server: Add the gcs SipHashKey

server/app/com/xsn/explorer/gcs/SipHashKey.scala

@@ -0,0 +1,32 @@
+package com.xsn.explorer.gcs
+
+import com.google.common.primitives.Longs
+
+/**
+ * Represents a SipHash key using a 128-bit value, compatible with Guava.
+ *
+ * @param k0 the first half of the key
+ * @param k1 the second half of the key
+ */
+case class SipHashKey(k0: Long, k1: Long)
+
+object SipHashKey {
+
+  /**
+   * Parses a SipHash key in the same way that the Btcutil (https://github.com/btcsuite/btcutil)
+   * library does, which uses https://github.com/aead/siphash
+   *
+   * @param key 16 bytes representing the key
+   */
+  def fromBtcutil(key: List[Byte]): SipHashKey = {
+    require(key.size == 16, "Invalid SipHash key, it must have 16 bytes")
+
+    /**
+     * the bytes are represented as a 128-bit encoded in little-endian
+     * while guava parses the values in big-endian, that's the reason to reverse them.
+     */
+    val k0 = Longs.fromByteArray(key.take(8).reverse.toArray)
+    val k1 = Longs.fromByteArray(key.drop(8).reverse.toArray)
+    SipHashKey(k0, k1)
+  }
+}

server/app/com/xsn/explorer/gcs/package.scala

@@ -0,0 +1,9 @@
+package com.xsn.explorer
+
+/**
+ * The package does similar operations for Golomb-Coded Sets similar to what
+ * the Btcutil library does (https://github.com/btcsuite/btcutil/tree/master/gcs).
+ *
+ * Everything is based on https://github.com/bitcoin/bips/blob/master/bip-0158.mediawiki
+ */
+package object gcs

server/test/com/xsn/explorer/gcs/SipHashKeySpec.scala

@@ -0,0 +1,19 @@
+package com.xsn.explorer.gcs
+
+import org.scalatest.MustMatchers._
+import org.scalatest.WordSpec
+
+class SipHashKeySpec extends WordSpec {
+
+  "parsing a Btcutil-like key" should {
+    "parse the right values" in {
+      val bytes = List(
+        0x4c, 0xb1, 0xab, 0x12, 0x57, 0x62, 0x1e, 0x41,
+        0x3b, 0x8b, 0x0e, 0x26, 0x64, 0x8d, 0x4a, 0x15).map(_.asInstanceOf[Byte])
+
+      val key = SipHashKey.fromBtcutil(bytes)
+      key.k0 must be(4692295987881554252L)
+      key.k1 must be(1534194084347808571l)
+    }
+  }
+}