Handles the case where InputStream.skip provides fewer bytes than req…

…uested before reaching EOF.

src/main/java/com/amazon/ion/impl/IonCursorBinary.java

@@ -699,17 +699,22 @@ private boolean slowSeek(long numberOfBytes) {
             return false;
         }
         offset = limit;
+        long shortfall;
         long skipped = 0;
-        try {
-            skipped = refillableState.inputStream.skip(unbufferedBytesToSkip);
-        } catch (EOFException e) {
-            // Certain InputStream implementations (e.g. GZIPInputStream) throw EOFException if more bytes are requested
-            // to skip than are currently available (e.g. if a header or trailer is incomplete).
-        } catch (IOException e) {
-            throwAsIonException(e);
-        }
-        refillableState.totalDiscardedBytes += skipped;
-        long shortfall = numberOfBytes - (skipped + size);
+        do {
+            try {
+                skipped = refillableState.inputStream.skip(unbufferedBytesToSkip);
+            } catch (EOFException e) {
+                // Certain InputStream implementations (e.g. GZIPInputStream) throw EOFException if more bytes are requested
+                // to skip than are currently available (e.g. if a header or trailer is incomplete).
+                skipped = 0;
+            } catch (IOException e) {
+                throwAsIonException(e);
+            }
+            refillableState.totalDiscardedBytes += skipped;
+            shortfall = unbufferedBytesToSkip - skipped;
+            unbufferedBytesToSkip = shortfall;
+        } while (shortfall > 0 && skipped > 0);
         if (shortfall <= 0) {
             refillableState.bytesRequested = 0;
             refillableState.state = State.READY;

src/test/java/com/amazon/ion/impl/IonReaderContinuableTopLevelBinaryTest.java

@@ -38,7 +38,6 @@
 import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
 import java.io.EOFException;
-import java.io.FilterInputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.math.BigDecimal;
@@ -52,7 +51,6 @@
 import java.util.concurrent.atomic.AtomicLong;
 import java.util.function.Consumer;
 import java.util.function.Function;
-import java.util.function.Supplier;
 import java.util.zip.GZIPInputStream;
 
 import static com.amazon.ion.BitUtils.bytes;
@@ -3376,6 +3374,11 @@ public int read(byte[] b, int off, int len) throws IOException {
         @Override
         public long skip(long len) {
             int numberOfBytesToSkip = calculateNumberOfBytesToReturn((int) len);
+            if (numberOfBytesToSkip < 0) {
+                // The contract for InputStream.skip() does not use -1 to indicate EOF. It always returns the actual
+                // number of bytes skipped.
+                return 0;
+            }
             offset += numberOfBytesToSkip;
             return numberOfBytesToSkip;
         }
@@ -3399,17 +3402,59 @@ public void shouldNotFailWhenAnInputStreamProvidesFewerBytesThanRequestedWithout
         reader.close();
     }
 
-    @Test
-    public void shouldNotFailWhenAnInputStreamProvidesFewerBytesThanRequestedWithoutReachingEofAndTheReaderSkipsTheValue() throws Exception {
-        reader = boundedReaderFor(new ThrottlingInputStream(bytes(0xE0, 0x01, 0x00, 0xEA, 0x89, 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 0x20), false), 8, 8, byteAndOversizedValueCountingHandler);
+    @ParameterizedTest(name = "throwOnEof={0}")
+    @ValueSource(booleans = {true, false})
+    public void shouldNotFailWhenAnInputStreamProvidesFewerBytesThanRequestedWithoutReachingEofAndTheIncrementalReaderSkipsTheValue(boolean throwOnEof) throws Exception {
+        readerBuilder = readerBuilder.withIncrementalReadingEnabled(true);
+        reader = boundedReaderFor(new ThrottlingInputStream(bytes(0xE0, 0x01, 0x00, 0xEA, 0x89, 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 0x20), throwOnEof), 8, 8, byteAndOversizedValueCountingHandler);
         assertSequence(
+            // The string value is oversized, and is automatically skipped to comply with the incremental reader's
+            // guarantee that next() results in a fully-buffered top-level value.
             next(IonType.INT), intValue(0),
             next(null)
         );
         reader.close();
         assertEquals(1, oversizedCounter.get());
     }
 
+    @ParameterizedTest(name = "throwOnEof={0}")
+    @ValueSource(booleans = {true, false})
+    public void shouldNotFailWhenAnInputStreamProvidesFewerBytesThanRequestedWithoutReachingEofAndTheNonIcrementalReaderSkipsTheValue(boolean throwOnEof) throws Exception {
+        readerBuilder = readerBuilder.withIncrementalReadingEnabled(false);
+        reader = boundedReaderFor(new ThrottlingInputStream(bytes(0xE0, 0x01, 0x00, 0xEA, 0x89, 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 0x20), throwOnEof), 8, 8, byteAndOversizedValueCountingHandler);
+        assertSequence(
+            // The string value is oversized, but since the reader is non-incremental, an error is only surfaced if the
+            // user tries to materialize it.
+            next(IonType.STRING),
+            next(IonType.INT), intValue(0),
+            next(null)
+        );
+        reader.close();
+        assertEquals(0, oversizedCounter.get());
+    }
+
+    @ParameterizedTest(name = "incrementalReadingEnabled={0},throwOnEof={1}")
+    @CsvSource({
+        "true, true",
+        "true, false",
+        "false, true",
+        "false, false"
+    })
+    public void shouldNotFailWhenAnInputStreamProvidesFewerBytesThanRequestedWithoutReachingEofWithAnUnboundedBufferAndTheReaderSkipsTheValue(boolean incrementalReadingEnabled, boolean throwOnEof) throws Exception {
+        readerBuilder = readerBuilder.withIncrementalReadingEnabled(incrementalReadingEnabled);
+        // The reader's buffer size is unbounded, but the string value is larger than the initial buffer size. Skipping
+        // the value therefore causes some of its bytes to be skipped without ever being buffered, by calling
+        // InputStream.skip().
+        reader = boundedReaderFor(new ThrottlingInputStream(bytes(0xE0, 0x01, 0x00, 0xEA, 0x89, 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 0x20), throwOnEof), 6, Integer.MAX_VALUE, byteAndOversizedValueCountingHandler);
+        assertSequence(
+            next(IonType.STRING), // skip the string value, causing unbuffered bytes to be skipped
+            next(IonType.INT), intValue(0),
+            next(null)
+        );
+        reader.close();
+        assertEquals(0, oversizedCounter.get());
+    }
+
     @Test
     public void shouldNotFailWhenGZIPBoundaryIsEncounteredInStringValue() throws Exception {
         ResizingPipedInputStream pipe = new ResizingPipedInputStream(128);