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aws-scala-s3

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package io.atlassian.aws.s3

import java.io.InputStream

import scalaz.concurrent.Task

/**
 * Useful input stream utils.
 */
object InputStreams {
  sealed trait ReadBytes
  object ReadBytes {
    case object End extends ReadBytes
    case class Chunk(read: Int) extends ReadBytes
  }

  /**
   * Fill the given buffer with data from the given inputstream. Blocks until the input stream has enough data to fill
   * the buffer or is closed.
   *
   * @param is The input stream
   * @param buffer the buffer to fill
   * @return state of input stream and the bytes read
   */
  def readFully(is: InputStream, buffer: Array[Byte]): Task[ReadBytes] = {
    def go(start: Int, length: Int, total: Int): Task[ReadBytes] =
      for {
        read <- Task.delay { is.read(buffer, start, length) }
        result <- read match {
          case -1 =>
            Task.now {
              if (total == 0) ReadBytes.End else ReadBytes.Chunk(total)
            }
          case read if read < length => go(start + read, length - read, total + read)
          case read                  => Task.now(ReadBytes.Chunk(total + read))
        }
      } yield result

    go(0, buffer.size, 0)
  }

}