From 124fd35527601c61c20f7f9e4a3d099c5e0b883b Mon Sep 17 00:00:00 2001
From: Jakob Odersky <jakob@driver.xyz>
Date: Tue, 25 Jul 2017 00:16:26 -0700
Subject: Add streaming download to file storage.

This enables downloading of content without saving it to a file.
---
 .../scala/xyz/driver/core/file/GcsStorage.scala    | 31 +++++++++++++++++++++-
 1 file changed, 30 insertions(+), 1 deletion(-)

(limited to 'src/main/scala/xyz/driver/core/file/GcsStorage.scala')

diff --git a/src/main/scala/xyz/driver/core/file/GcsStorage.scala b/src/main/scala/xyz/driver/core/file/GcsStorage.scala
index deb8a0e..4ceab79 100644
--- a/src/main/scala/xyz/driver/core/file/GcsStorage.scala
+++ b/src/main/scala/xyz/driver/core/file/GcsStorage.scala
@@ -1,7 +1,12 @@
 package xyz.driver.core.file
 
+import akka.NotUsed
+import akka.stream.scaladsl.Source
+import akka.util.ByteString
+import com.google.cloud.ReadChannel
 import java.io.{BufferedOutputStream, File, FileInputStream, FileOutputStream}
 import java.net.URL
+import java.nio.ByteBuffer
 import java.nio.file.{Path, Paths}
 import java.util.concurrent.TimeUnit
 
@@ -15,7 +20,10 @@ import scala.concurrent.duration.Duration
 import scala.concurrent.{ExecutionContext, Future}
 import scalaz.{ListT, OptionT}
 
-class GcsStorage(storageClient: Storage, bucketName: Name[Bucket], executionContext: ExecutionContext)
+class GcsStorage(storageClient: Storage,
+                 bucketName: Name[Bucket],
+                 executionContext: ExecutionContext,
+                 chunkSize: Int = 4096)
     extends SignedFileStorage {
   implicit private val execution: ExecutionContext = executionContext
 
@@ -48,6 +56,27 @@ class GcsStorage(storageClient: Storage, bucketName: Name[Bucket], executionCont
     })
   }
 
+  override def stream(filePath: Path): OptionT[Future, Source[ByteString, NotUsed]] =
+    OptionT.optionT(Future {
+      def readChunk(rc: ReadChannel): Option[ByteString] = {
+        val buffer = ByteBuffer.allocate(chunkSize)
+        val length = rc.read(buffer)
+        if (length > 0) {
+          Some(ByteString.fromByteBuffer(buffer))
+        } else {
+          None
+        }
+      }
+
+      Option(storageClient.get(bucketName.value, filePath.toString)).map { blob =>
+        Source.unfoldResource[ByteString, ReadChannel](
+          create = () => blob.reader(),
+          read = channel => readChunk(channel),
+          close = channel => channel.close()
+        )
+      }
+    })
+
   override def delete(filePath: Path): Future[Unit] = Future {
     storageClient.delete(BlobId.of(bucketName.value, filePath.toString))
   }
-- 
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