org.apache.james.transport.mailets.PerRecipientRateLimit.scala Maven / Gradle / Ivy

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Rate limiting for Apache James email processing
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package org.apache.james.transport.mailets

import java.time.Duration
import java.util
import com.google.common.annotations.VisibleForTesting
import com.google.common.collect.ImmutableList

import javax.inject.Inject
import org.apache.james.core.MailAddress
import org.apache.james.lifecycle.api.LifecycleUtil
import org.apache.james.rate.limiter.api.{AcceptableRate, RateExceeded, RateLimiter, RateLimiterFactory, RateLimitingKey, RateLimitingResult}
import org.apache.james.transport.mailets.ConfigurationOps.{DurationOps, OptionOps}
import org.apache.james.util.ReactorUtils.DEFAULT_CONCURRENCY
import org.apache.mailet.base.GenericMailet
import org.apache.mailet.{Mail, ProcessingState}
import org.reactivestreams.Publisher
import reactor.core.scala.publisher.{SFlux, SMono}

import scala.jdk.CollectionConverters._
import scala.util.Using

case class PerRecipientRateLimiter(rateLimiter: RateLimiter, keyPrefix: Option[KeyPrefix], entityType: EntityType) {
  def rateLimit(recipient: MailAddress, mail: Mail): Publisher[RateLimitingResult] =
    EntityType.extractQuantity(entityType, mail)
      .map(increment => rateLimiter.rateLimit(RecipientKey(keyPrefix, entityType, recipient), increment))
      .getOrElse(SMono.just[RateLimitingResult](RateExceeded))
}

case class RecipientKey(keyPrefix: Option[KeyPrefix], entityType: EntityType, mailAddress: MailAddress) extends RateLimitingKey {
  override def asString(): String = s"${
    keyPrefix.map(prefix => prefix.value + "_")
      .getOrElse("")
  }${entityType.asString}_${mailAddress.asString()}"
}

/**
 * PerRecipientRateLimit allows defining and enforcing rate limits for the recipients of matching emails.
 *
 * This allows writing rules like:
 *   A recipient can receive 10 emails per hour
 *   A recipient can receive 100 MB of emails per hour
 * 
 *
 * Depending on its position and the matcher it is being combined with, those rate limiting rules could be applied to
 * submitted emails, received emails or emitted email being relayed to third parties.
 *
 *  Here are supported configuration parameters:
 *    keyPrefix: An optional key prefix to apply to rate limiting. Choose distinct values if you specify
 *    this mailet twice within your mailetcontainer.xml file. Defaults to none.
 *    exceededProcessor: Processor to which emails whose rate is exceeded should be redirected to. Defaults to error.
 *    Use this to customize the behaviour upon exceeded rate.
 *    duration: Duration during which the rate limiting shall be applied. Compulsory, must be a valid duration of at least one second. Supported units includes s (second), m (minute), h (hour), d (day).
 *    count: Count of emails allowed for a given sender during duration. Optional, if unspecified this rate limit is not applied.
 *    size: Size of emails allowed for a given sender during duration (each email count one time, regardless of recipient count). Optional, if unspecified this rate limit is not applied. Supported units : B ( 2^0 ), K ( 2^10 ), M ( 2^20 ), G ( 2^30 ), defaults to B.
 *  
 *
 *  For instance, to apply all the examples given above:
 *
 *   
 * <mailet matcher="All" class="PerRecipientRateLimit">
 *     <keyPrefix>myPrefix</keyPrefix>
 *     <duration>1h</duration>
 *     <count>10</count>
 *     <size>100M</size>
 *     <exceededProcessor>tooMuchMails</exceededProcessor>
 * </mailet>
 *   
 *
 *  Note that to use this extension you need to place the rate-limiter JAR in the extensions-jars folder
 *  and need to configure a viable option to invoke RateLimiterFactory which can be done by
 *  loading org.apache.james.rate.limiter.memory.MemoryRateLimiterModule Guice module within the
 *  guice.extension.module in extensions.properties configuration file. Note that other Rate
 *  limiter implementation might require extra configuration parameters within your mailet.
 *
 * @param rateLimiterFactory Allows instantiations of the underlying rate limiters.
 */
class PerRecipientRateLimit @Inject()(rateLimiterFactory: RateLimiterFactory) extends GenericMailet {
  private var exceededProcessor: String = _
  private var rateLimiters: Seq[PerRecipientRateLimiter] = _

  override def init(): Unit = {
    val duration: Duration = parseDuration()
    val precision: Option[Duration] = getMailetConfig.getDuration("precision")
    val keyPrefix: Option[KeyPrefix] = getMailetConfig.getOptionalString("keyPrefix").map(KeyPrefix)
    exceededProcessor = getMailetConfig.getOptionalString("exceededProcessor").getOrElse(Mail.ERROR)

    def perRecipientRateLimiter(entityType: EntityType): Option[PerRecipientRateLimiter] = createRateLimiter(entityType, duration, precision, rateLimiterFactory, keyPrefix)

    rateLimiters = Seq(Size, Count).flatMap(perRecipientRateLimiter)
  }

  override def service(mail: Mail): Unit = {
    if (!mail.getRecipients.isEmpty) {
      val rateLimitResults: Seq[(MailAddress, RateLimitingResult)] = applyRateLimiter(mail)

      val rateLimitedRecipients: Seq[MailAddress] = rateLimitResults.filter(_._2.equals(RateExceeded)).map(_._1)
      val acceptableRecipients: Seq[MailAddress] = rateLimitResults.filter(_._2.equals(AcceptableRate)).map(_._1)

      (acceptableRecipients, rateLimitedRecipients) match {
        case (acceptable, _) if acceptable.isEmpty => mail.setState(exceededProcessor)
        case (_, exceeded) if exceeded.isEmpty => // do nothing
        case _ =>
          mail.setRecipients(ImmutableList.copyOf(acceptableRecipients.asJava))

          Using(mail.duplicate())(newMail => {
            newMail.setRecipients(ImmutableList.copyOf(rateLimitedRecipients.asJava))
            getMailetContext.sendMail(newMail, exceededProcessor)
          })(LifecycleUtil.dispose(_))
      }
    }
  }

  @VisibleForTesting
  def parseDuration(): Duration = getMailetConfig.getDuration("duration")
    .getOrElse(throw new IllegalArgumentException("'duration' is compulsory"))

  private def createRateLimiter(entityType: EntityType, duration: Duration, precision: Option[Duration],
                                rateLimiterFactory: RateLimiterFactory, keyPrefix: Option[KeyPrefix]): Option[PerRecipientRateLimiter] =
    EntityType.extractRules(entityType, duration, getMailetConfig)
      .map(rateLimiterFactory.withSpecification(_, precision))
      .map(PerRecipientRateLimiter(_, keyPrefix, entityType))


  private def applyRateLimiter(mail: Mail): Seq[(MailAddress, RateLimitingResult)] =
    SFlux.fromIterable(mail.getRecipients.asScala)
      .flatMap(recipient => SFlux.merge(rateLimiters.map(rateLimiter => rateLimiter.rateLimit(recipient, mail)))
        .fold[RateLimitingResult](AcceptableRate)((a, b) => a.merge(b))
        .map(rateLimitingResult => (recipient, rateLimitingResult)), DEFAULT_CONCURRENCY)
      .collectSeq()
      .block()


  override def requiredProcessingState(): util.Collection[ProcessingState] = ImmutableList.of(new ProcessingState(exceededProcessor))

}