alfozan commented on a change in pull request #29085:
URL: https://github.com/apache/spark/pull/29085#discussion_r454298255



##########
File path: 
sql/core/src/main/scala/org/apache/spark/sql/execution/SparkScriptTransformationExec.scala
##########
@@ -0,0 +1,187 @@
+/*
+ * 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.sql.execution
+
+import java.io._
+import java.nio.charset.StandardCharsets
+
+import scala.collection.JavaConverters._
+import scala.util.control.NonFatal
+
+import org.apache.hadoop.conf.Configuration
+
+import org.apache.spark.TaskContext
+import org.apache.spark.sql.catalyst.{CatalystTypeConverters, InternalRow}
+import org.apache.spark.sql.catalyst.expressions._
+import org.apache.spark.sql.catalyst.plans.logical.ScriptInputOutputSchema
+import org.apache.spark.sql.types.DataType
+import org.apache.spark.util.{CircularBuffer, RedirectThread}
+
+/**
+ * Transforms the input by forking and running the specified script.
+ *
+ * @param input the set of expression that should be passed to the script.
+ * @param script the command that should be executed.
+ * @param output the attributes that are produced by the script.
+ */
+case class SparkScriptTransformationExec(
+    input: Seq[Expression],
+    script: String,
+    output: Seq[Attribute],
+    child: SparkPlan,
+    ioschema: SparkScriptIOSchema)
+  extends BaseScriptTransformationExec {
+
+  override def processIterator(inputIterator: Iterator[InternalRow], 
hadoopConf: Configuration)
+  : Iterator[InternalRow] = {
+    val cmd = List("/bin/bash", "-c", script)
+    val builder = new ProcessBuilder(cmd.asJava)
+
+    val proc = builder.start()
+    val inputStream = proc.getInputStream
+    val outputStream = proc.getOutputStream
+    val errorStream = proc.getErrorStream
+
+    // In order to avoid deadlocks, we need to consume the error output of the 
child process.
+    // To avoid issues caused by large error output, we use a circular buffer 
to limit the amount
+    // of error output that we retain. See SPARK-7862 for more discussion of 
the deadlock / hang
+    // that motivates this.
+    val stderrBuffer = new CircularBuffer(2048)
+    new RedirectThread(
+      errorStream,
+      stderrBuffer,
+      "Thread-ScriptTransformation-STDERR-Consumer").start()
+
+    val outputProjection = new InterpretedProjection(input, child.output)
+
+    // This new thread will consume the ScriptTransformation's input rows and 
write them to the
+    // external process. That process's output will be read by this current 
thread.
+    val writerThread = new ScriptTransformationWriterThread(
+      inputIterator.map(outputProjection),
+      input.map(_.dataType),
+      ioschema,
+      outputStream,
+      proc,
+      stderrBuffer,
+      TaskContext.get(),
+      hadoopConf
+    )
+
+    val reader = new BufferedReader(new InputStreamReader(inputStream, 
StandardCharsets.UTF_8))
+    val outputIterator: Iterator[InternalRow] = new Iterator[InternalRow] {
+      var curLine: String = null
+      val mutableRow = new SpecificInternalRow(output.map(_.dataType))
+
+      override def hasNext: Boolean = {
+        try {
+          if (curLine == null) {
+            curLine = reader.readLine()
+            if (curLine == null) {
+              checkFailureAndPropagate(writerThread, null, proc, stderrBuffer)
+              return false
+            }
+          }
+          true
+        } catch {
+          case NonFatal(e) =>
+            // If this exception is due to abrupt / unclean termination of 
`proc`,
+            // then detect it and propagate a better exception message for end 
users
+            checkFailureAndPropagate(writerThread, e, proc, stderrBuffer)
+
+            throw e
+        }
+      }
+
+      override def next(): InternalRow = {
+        if (!hasNext) {
+          throw new NoSuchElementException
+        }
+        val prevLine = curLine
+        curLine = reader.readLine()
+        if (!ioschema.schemaLess) {
+          new GenericInternalRow(
+            
prevLine.split(ioschema.outputRowFormatMap("TOK_TABLEROWFORMATFIELD"))
+              .map(CatalystTypeConverters.convertToCatalyst))
+        } else {
+          new GenericInternalRow(
+            
prevLine.split(ioschema.outputRowFormatMap("TOK_TABLEROWFORMATFIELD"), 2)
+              .map(CatalystTypeConverters.convertToCatalyst))
+        }
+      }
+    }
+
+    writerThread.start()
+
+    outputIterator
+  }
+}
+
+private class ScriptTransformationWriterThread(
+    iter: Iterator[InternalRow],
+    inputSchema: Seq[DataType],
+    ioSchema: SparkScriptIOSchema,
+    outputStream: OutputStream,
+    proc: Process,
+    stderrBuffer: CircularBuffer,
+    taskContext: TaskContext,
+    conf: Configuration)
+  extends BaseScriptTransformationWriterThread(
+    iter,
+    inputSchema,
+    ioSchema,
+    outputStream,
+    proc,
+    stderrBuffer,
+    taskContext,
+    conf) {
+
+  setDaemon(true)
+
+  override def processRows(): Unit = {
+    processRowsWithoutSerde()
+  }
+}
+
+object SparkScriptIOSchema {
+  def apply(input: ScriptInputOutputSchema): SparkScriptIOSchema = {
+    SparkScriptIOSchema(
+      input.inputRowFormat,
+      input.outputRowFormat,
+      input.inputSerdeClass,
+      input.outputSerdeClass,
+      input.inputSerdeProps,
+      input.outputSerdeProps,
+      input.recordReaderClass,
+      input.recordWriterClass,
+      input.schemaLess)
+  }
+}
+
+/**
+ * The wrapper class of Spark script transformation input and output schema 
properties
+ */
+case class SparkScriptIOSchema (

Review comment:
       The implementation here offers a very limited support for `ROW FORMAT 
DELIMITED` format. 
   
   A full implementation (SerDes class for ROW FORMAT DELIMITED) can be added 
later and will live in the same folder.
   https://github.com/apache/spark/pull/29085#issuecomment-658131729




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