akka-http-cors

CORS (Cross Origin Resource Sharing) is a mechanism to enable cross origin requests.

This is a Scala/Java implementation for the server-side targeting the akka-http library.

A version supporting the Apache Pekko fork is also available in pekko-http-cors.

Versions

Some less interesting versions are not listed in the above table. The complete list can be found in the CHANGELOG file.

Getting Akka Http Cors

akka-http-cors is deployed to Maven Central. Add it to your build.sbt or Build.scala:

libraryDependencies += "ch.megard" %% "akka-http-cors" % "1.2.0"

Quick Start

The simplest way to enable CORS in your application is to use the cors directive. Settings are passed as a parameter to the directive, with your overrides loaded from the application.conf.

import ch.megard.akka.http.cors.scaladsl.CorsDirectives._

val route: Route = cors() {
  complete(...)
}

The settings can be updated programmatically too.

val settings = CorsSettings(...).withAllowGenericHttpRequests(false)
val strictRoute: Route = cors(settings) {
  complete(...)
}

A full example, with proper exception and rejection handling, is available in the akka-http-cors-example sub-project.

Rejection

The CORS directives can reject requests using the CorsRejection class. Requests can be either malformed or not allowed to access the resource.

A rejection handler is provided by the library to return meaningful HTTP responses. Read the akka documentation to learn more about rejections, or if you need to write your own handler.

import akka.http.scaladsl.server.directives.ExecutionDirectives._
import ch.megard.akka.http.cors.scaladsl.CorsDirectives._

val route: Route = handleRejections(corsRejectionHandler) {
  cors() {
    complete(...)
  }
}

Java support

Starting from version 0.2.1 Java is supported, mirroring the Scala API. For usage, look at the full Java CorsServer example.

Configuration

Reference configuration.

allowGenericHttpRequests

Boolean with default value true.

If true, allow generic requests (that are outside the scope of the specification) to pass through the directive. Else, strict CORS filtering is applied and any invalid request will be rejected.

allowCredentials

Boolean with default value true.

Indicates whether the resource supports user credentials. If true, the header Access-Control-Allow-Credentials is set in the response, indicating the actual request can include user credentials.

Examples of user credentials are: cookies, HTTP authentication or client-side certificates.

allowedOrigins

HttpOriginMatcher with default value HttpOriginMatcher.*.

List of origins that the CORS filter must allow. Can also be set to * to allow access to the resource from any origin. Controls the content of the Access-Control-Allow-Origin response header:

• if parameter is * and credentials are not allowed, a * is set in Access-Control-Allow-Origin.
• otherwise, the origins given in the Origin request header are echoed.

Hostname starting with *. will match any sub-domain. The scheme and the port are always strictly matched.

The actual or preflight request is rejected if any of the origins from the request is not allowed.

allowedHeaders

HttpHeaderRange with default value HttpHeaderRange.*.

List of request headers that can be used when making an actual request. Controls the content of the Access-Control-Allow-Headers header in a preflight response:

• if parameter is *, the headers from Access-Control-Request-Headers are echoed.
• otherwise the parameter list is returned as part of the header.

allowedMethods

Seq[HttpMethod] with default value Seq(GET, POST, HEAD, OPTIONS).

List of methods that can be used when making an actual request. The list is returned as part of the Access-Control-Allow-Methods preflight response header.

The preflight request will be rejected if the Access-Control-Request-Method header's method is not part of the list.

exposedHeaders

Seq[String] with default value Seq.empty.

List of headers (other than simple response headers) that browsers are allowed to access. If not empty, this list is returned as part of the Access-Control-Expose-Headers header in the actual response.

maxAge

Option[Long] (in seconds) with default value Some (30 * 60).

When set, the amount of seconds the browser is allowed to cache the results of a preflight request. This value is returned as part of the Access-Control-Max-Age preflight response header. If None, the header is not added to the preflight response.

Benchmarks

Using the sbt-jmh plugin, preliminary benchmarks have been performed to measure the impact of the cors directive on the performance. The first results are shown below.

Results are not all coming from the same machine.

v0.1.2 (Akka 2.4.4)

> jmh:run -i 40 -wi 30 -f2 -t1
Benchmark                         Mode  Cnt     Score     Error  Units
CorsBenchmark.baseline           thrpt   80  3601.121 ± 102.274  ops/s
CorsBenchmark.default_cors       thrpt   80  3582.090 ±  95.304  ops/s
CorsBenchmark.default_preflight  thrpt   80  3482.716 ±  89.124  ops/s

v0.1.3 (Akka 2.4.7)

> jmh:run -i 40 -wi 30 -f2 -t1
Benchmark                         Mode  Cnt     Score     Error  Units
CorsBenchmark.baseline           thrpt   80  3657.762 ± 141.409  ops/s
CorsBenchmark.default_cors       thrpt   80  3687.351 ±  35.176  ops/s
CorsBenchmark.default_preflight  thrpt   80  3645.629 ±  30.411  ops/s

v0.2.2 (Akka HTTP 10.0.6)

> jmh:run -i 40 -wi 30 -f2 -t1
Benchmark                         Mode  Cnt     Score     Error  Units
CorsBenchmark.baseline           thrpt   80  9730.001 ±  25.281  ops/s
CorsBenchmark.default_cors       thrpt   80  9159.320 ±  25.459  ops/s
CorsBenchmark.default_preflight  thrpt   80  9172.938 ±  26.794  ops/s

References

• W3C Specification: CORS
• RFC-6454: The Web Origin Concept

License

This code is open source software licensed under the Apache 2.0 License.