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Scamper is the HTTP library for Scala. It defines the interface for reading and writing HTTP messages. In addition, it provides client and server implementations, both of which support WebSockets with permessage-deflate.

The client handles content and transfer encoding, as well as manages cookies.

The server is integrated into a lightweight web framework, which allows developers to create web applications as pipelines of request handlers.

Maven Central

Table of Contents

Getting Started

To use Scamper, start by adding it as a dependency to your project:

libraryDependencies += "com.github.losizm" %% "scamper" % "19.2.0"

HTTP Messages

At the core of Scamper is HttpMessage, which is a trait that defines the fundamental characteristics of an HTTP message. HttpRequest and HttpResponse extend the specification to define characteristics specific to their respective message types.

Building Requests

An HttpRequest can be created using a factory method defined in its companion object. Or you can start with a RequestMethod and use builder methods to further define the request.

import scamper.Implicits.stringToUri
import scamper.RequestMethod.Registry.Get
import scamper.headers.{ Accept, Host}
import scamper.types.Implicits.stringToMediaRange

val req = Get("/motd")
  .withAccept("text/plain", "*/*; q=0.5")

Building Responses

An HttpResponse can be created using a factory method defined in its companion object. Or you can start with a ResponseStatus and use builder methods to further define the response.

import scamper.Implicits.stringToEntity
import scamper.ResponseStatus.Registry.Ok
import scamper.headers.{ Connection, ContentType }
import scamper.types.Implicits.stringToMediaType

val res = Ok("There is an answer.")

Specialized Header Access

There is a set of methods in HttpMessage that provides generalized header access. With these methods, the header name is a String, which is case-insensitive, and the header value is a String.

import scamper.Implicits.{ stringToUri, tupleToHeader }
import scamper.RequestMethod.Registry.Post

val req = Post("/api/users").withHeader("Content-Type" -> "application/json")

val contentType: Option[String] = req.getHeaderValue("Content-Type")

This gets the job done in many cases; however, HttpMessage can be extended for specialized header access. There are extension methods provided by type classes defined in scamper.headers.

For example, ContentType adds the following methods:

/** Gets Content-Type header value. */
def contentType: MediaType

/** Gets Content-Type header value if present. */
def getContentType: Option[MediaType]

/** Tests for Content-Type header. */
def hasContentType: Boolean

/** Creates message with Content-Type header set to supplied value. */
def withContentType(value: MediaType): HttpMessage

/** Creates message removing Content-Type header. */
def removeContentType(): HttpMessage

So you can work with the header using specialized header types.

import scamper.Implicits.stringToUri
import scamper.RequestMethod.Registry.Post
import scamper.headers.ContentType
import scamper.types.MediaType

val req = Post("/api/users").withContentType(MediaType("application", "json"))
println(req.contentType.mainType) // application
println(req.contentType.subtype) // json

And, with utilities defined in scamper.types.Implicits, you can implicitly convert values to header types.

import scamper.Implicits.stringToUri
import scamper.RequestMethod.Registry.Post
import scamper.headers.ContentType
import scamper.types.Implicits.stringToMediaType

val req = Post("/api/users").withContentType("application/json")
println(req.contentType.mainType) // application
println(req.contentType.subtype) // json

Specialized Cookie Access

In much the same way specialized access to headers is available, so too is the case for cookies. Specialized access is provided by classes in scamper.cookies.

Request Cookies

In HttpRequest, cookies are stringed together in the Cookie header. You may access the cookies in their unbaked form using generalized header access. Or you can access them using the extension methods provided by RequestCookies, with each cookie presented as PlainCookie.

import scamper.Implicits.stringToUri
import scamper.RequestMethod.Registry.Get
import scamper.cookies.{ PlainCookie, RequestCookies }

val req = Get("https://localhost:8080/motd").withCookies(
  PlainCookie("ID", "bG9zCg"), PlainCookie("Region", "SE-US")

// Print name and value of both cookies
req.cookies.foreach(cookie => println(s"${}=${cookie.value}"))

// Get cookies by name
val id: Option[PlainCookie] = req.getCookie("ID")
val region: Option[PlainCookie] = req.getCookie("Region")

// Get cookie values by name

// Get unbaked cookies
assert(req.getHeaderValue("Cookie").contains("ID=bG9zCg; Region=SE-US"))

Response Cookies

In HttpResponse, the cookies are a collection of Set-Cookie header values. Specialized access is provided by ResponseCookies, with each cookie presented as SetCookie.

Along with name and value, SetCookie provides additional attributes, such as the path to which the cookie is valid, when the cookie expires, whether the cookie should be sent over secure channels only, and a few others.

import scamper.Implicits.stringToEntity
import scamper.ResponseStatus.Registry.Ok
import scamper.cookies.{ ResponseCookies, SetCookie }

val res = Ok("There is an answer.").withCookies(
  SetCookie("ID", "bG9zCg", path = Some("/motd"), secure = true),
  SetCookie("Region", "SE-US")

// Print both cookies

// Get cookies by name
val id: Option[SetCookie] = res.getCookie("ID")
val region: Option[SetCookie] = res.getCookie("Region")

// Get attributes of ID cookie
val path: String = id.flatMap(_.path).getOrElse("/")
val secure: Boolean =

// Get cookie values by name

// Get unbaked cookies
assert(res.getHeaderValue("Set-Cookie").contains("ID=bG9zCg; Path=/motd; Secure"))
assert(res.getHeaderValues("Set-Cookie").size == 2)

Note: Each response cookie is presented in its own Set-Cookie header. Whereas getHeaderValue() retrieves the first header value only, getHeaderValues() collects all header values into a Seq[String].

Message Body

The message body is represented as an Entity, which provides access to an InputStream.

Creating Body

When building a message, use the Entity factory to create the body. For example, you can create a message with text content.

import scamper.Entity
import scamper.ResponseStatus.Registry.Ok
import scamper.headers.ContentType
import scamper.types.Implicits.stringToMediaType

val body = Entity("""
<!DOCTYPE html>
    <p>Hello, world!</p>
val res = Ok(body).withContentType("text/html; charset=utf-8")

Or create a message using file content.

import scamper.Entity
import scamper.ResponseStatus.Registry.Ok
import scamper.headers.ContentType
import scamper.types.Implicits.stringToMediaType

val body = Entity(new File("./index.html"))
val res = Ok(body).withContentType("text/html; charset=utf-8")

There are implicit converters available for common entity types, so you aren't required to create them explicitly.

import scamper.Implicits.fileToEntity
import scamper.ResponseStatus.Registry.Ok
import scamper.headers.ContentType
import scamper.types.Implicits.stringToMediaType

val res = Ok(new File("./index.html")).withContentType("text/html; charset=utf-8")

Parsing Body

When handling an incoming message, use an appropriate BodyParser to parse the message body. There are factory methods available, such as one used for creating a text body parser.

import scamper.{ BodyParser, HttpMessage }

// Create text body parser
implicit val parser = BodyParser.text(maxLength = 1024)

def printText(message: HttpMessage): Unit = {
  // Parse message body to String using implicit parser
  val text =[String]


And you can implement your own parser. Here's one powered by little-json:

import javax.json.{ JsonObject, JsonValue }
import little.json.{ Json, JsonInput }
import little.json.Implicits._
import scamper.{ BodyParser, HttpMessage }

case class User(id: Int, name: String)

implicit object UserParser extends BodyParser[User] {
  // Define how to convert JsonObject to User
  implicit val userInput: JsonInput[User] = {
    case json: JsonObject => User(json.getInt("id"), json.getString("name"))
    case json: JsonValue  => throw new IllegalArgumentException("Not an OBJECT")

  // Parses JSON message body to User
  def parse(message: HttpMessage): User =

def printUser(message: HttpMessage): Unit = {
  // Parse message body to User (implicitly using UserParser)
  val user =[User]


Multipart Message Body

You can create a message with multipart form-data, which is generally required for form submission containing file content. When the multipart body is added to the message, the Content-Type header is set to multipart/form-data with a boundary parameter whose value is used to delimit parts in the encoded body.

import scamper.{ Multipart, TextPart, FilePart }
import scamper.Implicits.{ HttpMessageType, stringToUri }
import scamper.RequestMethod.Registry.Post

// Build multipart form-data with text and file content
val formData = Multipart(
  TextPart("title", "Form Of Intellect"),
  TextPart("artist", "Gang Starr"),
  TextPart("album", "Step In The Arena"),
  FilePart("media", new File("/music/gang_starr/form_of_intellect.m4a"))

// Create request with multipart body
val req = Post("").withMultipartBody(formData)

And for an incoming message with multipart form-data, there's a standard BodyParser for parsing the message content.

import scamper.{ BodyParser, HttpRequest, Multipart }

def saveTrack(req: HttpRequest): Unit = {
  // Get parser for multipart message body
  implicit val parser = BodyParser.multipart()

  // Parse message to Multipart instance
  val multipart =[Multipart]

  // Extracts content from the parts
  val title = multipart.getText("title")
  val artist = multipart.getText("artist")
  val album = multipart.getText("album")
  val track = multipart.getFile("media")


Message Attributes

Attributes are arbitrary key-value pairs associated with a message.

import scala.concurrent.duration.{ Deadline, DurationInt }
import scamper.Implicits.stringToUri
import scamper.{ HttpRequest, HttpResponse }
import scamper.RequestMethod.Registry.Get

def send(req: HttpRequest): HttpResponse = ???

val req = Get("/motd").withAttribute("send-before" -> ( + 1.minute))

val res = req.getAttribute[Deadline]("send-before")
  .map(_ => send(req))

Note: Attributes are not included in the transmitted message.

HTTP Authentication

Scamper includes a separate package (i.e., scamper.auth) for working with authentication headers.

Challenges and Credentials

When working with authentication, a Challenge is presented in the response, and Credentials in the request. Each of these has an assigned scheme, which is associated with either a token or a set of parameters.

import scamper.Implicits.stringToUri
import scamper.RequestMethod.Registry.Get
import scamper.ResponseStatus.Registry.Unauthorized
import scamper.auth.{ Authorization, Challenge, Credentials, WwwAuthenticate }

// Present response challenge (scheme and parameters)
val challenge = Challenge("Bearer", "realm" -> "developer")
val res = Unauthorized().withWwwAuthenticate(challenge)

// Present request credentials (scheme and token)
val credentials = Credentials("Bearer", "QWxsIEFjY2VzcyEhIQo=")
val req = Get("/dev/projects").withAuthorization(credentials)

Note: The Authorization and WwwAuthenticate header classes are for authentication between user agent and origin server. There are other header classes available for proxy authentication – see scaladoc for details.

Basic Authentication

There are subclasses defined for Basic authentication: BasicChallenge and BasicCredentials.

import scamper.Implicits.stringToUri
import scamper.RequestMethod.Registry.Get
import scamper.ResponseStatus.Registry.Unauthorized
import scamper.auth.{ Authorization, BasicChallenge, BasicCredentials, WwwAuthenticate }

// Provide realm and optional parameters
val challenge = BasicChallenge("admin", "title" -> "Admin Console")
val res = Unauthorized().withWwwAuthenticate(challenge)

// Provide user and password
val credentials = BasicCredentials("sa", "l3tm31n")
val req = Get("/admin/users").withAuthorization(credentials)

In addition, there are methods for Basic authentication defined in the header classes.

import scamper.Implicits.stringToUri
import scamper.RequestMethod.Registry.Get
import scamper.ResponseStatus.Registry.Unauthorized
import scamper.auth.{ Authorization, WwwAuthenticate }

// Provide realm and optional parameters
val res = Unauthorized().withBasic("admin", "title" -> "Admin Console")

// Access basic auth in response
printf(s"Realm: %s%n", res.basic.realm)
printf(s"Title: %s%n", res.basic.params("title"))

// Provide user and password
val req = Get("/admin/users").withBasic("sa", "l3tm3m1n")

// Access basic auth in request
printf(s"User: %s%n", req.basic.user)
printf(s"Password: %s%n", req.basic.password)

Bearer Authentication

There are subclasses defined for Bearer authentication: BearerChallenge and BearerCredentials. In addition, there are Bearer-specific methods available in the header classes.

import scamper.Implicits.stringToUri
import scamper.RequestMethod.Registry.Get
import scamper.ResponseStatus.Registry.Unauthorized
import scamper.auth.{ Authorization, WwwAuthenticate }

// Provide challenge parameters
val res = Unauthorized().withBearer(
  "scope" -> "user profile",
  "error" -> "invalid_token",
  "error_description" -> "Expired access token"

// Print optional realm parameter

// Print scope from space-delimited parameter
val scope: Seq[String] = res.bearer.scope

// Print error parameters

// Test for error conditions

// Create request with Bearer token
val req = Get("/users").withBearer("R290IDUgb24gaXQhCg==")

// Access bearer auth in request
printf("Token: %s%n", req.bearer.token)

HTTP Client

Scamper provides HttpClient for sending requests and handling the responses.

import scamper.Implicits.{ stringToEntity, stringToUri }
import scamper.RequestMethod.Registry.Post
import scamper.client.HttpClient
import scamper.headers.ContentType
import scamper.types.Implicits.stringToMediaType

val req = Post("https://localhost:8080/users")
  .withBody(s"""{ "id": 500, "name": "guest" }""")

// Send request and print response status
HttpClient.send(req) { res =>

Note: The outgoing request must be created with an absolute URI to make effective use of the client.

Creating Client

In the previous example, the HttpClient object is used as the client. Behind the scenes, this creates an HttpClient instance for one-time usage.

If you plan to send multiple requests, you can create and maintain a reference to a client. With it, you also get access to methods corresponding to standard HTTP request methods.

import scamper.BodyParser
import scamper.Implicits.stringToUri
import scamper.client.HttpClient

implicit val parser = BodyParser.text()

// Create client instance
val client = HttpClient()

def getMessageOfTheDay(): Either[Int, String] = {
  // Use client instance
  client.get("http://localhost:8080/motd") { res =>
    res.isSuccessful match {
      case true  => Right([String])
      case false => Left(res.statusCode)

And, if an implicit client is in scope, you can make use of send() on the request itself.

import scamper.BodyParser
import scamper.Implicits.stringToUri
import scamper.RequestMethod.Registry.Get
import scamper.client.HttpClient
import scamper.client.Implicits.ClientHttpRequest // Adds send method to request
import scamper.headers.{ Accept, AcceptLanguage }
import scamper.types.Implicits.{ stringToMediaRange, stringToLanguageRange }

implicit val client = HttpClient()
implicit val parser = BodyParser.text(4096)

  .withAcceptLanguage("fr-CA; q=0.6", "en-CA; q=0.4")
  .send(res => println([String])) // Send request and print response

Configuring Client

You can also create a client using ClientSettings, which allows you to configure the client before creating it.

import scamper.Implicits.{ stringToEntity, stringToUri }
import scamper.client.HttpClient
import scamper.cookies.CookieStore
import scamper.types.Implicits.stringToContentCodingRange

// Build client from settings
val client = HttpClient.settings()
  .acceptEncodings("gzip", "deflate")
  .trust(new File("/path/to/truststore"))
  .create()"https://localhost:3000/messages", body = "Hello there!") { res =>
  assert(res.isSuccessful, s"Message not posted: ${res.statusCode}")

The acceptEncodings provides a list of content coding ranges, which are used to set the Accept-Encoding header on each outgoing request.

The bufferSize is the size in bytes used for the client send and receive buffers.

The readTimeout sets how long (in milliseconds) a read on the client socket blocks before a SocketTimeoutException is thrown.

The continueTimeout specifies how long (in milliseconds) the client waits for a 100 Continue response from the server before the client sends the request body. This behavior is effected only if the request includes an Expect header set to 100-Continue.

The cookieStore is used to store cookies included in HTTP responses. Using the cookie store, the client automatically adds the appropriate cookies to each outgoing request.

You can supply a truststore using trust, as demonstrated in the previous example. Or, if greater control is required for securing connections, you can supply a trust manager instead.

import scamper.Implicits.stringToUri
import scamper.client.HttpClient

class SingleSiteTrustManager(address: String) extends TrustManager {
  // Provide TrustManager implementation

// Build client from settings
val client = HttpClient.settings()
  // Use supplied trust manager
  .trust(new SingleSiteTrustManager(""))

client.get("") { res =>
  // Handle response

Adding Request and Response Filters

To perform common operations on client requests and their responses, you can add filters to the client.

import scamper.Uri
import scamper.client.HttpClient
import scamper.client.Implicits._
import scamper.cookies._

val settings = HttpClient.settings()

settings.readTimeout(30 * 1000)

// Add request filter
settings.outgoing { req =>
  def findCookies(target: Uri): Seq[PlainCookie] = ???

  // Add cookies to request
  req.withCookies { findCookies(req.absoluteTarget) }

// Add response filter
settings.incoming { res =>
  def storeCookies(target: Uri, cookies: Seq[SetCookie]): Unit = ???

  // Store cookies from response
  storeCookies(res.absoluteTarget, res.cookies)

// Create client
val client = settings.create()

You can add multiple request and response filters. If multiple filters are added, each is executed in the order it is added. That is, request filters are executed in order, and response filters are executed in order.

Using WebSocket Client

The client instance can also be used as a WebSocket client.

import scamper.Implicits.stringToUri
import scamper.client.HttpClient

HttpClient().websocket("ws://localhost:9090/hello") { session =>
  session.onText { message =>
    println(s"Received text message: $message")

    if (message.equalsIgnoreCase("bye"))

  session.onPing { data =>
    println(s"Received ping message.")

  session.onPong { data =>
    println(s"Received pong message.")

  session.onError { err =>
    println(s"Encountered error: $err")

  session.onClose { statusCode =>
    println(s"WebSocket connection closed: $statusCode")

  session.send("Hello, server!")

In the above example, the client establishes a WebSocket connection to the specified target URI. (Note use ws scheme. For secure connections, use wss instead.)

After the client and server perform the opening handshake, a WebSocketSession is passed to the supplied handler. The handler then applies subsequent handlers for various message types along with an error handler.

It then sets the session's idle timeout. If no messages are received in any 5 second span, the session will be closed automatically.

Before the session begins reading incoming messages, it must first be opened. And, to kick things off, a simple text message is sent to the server.

See WebSocketSession in scaladoc for additional details.

HTTP Server

Scamper includes an extensible server framework. To demonstrate, let's begin with a simple example.

import scamper.Implicits.stringToEntity
import scamper.ResponseStatus.Registry.Ok
import scamper.server.HttpServer

val server = HttpServer(8080) { req =>
  Ok("Hello, world!")

This is as bare-bones as it gets. We create a server at port 8080, and on each incoming request, we send a simple text message back to the client. Although trite, it demonstrates how easy it is to get going.

We'll use the remainder of this documentation to describe what goes into creating more practical applications.

Server Application

To build a server, you begin with ServerApplication. This is a mutable structure to which you apply changes to configure the server. Once the desired settings are applied, you invoke one of several methods to create the server.

You can obtain an instance of ServerApplication from the HttpServer object.

val app =

This gives you the default application as a starting point. With this in hand, you can set the location of the server log.

app.logger(new File("/tmp/server.log"))

And there are performance-related settings that can be tweaked as well.

app.keepAlive(5, 10)

The backlogSize specifies the maximum number of incoming connections that can wait for acceptance. Incoming connections that exceed this limit are refused.

The poolSize specifies the maximum number of requests processed concurrently.

The queueSize specifies the maximum number of requests permitted to wait for processing. Incoming requests that exceed this limit are sent 503 Service Unavailable.

The bufferSize is the length in bytes of the buffer used when reading from and writing to a socket.

The readTimeout controls how long a read from a socket blocks before it times out, whereafter 408 Request Timeout is sent to client.

The headerLimit sets the maximum number of request headers allowed. Incoming requests that exceed this limit are sent 431 Request Header Fields Too Large.

The keepAlive settings enable persistent connections using the specified timeout (in seconds) and max requests per connection.

Request Handlers

You define application-specific logic in instances of RequestHandler and add them to the application. The request handler accepts an HttpRequest and returns either an HttpRequest or an HttpResponse. If the handler does not satisfy the request, it returns an HttpRequest so that the next handler has its turn. Otherwise, it returns an HttpResponse, and any remaining handlers are effectively ignored.

import scamper.RequestMethod.Registry.{ Get, Head }
import scamper.ResponseStatus.Registry.MethodNotAllowed
import scamper.headers.Allow

// Add handler to log request line and headers to stdout
app.incoming { req =>
  req // Return request for next handler

// Add handler to allow GET and HEAD requests only
app.incoming { req =>
  (req.isGet || req.isHead) match {
    // Return request for next handler
    case true  => req
    // Otherwise return response to end request chain
    case false => MethodNotAllowed().withAllow(Get, Head)

The order in which handlers are applied matters. For instance, in the example above, you'd swap the order of handlers if you wanted to log GET and HEAD requests only, and all other requests would immediately be sent 405 Method Not Allowed and never make it to the request logger.

And a request handler is not restricted to returning the same request it accepted.

import scamper.BodyParser
import scamper.Implicits.stringToEntity
import scamper.headers.ContentLanguage
import scamper.types.LanguageTag
import scamper.types.Implicits.stringToLanguageTag

// Translates message body from French (Oui, oui.)
app.incoming { req =>
  val translator: BodyParser[String] = ???

  (req.isPost && req.contentLanguage.contains("fr")) match {
    case true  => req.withBody(translator.parse(req)).withContentLanguage("en")
    case false => req

Targeted Handling

A handler can be added to a targeted path with or without a targeted request method.

import scamper.Implicits.stringToEntity
import scamper.RequestMethod.Registry.Get
import scamper.ResponseStatus.Registry.{ Forbidden, Ok }

// Match request method and exact path
app.incoming(Get, "/about") { req =>
  Ok("This server is powered by Scamper.")

// Match exact path and any method
app.incoming("/private") { req =>

And handlers can be added using methods corresponding to the standard HTTP request methods.

import scamper.Implicits.stringToUri
import scamper.ResponseStatus.Registry.{ Created, Ok }
import scamper.headers.Location

// Match GET requests to given path
app.get("/about") { req =>
  Ok("This server is powered by Scamper.")

// Match POST requests to given path"/messages") { req =>
  def post(message: String): Int = ???

  implicit val parser = BodyParser.text()

  val id = post([String])

Path Parameters

Parameters can be specified in the path and their resolved values made available to the handler. When a parameter is specified as :param, it matches a single path segment; whereas, *param matches the path segment along with any remaining segments, including intervening path separators (i.e., /).

import scamper.Implicits.fileToEntity
import scamper.ResponseStatus.Registry.{ Accepted, NotFound, Ok }
import scamper.server.Implicits.ServerHttpRequest

// Match request method and parameterized path
app.delete("/orders/:id") { req =>
  def deleteOrder(id: Int): Boolean = ???

  // Get resolved parameter
  val id = req.params.getInt("id")

  deleteOrder(id) match {
    case true  => Accepted()
    case false => NotFound()

// Match prefixed path with any request method
app.get("/archive/*path") { req =>
  def findFile(path: String): Option[File] = ???

  // Get resolved parameter
  val path = req.params.getString("path")


There can be at most one *param, which must be specified as the the last segment in the path; however, there can be multiple :param instances specified.

import scamper.BodyParser
import scamper.Implicits.stringToEntity
import scamper.ResponseStatus.Registry.Ok
import scamper.server.Implicits.ServerHttpRequest

// Match path with two parameters"/translate/:in/to/:out") { req =>
  def translator(from: String, to: String): BodyParser[String] = ???

  val from = req.params.getString("in")
  val to = req.params.getString("out")

  Ok(translator(from, to).parse(req))

Serving Static Files

You can add a request handler at a mount path to serve static files from a source directory.

app.files("/app/main", new File("/path/to/public"))

This adds a handler to serve files from the directory at /path/to/public. The files are mapped based on the request path excluding the mount path. For example, http://localhost:8080/app/main/images/logo.png would map to /path/to/public/images/logo.png.

Serving Static Resources

If your web assets are bundled in a jar file, just drop the jar on the classpath, and you can configure the application to serve its contents.

app.resources("/app/main", "assets")

In the above configuration, requests prefixed with /app/main are served resources from the assets directory. The mapping works similiar to static files, only the resources are located using a class loader. (See ServerApplication.resources() in scaladoc for additional details.)

Aborting Response

At times, you may wish to omit a response for a particular request. On such occassions, you'd throw ResponseAborted from the request handler.

import scamper.headers.Referer
import scamper.server.ResponseAborted

// Ignore requests originating from evil site
app.incoming { req =>
  if (req.referer.getHost == "")
    throw ResponseAborted("Not trusted")

WebSocket Session

As a special case of request handling, you can define a WebSocket endpoint and manage the session. The server takes care of the opening handshake and passes the session to your handler.

app.websocket("/hello") { session =>
  // Log ping message and send corresponding pong
  session.onPing { data =>"Received ping message.")

  // Log pong message
  session.onPong { data =>"Received pong message.")

  // Log text message and close session after sending reply
  session.onText { message =>"Received text message: $message")

  // Log status code when session is closed
  session.onClose { status =>"Session closed: $status")

  // Open session to incoming messages

  // Send ping message

See WebSocketSession in scaladoc for additional details.

Error Handler

You can define an ErrorHandler to handle exceptions thrown from your request handlers.

import scamper.ResponseStatus.Registry.{ BadRequest, InternalServerError }

// Accepts Throwable and HttpRequest; returns HttpResponse
app.error { (err, req) =>
  def isClientError(err: Throwable): Boolean = ???

  isClientError(err) match {
    case true  => BadRequest("Your bad.")
    case false => InternalServerError("My bad.")


Use Router to structure the application routes hierarchically. Router works in much the same way as ServerApplication, except it is configured for request handling only, and all router paths are relative to its mount path.

import scamper.Implicits.stringToEntity
import scamper.ResponseStatus.Registry.{ NotFound, Ok }
import scamper.server.HttpServer
import scamper.server.Implicits.ServerHttpRequest

val app =

// Mount router to /api
app.use("/api") { router =>
  val messages = Map(1 -> "Hello, world!", 2 -> "Goodbye, cruel world!")

  // Map handler to /api/messages
  router.get("/messages") { req =>

  // Map handler to /api/messages/:id
  router.get("/messages/:id") { req =>
    val id = req.params.getInt("id")

Response Filters

Response filtering is performed by adding instances of ResponseFilter to the application. They are applied, in order, after a request handler generates a response.

app.outgoing { res =>
  res // Return response for next filter

This is pretty much the same as the request logger from earlier, only instead of HttpRequest, it accepts and returns HttpResponse.

And the filter is not restricted to returning the same response it accepts.

import scamper.server.Implicits.ServerHttpResponse

// Gzip response body if not empty
app.outgoing { res =>
  res.body.isKnownEmpty match {
    case true  => res
    case false => res.withGzipContentEncoding()

Securing Server

The last piece of configuration is whether to secure the server using SSL/TLS. To use a secure transport, you must supply an appropriate key and certificate. File("/path/to/private.key"), new File("/path/to/public.crt"))

Or, if you have them tucked away in a keystore, you can supply the keystore location.

// Supply location, password, and store type (i.e., JKS, JCEKS, PCKS12) File("/path/to/keystore"), "s3cr3t", "pkcs12")

Creating Server

When the application has been configured, you can create the server.

val server = app.create(8080)

If the server must bind to a particular host, you can provide the host name or IP address.

val server = app.create("", 8080)

An instance of HttpServer is returned, which can be used to query server details.

printf("Host: %s%n",
printf("Port: %d%n", server.port)
printf("Secure: %s%n", server.isSecure)
printf("Logger: %s%n", server.logger)
printf("Backlog Size: %d%n", server.backlogSize)
printf("Pool Size: %d%n", server.poolSize)
printf("Queue Size: %d%n", server.queueSize)
printf("Buffer Size: %d%n", server.bufferSize)
printf("Read Timeout: %d%n", server.readTimeout)
printf("Header Limit: %d%n", server.headerLimit)
printf("Keep-Alive: %s%n", server.keepAlive.getOrElse("disabled"))
printf("Closed: %s%n", server.isClosed)

And, ultimately, it is used to gracefully shut down the server.

server.close() // Good-bye, world.

API Documentation

See scaladoc for additional details.


Scamper is licensed under the Apache License, Version 2. See LICENSE file for more information.