.client4.quick._
import sttp.model.Uri

val book = "programming in scala"
val bookUri: Uri = uri"https://example.com/books/$book"

println(bookUri)
// prints: https://example.com/books/programming%20in%20scala

import sttp.client4.quick.*
import sttp.model.Uri

val book = "programming in scala"
val bookUri: Uri = uri"https://example.com/books/$book"

println(bookUri)
// prints: https://example.com/books/programming%20in%20scala

Query parameters

A query parameter is a key-value pair that is appended to the end of a URI in an HTTP request to specify additional details about the request. The web server can use those parameters to compute the appropriate response.

For example, consider the following URL:

https://example.com/search?q=scala&limit=10&page=1

It contains three query parameters: q=scala, limit=10 and page=1.

Using a map of query parameters

The uri interpolator can interpolate a Map[String, String] as query parameters:

val queryParams = Map(
  "q" -> "scala",
  "limit" -> "10",
  "page" -> "1"
)
val uriWithQueryParams = uri"https://example.com/search?$queryParams"
println(uriWithQueryParams)
// prints: https://example.com/search?q=scala&limit=10&page=1

For safety, special characters in the parameters are automatically escaped by the interpolator.

Using an optional query parameter

A query parameter might be optional. The uri interpolator can interpolate Options:

def getUri(limit: Option[Int]): Uri =
  uri"https://example.com/all?limit=$limit"

println(getUri(Some(10)))
// prints: https://example.com/all?limit=100

println(getUri(None))
// prints: https://example.com/all

Notice that the query parameter disappears entirely when limit is None.

Using a sequence as values of a single query parameter

A query parameter can be repeated in a URI to represent a list of values. For example, the version parameter in ?version=1.0.0&version=1.0.1&version=1.1.0 contains 3 values: 1.0.0, 1.0.1 and 1.1.0.

To build such query parameter in a URI, you can interpolate a Seq (or List, Array, etc) in a uri"...".

def getUri(versions: Seq[String]): Uri =
  uri"https://example.com/scala?version=$versions"

println(getUri(Seq("3.2.2")))
// prints: https://example.com/scala?version=3.2.2

println(getUri(Seq("2.13.8", "2.13.9", "2.13.10")))
// prints: https://example.com/scala?version=2.13.8&version=2.13.9&version=2.13.10

println(getUri(Seq.empty))
// prints: https://example.com/scala