Reject trailing text after the date in Converter.DATE (#435)

* reject trailing text after the date in Converter.DATE

* Only fall back to English locale when the date fails to parse

Restrict the English retry to when the default-locale parse matches nothing;
a partial match is a trailing-text failure and now throws with the parse
position instead of retrying and reporting a misleading offset.

Author: farkhalit

src/main/java/org/apache/commons/cli/Converter.java

@@ -22,6 +22,7 @@ Licensed to the Apache Software Foundation (ASF) under one or more
 import java.nio.file.InvalidPathException;
 import java.nio.file.Path;
 import java.nio.file.Paths;
+import java.text.ParsePosition;
 import java.text.SimpleDateFormat;
 import java.util.Date;
 import java.util.Locale;
@@ -82,15 +83,26 @@ public interface Converter<T, E extends Exception> {
         final SimpleDateFormat format = new SimpleDateFormat(pattern);
         // reject out-of-range fields (for example "Feb 30") instead of silently rolling them over.
         format.setLenient(false);
-        try {
-            return format.parse(s);
-        } catch (final java.text.ParseException e) {
+        // SimpleDateFormat.parse(String) stops at the first character it cannot use and ignores any
+        // trailing text, so "<valid date> garbage" would be accepted. Parse from an explicit position
+        // and reject the value unless the whole string is consumed.
+        final ParsePosition pos = new ParsePosition(0);
+        Date date = format.parse(s, pos);
+        if (date == null) {
             // Date.toString() always emits English month/day names, so fall back to Locale.ENGLISH
-            // when the default locale rejects the documented format.
+            // when the default locale rejects the documented format. Only retry when the default
+            // locale matched nothing; a partial match is a trailing-text failure, handled below.
             final SimpleDateFormat englishFormat = new SimpleDateFormat(pattern, Locale.ENGLISH);
             englishFormat.setLenient(false);
-            return englishFormat.parse(s);
+            pos.setIndex(0);
+            pos.setErrorIndex(-1);
+            date = englishFormat.parse(s, pos);
         }
+        if (date == null || pos.getIndex() != s.length()) {
+            final int errorIndex = pos.getErrorIndex() >= 0 ? pos.getErrorIndex() : pos.getIndex();
+            throw new java.text.ParseException(String.format("Unparseable date: \"%s\"", s), errorIndex);
+        }
+        return date;
     };
 
     /**

src/test/java/org/apache/commons/cli/ConverterTests.java

@@ -86,6 +86,24 @@ void testDate() throws Exception {
         assertThrows(java.text.ParseException.class, () -> Converter.DATE.apply("Jun 06 17:48:57 EDT 2002"));
     }
 
+    @Test
+    void testDateRejectsTrailingText() throws Exception {
+        final Date expected = new Date(1023400137000L);
+        final String formatted = new SimpleDateFormat("EEE MMM dd HH:mm:ss zzz yyyy").format(expected);
+        assertThrows(java.text.ParseException.class, () -> Converter.DATE.apply(formatted + " trailing"));
+    }
+
+    @Test
+    @DefaultLocale(language = "de", country = "DE")
+    void testDateRejectsTrailingTextLocaleDe() throws Exception {
+        // Trailing text must be rejected even when a non-English default locale parses the date, and
+        // the reported error position should point past the parsed date rather than at index 0.
+        final Date expected = new Date(1023400137000L);
+        final String formatted = new SimpleDateFormat("EEE MMM dd HH:mm:ss zzz yyyy").format(expected);
+        final java.text.ParseException e = assertThrows(java.text.ParseException.class, () -> Converter.DATE.apply(formatted + " trailing"));
+        assertEquals(formatted.length(), e.getErrorOffset());
+    }
+
     @Test
     @DefaultLocale(language = "de", country = "DE")
     void testDateLocaleDe() throws Exception {