A QUIC implementation in Java

Kwik is an implementation of the QUIC protocol in (100%) Java. Kwik started as client (library) only, but since May 2021 it supports both client and server.

QUIC is a brand-new transport protocol developed by the IETF, and is the transport layer for the (also new) HTTP3 protocol. Although necessary for HTTP3, QUIC is more than just the transport protocol for HTTP3: most people consider QUIC as the "next generation TCP". It has similar properties as TCP, e.g. provide a reliable ordered stream, but is better in many ways:

• it can serve multiple streams (concurrently and sequential) over the same QUIC connection
• it does not suffer from the "head of line blocking" problem
• it's encrypted and secured by TLS (not as a separate layer, but embedded in the protocol)
• it requires at most only one network roundtrip to setup the connection (the combination of TCP and TLS needs much more)

If you want to know more about QUIC and are able to understand the dutch language, check out my presentation on Luminis DevCon 2019.

If you're looking for a Java HTTP3 client or server, check out Flupke, which is built on top of Kwik.

Kwik is created and maintained by Peter Doornbosch. The latest greatest can always be found on BitBucket.

Status

Kwik implements all QUIC features, except that the server does not yet support connection migration (work in progress). With respect to the interface Kwik offers to applications, it provides all necessary operations to exchange data, but it does not support specifying stream priorities. For both roles, interoperability is tested with a large number of other implementations, see automated interoperability tests. Due to the fact that most implementations are still in active development, and that some test cases (specifically testing behaviour in the context of packet loss and packet corruption) are non-deterministic, the results of the automatic interoperability test vary with each run, but usually, Kwik is amongst the best w.r.t. the number of successful testcases.

Kwik is still in active development, see git history.

HTTP3 on top of Kwik is supported by Flupke, the pure Java HTTP3 implementation.

Kwik supports QUIC v1 (RFC 9000) and QUIC v2 (RFC 9369).

Implemented QUIC features

• (QUIC v1) version negotiation
• handshake based on TLS 1.3
• data exchange over bidirectional and unidirectional streams
• stateless retry
• cipher suites TLS_AES_128_GCM_SHA256, TLS_AES_256_GCM_SHA384 and TLS_CHACHA20_POLY1305_SHA256
• key update
• session resumption
• 0-RTT
• compatible version negotiation draft-ietf-quic-version-negotiation-09
• QUIC V2

Client only:

• connection migration (use the interactive mode of the sample client to try it)

Is Kwik ready for production use?

It really depends on your use-case. First of all, as with all open source software, there is no guarantee the software will work, it is provided "as is". Having said that, interoperability with other implementations is heavily tested and ok, so you can assume it works. However, Kwik is not tested in various or extreme networking conditions, so your mileage may vary.
As development focus has been on correctness and features (in that order), performance is not optimal yet.

Kwik does not yet implement all QUIC requirements. Specifically, it does not enable applications or application protocols to specify the relative priority of streams. Note that this will not introduce interoperability issues, because the concept of priorities only exists in a peer; it does not affect the wire protocol. However, the division of network capacity over streams cannot be influenced and might not even be fair (although in practice it probably will). When wondering whether limitations would harm your use case: just go ahead and test it! When in doubt, you can always contact the author (see contact details below) for more information or help.

Is Kwik secure?

The TLS library used by Kwik is also "home made". Although all security features are implemented (e.g. certificates are checked as well as the Certificate Verify message that proofs possession of the certificate private key), and only crypto algorithms provided by the JDK are used, it is not security tested nor reviewed by security experts. So if you plan to transfer sensitive data or are afraid of intelligence services trying to spy on you, using Kwik is probably not the best idea.

Usage

Maven

Kwik is available in the Maven Central Repository. To use it in your project, add the following dependency to your pom.xml:

<dependency>
    <groupId>tech.kwik</groupId>
    <artifactId>kwik</artifactId>
    <version>0.8.10</version>
</dependency>

Client

To connect to a QUIC server, first create a connection object with the builder, e.g.

String applicationProtocolId = "....";
QuicClientConnection connection = QuicClientConnection.newBuilder()
        .uri(URI.create("https://sample.com:443"))
        .applicationProtocol(applicationProtocolId)
        .build();

You need to provide the ALPN protocol ID of the application protocol that you want to run on top of QUIC (and that the server you connect to supports). On the connection object simply call connect():

connection.connect();

Once connected, you can create a stream and start sending/receiving data, e.g.

QuicStream quicStream = connection.createStream(true);
OutputStream output = quicStream.getOutputStream();
output.write(...)
output.close();
InputStream input = quicStream.getInputStream();
input.read(...)

As QUIC servers generally limit the number of streams that clients can open concurrently, it is wise to close streams when not used anymore. Kwik does this automatically when you close() the OutputStream and read all data from the InputStream. If, for some reason, you do not read all data from the InputStream, call QuicStream.abortReading() to free resources and let the server you know you abandoned the stream.

When, for example with local development, the server uses self-signed certificates, you need to disable certificate checking. The builder has a method for this:

builder.noServerCertificateCheck()

The builder has a lot more methods for configuring the connection, most of which are self-explanatory; see the Builder interface in QuicClientConnection.

The builder method logger() requires an implementation of the Logger interface; Kwik provides two convenient implementations that you can use: SysOutLogger and FileLogger. Various log categories can be enabled or disabled by the logXXX() methods, e.g. logger.logInfo(true).

Take a look at the samples in the sample package for more inspiration.

Server

Creating a QUIC server with Kwik consist of a few steps. First you need to create an application protocol handler by implementing the ApplicationProtocolConnectionFactory interface. Its createConnection method should return an implementation of ApplicationProtocolConnection that, as the name suggests, represents your application protocol connection. It's acceptPeerInitiatedStream method is the handler that is called by Kwik when a client initiates a stream for the given protocol. The implementation of this acceptPeerInitiatedStream method should start a stream handler, but should itself return immediately, as it is called on the thread that handles incoming QUIC messages. If, for example, your application protocol follows the request-response model, the stream handler reads the request from the QUIC stream, processes it, creates a response, writes the response to the QUIC stream and closes the stream.

To complete the ApplicationProtocolConnectionFactory you should at least override the following two methods of the ApplicationProtocolSettings interface:

int maxConcurrentPeerInitiatedUnidirectionalStreams()
int maxConcurrentPeerInitiatedBidirectionalStreams()

These methods communicate to Kwik how many (concurrent) streams the protocol needs. In most cases, these methods return either 0 or Long.MAX_VALUE, to indicate that unidirectional or bidirectional streams are used (Long.MAX_VALUE) or are not used (value 0) by the application protocol. Some protocols define an exact number of unidirectional streams to be used as control stream, for example HTTP/3 needs 3 unidirectional streams, no more, no less. In such cases, the maxConcurrentUnidirectionalStreams method should return the exact number.

Once you have a proper implementations of ApplicationProtocolConnectionFactory and ApplicationProtocolConnection, you can create a ServerConnector and register the ApplicationProtocolConnectionFactory. The ServerConnector listens for new connections on a given port and handles them according to protocols that are registered on it. To create a ServerConnector, use the builder, e.g.

ServerConnector serverConnector = ServerConnector.builder()
        .withPort(443)
        .withCertificate(new FileInputStream("server.cert"), new FileInputStream("servercert.key"))
        .withConfiguration(serverConnectionConfig)
        .withLogger(log)
        .build(); 

register your protocol handler:

serverConnector.registerApplicationProtocol("myapplicationprotocol", new MyApplicationProtocolConnectionFactory);

and start the connector:

serverConnector.start();

The serverConnectionConfig that is needed by the ServerConnector.Builder defines the configuration for your server. For most settings you can get away with the defaults, except for one thing: you need to specify how many streams the client is allowed to have open concurrently in one QUIC connection. A larger value means your client(s) can do more work in parallel, but also can claim more resources. So infinite would be a bad choice, as that would make your server an easy victim for a denial of service attack. Furthermore: only allow the type of stream (unidirectional or bidirectional) that you actually support in the application protocol handler; again, if you fail to do so, you give attackers a change to claim resources that are not used. For example, if your application protocol does not use unidirectional streams, just don't set maxOpenUnidirectionalStreams as the default is 0, and provide a valid value for bidirectional streams, e.g.

ServerConnectionConfig.builder()
        .maxOpenPeerInitiatedBidirectionalStreams(50)  // Mandatory setting to maximize concurrent streams on a connection.
        .build();

That concludes creating a server. You can find working examples in the sample directory.

Development

To build the project:

• clone the git repository and cd into the directory
• build with gradle wrapper: ./gradlew build (or gradlew.bat build on Windows).

Gradle will write the output to build/libs.

To use IntelliJ for development, either just open the project directory in IntelliJ and it will pick up the gradle file, or generate IntelliJ project files with gradle idea and open the generated kwik.ipr file. The second option will give a better developer experience.

Sample Client

Kwik also provides a command line client that can be used to experiment with the QUIC protocol and even provides an interactive shell for more QUIC fun.

To run the sample client, execute the kwik.sh script or run java -jar build/libs/kwik.jar.

Usage of the sample client:

kwik <host>:<port> OR quic <host> <port> OR kwik http[s]://host:port
 -A,--alpn <arg>                set alpn (default is hq-xx)
    --aes128gcm                 use AEAD_AES_128_GCM cipher suite
    --aes256gcm                 use AEAD_AES_256_GCM cipher suite
 -c,--connectionTimeout <arg>   connection timeout in seconds
    --chacha20                  use ChaCha20 as only cipher suite     
    --clientCertificate <arg>   certificate (file) for client
                                authentication
    --clientKey <arg>           private key (file) for client certificate
 -h,--help                      show help
 -H,--http <arg>                send HTTP GET request, arg is path, e.g.
                                '/index.html'
 -i,--interactive               start interactive shell
    --initialRtt <arg>          custom initial RTT value (default is 500)
 -k,--keepAlive <arg>           connection keep alive time in seconds
 -l,--log <arg>                 logging options: [pdrcsiRSD]: (p)ackets
                                received/sent, (d)ecrypted bytes, (r)ecovery,
                                (c)ongestion control, (s)tats, (i)nfo, (R)aw
                                bytes, (S)ecrets, (D)ebug; default is "ip", use
                                (n)one to disable
 -L,--logFile <arg>             file to write log message too
    --noCertificateCheck        do not check server certificate
 -O,--output <arg>              write server response to file
 -R,--resumption key <arg>      session ticket file
    --reservedVersion           use reserved version to trigger version
 -S,--storeTickets <arg>        basename of file to store new session tickets
    --saveServerCertificates <arg>   store server certificates in given file
    --secrets <arg>             write secrets to file (Wireshark format)
 -T,--relativeTime              log with time (in seconds) since first packet 
 -v,--version                   show Kwik version
 -v1                            use Quic version 1           
 -v1v2                          use Quic version 1, request version 2
 -v2                            use Quic version 2
 -Z,--use0RTT                   use 0-RTT if possible (requires -H and -R)

If you do not provide the --http or the --keepAlive option, the Quic connection will be closed immediately after setup.

Plain Kwik will use HTTP 0.9 for http requests. However, if the flupke.jar is on the classpath (when using the kwik.sh script, it will try to load the plugin from the libs directory), it will use Flupke HTTP3 client for the HTTP request.

Sample Server

To run the demo web server, execute java -cp kwik.jar net.luminis.quic.run.SampleWebServer with the following arguments:

• certificate file
• private key file
• port number
• www directory to serve

This will start the server in retry-mode (see https://quicwg.org/base-drafts/rfc9000.html#name-address-validation-using-re). To run without retry-mode, add the --noRetry flag as first argument.

Adding HTTP/3 Support to Kwik client or server.

A plain Kwik client or server will only provide "HTTP/0.9", which is a very simplified form of HTTP/1, which the QUIC implementors have been using for early testing.

To add HTTP/3 to Kwik you should use the flupke plugin:

• Download the flupke jar from Maven
• Add the flupke jar to the client or server classpath, e.g. for the server run java -cp kwik.jar:flupke-<version>.jar net.luminis.quic.run.SampleWebServer.

Contact

If you have questions about this project, please mail the author (peter dot doornbosch) at luminis dot eu.

Acknowledgements

Thanks to Piet van Dongen for creating the marvellous logo!

License

This program is open source and licensed under LGPL (see the LICENSE.txt and LICENSE-LESSER.txt files in the distribution). This means that you can use this program for anything you like, and that you can embed it as a library in other applications, even commercial ones. If you do so, the author would appreciate if you include a reference to the original.

As of the LGPL license, all modifications and additions to the source code must be published as (L)GPL as well.

If you want to use the source with a different open source license, contact the author.