Chapter 9. Around Lift

This chapter looks at interacting with other systems from within Lift, such as sending email, calling URLs, or scheduling tasks.

Many of the recipes in this chapter have code examples in a project at https://github.com/LiftCookbook/cookbook_around.

Sending Plain-Text Email

Problem

You want to send a plain-text email from your Lift application.

Solution

Use the Mailer:

import net.liftweb.util.Mailer
import net.liftweb.util.Mailer._

Mailer.sendMail(
  From("you@example.org"),
  Subject("Hello"),
  To("other@example.org"),
  PlainMailBodyType("Hello from Lift") )

Discussion

Mailer sends the message asynchronously, meaning sendMail will return immediately, so you don’t have to worry about the time costs of negotiating with an SMTP server. However, there’s also a blockingSendMail method if you do need to wait.

By default, the SMTP server used will be localhost. You can change this by setting the mail.smtp.host property. For example, edit src/mail/resources/props/default.props and add the line:

mail.smtp.host=smtp.example.org

The signature of sendMail requires a From, Subject, and then any number of MailTypes:

To, CC, and BCC
The recipient email address
ReplyTo
The address that mail clients should use for replies
MessageHeader
Key/value pairs to include as headers in the message
PlainMailBodyType
A plain-text email sent with UTF-8 encoding
PlainPlusBodyType
A plain-text email, where you specify the encoding
XHTMLMailBodyType
For HTML email (“HTML Email”)
XHTMLPlusImages
For attachments (“Sending Email with Attachments”)

In the previous example, we added two types: PlainMailBodyType and To. Adding more is as you’d expect:

Mailer.sendMail(
  From("you@example.org"),
  Subject("Hello"),
  To("other@example.org"),
  To("someone@example.org"),
  MessageHeader("X-Ignore-This", "true"),
  PlainMailBodyType("Hello from Lift") )

The address-like MailTypes (To, CC, BCC, ReplyTo) can be given an optional "personal name":

From("you@example.org", Full("Example Corporation"))

This would appear in your mailbox as:

From: Example Corporation <you@example.org>

The default character set is UTF-8. If you need to change this, replace the use of PlainMailBodyType with PlainPlusBodyType("Hello from Lift", "ISO8859_1").

See Also

“Sending Email with Attachments” describes email with attachments.

For HTML email, see “HTML Email”.

Logging Email Rather than Sending

Problem

You don’t want email sent when developing your Lift application locally, but you do want to see what would have been sent.

Solution

Assign a logging function to Mailer.devModeSend in Boot.scala:

import net.liftweb.util.Mailer._
import javax.mail.internet.{MimeMessage,MimeMultipart}

Mailer.devModeSend.default.set( (m: MimeMessage) =>
  logger.info("Would have sent: "+m.getContent)
)

When you send an email with Mailer, no SMTP server will be contacted, and instead, you’ll see output to your log:

Would have sent: Hello from Lift

Discussion

The key part of this recipe is setting a MimeMessage => Unit function on Mailer.devModeSend. We happen to be logging, but you can use this function to handle the email any way you want.

The Lift Mailer allows you to control how email is sent at each run mode: by default, email is sent for devModeSend, profileModeSend, pilotModeSend, stagingModeSend, and productionModeSend; whereas, by default, testModeSend only logs that a message would have been sent.

The testModeSend logs a reference to the MimeMessage, meaning your log would show a message like:

Sending javax.mail.internet.MimeMessage@4a91a883

This recipe has changed the behaviour of Mailer when your Lift application is in developer mode (which it is by default). We’re logging just the body part of the message.

Java Mail doesn’t include a utility to display all the parts of an email, so if you want more information, you’ll need to roll your own function. For example:

def display(m: MimeMessage) : String = {

  val nl = System.getProperty("line.separator")

  val from = "From: "+m.getFrom.map(_.toString).mkString(",")

  val subj = "Subject: "+m.getSubject

  def parts(mm: MimeMultipart) = (0 until mm.getCount).map(mm.getBodyPart)

  val body = m.getContent match {
    case mm: MimeMultipart =>
      val bodyParts = for (part <- parts(mm)) yield part.getContent.toString
      bodyParts.mkString(nl)

    case otherwise => otherwise.toString
  }

  val to = for {
    rt <- List(RecipientType.TO, RecipientType.CC, RecipientType.BCC)
    address <- Option(m.getRecipients(rt)) getOrElse Array()
  } yield rt.toString + ": " + address.toString

  List(from, to.mkString(nl), subj, body) mkString nl
}

Mailer.devModeSend.default.set( (m: MimeMessage) =>
  logger.info("Would have sent: "+display(m))
)

This would produce output of the form:

Would have sent: From: you@example.org
To: other@example.org
To: someone@example.org
Subject: Hello
Hello from Lift

This example display function is long but mostly straightforward. The body value handles multipart messages by extracting each body part. This is triggered when sending more structured emails, such as the HTML emails described in “HTML Email”.

If you want to debug the mail system while it’s actually sending the email, enable the Java Mail debug mode. In default.props add:

mail.debug=true

This produces low-level output from the Java Mail system when email is sent:

DEBUG: JavaMail version 1.4.4
DEBUG: successfully loaded resource: /META-INF/javamail.default.providers
DEBUG SMTP: useEhlo true, useAuth false
DEBUG SMTP: trying to connect to host "localhost", port 25, isSSL false
...

See Also

Run modes are described on the Lift wiki.

HTML Email

Problem

You want to send an HTML email from your Lift application.

Solution

Give Mailer a NodeSeq containing your HTML message:

import net.liftweb.util.Mailer
import net.liftweb.util.Mailer._

val msg = <html>
   <head>
     <title>Hello</title>
   </head>
   <body>
    <h1>Hello</h1>
   </body>
  </html>

Mailer.sendMail(
  From("me@example.org"),
  Subject("Hello"),
  To("you@example.org"),
  msg)

Discussion

An implicit converts the NodeSeq into an XHTMLMailBodyType. This ensures the mime type of the email is text/html. Despite the name of "XHTML," the message is converted for transmission using HTML5 semantics.

The character encoding for HTML email, UTF-8, can be changed by setting mail.charset in your Lift properties file.

If you want to set both the text and HTML version of a message, supply each body wrapped in the appropriate BodyType class:

val html = <html>
  <head>
    <title>Hello</title>
  </head>
  <body>
    <h1>Hello!</h1>
  </body>
</html>

var text = "Hello!"

Mailer.sendMail(
  From("me@example.org"),
  Subject("Hello"),
  To("you@example.org"),
  PlainMailBodyType(text),
  XHTMLMailBodyType(html)
)

This message would be sent as a multipart/alternative:

Content-Type: multipart/alternative;
  boundary="----=_Part_1_1197390963.1360226660982"
Date: Thu, 07 Feb 2013 02:44:22 -0600 (CST)

------=_Part_1_1197390963.1360226660982
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit

Hello!
------=_Part_1_1197390963.1360226660982
Content-Type: text/html; charset=UTF-8
Content-Transfer-Encoding: 7bit

<html>
      <head>
        <title>Hello</title>
      </head>
      <body>
        <h1>Hello!</h1>
      </body>
    </html>
------=_Part_1_1197390963.1360226660982--

When receiving a message with this content, it is up to the mail client to decide which version to show (text or HTML).

See Also

For sending with attachments, see “Sending Email with Attachments”.

Sending Authenticated Email

Problem

You need to authenticate with an SMTP server to send email.

Solution

Set the Mailer.authenticator in Boot with the credentials for your SMTP server, and enable the mail.smtp.auth flag in your Lift properties file.

Modify Boot.scala to include:

import net.liftweb.util.{Props, Mailer}
import javax.mail.{Authenticator,PasswordAuthentication}

Mailer.authenticator = for {
  user <- Props.get("mail.user")
  pass <- Props.get("mail.password")
} yield new Authenticator {
  override def getPasswordAuthentication =
    new PasswordAuthentication(user,pass)
}

In this example, we expect the username and password to come from Lift properties, so we need to modify src/main/resources/props/default.props to include them:

mail.smtp.auth=true
mail.user=me@example.org
mail.password=correct horse battery staple
mail.smtp.host=smtp.sendgrid.net

When you send email, the credentials in default.props will be used to authenticate with the SMTP server.

Discussion

We’ve used Lift properties as a way to configure SMTP authentication. This has the benefit of allowing us to enable authentication for just some run modes. For example, if our default.props did not contain authentication settings, but our production.default.props did, then no authentication would happen in development mode, ensuring we can’t accidentally send email outside of a production environment.

You don’t have to use a properties file for this: the Lift Mailer also supports JNDI, or you could look up a username and password some other way and set Mailer.authenticator when you have the values.

However, some mail services such as SendGrid do require mail.smtp.auth=true to be set, and that should go into your Lift properties file or set as a JVM argument: -Dmail.smtp.auth=true.

See Also

As well as mail.smtp.auth, there are a range of settings to control the Java Mail API. Examples include controlling port numbers and timeouts.

Sending Email with Attachments

Problem

You want to send an email with one or more attachments.

Solution

Use the Mailer XHTMLPlusImages to package a message with attachments.

Suppose we want to construct a CSV file and send it via email:

val content = "Planet,Discoverer\r\n" +
  "HR 8799 c, Marois et al\r\n" +
  "Kepler-22b, Kepler Science Team\r\n"

case class CSVFile(bytes: Array[Byte],
  filename: String = "file.csv",
  mime: String = "text/csv; charset=utf8; header=present" )

val attach = CSVFile(content.mkString.getBytes("utf8"))

val body = <p>Please research the enclosed.</p>

val msg = XHTMLPlusImages(body,
  PlusImageHolder(attach.filename, attach.mime, attach.bytes))

Mailer.sendMail(
  From("me@example.org",
  Subject("Planets"),
  To("you@example.org"),
  msg)

What’s happening here is that our message is an XHTMLPlusImages instance, which accepts a body message and attachment. The attachment, the PlusImageHolder, is an Array[Byte], mime type, and a filename.

Discussion

XHTMLPlusImages can also accept more than one PlusImageHolder if you have more than one file to attach. Although the name PlusImageHolder may suggest it is for attachment images, you can attach any kind of data as an Array[Byte] with an appropriate mime type.

By default, the attachment is sent with an inline disposition. This controls the Content-Disposition header in the message, and inline means the content is intended for display automatically when the message is shown. The alternative is attachment, and this can be indicated with an optional final parameter to PlusImageHolder:

PlusImageHolder(attach.filename, attach.mime, attach.bytes, attachment=true)

In reality, the mail client will display the message how it wants to, but this extra parameter may give you a little more control.

To attach a premade file, you can use LiftRules.loadResource to fetch content from the classpath. If our project contained a file called Kepler-22b_System_Diagram.jpg in the src/main/resources/ folder, we could load and attach it like this:

val filename = "Kepler-22b_System_Diagram.jpg"

val msg =
  for ( bytes <- LiftRules.loadResource("/"+filename) )
  yield XHTMLPlusImages(
    <p>Please research this planet.</p>,
    PlusImageHolder(filename, "image/jpg", bytes) )

msg match {
  case Full(m) =>
    Mailer.sendMail(
      From("me@example.org"),
      Subject("Planet attachment"),
      To("you@example.org"),
      m)

  case _ =>
    logger.error("Planet file not found")
}

As the content of src/main/resources is included on the classpath, we pass the filename to loadResource with a leading / character so the file can be found at the right place on the classpath.

The loadResource returns a Box[Array[Byte]] as we have no guarantee the file will exist. We map this to a Box[XHTMLPlusImages] and match on that result to either send the email or log that the file wasn’t found.

See Also

Messages are sent using the multipart/related mime heading, with an inline disposition. Lift ticket #1197 links to a discussion regarding multipart/mixed that may be preferable for working around issues with Microsoft Exchange.

RFC 2183 describes the Content-Disposition header.

Run a Task Later

Problem

You want to schedule code to run at some future time.

Solution

Use net.liftweb.util.Schedule:

import net.liftweb.util.Schedule
import net.liftweb.util.Helpers._

Schedule(() => println("doing it"), 30 seconds)

This would cause "doing it" to be printed on the console 30 seconds from now.

Discussion

The signature for Schedule used previously expects a function of type () => Unit, which is the thing we want to happen in the future, and a TimeSpan from Lift’s TimeHelpers, which is when we want it to happen. The 30 seconds value gives us a TimeSpan via the Helpers._ import, but there’s a variation called perform that accepts a Long millisecond value if you prefer that:

Schedule.perform(() => println("doing it"), 30*1000L)

Behind the scenes, Lift is making use of the ScheduledExecutorService from java.util.concurrent and, as such, returns a ScheduledFuture[Unit]. You can use this future to cancel the operation before it runs.

It may be a surprise to find that you can call Schedule with just a function as an argument, and not a delay value. This version runs the function immediately, but on a worker thread. This is a convenient way to asynchronously run other tasks without going to the trouble of creating an actor for the purpose.

There is also a Schedule.schedule method that will send an actor a specified message after a given delay. This takes a TimeSpan delay, but again there’s also a Schedule.perform version that accepts a Long as a delay.

The Helpers._ import brings with it some implicit conversions for TimeSpan. For example, a JodaTime Period can be given to schedule and that will be used as a delay before executing your function. Don’t be tempted in this situation to use a JodaTime DateTime. This would be converted to a TimeSpan, but doesn’t make sense as a delay.

See Also

“Run Tasks Periodically” includes an example of scheduling with actors.

ScheduledFuture is documented via the Java Doc for Future. If you’re building complex, low-level, cancellable concurrency functions, it’s advisable to have a copy of Java Concurrency in Practice close by (written by Goetz, et al., Addison-Wesley Professional).

Run Tasks Periodically

Problem

You want a scheduled task to run periodically (repeatedly).

Solution

Use net.liftweb.util.Schedule ensuring that you call schedule again during your task to reschedule it. For example, using an actor:

import net.liftweb.util.Schedule
import net.liftweb.actor.LiftActor
import net.liftweb.util.Helpers._

object MyScheduledTask extends LiftActor {

  case class DoIt()
  case class Stop()

  private var stopped = false

   def messageHandler = {
     case DoIt if !stopped =>
        Schedule.schedule(this, DoIt, 10 minutes)
       // ... do useful work here

     case Stop =>
       stopped = true
   }
}

The example creates a LiftActor for the work to be done. On receipt of a DoIt message, the actor reschedules itself before doing whatever useful work needs to be done. In this way, the actor will be called every 10 minutes.

Discussion

The Schedule.schedule call is ensuring that this actor is sent the DoIt message after 10 minutes.

To start this process off, possibly in Boot.scala, just send the DoIt message to the actor:

MyScheduledTask ! MyScheduledTask.DoIt

To ensure the process stops correctly when Lift shuts down, we register a shutdown hook in Boot.scala to send the Stop message to prevent future reschedules:

LiftRules.unloadHooks.append( () => MyScheduledTask ! MyScheduledTask.Stop )

Without the Stop message, the actor would continue to be rescheduled until the JVM exits. This may be acceptable, but note that during development with SBT, without the Stop message, you will continue to schedule tasks after issuing the container:stop command.

Schedule returns a ScheduledFuture[Unit] from the Java concurrency library, which allows you to cancel the activity.

See Also

Chapter 1 of Lift in Action (by Perrett, Manning Publications, Co.) includes a Comet Actor clock example that uses Schedule.

Fetching URLs

Problem

You want your Lift application to fetch a URL and process it as text, JSON, XML, or HTML.

Solution

Use Dispatch, "a library for asynchronous HTTP interaction."

Before you start, include Dispatch dependency in build.sbt:

libraryDependencies += "net.databinder.dispatch" %% "dispatch-core" % "0.9.5"

Using the example from the Dispatch documentation, we can make an HTTP request to try to determine the country from the service at http://www.hostip.info/use.html:

import dispatch._
val svc = url("http://api.hostip.info/country.php")
val country : Promise[String] = Http(svc OK as.String)

println(country())

Note that the result country is not a String but a Promise[String], and we use apply to wait for the resulting value.

The result printed will be a country code such as GB, or XX if the country cannot be determined from your IP address.

Discussion

This short example expects a 200 (OK) status result and turns the result into a String, but that’s a tiny part of what Dispatch is capable of. We’ll explore further in this section.

What if the request doesn’t return a 200? In that case, with the code we have, we’d get an exception such as: "Unexpected response status: 404." There are a few ways to change that.

We can ask for an Option:

val result : Option[String] = country.option()

As you’d expect, this will give a None or Some[String]. However, if you have debug level logging enabled in your application, you’ll see the request and response and error messages from the underlying Netty library. You can tune these messages by adding a logger setting to default.logback.xml file:

<logger name="com.ning.http.client" level="WARN"/>

A second possibility is to use either with the usual convention that the Right is the expected result and Left signifies a failure:

country.either() match {
  case Left(status) => println(status.getMessage)
  case Right(cc) => println(cc)
}

This will print a result as we are forcing the evaluation with an apply via either().

Promise[T] implements map, flatMap, filter, fold, and all the usual methods you’d expect it to allow you to compose. This means you can use the promise with a for comprehension:

val codeLength = for (cc <- country) yield cc.length

Note that codeLength is a Promise[Int]. To get the value, you can evaluate codeLength() and you’ll get a result of 2.

As well as extracting string values with as.String, there are other options, including:

as.Bytes
To work with Promise[Array[Byte]]
as.File
To write to a file, as in Http(svc > as.File(new File("/tmp/cc")))
as.Response
To allow you to provide a client.Response => T function to use on the response
as.xml.Elem
To parse an XML response

As an example of as.xml.Elem:

val svc = url("http://api.hostip.info/?ip=12.215.42.19")
val country  = Http(svc > as.xml.Elem)
println(country.map(_ \\ "description")())

This example is parsing the XML response to the request, which returns a Promise[scala.xml.Elem]. We’re picking out the description node of the XML via a map, which will be a Promise[NodeSeq] that we then force to evaluate. The output is something like:

<gml:description
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns:gml="http://www.opengis.net/gml">
     This is the Hostip Lookup Service
</gml:description>

That example assumes the request is going to be well formed. In addition to the core Databinder library, there are extensions for JSoup and TagSoup to assist in parsing HTML that isn’t necessarily well formed.

For example, to use JSoup, include the dependency:

libraryDependencies += "net.databinder.dispatch" %% "dispatch-jsoup" % "0.9.5"

You can then use the features of JSoup, such as picking out elements of a page using CSS selectors:

import org.jsoup.nodes.Document

val svc = url("http://www.example.org").setFollowRedirects(true)
val title = Http(svc > as.jsoup.Document).map(_.select("h1").text).option
println( title() getOrElse "unknown title" )

Here we are applying JSoup’s select function to pick out the <h1> element on the page, taking the text of the element, which we turn into a Promise[Option[String]]. The result, unless example.org has changed, will be "Example Domain."

As a final example of using Dispatch, we can pipe a request into Lift’s JSON library:

import net.liftweb.json._
import com.ning.http.client

object asJson extends (client.Response => JValue) {
  def apply(r: client.Response) = JsonParser.parse(r.getResponseBody)
}

val svc = url("http://api.hostip.info/get_json.php?ip=212.58.241.131")
val json : Promise[JValue] = Http(svc > asJson)

case class HostInfo(country_name: String, country_code: String)
implicit val formats = DefaultFormats

val hostInfo = json.map(_.extract[HostInfo])()

The URL we’re calling returns a JSON representation for location information of the IP address we’ve passed.

By providing a Response => JValue to Dispatch, we’re able to pass the response body through to the JSON parser. We can then map on the Promise[JValue] to apply whatever Lift JSON functions we want to. In this case, we’re extracting a simple case class.

The result would show hostInfo as:

HostInfo(UNITED KINGDOM,GB)

See Also

The Dispatch documentation is well written and guides you through the way Dispatch approaches HTTP. Do spend some time with it.

For questions about Dispatch, the best place is the Dispatch Google Group.

The previous major version of Dispatch, 0.8.x ("Dispatch Classic"), is quite different from the "reboot" of the project as version 0.9. Consequently, examples you may see that use 0.8.x will need some conversion to run with 0.9.x. Nathan Hamblen’s blog describes the change.

For working with JSoup, take a look at the JSoup Cookbook.