[IO-891] Fix BoundedReader.skip(long) accounting and bounds handling (#860)

* [IO-891] Fix BoundedReader skip accounting
Limit skip requests to the remaining bound and update charsRead with the actual skipped count.

* [IO-891] Refine BoundedReader skip bounds fix
         Keep skip(long) focused on maxCharsFromTargetReader and actual skipped count, without treating mark read-ahead as a hard limit.

* Fix Checkstyle build failure

---------

Co-authored-by: Sarankumar Baskar <sbaskar@redhat.com>
Co-authored-by: Gary Gregory <garydgregory@users.noreply.github.com>

Author: 3 people

src/main/java/org/apache/commons/io/input/BoundedReader.java

@@ -132,7 +132,15 @@ public void reset() throws IOException {
 
     @Override
     public long skip(final long n) throws IOException {
-        charsRead += n;
-        return super.skip(n);
+        if (n <= 0) {
+            return super.skip(n);
+        }
+        final int remaining = maxCharsFromTargetReader - charsRead;
+        if (remaining <= 0) {
+            return 0;
+        }
+        final long skipped = super.skip(Math.min(n, remaining));
+        charsRead += (int) skipped;
+        return skipped;
     }
 }

src/test/java/org/apache/commons/io/input/BoundedReaderTest.java

@@ -24,6 +24,7 @@
 
 import java.io.BufferedReader;
 import java.io.File;
+import java.io.FilterReader;
 import java.io.IOException;
 import java.io.LineNumberReader;
 import java.io.Reader;
@@ -242,4 +243,33 @@ void testSkipTest() throws IOException {
             assertEquals(-1, mr.read());
         }
     }
+
+    @Test
+    void testSkipDoesNotExceedBound() throws IOException {
+        try (BoundedReader mr = new BoundedReader(new StringReader("01234567890"), 3)) {
+            assertEquals(3, mr.skip(100));
+            assertEquals(-1, mr.read());
+        }
+    }
+
+    @Test
+    void testSkipDoesNotOverflowCharsRead() throws IOException {
+        try (BoundedReader mr = new BoundedReader(new StringReader("01234567890"), 3)) {
+            assertEquals(3, mr.skip(Long.MAX_VALUE));
+            assertEquals(-1, mr.read());
+        }
+    }
+
+    @Test
+    void testSkipUsesActualSkippedCount() throws IOException {
+        try (BoundedReader mr = new BoundedReader(new FilterReader(new StringReader("01234567890")) {
+            @Override
+            public long skip(final long n) throws IOException {
+                return super.skip(Math.min(n, 2));
+            }
+        }, 5)) {
+            assertEquals(2, mr.skip(5));
+            assertEquals('2', mr.read());
+        }
+    }
 }