Fix or suppress LGTM findings (#10689)

Motivation:

LGTM reports multiple issues. They need to be triaged,
and real ones should be fixed.

Modifications:
- Fixed multiple issues reported by LGTM, such as redundant conditions,
  resource leaks, typos, possible integer overflows.
- Suppressed false-positives.
- Added a few testcases.

Result:

Fixed several possible issues, get rid of false alarms in the LGTM report.

buffer/src/main/java/io/netty/buffer/ByteBufInputStream.java

@@ -153,8 +153,9 @@ public class ByteBufInputStream extends InputStream implements DataInput {
         return endIndex - buffer.readerIndex();
     }
 
+    // Suppress a warning since the class is not thread-safe
     @Override
-    public void mark(int readlimit) {
+    public void mark(int readlimit) { // lgtm[java/non-sync-override]
         markReaderIndex = buffer.readerIndex();
     }
 
@@ -184,8 +185,9 @@ public class ByteBufInputStream extends InputStream implements DataInput {
         return len;
     }
 
+    // Suppress a warning since the class is not thread-safe
     @Override
-    public void reset() throws IOException {
+    public void reset() throws IOException { // lgtm[java/non-sync-override]
         buffer.readerIndex(markReaderIndex);
     }
 

buffer/src/main/java/io/netty/buffer/ByteBufOutputStream.java

@@ -42,6 +42,7 @@ public class ByteBufOutputStream extends OutputStream implements DataOutput {
     private final ByteBuf buffer;
     private final int startIndex;
     private DataOutputStream utf8out; // lazily-instantiated
+    private boolean closed;
 
     /**
      * Creates a new stream which writes data to the specified {@code buffer}.
@@ -135,7 +136,11 @@ public class ByteBufOutputStream extends OutputStream implements DataOutput {
     public void writeUTF(String s) throws IOException {
         DataOutputStream out = utf8out;
         if (out == null) {
-            utf8out = out = new DataOutputStream(this);
+            if (closed) {
+                throw new IOException("The stream is closed");
+            }
+            // Suppress a warning since the stream is closed in the close() method
+            utf8out = out = new DataOutputStream(this); // lgtm[java/output-resource-leak]
         }
         out.writeUTF(s);
     }
@@ -146,4 +151,20 @@ public class ByteBufOutputStream extends OutputStream implements DataOutput {
     public ByteBuf buffer() {
         return buffer;
     }
+
+    @Override
+    public void close() throws IOException {
+        if (closed) {
+            return;
+        }
+        closed = true;
+
+        try {
+            super.close();
+        } finally {
+            if (utf8out != null) {
+                utf8out.close();
+            }
+        }
+    }
 }

codec-haproxy/src/main/java/io/netty/handler/codec/haproxy/HAProxyMessageDecoder.java

@@ -151,7 +151,7 @@ public class HAProxyMessageDecoder extends ByteToMessageDecoder {
             v2MaxHeaderSize = V2_MAX_LENGTH;
         } else {
             int calcMax = maxTlvSize + V2_MIN_LENGTH;
-            if (calcMax > V2_MAX_LENGTH) {
+            if (calcMax > V2_MAX_LENGTH) {  // lgtm[java/constant-comparison]
                 v2MaxHeaderSize = V2_MAX_LENGTH;
             } else {
                 v2MaxHeaderSize = calcMax;

codec-http/src/main/java/io/netty/handler/codec/http/HttpObjectDecoder.java

@@ -977,7 +977,8 @@ public abstract class HttpObjectDecoder extends ByteToMessageDecoder {
 
         @Override
         public AppendableCharSequence parse(ByteBuf buffer) {
-            reset();
+            // Suppress a warning because HeaderParser.reset() is supposed to be called
+            reset();    // lgtm[java/subtle-inherited-call]
             return super.parse(buffer);
         }
 

codec-http/src/main/java/io/netty/handler/codec/http/ReadOnlyHttpHeaders.java

@@ -78,7 +78,8 @@ public final class ReadOnlyHttpHeaders extends HttpHeaders {
         for (int i = 0; i < nameValuePairs.length; i += 2) {
             CharSequence roName = nameValuePairs[i];
             if (AsciiString.hashCode(roName) == nameHash && contentEqualsIgnoreCase(roName, name)) {
-                return nameValuePairs[i + 1];
+                // Suppress a warning out of bounds access since the constructor allows only pairs
+                return nameValuePairs[i + 1]; // lgtm[java/index-out-of-bounds]
             }
         }
         return null;
@@ -136,7 +137,7 @@ public final class ReadOnlyHttpHeaders extends HttpHeaders {
         for (int i = 0; i < nameValuePairs.length; i += 2) {
             CharSequence roName = nameValuePairs[i];
             if (AsciiString.hashCode(roName) == nameHash && contentEqualsIgnoreCase(roName, name)) {
-                values.add(nameValuePairs[i + 1].toString());
+                values.add(nameValuePairs[i + 1].toString()); // lgtm[java/index-out-of-bounds]
             }
         }
         return values;
@@ -150,7 +151,7 @@ public final class ReadOnlyHttpHeaders extends HttpHeaders {
         List<Map.Entry<String, String>> entries = new ArrayList<>(size());
         for (int i = 0; i < nameValuePairs.length; i += 2) {
             entries.add(new SimpleImmutableEntry<>(nameValuePairs[i].toString(),
-                    nameValuePairs[i + 1].toString()));
+                    nameValuePairs[i + 1].toString())); // lgtm[java/index-out-of-bounds]
         }
         return entries;
     }
@@ -170,14 +171,14 @@ public final class ReadOnlyHttpHeaders extends HttpHeaders {
         if (ignoreCase) {
             for (int i = 0; i < nameValuePairs.length; i += 2) {
                 if (contentEqualsIgnoreCase(nameValuePairs[i], name) &&
-                        contentEqualsIgnoreCase(nameValuePairs[i + 1], value)) {
+                        contentEqualsIgnoreCase(nameValuePairs[i + 1], value)) { // lgtm[java/index-out-of-bounds]
                     return true;
                 }
             }
         } else {
             for (int i = 0; i < nameValuePairs.length; i += 2) {
                 if (contentEqualsIgnoreCase(nameValuePairs[i], name) &&
-                        contentEquals(nameValuePairs[i + 1], value)) {
+                        contentEquals(nameValuePairs[i + 1], value)) { // lgtm[java/index-out-of-bounds]
                     return true;
                 }
             }

codec-http/src/main/java/io/netty/handler/codec/http/websocketx/WebSocketUtil.java

@@ -27,14 +27,14 @@ import java.util.concurrent.ThreadLocalRandom;
  */
 final class WebSocketUtil {
 
-    // Suppress a warning about weak hash algorithm since it's defined in draft-ietf-hybi-thewebsocketprotocol-00
-    @SuppressWarnings("lgtm[java/weak-cryptographic-algorithm]")
     private static final FastThreadLocal<MessageDigest> MD5 = new FastThreadLocal<MessageDigest>() {
         @Override
         protected MessageDigest initialValue() throws Exception {
             try {
                 //Try to get a MessageDigest that uses MD5
-                return MessageDigest.getInstance("MD5");
+                //Suppress a warning about weak hash algorithm
+                //since it's defined in draft-ietf-hybi-thewebsocketprotocol-00
+                return MessageDigest.getInstance("MD5"); // lgtm [java/weak-cryptographic-algorithm]
             } catch (NoSuchAlgorithmException e) {
                 //This shouldn't happen! How old is the computer?
                 throw new InternalError("MD5 not supported on this platform - Outdated?");
@@ -42,14 +42,14 @@ final class WebSocketUtil {
         }
     };
 
-    // Suppress a warning about weak hash algorithm since it's defined in draft-ietf-hybi-thewebsocketprotocol-00
-    @SuppressWarnings("lgtm[java/weak-cryptographic-algorithm]")
     private static final FastThreadLocal<MessageDigest> SHA1 = new FastThreadLocal<MessageDigest>() {
         @Override
         protected MessageDigest initialValue() throws Exception {
             try {
                 //Try to get a MessageDigest that uses SHA1
-                return MessageDigest.getInstance("SHA1");
+                //Suppress a warning about weak hash algorithm
+                //since it's defined in draft-ietf-hybi-thewebsocketprotocol-00
+                return MessageDigest.getInstance("SHA1"); // lgtm [java/weak-cryptographic-algorithm]
             } catch (NoSuchAlgorithmException e) {
                 //This shouldn't happen! How old is the computer?
                 throw new InternalError("SHA-1 not supported on this platform - Outdated?");

codec-http/src/test/java/io/netty/handler/codec/http/ReadOnlyHttpHeadersTest.java

@@ -119,6 +119,18 @@ public class ReadOnlyHttpHeadersTest {
                 ACCEPT, APPLICATION_JSON, AsciiString.cached(" "));
     }
 
+    @Test(expected = IllegalArgumentException.class)
+    public void emptyHeaderName() {
+        new ReadOnlyHttpHeaders(true,
+                                ACCEPT, APPLICATION_JSON, AsciiString.cached(" "), ZERO);
+    }
+
+    @Test(expected = IllegalArgumentException.class)
+    public void headerWithoutValue() {
+        new ReadOnlyHttpHeaders(false,
+                                ACCEPT, APPLICATION_JSON, CONTENT_LENGTH);
+    }
+
     private static void assert3ParisEquals(Iterator<Entry<String, String>> itr) {
         assertTrue(itr.hasNext());
         Entry<String, String> next = itr.next();

codec-mqtt/src/main/java/io/netty/handler/codec/mqtt/MqttConnectReturnCode.java

@@ -57,7 +57,8 @@ public enum MqttConnectReturnCode {
         VALUES = new MqttConnectReturnCode[160];
         for (MqttConnectReturnCode code : values) {
             final int unsignedByte = code.byteValue & 0xFF;
-            VALUES[unsignedByte] = code;
+            // Suppress a warning about out of bounds access since the enum contains only correct values
+            VALUES[unsignedByte] = code;    // lgtm [java/index-out-of-bounds]
         }
     }
 

codec-xml/src/main/java/io/netty/handler/codec/xml/XmlElement.java

@@ -69,7 +69,7 @@ public abstract class XmlElement {
         if (namespace != null ? !namespace.equals(that.namespace) : that.namespace != null) {
             return false;
         }
-        if (namespaces != null ? !namespaces.equals(that.namespaces) : that.namespaces != null) {
+        if (!namespaces.equals(that.namespaces)) {
             return false;
         }
         if (prefix != null ? !prefix.equals(that.prefix) : that.prefix != null) {
@@ -84,7 +84,7 @@ public abstract class XmlElement {
         int result = name.hashCode();
         result = 31 * result + (namespace != null ? namespace.hashCode() : 0);
         result = 31 * result + (prefix != null ? prefix.hashCode() : 0);
-        result = 31 * result + (namespaces != null ? namespaces.hashCode() : 0);
+        result = 31 * result + namespaces.hashCode();
         return result;
     }
 

codec-xml/src/main/java/io/netty/handler/codec/xml/XmlElementStart.java

@@ -47,7 +47,7 @@ public class XmlElementStart extends XmlElement {
 
         XmlElementStart that = (XmlElementStart) o;
 
-        if (attributes != null ? !attributes.equals(that.attributes) : that.attributes != null) {
+        if (!attributes.equals(that.attributes)) {
             return false;
         }
 
@@ -57,7 +57,7 @@ public class XmlElementStart extends XmlElement {
     @Override
     public int hashCode() {
         int result = super.hashCode();
-        result = 31 * result + (attributes != null ? attributes.hashCode() : 0);
+        result = 31 * result + attributes.hashCode();
         return result;
     }
 

codec/src/main/java/io/netty/handler/codec/compression/JZlibEncoder.java

@@ -372,7 +372,9 @@ public class JZlibEncoder extends ZlibEncoder {
             if (resultCode != JZlib.Z_OK && resultCode != JZlib.Z_STREAM_END) {
                 promise.setFailure(ZlibUtil.deflaterException(z, "compression failure", resultCode));
                 return promise;
-            } else if (z.next_out_index != 0) {
+            } else if (z.next_out_index != 0) { // lgtm[java/constant-comparison]
+                // Suppressed a warning above to be on the safe side
+                // even if z.next_out_index seems to be always 0 here
                 footer = Unpooled.wrappedBuffer(out, 0, z.next_out_index);
             } else {
                 footer = Unpooled.EMPTY_BUFFER;

codec/src/main/java/io/netty/handler/codec/serialization/ObjectDecoderInputStream.java

@@ -127,8 +127,9 @@ public class ObjectDecoderInputStream extends InputStream implements
         in.close();
     }
 
+    // Suppress a warning since the class is not thread-safe
     @Override
-    public void mark(int readlimit) {
+    public void mark(int readlimit) {   // lgtm[java/non-sync-override]
         in.mark(readlimit);
     }
 
@@ -137,8 +138,9 @@ public class ObjectDecoderInputStream extends InputStream implements
         return in.markSupported();
     }
 
+    // Suppress a warning since the class is not thread-safe
     @Override
-    public int read() throws IOException {
+    public int read() throws IOException {  // lgtm[java/non-sync-override]
         return in.read();
     }
 

common/src/main/java/io/netty/util/ResourceLeakDetector.java

@@ -614,8 +614,10 @@ public class ResourceLeakDetector<T> {
                 // Strip the noisy stack trace elements.
                 String[] exclusions = excludedMethods.get();
                 for (int k = 0; k < exclusions.length; k += 2) {
+                    // Suppress a warning about out of bounds access
+                    // since the length of excludedMethods is always even, see addExclusions()
                     if (exclusions[k].equals(element.getClassName())
-                            && exclusions[k + 1].equals(element.getMethodName())) {
+                            && exclusions[k + 1].equals(element.getMethodName())) { // lgtm[java/index-out-of-bounds]
                         continue out;
                     }
                 }

common/src/main/java/io/netty/util/Signal.java

@@ -64,13 +64,15 @@ public final class Signal extends Error implements Constant<Signal> {
         }
     }
 
+    // Suppress a warning since the method doesn't need synchronization
     @Override
-    public Throwable initCause(Throwable cause) {
+    public Throwable initCause(Throwable cause) {   // lgtm[java/non-sync-override]
         return this;
     }
 
+    // Suppress a warning since the method doesn't need synchronization
     @Override
-    public Throwable fillInStackTrace() {
+    public Throwable fillInStackTrace() {   // lgtm[java/non-sync-override]
         return this;
     }
 

common/src/main/java/io/netty/util/concurrent/DefaultPromise.java

@@ -128,8 +128,9 @@ public class DefaultPromise<V> implements Promise<V> {
     private static final class LeanCancellationException extends CancellationException {
         private static final long serialVersionUID = 2794674970981187807L;
 
+        // Suppress a warning since the method doesn't need synchronization
         @Override
-        public Throwable fillInStackTrace() {
+        public Throwable fillInStackTrace() {   // lgtm[java/non-sync-override]
             setStackTrace(CANCELLATION_STACK);
             return this;
         }

example/src/main/resources/cors/cors.html

@@ -30,7 +30,7 @@
                     return document.getElementById('responseText');
                 }
 
-                function appendTextArea(newData) {
+                function appendTextArea(newData) {  // lgtm[js/unused-local-variable]
                     var el = getTextAreaElement();
                     el.value = el.value + '\n' + newData;
                 }

handler/src/main/java/io/netty/handler/ssl/ReferenceCountedOpenSslEngine.java

@@ -1624,7 +1624,7 @@ public class ReferenceCountedOpenSslEngine extends SSLEngine implements Referenc
                     if (minProtocolIndex > OPENSSL_OP_NO_PROTOCOL_INDEX_SSLV2) {
                         minProtocolIndex = OPENSSL_OP_NO_PROTOCOL_INDEX_SSLV2;
                     }
-                    if (maxProtocolIndex < OPENSSL_OP_NO_PROTOCOL_INDEX_SSLV2) {
+                    if (maxProtocolIndex < OPENSSL_OP_NO_PROTOCOL_INDEX_SSLV2) { // lgtm[java/constant-comparison]
                         maxProtocolIndex = OPENSSL_OP_NO_PROTOCOL_INDEX_SSLV2;
                     }
                     break;

handler/src/main/java/io/netty/handler/ssl/SslContextBuilder.java

@@ -390,7 +390,7 @@ public final class SslContextBuilder {
     public SslContextBuilder keyManager(PrivateKey key, String keyPassword, X509Certificate... keyCertChain) {
         if (forServer) {
             requireNonNull(keyCertChain, "keyCertChain required for servers");
-            if (keyCertChain.length == 0) {
+            if (keyCertChain.length == 0) { // lgtm[java/dereferenced-value-may-be-null]
                 throw new IllegalArgumentException("keyCertChain must be non-empty");
             }
             requireNonNull(key, "key required for servers");

handler/src/main/java/io/netty/handler/timeout/TimeoutException.java

@@ -32,8 +32,9 @@ public class TimeoutException extends ChannelException {
         super(null, null, shared);
     }
 
+    // Suppress a warning since the method doesn't need synchronization
     @Override
-    public Throwable fillInStackTrace() {
+    public Throwable fillInStackTrace() {   // lgtm[java/non-sync-override]
         return this;
     }
 }

resolver-dns/src/main/java/io/netty/resolver/dns/DnsNameResolverException.java

@@ -67,8 +67,9 @@ public class DnsNameResolverException extends RuntimeException {
         return question;
     }
 
+    // Suppress a warning since the method doesn't need synchronization
     @Override
-    public Throwable fillInStackTrace() {
+    public Throwable fillInStackTrace() {   // lgtm[java/non-sync-override]
         setStackTrace(EmptyArrays.EMPTY_STACK_TRACE);
         return this;
     }

resolver-dns/src/main/java/io/netty/resolver/dns/DnsResolveContext.java

@@ -252,8 +252,9 @@ abstract class DnsResolveContext<T> {
             initCause(cause.getCause());
         }
 
+        // Suppress a warning since this method doesn't need synchronization
         @Override
-        public Throwable fillInStackTrace() {
+        public Throwable fillInStackTrace() {   // lgtm[java/non-sync-override]
             return this;
         }
     }

resolver-dns/src/main/java/io/netty/resolver/dns/UnixResolverDnsServerAddressStreamProvider.java

@@ -100,7 +100,8 @@ public final class UnixResolverDnsServerAddressStreamProvider implements DnsServ
         final boolean useEtcResolverFiles = etcResolverFiles != null && etcResolverFiles.length != 0;
         domainToNameServerStreamMap = useEtcResolverFiles ? parse(etcResolverFiles) : etcResolvConfMap;
 
-        DnsServerAddresses defaultNameServerAddresses = etcResolvConfMap.get(etcResolvConf.getName());
+        DnsServerAddresses defaultNameServerAddresses
+                = etcResolvConfMap.get(etcResolvConf.getName());  // lgtm[java/dereferenced-value-may-be-null]
         if (defaultNameServerAddresses == null) {
             Collection<DnsServerAddresses> values = etcResolvConfMap.values();
             if (values.isEmpty()) {

resolver/src/main/java/io/netty/resolver/HostsFileParser.java

@@ -127,11 +127,16 @@ public final class HostsFileParser {
         requireNonNull(charsets, "charsets");
         if (file.exists() && file.isFile()) {
             for (Charset charset: charsets) {
-                HostsFileEntries entries = parse(new BufferedReader(new InputStreamReader(
+                BufferedReader reader = new BufferedReader(
-                        new FileInputStream(file), charset)));
+                        new InputStreamReader(new FileInputStream(file), charset));
+                try {
+                    HostsFileEntries entries = parse(reader);
                     if (entries != HostsFileEntries.EMPTY) {
                         return entries;
                     }
+                } finally {
+                    reader.close();
+                }
             }
         }
         return HostsFileEntries.EMPTY;

transport-native-epoll/src/main/java/io/netty/channel/epoll/EpollEventArray.java

@@ -109,7 +109,8 @@ final class EpollEventArray {
 
     private int getInt(int index, int offset) {
         if (PlatformDependent.hasUnsafe()) {
-            return PlatformDependent.getInt(memoryAddress + index * EPOLL_EVENT_SIZE + offset);
+            long n = (long) index * (long) EPOLL_EVENT_SIZE;
+            return PlatformDependent.getInt(memoryAddress + n + offset);
         }
         return memory.getInt(index * EPOLL_EVENT_SIZE + offset);
     }

transport/src/main/java/io/netty/channel/AbstractChannel.java

@@ -1136,8 +1136,9 @@ public abstract class AbstractChannel extends DefaultAttributeMap implements Cha
             initCause(exception);
         }
 
+        // Suppress a warning since this method doesn't need synchronization
         @Override
-        public Throwable fillInStackTrace() {
+        public Throwable fillInStackTrace() {   // lgtm[java/non-sync-override]
             return this;
         }
     }
@@ -1151,8 +1152,9 @@ public abstract class AbstractChannel extends DefaultAttributeMap implements Cha
             initCause(exception);
         }
 
+        // Suppress a warning since this method doesn't need synchronization
         @Override
-        public Throwable fillInStackTrace() {
+        public Throwable fillInStackTrace() {   // lgtm[java/non-sync-override]
             return this;
         }
     }
@@ -1166,8 +1168,9 @@ public abstract class AbstractChannel extends DefaultAttributeMap implements Cha
             initCause(exception);
         }
 
+        // Suppress a warning since this method doesn't need synchronization
         @Override
-        public Throwable fillInStackTrace() {
+        public Throwable fillInStackTrace() {   // lgtm[java/non-sync-override]
             return this;
         }
     }

transport/src/main/java/io/netty/channel/AdaptiveRecvByteBufAllocator.java

@@ -50,7 +50,8 @@ public class AdaptiveRecvByteBufAllocator extends DefaultMaxMessagesRecvByteBufA
             sizeTable.add(i);
         }
 
-        for (int i = 512; i > 0; i <<= 1) {
+        // Suppress a warning since i becomes negative when an integer overflow happens
+        for (int i = 512; i > 0; i <<= 1) { // lgtm[java/constant-comparison]
             sizeTable.add(i);
         }
 

transport/src/main/java/io/netty/channel/ChannelOutboundBuffer.java

@@ -602,7 +602,7 @@ public final class ChannelOutboundBuffer {
             final int oldValue = unwritable;
             final int newValue = oldValue | 1;
             if (UNWRITABLE_UPDATER.compareAndSet(this, oldValue, newValue)) {
-                if (oldValue == 0 && newValue != 0) {
+                if (oldValue == 0) {
                     fireChannelWritabilityChanged(invokeLater);
                 }
                 break;

transport/src/main/java/io/netty/channel/StacklessClosedChannelException.java

@@ -30,7 +30,8 @@ final class StacklessClosedChannelException extends ClosedChannelException {
 
     @Override
     public Throwable fillInStackTrace() {
-        return this;
+        // Suppress a warning since this method doesn't need synchronization
+        return this; // lgtm [java/non-sync-override]
     }
 
     /**

transport/src/main/java/io/netty/channel/group/VoidChannelGroupFuture.java

@@ -25,7 +25,8 @@ import java.util.Collections;
 import java.util.Iterator;
 import java.util.concurrent.TimeUnit;
 
-final class VoidChannelGroupFuture implements ChannelGroupFuture {
+// Suppress a warning about returning the same iterator since it always returns an empty iterator
+final class VoidChannelGroupFuture implements ChannelGroupFuture {  // lgtm[java/iterable-wraps-iterator]
 
     private static final Iterator<ChannelFuture> EMPTY = Collections.<ChannelFuture>emptyList().iterator();
     private final DefaultChannelGroup group;