Added a coursier.cache.protocol.S3Handler class that does not seem to…

… get picked up by Coursier

src/main/scala/coursier/cache/protocol/S3Handler.scala

@@ -0,0 +1,42 @@
+/*
+ * Copyright 2019 Frugal Mechanic (http://frugalmechanic.com)
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package coursier.cache.protocol
+
+import fm.sbt.s3.S3URLConnection
+import java.net.{URL, URLConnection, URLStreamHandler, URLStreamHandlerFactory}
+
+/**
+ * Coursier will look for a coursier.cache.protocol.S3Handler class when it sees the "s3" protocol.
+ *
+ * This appears to be new (at least to me as of 2019-09-05) so this is being added as an alternative to directly
+ * registering the "s3" protocol with java.net.URL.setURLStreamHandlerFactory().
+ *
+ * Note: This implements both URLStreamHandler and URLStreamHandlerFactory because the Coursier code comments say
+ *       it should be a URLStreamHandler but the actual code is casting it to a URLStreamHandlerFactory.  So we will
+ *       just implement both in case it ever changes on the Coursier side from one to the other.
+ */
+final class S3Handler extends URLStreamHandler with URLStreamHandlerFactory {
+  println("fm-sbt-s3-resolver - coursier.cache.protocol.S3Handler created")
+
+  // URLStreamHandlerFactory implementation
+  def createURLStreamHandler(protocol: String): URLStreamHandler = {
+    if (protocol.equalsIgnoreCase("s3")) this
+    else null
+  }
+
+  // URLStreamHandler implementation
+  def openConnection(url: URL): URLConnection = new S3URLConnection(url)
+}