zio · iravid · Jun 4, 2020 · May 27, 2020 · May 27, 2020 · May 27, 2020
diff --git a/streams-tests/jvm/src/test/scala/zio/stream/ZSinkPlatformSpecificSpec.scala b/streams-tests/jvm/src/test/scala/zio/stream/ZSinkPlatformSpecificSpec.scala
@@ -0,0 +1,27 @@
+package zio.stream
+
+import java.nio.file.Files
+
+import zio._
+import zio.test.Assertion._
+import zio.test._
+
+object ZSinkPlatformSpecificSpec extends ZIOBaseSpec {
+  override def spec = suite("ZSink JVM")(
+    suite("fromFile")(
+      testM("writes to an existing file") {
+        val data = (0 to 100).mkString
+
+        Task(Files.createTempFile("stream", "fromFile"))
+          .bracket(path => Task(Files.delete(path)).orDie) { path =>
+            for {
+              bytes  <- Task(data.getBytes("UTF-8"))
+              length <- ZStream.fromIterable(bytes).run(ZSink.fromFile(path))
+              str    <- Task(new String(Files.readAllBytes(path)))
+            } yield assert(data)(equalTo(str)) && assert(bytes.length.toLong)(equalTo(length))
+          }
+
+      }
+    )
+  )
+}
diff --git a/streams/jvm/src/main/scala/zio/stream/platform.scala b/streams/jvm/src/main/scala/zio/stream/platform.scala
@@ -3,7 +3,8 @@ package zio.stream
 import java.io.{ IOException, InputStream, OutputStream }
 import java.nio.ByteBuffer
 import java.nio.channels.FileChannel
-import java.nio.file.Path
+import java.nio.file.StandardOpenOption._
+import java.nio.file.{ OpenOption, Path }
 import java.{ util => ju }
 
 import zio._
@@ -29,6 +30,46 @@ trait ZSinkPlatformSpecificConstructors { self: ZSink.type =>
         case e: IOException => e
       }
     }
+
+  /**
+   * Uses the provided `Path` to create a [[ZSink]] that consumes byte chunks
+   * and writes them to the `File`. The sink will yield count of bytes written.
+   */
+  final def fromFile(
+    path: => Path,
+    position: Long = 0L,
+    options: Set[OpenOption] = Set(WRITE, TRUNCATE_EXISTING, CREATE)
+  ): ZSink[Blocking, Throwable, Byte, Long] =
+    ZSink {
+      for {
+        state <- Ref.make(0L).toManaged_
+        channel <- ZManaged.make(
+                    blocking
+                      .effectBlockingInterrupt(
+                        FileChannel
+                          .open(
+                            path,
+                            options.foldLeft(new ju.HashSet[OpenOption]()) { (acc, op) =>
+                              acc.add(op); acc
+                            } // for avoiding usage of different Java collection converters for different scala versions
+                          )
+                          .position(position)
+                      )
+                      .orDie
+                  )(chan => blocking.effectBlocking(chan.close()).orDie)
+        push = (is: Option[Chunk[Byte]]) =>
+          is match {
+            case None => state.get.flatMap(Push.emit)
+            case Some(byteChunk) =>
+              for {
+                justWritten <- blocking.effectBlockingInterrupt {
+                                channel.write(ByteBuffer.wrap(byteChunk.toArray))
+                              }.mapError(Left(_))
+                more <- state.update(_ + justWritten) *> Push.more
+              } yield more
+          }
+      } yield push
+    }
 }
 
 trait ZStreamPlatformSpecificConstructors { self: ZStream.type =>