[SPARK-19715][STRUCTURED STREAMING] Option to Strip Paths in FileSource

## What changes were proposed in this pull request?

Today, we compare the whole path when deciding if a file is new in the FileSource for structured streaming. However, this would cause false negatives in the case where the path has changed in a cosmetic way (i.e. changing `s3n` to `s3a`).

This patch adds an option `fileNameOnly` that causes the new file check to be based only on the filename (but still store the whole path in the log).

## Usage

```scala
spark
  .readStream
  .option("fileNameOnly", true)
  .text("s3n://bucket/dir1/dir2")
  .writeStream
  ...
```
## How was this patch tested?

Added a test case

Author: Liwei Lin <lwlin7@gmail.com>

Closes #17120 from lw-lin/filename-only.

2 files changed, 42 insertions, 17 deletions

diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/FileStreamOptions.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/FileStreamOptions.scala
index e7ba901945..d54ed44b43 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/FileStreamOptions.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/FileStreamOptions.scala
@@ -61,13 +61,29 @@ class FileStreamOptions(parameters: CaseInsensitiveMap[String]) extends Logging
    * Whether to scan latest files first. If it's true, when the source finds unprocessed files in a
    * trigger, it will first process the latest files.
    */
-  val latestFirst: Boolean = parameters.get("latestFirst").map { str =>
-    try {
-      str.toBoolean
-    } catch {
-      case _: IllegalArgumentException =>
-        throw new IllegalArgumentException(
-          s"Invalid value '$str' for option 'latestFirst', must be 'true' or 'false'")
-    }
-  }.getOrElse(false)
+  val latestFirst: Boolean = withBooleanParameter("latestFirst", false)
+
+  /**
+   * Whether to check new files based on only the filename instead of on the full path.
+   *
+   * With this set to `true`, the following files would be considered as the same file, because
+   * their filenames, "dataset.txt", are the same:
+   * - "file:///dataset.txt"
+   * - "s3://a/dataset.txt"
+   * - "s3n://a/b/dataset.txt"
+   * - "s3a://a/b/c/dataset.txt"
+   */
+  val fileNameOnly: Boolean = withBooleanParameter("fileNameOnly", false)
+
+  private def withBooleanParameter(name: String, default: Boolean) = {
+    parameters.get(name).map { str =>
+      try {
+        str.toBoolean
+      } catch {
+        case _: IllegalArgumentException =>
+          throw new IllegalArgumentException(
+            s"Invalid value '$str' for option '$name', must be 'true' or 'false'")
+      }
+    }.getOrElse(default)
+  }
 }
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/FileStreamSource.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/FileStreamSource.scala
index 0f09b0a0c8..411a15ffce 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/FileStreamSource.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/FileStreamSource.scala
@@ -17,6 +17,8 @@
 
 package org.apache.spark.sql.execution.streaming
 
+import java.net.URI
+
 import scala.collection.JavaConverters._
 
 import org.apache.hadoop.fs.{FileStatus, Path}
@@ -79,9 +81,16 @@ class FileStreamSource(
     sourceOptions.maxFileAgeMs
   }
 
+  private val fileNameOnly = sourceOptions.fileNameOnly
+  if (fileNameOnly) {
+    logWarning("'fileNameOnly' is enabled. Make sure your file names are unique (e.g. using " +
+      "UUID), otherwise, files with the same name but under different paths will be considered " +
+      "the same and causes data lost.")
+  }
+
   /** A mapping from a file that we have processed to some timestamp it was last modified. */
   // Visible for testing and debugging in production.
-  val seenFiles = new SeenFilesMap(maxFileAgeMs)
+  val seenFiles = new SeenFilesMap(maxFileAgeMs, fileNameOnly)
 
   metadataLog.allFiles().foreach { entry =>
     seenFiles.add(entry.path, entry.timestamp)
@@ -268,7 +277,7 @@ object FileStreamSource {
    * To prevent the hash map from growing indefinitely, a purge function is available to
    * remove files "maxAgeMs" older than the latest file.
    */
-  class SeenFilesMap(maxAgeMs: Long) {
+  class SeenFilesMap(maxAgeMs: Long, fileNameOnly: Boolean) {
     require(maxAgeMs >= 0)
 
     /** Mapping from file to its timestamp. */
@@ -280,9 +289,13 @@ object FileStreamSource {
     /** Timestamp for the last purge operation. */
     private var lastPurgeTimestamp: Timestamp = 0L
 
+    @inline private def stripPathIfNecessary(path: String) = {
+      if (fileNameOnly) new Path(new URI(path)).getName else path
+    }
+
     /** Add a new file to the map. */
     def add(path: String, timestamp: Timestamp): Unit = {
-      map.put(path, timestamp)
+      map.put(stripPathIfNecessary(path), timestamp)
       if (timestamp > latestTimestamp) {
         latestTimestamp = timestamp
       }
@@ -295,7 +308,7 @@ object FileStreamSource {
     def isNewFile(path: String, timestamp: Timestamp): Boolean = {
       // Note that we are testing against lastPurgeTimestamp here so we'd never miss a file that
       // is older than (latestTimestamp - maxAgeMs) but has not been purged yet.
-      timestamp >= lastPurgeTimestamp && !map.containsKey(path)
+      timestamp >= lastPurgeTimestamp && !map.containsKey(stripPathIfNecessary(path))
     }
 
     /** Removes aged entries and returns the number of files removed. */
@@ -314,9 +327,5 @@ object FileStreamSource {
     }
 
     def size: Int = map.size()
-
-    def allEntries: Seq[(String, Timestamp)] = {
-      map.asScala.toSeq
-    }
   }
 }