Re: [PR] [SPARK-46361][PYTHON][CORE] Spark dataset chunk read api [spark]

["WeichenXu123 (via GitHub)" <gi...@apache.org>]

WeichenXu123 commented on code in PR #44294:
URL: https://github.com/apache/spark/pull/44294#discussion_r1439121654


##########
core/src/main/scala/org/apache/spark/api/python/CachedArrowBatchServer.scala:
##########
@@ -0,0 +1,137 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.api.python
+
+import java.io.{BufferedOutputStream, DataInputStream, DataOutputStream}
+import java.net.{InetAddress, ServerSocket, Socket, SocketException}
+import java.nio.charset.StandardCharsets.UTF_8
+
+import org.apache.spark.SparkConf
+import org.apache.spark.internal.Logging
+import org.apache.spark.network.util.JavaUtils
+import org.apache.spark.security.SocketAuthHelper
+import org.apache.spark.storage.{ArrowBatchBlockId, BlockId, BlockManager}
+
+
+class CachedArrowBatchServer(
+  val sparkConf: SparkConf,
+  val blockManager: BlockManager
+) extends Logging {
+
+  val authHelper = new SocketAuthHelper(sparkConf)
+
+  val serverSocket = new ServerSocket(
+    0, 1, InetAddress.getLoopbackAddress()
+  )
+
+  protected def readUtf8(s: Socket): String = {
+    val din = new DataInputStream(s.getInputStream())
+    val len = din.readInt()
+    val bytes = new Array[Byte](len)
+    din.readFully(bytes)
+    new String(bytes, UTF_8)
+  }
+
+  protected def writeUtf8(str: String, s: Socket): Unit = {
+    val bytes = str.getBytes(UTF_8)
+    val dout = new DataOutputStream(s.getOutputStream())
+    dout.writeInt(bytes.length)
+    dout.write(bytes, 0, bytes.length)
+    dout.flush()
+  }
+
+  private def handleConnection(sock: Socket): Unit = {
+    val blockId = BlockId(readUtf8(sock))
+    assert(blockId.isInstanceOf[ArrowBatchBlockId])
+
+    var errMessage = "ok"
+    var blockDataOpt: Option[Array[Byte]] = None
+
+    try {
+      val blockResult = blockManager.get[Array[Byte]](blockId)
+      if (blockResult.isDefined) {
+        blockDataOpt = Some(blockResult.get.data.next().asInstanceOf[Array[Byte]])
+      } else {
+        errMessage = s"The chunk $blockId data cache does not exist or has been removed"
+      }
+    } catch {
+      case e: Exception =>
+        errMessage = e.getMessage
+    }
+
+    writeUtf8(errMessage, sock)
+
+    if (blockDataOpt.isDefined) {
+      val out = new BufferedOutputStream(sock.getOutputStream())
+      out.write(blockDataOpt.get)
+      out.flush()
+    }
+  }
+
+  def createConnectionThread(sock: Socket, threadName: String): Unit = {
+    new Thread(threadName) {
+      setDaemon(true)
+
+      override def run(): Unit = {
+        try {
+          authHelper.authClient(sock)

Review Comment:
   No. "write a string ok " will write the length of the string first, then write utf8 encoded bytes of the string, for receiver side, it reads string length first then decode following bytes. 



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