[ML] Include message in field_stats for text log files (#34861)

This change ensures the `message` field is always included
in the `field_stats` for the semi-structured text log file
file structure.  Previously it was not, as it will almost
certainly contain all distinct values.  However, for
consistency in the UI it's useful to include it.

Author: droberts195

x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/filestructurefinder/TextLogFileStructureFinder.java

@@ -89,6 +89,7 @@ static TextLogFileStructureFinder makeTextLogFileStructureFinder(List<String> ex
         mappings.put(FileStructureUtils.DEFAULT_TIMESTAMP_FIELD, Collections.singletonMap(FileStructureUtils.MAPPING_TYPE_SETTING, "date"));
 
         SortedMap<String, FieldStats> fieldStats = new TreeMap<>();
+        fieldStats.put("message", FileStructureUtils.calculateFieldStats(sampleMessages, timeoutChecker));
 
         GrokPatternCreator grokPatternCreator = new GrokPatternCreator(explanation, sampleMessages, mappings, fieldStats, timeoutChecker);
         // We can't parse directly into @timestamp using Grok, so parse to some other time field, which the date filter will then remove

x-pack/plugin/ml/src/test/java/org/elasticsearch/xpack/ml/filestructurefinder/TextLogFileStructureFinderTests.java

@@ -7,11 +7,16 @@
 
 import org.elasticsearch.common.collect.Tuple;
 import org.elasticsearch.common.util.set.Sets;
+import org.elasticsearch.xpack.core.ml.filestructurefinder.FieldStats;
 import org.elasticsearch.xpack.core.ml.filestructurefinder.FileStructure;
 import org.elasticsearch.xpack.ml.filestructurefinder.TimestampFormatFinder.TimestampMatch;
 
 import java.util.Collections;
 import java.util.Set;
+import java.util.stream.Collectors;
+
+import static org.hamcrest.Matchers.hasItem;
+import static org.hamcrest.Matchers.not;
 
 public class TextLogFileStructureFinderTests extends FileStructureTestCase {
 
@@ -127,6 +132,11 @@ public void testCreateConfigsGivenElasticsearchLog() throws Exception {
         assertEquals("\\[%{TIMESTAMP_ISO8601:timestamp}\\]\\[%{LOGLEVEL:loglevel} \\]\\[.*", structure.getGrokPattern());
         assertEquals("timestamp", structure.getTimestampField());
         assertEquals(Collections.singletonList("ISO8601"), structure.getJodaTimestampFormats());
+        FieldStats messageFieldStats = structure.getFieldStats().get("message");
+        assertNotNull(messageFieldStats);
+        for (String statMessage : messageFieldStats.getTopHits().stream().map(m -> (String) m.get("value")).collect(Collectors.toList())) {
+            assertThat(structureFinder.getSampleMessages(), hasItem(statMessage));
+        }
     }
 
     public void testCreateConfigsGivenElasticsearchLogAndTimestampFieldOverride() throws Exception {
@@ -158,6 +168,11 @@ public void testCreateConfigsGivenElasticsearchLogAndTimestampFieldOverride() th
         assertEquals("\\[%{TIMESTAMP_ISO8601:my_time}\\]\\[%{LOGLEVEL:loglevel} \\]\\[.*", structure.getGrokPattern());
         assertEquals("my_time", structure.getTimestampField());
         assertEquals(Collections.singletonList("ISO8601"), structure.getJodaTimestampFormats());
+        FieldStats messageFieldStats = structure.getFieldStats().get("message");
+        assertNotNull(messageFieldStats);
+        for (String statMessage : messageFieldStats.getTopHits().stream().map(m -> (String) m.get("value")).collect(Collectors.toList())) {
+            assertThat(structureFinder.getSampleMessages(), hasItem(statMessage));
+        }
     }
 
     public void testCreateConfigsGivenElasticsearchLogAndGrokPatternOverride() throws Exception {
@@ -191,6 +206,13 @@ public void testCreateConfigsGivenElasticsearchLogAndGrokPatternOverride() throw
             "\\[%{JAVACLASS:class} *\\] \\[%{HOSTNAME:node}\\] %{JAVALOGMESSAGE:message}", structure.getGrokPattern());
         assertEquals("timestamp", structure.getTimestampField());
         assertEquals(Collections.singletonList("ISO8601"), structure.getJodaTimestampFormats());
+        FieldStats messageFieldStats = structure.getFieldStats().get("message");
+        assertNotNull(messageFieldStats);
+        for (String statMessage : messageFieldStats.getTopHits().stream().map(m -> (String) m.get("value")).collect(Collectors.toList())) {
+            // In this case the "message" field was output by the Grok pattern, so "message"
+            // at the end of the processing will _not_ contain a complete sample message
+            assertThat(structureFinder.getSampleMessages(), not(hasItem(statMessage)));
+        }
     }
 
     public void testCreateConfigsGivenElasticsearchLogAndImpossibleGrokPatternOverride() {