Updates for compatibility with EU Frankfurt AWS Region (#49)

* Fixing s3 url construction for both us and eu
* Fix to us-east-1 region resolving as null

build.sbt

@@ -11,4 +11,4 @@ bucketSuffix := "era7.com"
 
 libraryDependencies += "ohnosequences" % "ivy-s3-resolver" % "0.9.0"
 
-wartremoverErrors in (Compile, compile) --= Seq(Wart.Any, Wart.NonUnitStatements)
+wartremoverErrors in (Compile, compile) --= Seq(Wart.Any, Wart.NonUnitStatements, Wart.Null)

src/main/scala/SBTS3Resolver.scala

@@ -1,7 +1,10 @@
 package ohnosequences.sbt
 
-import sbt._, Keys._
-import com.amazonaws.auth._, profile._
+import sbt._
+import Keys._
+import com.amazonaws.auth._
+import com.amazonaws.services.s3.model.Region
+import profile._
 
 object SbtS3Resolver extends AutoPlugin {
 
@@ -79,7 +82,22 @@ object SbtS3Resolver extends AutoPlugin {
 
       // convenience method, to use normal bucket addresses with `at`
       // without this resolver: "foo" at s3("maven.bucket.com").toHttps(s3region.value)
-      def toHttps(region: String): String = s"""https://s3-${region}.amazonaws.com/${url.stripPrefix("s3://")}"""
+      def toHttps(region: String): String = {
+        val bucketPath = url.stripPrefix("s3://")
+        val euCentral = Region.EU_Frankfurt.toString
+
+        //Correcting for fact that region enum resolves to null when provided US_STANDARD (us-east-1)
+        val correctedRegion = if(region == null) "us-east-1" else region
+
+        /*
+        Constructing host name based on region name. Frankfurt host name must be constructed using s3.{region}
+        for java sdk to sign its request using the v4 signature method (Frankfurt only supports v4 signing)
+         */
+        region match {
+          case euCentral => s"""https://s3.${correctedRegion}.amazonaws.com/${bucketPath}"""
+          case _ => s"""https://s3-${correctedRegion}.amazonaws.com/${bucketPath}"""
+        }
+      }
     }
   }
   import autoImport._