Support path prefixes (#3)

smithy4s-fetch.scala

@@ -137,7 +137,7 @@ private[smithy4s_fetch] case class SimpleRestJsonCodecs(
 
   def fromSmithy4sHttpUri(uri: smithy4s.http.HttpUri): String = {
     val qp = uri.queryParams
-    val newValue = {
+    val protocol = {
       uri.scheme match
         case Http  => "http"
         case Https => "https"
@@ -167,7 +167,7 @@ private[smithy4s_fetch] case class SimpleRestJsonCodecs(
 
         b
 
-    s"$newValue://$hostName$port$path$query"
+    s"$protocol://$hostName$port$path$query"
   }
 
   def toSmithy4sHttpResponse(
@@ -233,7 +233,14 @@ private[smithy4s_fetch] case class SimpleRestJsonCodecs(
       uriScheme,
       uri.host,
       uri.port.toIntOption,
-      uri.pathname.split("/"),
+      uri.pathname
+        // drop the guaranteed leading slash, so that we don't produce an empty segment for it
+        .tail
+        // splitting an empty path would produce a single element, so we special-case to empty
+        .match {
+          case ""    => IndexedSeq.empty
+          case other => other.split("/")
+        },
       uri.searchParams
         .entries()
         .toIterator

smithy4s-fetch.test.scala

@@ -24,6 +24,7 @@ import weaver.{FunSuiteIO, IOSuite}
 import scala.concurrent.duration.*
 import scala.scalajs.js.Promise
 import smithy4s.http.HttpUri
+import org.scalajs.dom.URL
 
 object UnitTest extends FunSuiteIO:
   val uri =
@@ -73,6 +74,44 @@ object UnitTest extends FunSuiteIO:
       "https://localhost:9999/1/2/3"
     )
 
+  test("Base URI with no path prefix"):
+    val result = smithy4s_fetch.SimpleRestJsonCodecs
+      .toSmithy4sHttpUri(new URL("http://localhost"))
+      .path
+
+    expect(result.isEmpty)
+
+  test("Base URI with no path prefix (with slash)"):
+    val result = smithy4s_fetch.SimpleRestJsonCodecs
+      .toSmithy4sHttpUri(new URL("http://localhost/"))
+      .path
+
+    expect(result.isEmpty)
+
+  test("Base URI with path prefix"):
+    expect.same(
+      smithy4s_fetch.SimpleRestJsonCodecs
+        .toSmithy4sHttpUri(new URL("http://localhost/prefix"))
+        .path,
+      IndexedSeq("prefix")
+    )
+
+  test("Base URI with no path prefix, including empty segments"):
+    expect.same(
+      smithy4s_fetch.SimpleRestJsonCodecs
+        .toSmithy4sHttpUri(new URL("http://localhost/foo//bar//baz/"))
+        .path,
+      IndexedSeq("foo", "", "bar", "", "baz")
+    )
+
+  test("Base URI with path prefix, trailing slash doesn't matter"):
+    expect.same(
+      smithy4s_fetch.SimpleRestJsonCodecs
+        .toSmithy4sHttpUri(new URL("http://localhost/foo/")),
+      smithy4s_fetch.SimpleRestJsonCodecs
+        .toSmithy4sHttpUri(new URL("http://localhost/foo"))
+    )
+
 @annotation.experimental
 object IntegrationTest extends IOSuite:
   val service = API.service[IOService]