The spray-http module contains a fully immutable, case-class based model of the major HTTP data structures, like HTTP requests, responses and common headers. It also includes a parser for the latter, which is able to construct the more structured header models from raw unstructured header name/value pairs.
spray-http depends on akka-actor (with ‘provided’ scope, i.e. you need to pull it in yourself). It also depends on parboiled, a lightweight PEG parsing library providing the basis for the header parser. Since parboiled is also written and maintained by the members of the spray team it’s not an “outside” dependency that we have no control over.
The Maven Repository chapter contains all the info about how to pull spray-http into your classpath.
Afterwards just import spray.http._ to bring all relevant identifiers into scope.
Since spray-http provides the central HTTP data structures for spray you will find the following import in quite a few places around the spray code base (and probably your own code as well):
This brings in scope all of the relevant things that are defined here and that you’ll want to work with, mainly:
- HttpRequest and HttpResponse, the central message models
- ChunkedRequestStart, ChunkedResponseStart, MessageChunk and ChunkedMessageEnd modeling the different message parts of request/response streams
- HttpHeaders, an object containing all the defined HTTP header models
- Supporting types like Uri, HttpMethods, MediaTypes, StatusCodes, etc.
A common pattern is that the model of a certain entity is represented by an immutable type (class or trait), while the actual instances of the entity defined by the HTTP spec live in an accompanying object carrying the name of the type plus a trailing ‘s’.
- The defined HttpMethod instances live in the HttpMethods object.
- The defined HttpCharset instances live in the HttpCharsets object.
- The defined HttpEncoding instances live in the HttpEncodings object.
- The defined HttpProtocol instances live in the HttpProtocols object.
- The defined MediaType instances live in the MediaTypes object.
- The defined StatusCode instances live in the StatusCodes object.
You get the point.
In order to develop a better understanding for how spray models HTTP you probably should take some time to browse around the spray-http sources (ideally with an IDE that supports proper code navigation).
One thing worth highlighting is the special treatment of the HTTP Content-Type header. Since the binary content of HTTP message entities can only be properly interpreted when the corresponding content-type is known spray-http puts the content-type value very close to the entity data. The HttpEntity.NonEmpty type (the non-empty variant of the HttpEntity) is essentially little more than a tuple of the ContentType and the entity’s bytes. All logic in spray that needs to access the content-type of an HTTP message always works with the ContentType value in the HttpEntity. Potentially existing instances of the Content-Type header in the HttpMessage‘s header list are ignored!
spray-http defines the most important media types from the IANA MIME media type registry in the MediaTypes object, which also acts as a registry that you can register your own CustomMediaType instances with:
import spray.http.MediaTypes._ val MarkdownType = register( MediaType.custom( mainType = "text", subType = "x-markdown", compressible = true, binary = false, fileExtensions = Seq("markdown", "mdown", "md")))
Once registered the custom type will be properly resolved, e.g. for incoming requests by spray-routing or incoming responses by spray-client. File extension resolution (as used for example by the FileAndResourceDirectives) will work as expected.