Improve WebSocket performance

Motivation:

Websocket performance is to a large account determined through the masking
and unmasking of frames. The current behavior of this in Netty can be
improved.

Modifications:

Perform the XOR operation not bytewise but in int blocks as long as
possible. This reduces the number of necessary operations by 4. Also don't
read the writerIndex in each iteration.
Added a unit test for websocket decoding and encoding for verifiation.

Result:

A large performance gain (up to 50%) in websocket throughput.
Avoid vectored writes for small websocket messages

Motivation:
The WebSocket08FrameEncoder contains an optimization path for small messages which copies the message content into the header buffer to avoid vectored writes. However this path is in the current implementation never taken because the target buffer is preallocated only for exactly the size of the header.

Modification:
For messages below a certain treshold allocate the buffer so that the message can be directly copied. Thereby the optimized path is taken.

Result:
A speedup of about 25% for 100byte messages. Declines with bigger message sizes. I have currently set the treshold to 1kB which is a point where I could still see a few percent speedup, but we should also avoid burning too many CPU cycles.
Fix the leak in the WebSocketClientProtocolHandshakeHandler

Motivation:
The WebSocketClientProtocolHandshakeHandler never releases the received handshake response.

Modification:
Release the message in a finally block.

Result:
No more leak
Adding a benchmark for websockets

Motivation:

It is often helpful to measure the performance of connections, e.g. the
latency and the throughput. This can be performed through benchmarks.

Modification:

This adds a simple but configurable benchmark for websockets into the
example directory. The Netty WebSocket server will echo all received
websocket frames and will provide an HTML/JS page which serves as the
client for the benchmark.
The benchmark also provides a verification mode that verifies the sent
against the received data. This can be used for the verification ob
websocket frame encoding and decoding funtionality.

Result:

A benchmark is added in form a further Netty websocket example.
With this benchmark it is easily possible to measure the performance between Netty and a browser
Add a test for handover from HTTP to Websocket

Motivation:
I was not fully reassured that whether everything works correctly when a websocket client receives the websocket handshake HTTP response and a websocket frame in a single ByteBuf (which can happen when the server sends a response directly or shortly after the connect). In this case some parts of the ByteBuf must be processed by HTTP decoder and the remaining by the websocket decoder.

Modification:
Adding a test that verifies that in this scenaria the handshake and the message are correctly interpreted and delivered by Netty.

Result:
One more test for Netty.
The test succeeds - No problems
Access autoRead via an AtomicIntegerFieldUpdater.

Motiviation:

Before this change, autoRead was a volatile boolean accessed directly.  Any thread that invoked the DefaultChannelConfig#setAutoRead(boolean) method would read the current value of autoRead, and then set a new value.  If the old value did not match the new value, some action would be immediately taken as part of the same method call.

As volatile only provides happens-before consistency, there was no guarantee that the calling thread was actually the thread mutating the state of the autoRead variable (such that it should be the one to invoke the follow-up actions).  For example, with 3 threads:
 * Thread 1: get = false
 * Thread 1: set = true
 * Thread 1: invokes read()
 * Thread 2: get = true
 * Thread 3: get = true
 * Thread 2: set = false
 * Thread 2: invokes autoReadCleared()
 * Event Loop receives notification from the Selector that data is available, but as autoRead has been cleared, cancels the operation and removes read interest
 * Thread 3: set = true

This results in a livelock - autoRead is set true, but no reads will happen even if data is available (as readyOps).  The only way around this livelock currently is to set autoRead to false, and then back to true.

Modifications:

Write access to the autoRead variable is now made using the getAndSet() method of an AtomicIntegerFieldUpdater, AUTOREAD_UPDATER.  This also changed the type of the underlying autoRead variable to be an integer, as no AtomicBooleanFieldUpdater class exists.  Boolean logic is retained by assuming that 1 is true and 0 is false.

Result:

There is no longer a race condition between retrieving the old value of the autoRead variable and setting a new value.
Add verification for websocket subprotocol on the client side.

Motivation:

Websocket clients can request to speak a specific subprotocol. The list of
subprotocols the client understands are sent to the server. The server
should select one of the protocols an reply this with the websocket
handshake response. The added code verifies that the reponded subprotocol
is valid.

Modifications:

Added verification of the subprotocol received from the server against the
subprotocol(s) that the user requests. If the user requests a subprotocol
but the server responds none or a non-requested subprotocol this is an
error and the handshake fails through an exception. If the user requests
no subprotocol but the server responds one this is also marked as an
error.

Addiontionally a getter for the WebSocketClientHandshaker in the
WebSocketClientProtocolHandler is added to enable the user of a
WebSocketClientProtocolHandler to extract the used negotiated subprotocol.

Result:

The subprotocol field which is received from a websocket server is now
properly verified on client side and clients and websocket connection
attempts will now only succeed if both parties can negotiate on a
subprotocol.
If the client sends a list of multiple possible subprotocols it can
extract the negotiated subprotocol through the added handshaker getter (WebSocketClientProtocolHandler.handshaker().actualSubprotocol()).
Fix a bug in NetUtil.createByteArrayFromIpAddressString()

Motivation:

An IPv6 string can have a zone index which is followed by the '%' sign.
When a user passes an IPv6 string with a zone index,
NetUtil.createByteArrayFromIpAddressString() returns an incorrect value.

Modification:

- Strip the zone index before conversion

Result:

An IPv6 string with a zone index is decoded correctly.
Add AbstractUnsafe.annotateConnectException()

Motivation:

JDK's exception messages triggered by a connection attempt failure do
not contain the related remote address in its message.  We currently
append the remote address to ConnectException's message, but I found
that we need to cover more exception types such as SocketException.

Modifications:

- Add AbstractUnsafe.annotateConnectException() to de-duplicate the
  code that appends the remote address

Result:

- Less duplication
- A transport implementor can annotate connection attempt failure
  message more easily
Do not consider PortUnreachableException to require channel closure

Motivation:

When a datagram packet is sent to a destination where nobody actually listens to,
the server O/S will respond with an ICMP Port Unreachable packet.
The ICMP Port Unreachable packet is translated into PortUnreachableException by JDK.
PortUnreachableException is not a harmful exception that prevents a user from sending a datagram.
Therefore, we should not close a datagram channel when PortUnreachableException is caught.

Modifications:

- Do not close a channel when the caught exception is PortUnreachableException.

Result:

A datagram channel is not closed unexpectedly anymore.
Make TestUtils.getFreePort() check both TCP and UDP

Motivation:

We see occational failures in the datagram tests saying 'address already
in use' when we attempt to bind on a port returned by
TestUtils.getFreePort().

It turns out that TestUtils.getFreePort() only checks if TCP port is
available.

Modifications:

Also check if UDP port is available, so that the datagram tests do not
fail because of the 'address already in use' error during a bind
attempt.

Result:

Less chance of datagram test failures
Fix an infinite loop when writing a zero-length FileRegion

Related: #2964

Motivation:

Writing a zero-length FileRegion to an NIO channel will lead to an
infinite loop.

Modification:

- Do not write a zero-length FileRegion by protecting with proper 'if'.
- Update the testsuite

Result:

Another bug fixed
Make Bootstrap and ServerBootstrap fully overridable

Related: #2034

Motivation:

Some users want to mock Bootstrap (or ServerBootstrap), and thus they
should not be final but be fully overridable and extensible.

Modifications:

Remove finals wherever possible

Result:

@daschl is happy.
Allowing negative keys in IntObjectHashMap.

Motivation:

IntObjectHashMap throws an exception when using negative values for
keys.

Modifications:

Changed hashIndex() to normalize the index if the mod operation returns
a negative number.

Result:

IntObjectHashMap supports negative key values.
Optimize IntObjectHashMap handling of negative keys.

Motivation:

The hashIndex method currently uses a conditional to handle negative
keys. This could be done without a conditional to slightly improve
performance.

Modifications:

Modified hashIndex() to avoid using a conditional.

Result:

Slight performance improvement to hashIndex().
Slight performance improvement to IntObjectHashMap.hashIndex()

Motivation:

Using a needless local copy of keys.length.

Modifications:

Using keys.length explicitly everywhere.

Result:

Slight performance improvement of hashIndex.
Disable SSLv3 to avoid POODLE vulnerability

Related: #3031

Motivation:

The only way to protect ourselves from POODLE vulnerability in Java for
now is to disable SSLv3.

- http://en.wikipedia.org/wiki/POODLE
- https://blogs.oracle.com/security/entry/information_about_ssl_poodle_vulnerability

Modifivation:

Disable SSLv3 in SslContext implementations

Result:

Prevent POODLE vulnerability when a user used SslContext with the
default configuration
Backport 4.1 to 4.0 on HttpPostRequestDecoder

Motivation
4.0 was not modified in the same time than 4.1 while the difference was
limited.
Include the fix on "=" character in Boundary.

Issue #3004 shows that "=" character was not supported as it should in
the HttpPostRequestDecoder in form-data boundary.

Modifications:
Backport from 4.1 to 4.0 while respecting interfaces.

Add 2 methods in StringUtil
- split with maxParm argument: String split with max parts only (to prevent multiple '='
to be source of extra split while not needed)
- substringAfter: String part after delimiter (since first part is not
needed)
Use those methods in HttpPostRequestDecoder.
Change and the HttpPostRequestDecoderTest to check using a boundary
beginning with "=".

Results:
Backport done (Issue #2886 fix)
Issue #3004 fix too
The fix implies more stability and fix the relative issues.
Fix missing version properties of transport-epoll in all-in-one JAR

Related: #2952

Motivation:

META-INF/io.netty.versions.properties in netty-all-*.jar does not
contain the version information about the netty-transport-epoll module.

Modifications:

Fix a bug in the regular expression in pom.xml, so that the artifacts
with a classifier is also included in the version properties file.

Result:

The version information of all modules are included in the version
properties file, and Version.identify() does not miss
netty-transport-epoll.