HTTP/2 HPACK Integer Encoding Bugs

Motivation:
- Decoder#decodeULE128 has a bounds bug and cannot decode Integer.MAX_VALUE
- Decoder#decodeULE128 doesn't support values greater than can be represented with Java's int data type. This is a problem because there are cases that require at least unsigned 32 bits (max header table size).
- Decoder#decodeULE128 treats overflowing the data type and invalid input the same. This can be misleading when inspecting the error that is thrown.
- Encoder#encodeInteger doesn't support values greater than can be represented with Java's int data type. This is a problem because there are cases that require at least unsigned 32 bits (max header table size).

Modifications:
- Correct the above issues and add unit tests.

Result:
Fixes https://github.com/netty/netty/issues/6210.

codec-http2/src/main/java/io/netty/handler/codec/http2/internal/hpack/Decoder.java

@@ -51,10 +51,12 @@ import static io.netty.util.AsciiString.EMPTY_STRING;
 import static io.netty.util.internal.ThrowableUtil.unknownStackTrace;
 
 public final class Decoder {
-    private static final Http2Exception DECODE_DECOMPRESSION_EXCEPTION = unknownStackTrace(
-            connectionError(COMPRESSION_ERROR, "HPACK - decompression failure"), Decoder.class, "decode(...)");
     private static final Http2Exception DECODE_ULE_128_DECOMPRESSION_EXCEPTION = unknownStackTrace(
             connectionError(COMPRESSION_ERROR, "HPACK - decompression failure"), Decoder.class, "decodeULE128(...)");
+    private static final Http2Exception DECODE_ULE_128_TO_LONG_DECOMPRESSION_EXCEPTION = unknownStackTrace(
+            connectionError(COMPRESSION_ERROR, "HPACK - long overflow"), Decoder.class, "decodeULE128(...)");
+    private static final Http2Exception DECODE_ULE_128_TO_INT_DECOMPRESSION_EXCEPTION = unknownStackTrace(
+            connectionError(COMPRESSION_ERROR, "HPACK - int overflow"), Decoder.class, "decodeULE128ToInt(...)");
     private static final Http2Exception DECODE_ILLEGAL_INDEX_VALUE = unknownStackTrace(
             connectionError(COMPRESSION_ERROR, "HPACK - illegal index value"), Decoder.class, "decode(...)");
     private static final Http2Exception INDEX_HEADER_ILLEGAL_INDEX_VALUE = unknownStackTrace(
@@ -184,7 +186,7 @@ public final class Decoder {
                     break;
 
                 case READ_MAX_DYNAMIC_TABLE_SIZE:
-                    setDynamicTableSize(decodeULE128(in, index));
+                    setDynamicTableSize(decodeULE128(in, (long) index));
                     state = READ_HEADER_REPRESENTATION;
                     break;
 
@@ -346,7 +348,7 @@ public final class Decoder {
         return dynamicTable.getEntry(index + 1);
     }
 
-    private void setDynamicTableSize(int dynamicTableSize) throws Http2Exception {
+    private void setDynamicTableSize(long dynamicTableSize) throws Http2Exception {
         if (dynamicTableSize > maxDynamicTableSize) {
             throw INVALID_MAX_DYNAMIC_TABLE_SIZE;
         }
@@ -422,26 +424,53 @@ public final class Decoder {
         return new IllegalArgumentException("decode only works with an entire header block! " + in);
     }
 
-    // Unsigned Little Endian Base 128 Variable-Length Integer Encoding
+    /**
-    private static int decodeULE128(ByteBuf in, int result) throws Http2Exception {
+     * Unsigned Little Endian Base 128 Variable-Length Integer Encoding
+     * <p>
+     * Visible for testing only!
+     */
+    static int decodeULE128(ByteBuf in, int result) throws Http2Exception {
+        final int readerIndex = in.readerIndex();
+        final long v = decodeULE128(in, (long) result);
+        if (v > Integer.MAX_VALUE) {
+            // the maximum value that can be represented by a signed 32 bit number is:
+            // [0x1,0x7f] + 0x7f + (0x7f << 7) + (0x7f << 14) + (0x7f << 21) + (0x6 << 28)
+            // OR
+            // 0x0 + 0x7f + (0x7f << 7) + (0x7f << 14) + (0x7f << 21) + (0x7 << 28)
+            // we should reset the readerIndex if we overflowed the int type.
+            in.readerIndex(readerIndex);
+            throw DECODE_ULE_128_TO_INT_DECOMPRESSION_EXCEPTION;
+        }
+        return (int) v;
+    }
+
+    /**
+     * Unsigned Little Endian Base 128 Variable-Length Integer Encoding
+     * <p>
+     * Visible for testing only!
+     */
+    static long decodeULE128(ByteBuf in, long result) throws Http2Exception {
         assert result <= 0x7f && result >= 0;
+        final boolean resultStartedAtZero = result == 0;
         final int writerIndex = in.writerIndex();
-        for (int readerIndex = in.readerIndex(), shift = 0;
+        for (int readerIndex = in.readerIndex(), shift = 0; readerIndex < writerIndex; ++readerIndex, shift += 7) {
-             readerIndex < writerIndex; ++readerIndex, shift += 7) {
             byte b = in.getByte(readerIndex);
-            if (shift == 28 && ((b & 0x80) != 0 || b > 6)) {
+            if (shift == 56 && ((b & 0x80) != 0 || b == 0x7F && !resultStartedAtZero)) {
-                // the maximum value that can be represented by a signed 32 bit number is:
+                // the maximum value that can be represented by a signed 64 bit number is:
-                // 0x7f + 0x7f + (0x7f << 7) + (0x7f << 14) + (0x7f << 21) + (0x6 << 28)
+                // [0x01L, 0x7fL] + 0x7fL + (0x7fL << 7) + (0x7fL << 14) + (0x7fL << 21) + (0x7fL << 28) + (0x7fL << 35)
+                // + (0x7fL << 42) + (0x7fL << 49) + (0x7eL << 56)
+                // OR
+                // 0x0L + 0x7fL + (0x7fL << 7) + (0x7fL << 14) + (0x7fL << 21) + (0x7fL << 28) + (0x7fL << 35) +
+                // (0x7fL << 42) + (0x7fL << 49) + (0x7fL << 56)
                 // this means any more shifts will result in overflow so we should break out and throw an error.
-                in.readerIndex(readerIndex + 1);
+                throw DECODE_ULE_128_TO_LONG_DECOMPRESSION_EXCEPTION;
-                break;
             }
 
             if ((b & 0x80) == 0) {
                 in.readerIndex(readerIndex + 1);
-                return result + ((b & 0x7F) << shift);
+                return result + ((b & 0x7FL) << shift);
             }
-            result += (b & 0x7F) << shift;
+            result += (b & 0x7FL) << shift;
         }
 
         throw DECODE_ULE_128_DECOMPRESSION_EXCEPTION;

codec-http2/src/main/java/io/netty/handler/codec/http2/internal/hpack/Encoder.java

@@ -204,7 +204,7 @@ public final class Encoder {
         this.maxHeaderTableSize = maxHeaderTableSize;
         ensureCapacity(0);
         // Casting to integer is safe as we verified the maxHeaderTableSize is a valid unsigned int.
-        encodeInteger(out, 0x20, 5, (int) maxHeaderTableSize);
+        encodeInteger(out, 0x20, 5, maxHeaderTableSize);
     }
 
     /**
@@ -227,20 +227,27 @@ public final class Encoder {
     }
 
     /**
-     * Encode integer according to Section 5.1.
+     * Encode integer according to <a href="https://tools.ietf.org/html/rfc7541#section-5.1">Section 5.1</a>.
      */
     private static void encodeInteger(ByteBuf out, int mask, int n, int i) {
+        encodeInteger(out, mask, n, (long) i);
+    }
+
+    /**
+     * Encode integer according to <a href="https://tools.ietf.org/html/rfc7541#section-5.1">Section 5.1</a>.
+     */
+    private static void encodeInteger(ByteBuf out, int mask, int n, long i) {
         assert n >= 0 && n <= 8 : "N: " + n;
         int nbits = 0xFF >>> (8 - n);
         if (i < nbits) {
-            out.writeByte(mask | i);
+            out.writeByte((int) (mask | i));
         } else {
             out.writeByte(mask | nbits);
-            int length = i - nbits;
+            long length = i - nbits;
             for (; (length & ~0x7F) != 0; length >>>= 7) {
-                out.writeByte((length & 0x7F) | 0x80);
+                out.writeByte((int) ((length & 0x7F) | 0x80));
             }
-            out.writeByte(length);
+            out.writeByte((int) length);
         }
     }
 

codec-http2/src/main/java/io/netty/handler/codec/http2/internal/hpack/HuffmanEncoder.java

@@ -118,7 +118,7 @@ final class HuffmanEncoder {
      * @param data the string literal to be Huffman encoded
      * @return the number of bytes required to Huffman encode <code>data</code>
      */
-    public int getEncodedLength(CharSequence data) {
+    int getEncodedLength(CharSequence data) {
         if (data instanceof AsciiString) {
             AsciiString string = (AsciiString) data;
             try {

codec-http2/src/test/java/io/netty/handler/codec/http2/internal/hpack/DecoderTest.java

@@ -38,7 +38,7 @@ import io.netty.handler.codec.http2.Http2Headers;
 import org.junit.Before;
 import org.junit.Test;
 
-import static io.netty.handler.codec.http2.Http2TestUtil.newTestDecoder;
+import static io.netty.handler.codec.http2.internal.hpack.Decoder.decodeULE128;
 import static io.netty.util.AsciiString.EMPTY_STRING;
 import static io.netty.util.AsciiString.of;
 import static java.lang.Integer.MAX_VALUE;
@@ -50,10 +50,6 @@ import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.verifyNoMoreInteractions;
 
 public class DecoderTest {
-
-    private static final int MAX_HEADER_LIST_SIZE = 8192;
-    private static final int MAX_HEADER_TABLE_SIZE = 4096;
-
     private Decoder decoder;
     private Http2Headers mockHeaders;
 
@@ -77,6 +73,109 @@ public class DecoderTest {
         mockHeaders = mock(Http2Headers.class);
     }
 
+    @Test
+    public void testDecodeULE128IntMax() throws Http2Exception {
+        byte[] input = {(byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0x07};
+        ByteBuf in = Unpooled.wrappedBuffer(input);
+        try {
+            assertEquals(Integer.MAX_VALUE, decodeULE128(in, 0));
+        } finally {
+            in.release();
+        }
+    }
+
+    @Test(expected = Http2Exception.class)
+    public void testDecodeULE128IntOverflow1() throws Http2Exception {
+        byte[] input = {(byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0x07};
+        ByteBuf in = Unpooled.wrappedBuffer(input);
+        final int readerIndex = in.readerIndex();
+        try {
+            decodeULE128(in, 1);
+        } finally {
+            assertEquals(readerIndex, in.readerIndex());
+            in.release();
+        }
+    }
+
+    @Test(expected = Http2Exception.class)
+    public void testDecodeULE128IntOverflow2() throws Http2Exception {
+        byte[] input = {(byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0x08};
+        ByteBuf in = Unpooled.wrappedBuffer(input);
+        final int readerIndex = in.readerIndex();
+        try {
+            decodeULE128(in, 0);
+        } finally {
+            assertEquals(readerIndex, in.readerIndex());
+            in.release();
+        }
+    }
+
+    @Test
+    public void testDecodeULE128LongMax() throws Http2Exception {
+        byte[] input = {(byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0xFF,
+                        (byte) 0xFF, (byte) 0x7F};
+        ByteBuf in = Unpooled.wrappedBuffer(input);
+        try {
+            assertEquals(Long.MAX_VALUE, decodeULE128(in, 0L));
+        } finally {
+            in.release();
+        }
+    }
+
+    @Test(expected = Http2Exception.class)
+    public void testDecodeULE128LongOverflow1() throws Http2Exception {
+        byte[] input = {(byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0xFF,
+                        (byte) 0xFF, (byte) 0xFF};
+        ByteBuf in = Unpooled.wrappedBuffer(input);
+        final int readerIndex = in.readerIndex();
+        try {
+            decodeULE128(in, 0L);
+        } finally {
+            assertEquals(readerIndex, in.readerIndex());
+            in.release();
+        }
+    }
+
+    @Test(expected = Http2Exception.class)
+    public void testDecodeULE128LongOverflow2() throws Http2Exception {
+        byte[] input = {(byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0xFF,
+                        (byte) 0xFF, (byte) 0x7F};
+        ByteBuf in = Unpooled.wrappedBuffer(input);
+        final int readerIndex = in.readerIndex();
+        try {
+            decodeULE128(in, 1L);
+        } finally {
+            assertEquals(readerIndex, in.readerIndex());
+            in.release();
+        }
+    }
+
+    @Test
+    public void testSetTableSizeWithMaxUnsigned32BitValueSucceeds() throws Http2Exception {
+        byte[] input = {(byte) 0x3F, (byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0x0E};
+        ByteBuf in = Unpooled.wrappedBuffer(input);
+        try {
+            final long expectedHeaderSize = 4026531870L; // based on the input above
+            decoder.setMaxHeaderTableSize(expectedHeaderSize);
+            decoder.decode(0, in, mockHeaders);
+            assertEquals(expectedHeaderSize, decoder.getMaxHeaderTableSize());
+        } finally {
+            in.release();
+        }
+    }
+
+    @Test(expected = Http2Exception.class)
+    public void testSetTableSizeOverLimitFails() throws Http2Exception {
+        byte[] input = {(byte) 0x3F, (byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0x0E};
+        ByteBuf in = Unpooled.wrappedBuffer(input);
+        try {
+            decoder.setMaxHeaderTableSize(4026531870L - 1); // based on the input above ... 1 less than is above.
+            decoder.decode(0, in, mockHeaders);
+        } finally {
+            in.release();
+        }
+    }
+
     @Test
     public void testLiteralHuffmanEncodedWithEmptyNameAndValue() throws Http2Exception {
         byte[] input = {0, (byte) 0x80, 0};
@@ -123,7 +222,7 @@ public class DecoderTest {
     }
 
     @Test(expected = Http2Exception.class)
-    public void testIncompleteIndex() throws Http2Exception, Http2Exception {
+    public void testIncompleteIndex() throws Http2Exception {
         byte[] compressed = Hex.decodeHex("FFF0".toCharArray());
         ByteBuf in = Unpooled.wrappedBuffer(compressed);
         try {

codec-http2/src/test/java/io/netty/handler/codec/http2/internal/hpack/EncoderTest.java

@@ -0,0 +1,60 @@
+/*
+ * Copyright 2017 The Netty Project
+ *
+ * The Netty Project licenses this file to you under the Apache License,
+ * version 2.0 (the "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at:
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ */
+package io.netty.handler.codec.http2.internal.hpack;
+
+import io.netty.buffer.ByteBuf;
+import io.netty.buffer.Unpooled;
+import io.netty.handler.codec.http2.Http2Exception;
+import io.netty.handler.codec.http2.Http2Headers;
+import org.junit.Before;
+import org.junit.Test;
+
+import static io.netty.handler.codec.http2.Http2CodecUtil.MAX_HEADER_TABLE_SIZE;
+import static org.junit.Assert.assertEquals;
+import static org.mockito.Mockito.mock;
+
+public class EncoderTest {
+    private Decoder decoder;
+    private Encoder encoder;
+    private Http2Headers mockHeaders;
+
+    @Before
+    public void setUp() throws Http2Exception {
+        encoder = new Encoder();
+        decoder = new Decoder();
+        mockHeaders = mock(Http2Headers.class);
+    }
+
+    @Test
+    public void testSetMaxHeaderTableSizeToMaxValue() throws Http2Exception {
+        ByteBuf buf = Unpooled.buffer();
+        encoder.setMaxHeaderTableSize(buf, MAX_HEADER_TABLE_SIZE);
+        decoder.setMaxHeaderTableSize(MAX_HEADER_TABLE_SIZE);
+        decoder.decode(0, buf, mockHeaders);
+        assertEquals(MAX_HEADER_TABLE_SIZE, decoder.getMaxHeaderTableSize());
+        buf.release();
+    }
+
+    @Test(expected = Http2Exception.class)
+    public void testSetMaxHeaderTableSizeOverflow() throws Http2Exception {
+        ByteBuf buf = Unpooled.buffer();
+        try {
+            encoder.setMaxHeaderTableSize(buf, MAX_HEADER_TABLE_SIZE + 1);
+        } finally {
+            buf.release();
+        }
+    }
+}

microbench/src/main/java/io/netty/microbench/http2/internal/hpack/DecoderULE128Benchmark.java

@@ -0,0 +1,156 @@
+/*
+ * Copyright 2017 The Netty Project
+ *
+ * The Netty Project licenses this file to you under the Apache License,
+ * version 2.0 (the "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at:
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ */
+package io.netty.microbench.http2.internal.hpack;
+
+import io.netty.buffer.ByteBuf;
+import io.netty.buffer.Unpooled;
+import io.netty.handler.codec.http2.Http2Error;
+import io.netty.handler.codec.http2.Http2Exception;
+import io.netty.microbench.util.AbstractMicrobenchmark;
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Fork;
+import org.openjdk.jmh.annotations.Measurement;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.OutputTimeUnit;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.Setup;
+import org.openjdk.jmh.annotations.State;
+import org.openjdk.jmh.annotations.Threads;
+import org.openjdk.jmh.annotations.Warmup;
+
+import java.util.concurrent.TimeUnit;
+
+@Threads(1)
+@State(Scope.Benchmark)
+@Fork(1)
+@Warmup(iterations = 5)
+@Measurement(iterations = 10)
+@OutputTimeUnit(TimeUnit.NANOSECONDS)
+public class DecoderULE128Benchmark extends AbstractMicrobenchmark {
+    private static final Http2Exception DECODE_ULE_128_TO_LONG_DECOMPRESSION_EXCEPTION =
+            new Http2Exception(Http2Error.COMPRESSION_ERROR);
+    private static final Http2Exception DECODE_ULE_128_TO_INT_DECOMPRESSION_EXCEPTION =
+            new Http2Exception(Http2Error.COMPRESSION_ERROR);
+    private static final Http2Exception DECODE_ULE_128_DECOMPRESSION_EXCEPTION =
+            new Http2Exception(Http2Error.COMPRESSION_ERROR);
+
+    private ByteBuf longMaxBuf;
+    private ByteBuf intMaxBuf;
+
+    @Setup
+    public void setup() {
+        byte[] longMax = {(byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0xFF,
+                          (byte) 0xFF, (byte) 0x7F};
+        longMaxBuf = Unpooled.wrappedBuffer(longMax);
+        byte[] intMax = {(byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0x07};
+        intMaxBuf = Unpooled.wrappedBuffer(intMax);
+    }
+
+    @Benchmark
+    @BenchmarkMode(Mode.AverageTime)
+    public long decodeMaxLong() throws Http2Exception {
+        long v = decodeULE128(longMaxBuf, 0L);
+        longMaxBuf.readerIndex(0);
+        return v;
+    }
+
+    @Benchmark
+    @BenchmarkMode(Mode.AverageTime)
+    public long decodeMaxIntWithLong() throws Http2Exception {
+        long v = decodeULE128(intMaxBuf, 0L);
+        intMaxBuf.readerIndex(0);
+        return v;
+    }
+
+    @Benchmark
+    @BenchmarkMode(Mode.AverageTime)
+    public int decodeMaxInt() throws Http2Exception {
+        int v = decodeULE128(intMaxBuf, 0);
+        intMaxBuf.readerIndex(0);
+        return v;
+    }
+
+    @Benchmark
+    @BenchmarkMode(Mode.AverageTime)
+    public int decodeMaxIntUsingLong() throws Http2Exception {
+        int v = decodeULE128UsingLong(intMaxBuf, 0);
+        intMaxBuf.readerIndex(0);
+        return v;
+    }
+
+    static int decodeULE128UsingLong(ByteBuf in, int result) throws Http2Exception {
+        final int readerIndex = in.readerIndex();
+        final long v = decodeULE128(in, (long) result);
+        if (v > Integer.MAX_VALUE) {
+            in.readerIndex(readerIndex);
+            throw DECODE_ULE_128_TO_INT_DECOMPRESSION_EXCEPTION;
+        }
+        return (int) v;
+    }
+
+    static long decodeULE128(ByteBuf in, long result) throws Http2Exception {
+        assert result <= 0x7f && result >= 0;
+        final boolean resultStartedAtZero = result == 0;
+        final int writerIndex = in.writerIndex();
+        for (int readerIndex = in.readerIndex(), shift = 0; readerIndex < writerIndex; ++readerIndex, shift += 7) {
+            byte b = in.getByte(readerIndex);
+            if (shift == 56 && ((b & 0x80) != 0 || b == 0x7F && !resultStartedAtZero)) {
+                // the maximum value that can be represented by a signed 64 bit number is:
+                // [0x01L, 0x7fL] + 0x7fL + (0x7fL << 7) + (0x7fL << 14) + (0x7fL << 21) + (0x7fL << 28) + (0x7fL << 35)
+                // + (0x7fL << 42) + (0x7fL << 49) + (0x7eL << 56)
+                // OR
+                // 0x0L + 0x7fL + (0x7fL << 7) + (0x7fL << 14) + (0x7fL << 21) + (0x7fL << 28) + (0x7fL << 35) +
+                // (0x7fL << 42) + (0x7fL << 49) + (0x7fL << 56)
+                // this means any more shifts will result longMaxBuf overflow so we should break out and throw an error.
+                throw DECODE_ULE_128_TO_LONG_DECOMPRESSION_EXCEPTION;
+            }
+
+            if ((b & 0x80) == 0) {
+                in.readerIndex(readerIndex + 1);
+                return result + ((b & 0x7FL) << shift);
+            }
+            result += (b & 0x7FL) << shift;
+        }
+
+        throw DECODE_ULE_128_DECOMPRESSION_EXCEPTION;
+    }
+
+    static int decodeULE128(ByteBuf in, int result) throws Http2Exception {
+        assert result <= 0x7f && result >= 0;
+        final boolean resultStartedAtZero = result == 0;
+        final int writerIndex = in.writerIndex();
+        for (int readerIndex = in.readerIndex(), shift = 0; readerIndex < writerIndex; ++readerIndex, shift += 7) {
+            byte b = in.getByte(readerIndex);
+            if (shift == 28 && ((b & 0x80) != 0 || !resultStartedAtZero && b > 6 || resultStartedAtZero && b > 7)) {
+                // the maximum value that can be represented by a signed 32 bit number is:
+                // [0x1,0x7f] + 0x7f + (0x7f << 7) + (0x7f << 14) + (0x7f << 21) + (0x6 << 28)
+                // OR
+                // 0x0 + 0x7f + (0x7f << 7) + (0x7f << 14) + (0x7f << 21) + (0x7 << 28)
+                // this means any more shifts will result longMaxBuf overflow so we should break out and throw an error.
+                throw DECODE_ULE_128_TO_INT_DECOMPRESSION_EXCEPTION;
+            }
+
+            if ((b & 0x80) == 0) {
+                in.readerIndex(readerIndex + 1);
+                return result + ((b & 0x7F) << shift);
+            }
+            result += (b & 0x7F) << shift;
+        }
+
+        throw DECODE_ULE_128_DECOMPRESSION_EXCEPTION;
+    }
+}