LambdaHandler.java

LambdaHandler.java

import java.util.List;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.nio.file.Paths;

import com.amazonaws.services.lambda.runtime.RequestStreamHandler;
import com.amazonaws.services.lambda.runtime.Context;

import org.jruby.embed.ScriptingContainer;
import org.jruby.embed.LocalVariableBehavior;
import org.jruby.embed.LocalContextScope;
import org.jruby.embed.PathType;
import org.jruby.CompatVersion;
import org.jruby.RubyInstanceConfig.CompileMode;



public class LambdaHandler implements RequestStreamHandler {
  public interface Handleable {
    String handle(String input);
  }

  private static final ScriptingContainer rubyRuntime;

  public final Handleable rubyHandler;

  static {
    rubyRuntime = new ScriptingContainer(LocalContextScope.SINGLETHREAD, LocalVariableBehavior.PERSISTENT);
    rubyRuntime.setCompatVersion(CompatVersion.RUBY2_0);
    rubyRuntime.setCompileMode(CompileMode.JIT);

    // Add Ruby file location to front of load path
    // List<String> loadPaths = rubyRuntime.getLoadPaths();
    // loadPaths.add(0, rubyLoadPath);
    // rubyRuntime.setLoadPaths(loadPaths);
  }

  // No Ruby handler name given; we have to infer it from the environment or
  // use the default "Handler"
  public LambdaHandler() {
    this(getHandlerNameFromEnv());
  }

  public LambdaHandler(String handlerName) {
    String handlerRequire = getRubyRequireName("handlers", handlerName);

    System.out.println("handlerName: " + handlerName);
    System.out.println("handlerRequire: " + handlerRequire);

    rubyRuntime.runScriptlet("require 'java'");
    rubyRuntime.runScriptlet(String.format("require '%s'", handlerRequire));    // rubyRuntime.runScriptlet("STDOUT.puts $LOAD_PATH");

    // rubyRuntime.runScriptlet(PathType.CLASSPATH, handlerFilename);
    Object handlerObject = rubyRuntime.runScriptlet(handlerName + ".new");
    rubyHandler = rubyRuntime.getInstance(handlerObject, Handleable.class);
  }

  public void handleRequest(InputStream inputStream, OutputStream outputStream, Context context)
      throws IOException {
    String input = readFromInputStream(inputStream);

    String output = rubyHandler.handle(input);

    outputStream.write(output.getBytes("UTF-8"));
    outputStream.close();
  }

  // Determines which Ruby handler to run, using either the HANDLER_NAME
  // environment variable or the named Lambda function, testing for the
  // existence of a Ruby script in src/main/ruby/handlers that matches.
  private static String getHandlerNameFromEnv() {
    String candidate;
    candidate = System.getenv("HANDLER_NAME");
    if (candidate != null) return candidate;
    candidate = System.getenv("AWS_LAMBDA_FUNCTION_NAME");
    if (candidate != null) return candidate;
    candidate = "Handler";
    return candidate;
  }

  private String getRubyRequireName(String subPath, String className) {
    String snakecase = className.replaceAll("(.)(\\p{Upper})", "$1_$2").toLowerCase();
    return Paths.get(subPath, snakecase).toString();
  }

  // https://stackoverflow.com/a/35446009
  private String readFromInputStream(InputStream inputStream) throws IOException {
    ByteArrayOutputStream result = new ByteArrayOutputStream();
    byte[] buffer = new byte[1024];
    int length;
    while ((length = inputStream.read(buffer)) != -1) {
      result.write(buffer, 0, length);
    }
    return result.toString("UTF-8");
  }
}