[fs] Fix incorrect seeking semantics of GoogleStorageFS

hail/src/main/scala/is/hail/io/fs/AzureStorageFS.scala

@@ -11,12 +11,12 @@ import is.hail.io.fs.FSUtil.{containsWildcard, dropTrailingSlash}
 import org.apache.log4j.Logger
 
 import java.net.URI
-import is.hail.utils.{fatal, defaultJSONFormats}
+import is.hail.utils.{defaultJSONFormats, fatal}
 import org.json4s
 import org.json4s.jackson.JsonMethods
 import org.json4s.Formats
 
-import java.io.{ByteArrayInputStream, FileNotFoundException, OutputStream}
+import java.io.{ByteArrayInputStream, ByteArrayOutputStream, FileNotFoundException, OutputStream}
 import java.nio.file.FileSystems
 import java.time.Duration
 import scala.collection.mutable
@@ -137,6 +137,8 @@ class AzureStorageFS(val credentialsJSON: Option[String] = None) extends FS {
     val is: SeekableInputStream = new FSSeekableInputStream {
       private[this] val client: BlobClient = blobClient
 
+      override def physicalSeek(newPos: Long): Unit = ()
+
       override def fill(): Int = {
         val pos = getPosition
         val numBytesRemainingInBlob = blobSize - pos

hail/src/main/scala/is/hail/io/fs/FS.scala

@@ -1,20 +1,20 @@
 package is.hail.io.fs
 
-import java.io._
-import java.nio.charset._
-import java.util.zip.GZIPOutputStream
-import is.hail.{HailContext, HailFeatureFlags}
 import is.hail.backend.BroadcastValue
 import is.hail.io.compress.{BGzipInputStream, BGzipOutputStream}
 import is.hail.io.fs.FSUtil.{containsWildcard, dropTrailingSlash}
-import is.hail.utils._
 import is.hail.services._
+import is.hail.utils._
+import is.hail.{HailContext, HailFeatureFlags}
 import org.apache.commons.compress.compressors.gzip.GzipCompressorInputStream
 import org.apache.commons.io.IOUtils
 import org.apache.hadoop
 
+import java.io._
 import java.nio.ByteBuffer
+import java.nio.charset._
 import java.nio.file.FileSystems
+import java.util.zip.GZIPOutputStream
 import scala.collection.mutable
 import scala.io.Source
 
@@ -153,6 +153,8 @@ abstract class FSSeekableInputStream extends InputStream with Seekable {
     toTransfer
   }
 
+  protected def physicalSeek(newPos: Long): Unit
+
   def seek(newPos: Long): Unit = {
     val distance = newPos - pos
     val bufferSeekPosition = bb.position() + distance
@@ -220,6 +222,7 @@ object FS {
         case cloud =>
           throw new IllegalArgumentException(s"Bad cloud: $cloud")
       }
+      physicalSeek(newPos)
     }
   }
 }

hail/src/main/scala/is/hail/io/fs/GoogleStorageFS.scala

@@ -1,5 +1,6 @@
 package is.hail.io.fs
 
+
 import java.io.{ByteArrayInputStream, FileNotFoundException}
 import java.net.URI
 import java.nio.ByteBuffer
@@ -208,8 +209,7 @@ class GoogleStorageFS(
         return n
       }
 
-      override def seek(newPos: Long): Unit = {
-        super.seek(newPos)
+      override def physicalSeek(newPos: Long): Unit = {
         seekHandlingRequesterPays(newPos)
       }
     }

hail/src/test/scala/is/hail/fs/FSSuite.scala

@@ -4,8 +4,9 @@ import java.io.FileNotFoundException
 import is.hail.HailSuite
 import is.hail.backend.ExecuteContext
 import is.hail.io.fs.FSUtil.dropTrailingSlash
-import is.hail.io.fs.{FS, FileStatus, Seekable}
+import is.hail.io.fs.{FS, FileStatus, GoogleStorageFS, Seekable}
 import is.hail.utils._
+import org.apache.commons.codec.binary.Hex
 import org.apache.commons.io.IOUtils
 import org.scalatest.testng.TestNGSuite
 import org.testng.annotations.Test
@@ -346,6 +347,36 @@ trait FSSuite extends TestNGSuite {
     fs.delete(f, false)
     assert(!fs.exists(f))
   }
+
+  @Test def testSeekAndReadStraddlingBufferSize(): Unit = {
+    val data = Array.tabulate(251)(_.toByte)
+    val f = t()
+    using(fs.create(f)) { os =>
+      var i = 0
+      // 66058 replicates are 8MB of data
+      while (i < 70000) {
+        os.write(data)
+        i += 1
+      }
+    }
+
+    using(fs.openNoCompression(f)) { is =>
+
+      is.seek(251)
+      assert(is.read() == 0)
+      assert(is.read() == 1)
+
+      val seekPos = 8 * 1024 * 1024 - 512
+      is.seek(8 * 1024 * 1024 - 512)
+      assert(is.getPosition == seekPos)
+      val toRead = new Array[Byte](512)
+      is.readFully(toRead)
+
+      (0 until toRead.length).foreach { i =>
+        assert(toRead(i) == ((seekPos + i) % 251).toByte)
+      }
+    }
+  }
 }
 
 class HadoopFSSuite extends HailSuite with FSSuite {