[IO-891] Fix BoundedReader skip accounting

Limit skip requests to the remaining bound and update charsRead with the actual skipped count.

Author: Sarankumar Baskar

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

@@ -132,7 +132,18 @@ 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);
+        }
+        int remaining = maxCharsFromTargetReader - charsRead;
+        if (markedAt >= 0) {
+            remaining = Math.min(remaining, readAheadLimit - (charsRead - markedAt));
+        }
+        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 +243,42 @@ 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());
+        }
+    }
+
+    @Test
+    void testSkipRespectsReadAheadLimit() throws IOException {
+        try (BoundedReader mr = new BoundedReader(new StringReader("01234567890"), 10)) {
+            mr.mark(3);
+            assertEquals(3, mr.skip(100));
+            assertEquals(-1, mr.read());
+        }
+    }
 }