Fix date format in warning headers

This commit fixes the date format in warning headers. There is some
confusion around whether or not RFC 1123 requires two-digit
days. However, the warning header specification very clearly relies on a
format that requires two-digit days. This commit removes the usage of
RFC 1123 date/time format from Java 8, which allows for one-digit days,
in favor of a format that forces two-digit days (it's otherwise
identical to RFC 1123 format, it is just fixed width).

Relates #23418

core/src/main/java/org/elasticsearch/common/logging/DeprecationLogger.java

@@ -29,14 +29,26 @@ import org.elasticsearch.common.util.concurrent.ThreadContext;
 import java.time.ZoneId;
 import java.time.ZonedDateTime;
 import java.time.format.DateTimeFormatter;
+import java.time.format.DateTimeFormatterBuilder;
+import java.time.format.SignStyle;
+import java.util.HashMap;
 import java.util.Iterator;
 import java.util.Locale;
+import java.util.Map;
 import java.util.Objects;
 import java.util.Set;
 import java.util.concurrent.CopyOnWriteArraySet;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
+import static java.time.temporal.ChronoField.DAY_OF_MONTH;
+import static java.time.temporal.ChronoField.DAY_OF_WEEK;
+import static java.time.temporal.ChronoField.HOUR_OF_DAY;
+import static java.time.temporal.ChronoField.MINUTE_OF_HOUR;
+import static java.time.temporal.ChronoField.MONTH_OF_YEAR;
+import static java.time.temporal.ChronoField.SECOND_OF_MINUTE;
+import static java.time.temporal.ChronoField.YEAR;
+
 /**
  * A logger that logs deprecation notices.
  */
@@ -128,6 +140,63 @@ public class DeprecationLogger {
                     Build.CURRENT.shortHash()) +
                     "\"%s\" \"%s\"";
 
+    /*
+     * RFC 7234 section 5.5 specifies that the warn-date is a quoted HTTP-date. HTTP-date is defined in RFC 7234 Appendix B as being from
+     * RFC 7231 section 7.1.1.1. RFC 7231 specifies an HTTP-date as an IMF-fixdate (or an obs-date referring to obsolete formats). The
+     * grammar for IMF-fixdate is specified as 'day-name "," SP date1 SP time-of-day SP GMT'. Here, day-name is
+     * (Mon|Tue|Wed|Thu|Fri|Sat|Sun). Then, date1 is 'day SP month SP year' where day is 2DIGIT, month is
+     * (Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec), and year is 4DIGIT. Lastly, time-of-day is 'hour ":" minute ":" second' where
+     * hour is 2DIGIT, minute is 2DIGIT, and second is 2DIGIT. Finally, 2DIGIT and 4DIGIT have the obvious definitions.
+     */
+    private static final DateTimeFormatter RFC_7231_DATE_TIME;
+
+    static {
+        final Map<Long, String> dow = new HashMap<>();
+        dow.put(1L, "Mon");
+        dow.put(2L, "Tue");
+        dow.put(3L, "Wed");
+        dow.put(4L, "Thu");
+        dow.put(5L, "Fri");
+        dow.put(6L, "Sat");
+        dow.put(7L, "Sun");
+        final Map<Long, String> moy = new HashMap<>();
+        moy.put(1L, "Jan");
+        moy.put(2L, "Feb");
+        moy.put(3L, "Mar");
+        moy.put(4L, "Apr");
+        moy.put(5L, "May");
+        moy.put(6L, "Jun");
+        moy.put(7L, "Jul");
+        moy.put(8L, "Aug");
+        moy.put(9L, "Sep");
+        moy.put(10L, "Oct");
+        moy.put(11L, "Nov");
+        moy.put(12L, "Dec");
+        RFC_7231_DATE_TIME = new DateTimeFormatterBuilder()
+                .parseCaseInsensitive()
+                .parseLenient()
+                .optionalStart()
+                .appendText(DAY_OF_WEEK, dow)
+                .appendLiteral(", ")
+                .optionalEnd()
+                .appendValue(DAY_OF_MONTH, 2, 2, SignStyle.NOT_NEGATIVE)
+                .appendLiteral(' ')
+                .appendText(MONTH_OF_YEAR, moy)
+                .appendLiteral(' ')
+                .appendValue(YEAR, 4)
+                .appendLiteral(' ')
+                .appendValue(HOUR_OF_DAY, 2)
+                .appendLiteral(':')
+                .appendValue(MINUTE_OF_HOUR, 2)
+                .optionalStart()
+                .appendLiteral(':')
+                .appendValue(SECOND_OF_MINUTE, 2)
+                .optionalEnd()
+                .appendLiteral(' ')
+                .appendOffset("+HHMM", "GMT")
+                .toFormatter(Locale.getDefault(Locale.Category.FORMAT));
+    }
+
     private static final ZoneId GMT = ZoneId.of("GMT");
 
     /**
@@ -195,13 +264,13 @@ public class DeprecationLogger {
 
     /**
      * Format a warning string in the proper warning format by prepending a warn code, warn agent, wrapping the warning string in quotes,
-     * and appending the RFC 1123 date.
+     * and appending the RFC 7231 date.
      *
      * @param s the warning string to format
      * @return a warning value formatted according to RFC 7234
      */
     public static String formatWarning(final String s) {
-        return String.format(Locale.ROOT, WARNING_FORMAT, escape(s), DateTimeFormatter.RFC_1123_DATE_TIME.format(ZonedDateTime.now(GMT)));
+        return String.format(Locale.ROOT, WARNING_FORMAT, escape(s), RFC_7231_DATE_TIME.format(ZonedDateTime.now(GMT)));
     }
 
     /**

test/framework/src/test/java/org/elasticsearch/test/rest/yaml/section/DoSectionTests.java

@@ -19,8 +19,6 @@
 
 package org.elasticsearch.test.rest.yaml.section;
 
-import org.elasticsearch.Version;
-import org.elasticsearch.common.hash.MessageDigests;
 import org.elasticsearch.common.logging.DeprecationLogger;
 import org.elasticsearch.common.xcontent.XContent;
 import org.elasticsearch.common.xcontent.XContentLocation;
@@ -29,7 +27,6 @@ import org.elasticsearch.common.xcontent.yaml.YamlXContent;
 import org.hamcrest.MatcherAssert;
 
 import java.io.IOException;
-import java.io.UnsupportedEncodingException;
 import java.util.Arrays;
 import java.util.Map;