Trireme

This is a set of libraries for running node.js scripts inside Java.

What is Trireme?

Trireme runs Node.js scripts inside the JVM. This is important because there is a lot of software out there (including our own) that is built in Java and isn't going to get rewritten in JavaScript now or in the future.

Trireme is specifically designed to be embeddable within any Java program. There is a lot of support inside Trireme for this specific case:

• Many Node.js scripts can run inside a single JVM, subject to memory constraints.
• Each script is totally isolated from the others -- there is no way for one script to affect the heap of the others.
• A sandbox is provided that lets the container control how, or if, the script gains access to the filesystem and to the network.
• The HTTP server implementation is pluggable. An "HTTP Adapter" is supported that allows a container to embed a Node.js script inside an existing HTTP container like a web server or other product. (A sample adapter, built using Netty 4.0, is included.)
• The sandbox supports a Rhino feature that makes it possible to limit the execution time for a script. With this feature enabled, a script that runs an infinite loop can be terminated after some time.

For a more detailed introduction, see our intro presentation:

• Introduction to Trireme

So, again, why would I use Trireme?

• To embed Node.js apps inside an existing Java application
• To run Node.js apps that take advantage of Java libraries you can't live without, like JDBC drivers and XML parsers

If neither of those reasons apply to you, then stick with "regular node!"

How do I get it?

From NPM

sudo npm install -g trireme
trireme -h
trireme <your script name here>

The NPM package for Trireme lets you run it on the command line just like "node".

Unfortunately, Trireme does not support the "repl" yet (and it's hard since Java gives us limited control over the TTY) so just running "trireme" with no arguments produces an error right now.

From Maven Central

The best reason to use Trireme is because it's important to embed Node.js code inside an existing Java application. In that case you will use the modules under "io.apigee.trireme" on Maven Central:

io.apigee.trireme

The "module map" later in this document shows which modules to use in which cases.

From GitHub

See the releases page to download the latest release files.

"trireme-x.y.z.jar" is always a stand-alone jar that you can run just like "node":

java -jar trireme-x.y.z.jar script.js

What version of Node.js does Trireme Support?

Trireme supports two versions of Node.js:

• 0.10.32. This is the default, fully-supported version.
• 0.12.7. This version is still a work in progress.

Support for Node.js 4.0 depends on more complete ES6 code in Rhino. The Rhino community is making progress on this but it will be quite some time before we are ready to support 4.0.

Running Trireme

Using NPM

If you installed Trireme using NPM, just run:

trireme <script name>

Trireme will execute your script just like Node.

In addition, the environment variable TRIREME_CLASSPATH may be used to add extra JARs or directories to the classpath used to run Trireme. Anything on this path will be appended to the classpath used to launch Trireme. This allows you to add JDBC drivers, etc.

For help, use:

trireme -h

Using Java

The "jar" module builds a self-contained JAR that may be used to launch Trireme on the command line just like regular Node.js:

mvn install
java -jar jar/target/trireme.X.Y.Z.jar <script name>

(and with no arguments it will launch the "repl" but that implementation is not complete)

For Apigee Edge Customers

Node.js apps on Apigee Edge run inside Trireme using a few specific settings that make them slightly different from the standard Trireme runtime. In particular, an "HTTP adaptor" is used, which is not 100% the same as the standard HTTP module. This does not affect most applications, but it may affect applications that depend on undocumented or internal functions and properties of the default HTTP module. (While this is a poor programming practice, it's quite common.)

In order to test applications that will run on Apigee Edge in the most compatible environment, the module "samples/apigee-edge-like-runner" will build a self-contained JAR that sets up Trireme this way. Use it just like the "Using Java" link above:

mvn install
java -jar samples/apigee-edge-like-runner/target/apigee-edge-like-launcher-X-Y-Z-SNAPSHOT.jar <script name>

Embedding Trireme as a servlet

The war sample is a sample that shows how to assemble a Node.js application into a WAR file. It uses the trireme-servlet module to link the servlet to the Node.js script. Any script that operates as an HTTP server using the "http" module can be embedded in this way.

Embedding Trireme Anywhere Else that Java Runs

There is JavaDoc for the "NodeEnvironment" and "NodeScript" classes, and many other features. Here are the basics:

import io.apigee.trireme.core.NodeEnvironment;
import io.apigee.trireme.core.NodeScript;

// The NodeEnvironment controls the environment for many scripts
NodeEnvironment env = new NodeEnvironment();

// Pass in the script file name, a File pointing to the actual script, and an Object[] containg "argv"
NodeScript script = env.createScript("my-test-script.js",
                                     new File("my-test-script.js"), null);

// Wait for the script to complete
ScriptStatus status = script.execute().get();

// Check the exit code
System.exit(status.getExitCode());

Selecting the Node version

The all-in-one JAR, and the "trireme" NPM package, include code for both Node.js 0.10 and 0.12. To select a version from the command-line, use the "--node-version" option, like this:

trireme --node-version=0.12 foo.js

When embedding Trireme, select the version using the "setNodeVersion" method in the NodeScript class.

With this scheme, both versions of Node can run inside the same JVM.

The version numbers are "semver-style" although they do not support every single feature of semver. The best bet is to use "0.10" and "0.12" to select each.

Trireme Extensions

There are a few NPM modules that only work in Trireme. These allow access to features of the Java platform that are normally accessed via native code in regular Node.js. These modules are as follows:

• trireme-jdbc: This module provides access to JDBC drivers from inside Node.js code. This makes it possible to use databases that have excellent JDBC drivers (such as Oracle) without compiling any native code.
• trireme-xslt: This module provides access to the XSLT processor inside the Java platform, which is faster and can support more of the XSLT standard than any of the native Node.js options.
• trireme-support: Additional Trireme-specific support functions. These include the ability to detect if Trireme is being used, and the ability to dyamically load additional Node.js modules from a JAR file.

Logging

Trireme uses slf4j for logging the stuff that is happening in Java. The pre-built JAR, and the NPM "trireme" wrapper, use "slf4j-simple". To turn on debug logging, set the system property "org.slf4j.simpleLogger.defaultLogLevel" to "debug". (Or "trace" for even more output.)

When embedding trireme, you can use any SLF4J-compatible logging framework you wish, such as logback.

How Complete is Trireme?

Trireme supports most of the Node.js APIs and passes much of the Node.js test suite.

The table below shows each module and its status. "Complete" means that a module is functionally complete, although it may not necessarily pass all the node.js tests.

What are the Major Differences with "real" node.js?

A few of the modules are different, some in major ways:

JavaScript Language

Trireme runs in the JVM on Rhino, which is the most complete JavaScript implementation for the JVM and the one that works on the largest variety of Java distributions. The latest version of Rhino has many of the new JavaScript language features that Node users are used to, but still does not have all the features that are supported when the "--harmony" flag is set.

For specifics, see the Rhino compatibility table. Trireme is currently using RHino 1.7.7.

Most of the time the differences between V8 and Rhino do not affect Node.js code, but occasionally there is a problem. We would love some help from the Rhino community to start to address these differences.

TLS/SSL and HTTPS

Trireme uses Java's standard "SSLEngine" for TLS/SSL and HTTPS support, whereas standard Node.js uses OpenSSL. The TLS implementation in Node.js is a fairly thin layer on top of OpenSSL and we chose not to try and replicate this in Java.

For the most part, TLS and HTTPS in Trireme will work just like they do in Node.js. However, they SSLEngine and OpenSSL are not exactly the same. There are a few differences:

1. Most notably, especially with Java 7, SSLEngine supports a different set of cipher suites, particularly the various elliptical curve ciphers. There are ciphers in common (otherwise almost everything will break) but there are many that are not. Many Node.js tests that rely on older cipher suites using DES or RC4 will not run on Trireme because many of these older and weaker cipher suites are disabled by default in Java. However, "OpenSSL style" names work in Trireme just as they do in regular Node and if the JVM supports a particular cipher suite from OpenSSL, you will get the same one in Trireme.

2. Java handles SSL sessions differently, and gives the user less control about it. Right now, Trireme is unable to support the ability of a TLS or HTTPS client to retrieve the session from an existing connection and re-use it for another TCP connection.

3. Java also will produce different certificate validation errors than OpenSSL does. The errors will still come in the same places and for the same reasons, but if your code depends on a specific error message, it will likely get a different one.

4. Java's SSLEngine relies on its own "keystore" files, whereas OpenSSL can operate on a variety of files but typically processes PEM files. Trireme handles this disparity by using the "Bouncy Castle" crypto framework to translate PEM files into keys and certificates that SSLEngine can understand. In addition, you can also use regular Java keystore files, as described below.

In order to support TLS and HTTPS using PEM files, the "trireme-crypto" module and its dependencies (Bouncy Castle) must be in the class path. If they are not present, then TLS is still available, but it will only work with Java keystore files (see below) or without using any keys at all. Trireme checks for this dependency at runtime, so it is simply a matter of including it on the class path, since it will fail at runtime if the dependency is needed, and work otherwise.

(For instance, Trireme can still execute a Node program that acts as an HTTPS client using only default certificates without requiring trireme-crypto. But if it needs to validate a particular CA certificate or if it needs to use a client-side certificate then trireme-crypto is also necessary.)

In addition, the TLS and HTTPS-related methods in Trireme can use a Java keystore instead of PEM files. There are three parameters that are relevant here:

• keystore: The file name of a Java ".jks" keystore file containing a key and certificate
• truststore: The file name of a Java ".jks" keystore file containing trusted CA certificates
• passphrase: The passphrase for the keystore and truststore

The corresponding Trireme script may be written like this, as it would be in any Node.js program. However, if the "trireme-crypto" module is not present in the classpath, then this will raise an exception:

var options = {
  key: fs.readFileSync(common.fixturesDir + '/keys/agent1-key.pem'),
  cert: fs.readFileSync(common.fixturesDir + '/keys/agent1-cert.pem')
};

var server = https.createServer(options, function(req, res) {
  console.log('got request');
});

In addition, the following is also valid, and "trireme-crypto" will not be needed:

var options = {
  keystore: common.fixturesDir + '/keys/agent1.jks',
  passphrase: 'secure'
};

var server = https.createServer(options, function(req, res) {
  console.log('got request');
});

Crypto

Like TLS, certain features (Sign/Verify in particular) only work if the "trireme-crypto" module and its dependencies are in the class path. If they are not present then these methods will throw an exception. This is primarily because the trireme-crypto module uses Bouncy Castle to implement PEM file reading and decryption. It is possible to run Trireme without Bouncy Castle if these features are not needed.

Child Process

Child processes are supported. Arbitrary commands may be executed, just like in standard Node.js. The Sandbox may be used to restrict whether particular commands may be executed, or if none should be executed at all.

When a Trireme script uses "fork" to spawn a new instance of itself, the script runs as a separate thread inside the same JVM, rather than as a separate OS process as it works in regular Node.js. The parent may use "send" on the child process to send messages to the child, and the child can use "process.send" to talk back to the parent. This "IPC" mechanism works just like regular Node.js except that it all happens inside the same JVM using a concurrent queue.

Support for "handles" is not currently implemented, however, so a parent may not send a TCP socket to the child and expect the child to be able to handle it.

Some Node.js scripts rely on the ability to spawn a process called "./node" in order to fork itself. Trireme looks for this and tries to use it to spawn a new thread but it does not work in all cases. It does seem to be mostly the Node.js test suite itself that does this.

Cluster

The "cluster" module is not yet supported. When it is, it will support running multiple scripts within a single JVM, like the child process module works as described above.

Filesystem

The filesystem is fairly complete, but remember that Java is an abstraction on top of the OS so it may not behave exactly the same as it does on Linux.

On Java 6, the filesystem implementation falls back to using only the APIs supported in this version of Java, which means that many things like symbolic links are not supported, and support for "chmod" and the like is not exactly the same as in standard Node.js. On Java 7, Trireme is able to use additional features and the filesystem support is much more complete.

Programs that make extensive use of the filesystem, such as NPM, work on Java 7 but we cannot guarantee that they will work on Java 6.

OS

Again, Trireme runs on top of the JVM, which presents an operating-system abstraction. Things that Node.js programs can do like set up signal handlers and the like are not supported.

How Fast is It?

Rhino on the JVM is much slower than V8. (In some benchmarks it is 50 times slower.) However, Node.js programs take advantage of a lot of native code, especially when HTTP and TLS are used, so Trireme generally fares much better.

In general, we have seen simple HTTP benchmarks run at about one-half the speed of the same programs on standard Node.js. Some things are slower than that, and others are faster -- it all depends, as it does with all benchmarks.

Furthermore, Java is notoriously slow to start up, and this especially hurts Trireme when it's used to run command-line tools. So please try it as a long-running server (which is Java's strong suit) before dismissing the whole thing because "trireme /tmp/hello-world.js" runs 40 times slower than node. Thanks!

Finally, we would love to be able to use a faster JavaScript implementation, which would speed up all of Trireme. However, for many programs, Trireme on Rhino will be just fine, and the ability to embed Trireme inside another container is especially helpful.

Package Map

Trireme today consists of several modules. A typical application will wish to include the following in CLASSPATH:

• trireme-kernel
• trireme-core
• trireme-node10src
• trireme-crypto
• trireme-util

The last two packages are optional for environments that are constrained by space or strong aversion to third- party dependencies.

The bare minimum set of required modules is:

• trireme-kernel
• trireme-core
• Either trireme-node10src or trireme-node12src

Note that if Maven is used, trireme-node10src, trireme-node12src, trireme-crypto, and trireme-util will not be automatically pulled in by trireme-core -- it is the responsibility of the calling application to include each one explicitly. This way, Trireme may be used in environments where space is an issue.

This table will help keep them straight:

Additional modules in this directory are used only for testing.

What Are the Dependencies?

Since Trireme is supposed to be highly embeddable, we try to minimize the dependencies.

Rhino

This is the most mature framework for running JavaScript under Java and it works all versions of Java. Nashorn (new in Java 8) is faster in nearly all cases, but making Trireme run on Nashorn is more of a re-write of Trireme than a simple "port."

Slf4j

This is the de facto standard logging API for Java.

Java SE 6

Trireme runs on Java 6 and up, although at least Java 7 is recommended. Java 7 supports a much richer filesystem abstraction, which the "fs" module depends upon. Certain more complex Node applications, such as "NPM," can only run on Trireme when Java 7 or higher is used.

Trireme works fine on Java 8. It uses the standalone version of Rhino, so it is not affected by the fact that the default JavaScript engine was changed between Java 7 and Java 8.

Design

Node.js Implementation

Trireme has a similar architecture to Node.js itself. Many of the core modules in standard Node.js rely on a JavaScript shell, with native modules underneath that are written in C++.

Trireme is similar, and in many cases it exposes Java modules that mimic the interfaces of the C++ native modules in Node.js. So for instance, Trireme implements a native "tcp_wrap" module in Java that uses NIO to emulate the same API as the "tcp_wrap" module in Node.js. The same goes for udp, HTTP parsing, and many other things.

Threading Model

Each Trireme script runs in a single thread. In other words, when the script is executed, it spawns a new thread and occupies it until the script exits. Ticks and timers are implemented within that single thread. If the script exits (has no ticks or timers, is not "pinned" by a library like http, and falls off the bottom of the code) then the thread exits.

This way, there is no need for synchronization for most of the things that the scripts do, just like in regular Node.js.

However, some modules, such as the filesystem, may block, so those modules dispatch to a thread pool, just like in many other Java programs.

Similarly, the "HTTP adapter" allows Trireme to be embedded inside an existing server container, and in that case HTTP requests may come from many different threads. For that reason, the main event loop for each Trireme script depends on underlying collections that are thread-safe, so that different threads may place events on the event loop.

In the future, we may choose to support multi-tenant script threads, so that many isolated scripts may run in the same thread. That would decrease memory usage and context switching for servers that run many scripts.

HTTP Adapter

The HTTP adapter is an interface that a server may implement and plug in to Trireme. When it is plugged in, the adapter is responsible for calling Trireme when new HTTP requests arrive, and for presenting the actual HTTP requests and responses.

When this is used, Trireme scripts work just as they do in standard Node.js, but the "server" part of http is delegated to the adapter. (The client side of http continues to work the same way, however.)

The Sandbox

The sandbox is an interface that a server may implement that allows control over what scripts are allowed to do. It allows a script to accept or reject requests to access the filesystem, access the network, and execute programs. Using the sandbox, it is possible to run Node.js scripts in a totally isolated environment in a multi-tenant server.