HTTP Model
Akka HTTP model contains a deeply structured, fully immutable, case-class based model of all the major HTTP data structures, like HTTP requests, responses and common headers. It lives in the akka-http-core module and forms the basis for most of Akka HTTP’s APIs.
Overview
Since akka-http-core provides the central HTTP data structures you will find the following import in quite a few places around the code base (and probably your own code as well):
- Scala
-
source
import akka.http.scaladsl.model._
- Java
-
source
import akka.http.javadsl.model.*; import akka.http.javadsl.model.headers.*; import java.util.Optional;
This brings all of the most relevant types in scope, mainly:
HttpRequest
HttpRequest
andHttpResponse
HttpResponse
, the central message modelheaders
, the package containing all the predefined HTTP header models and supporting types- Supporting types like
Uri
Uri
,HttpMethods
HttpMethods
,MediaTypes
MediaTypes
,StatusCodes
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 plural ‘s’.
For example:
- Defined
HttpMethod
HttpMethod
instances live inare defined as static fields of theHttpMethods
HttpMethods
objectclass. - Defined
HttpCharset
HttpCharset
instances live inare defined as static fields of theHttpCharsets
HttpCharsets
objectclass. - Defined
HttpEncoding
HttpEncoding
instances live inare defined as static fields of theHttpEncodings
HttpEncodings
objectclass. - Defined
HttpProtocol
HttpProtocol
instances live inare defined as static fields of theHttpProtocols
HttpProtocols
objectclass. - Defined
MediaType
MediaType
instances live inare defined as static fields of theMediaTypes
MediaTypes
objectclass. - Defined
StatusCode
StatusCode
instances live inare defined as static fields of theStatusCodes
StatusCodes
objectclass.
HttpRequest
HttpRequest
HttpRequest
and HttpResponse
HttpResponse
are the basic caseimmutable classes representing HTTP messages.
An HttpRequest
HttpRequest
consists of
- a method (GET, POST, etc.)
- a URI (see URI model for more information)
- a seq of headers
- an entity (body data)
- a protocol
Here are some examples how to construct an HttpRequest
HttpRequest
:
- Scala
-
source
import akka.http.scaladsl.model._ import HttpMethods._ // construct a simple GET request to `homeUri` val homeUri = Uri("/abc") HttpRequest(GET, uri = homeUri) // construct simple GET request to "/index" (implicit string to Uri conversion) HttpRequest(GET, uri = "/index") // construct simple POST request containing entity val data = ByteString("abc") HttpRequest(POST, uri = "/receive", entity = data) // customize every detail of HTTP request import HttpProtocols._ import MediaTypes._ import HttpCharsets._ val userData = ByteString("abc") val authorization = headers.Authorization(BasicHttpCredentials("user", "pass")) HttpRequest( PUT, uri = "/user", entity = HttpEntity(`text/plain` withCharset `UTF-8`, userData), headers = List(authorization), protocol = `HTTP/1.0`)
- Java
-
source
import akka.http.javadsl.model.*; import akka.http.javadsl.model.headers.*; import java.util.Optional; // construct a simple GET request to `homeUri` Uri homeUri = Uri.create("/home"); HttpRequest request1 = HttpRequest.create().withUri(homeUri); // construct simple GET request to "/index" using helper methods HttpRequest request2 = HttpRequest.GET("/index"); // construct simple POST request containing entity ByteString data = ByteString.fromString("abc"); HttpRequest postRequest1 = HttpRequest.POST("/receive").withEntity(data); // customize every detail of HTTP request //import HttpProtocols.* //import MediaTypes.* Authorization authorization = Authorization.basic("user", "pass"); HttpRequest complexRequest = HttpRequest.PUT("/user") .withEntity(HttpEntities.create(ContentTypes.TEXT_PLAIN_UTF8, "abc")) .addHeader(authorization) .withProtocol(HttpProtocols.HTTP_1_0);
All parameters of HttpRequest.apply
have default values set, so headers
for example don’t need to be specified if there are none. Many of the parameters types (like HttpEntity
HttpEntity
and Uri
Uri
) define implicit conversions for common use cases to simplify the creation of request and response instances.
In its basic form HttpRequest.create
creates an empty default GET request without headers which can then be transformed using one of the withX
methods, addHeader
, or addHeaders
. Each of those will create a new immutable instance, so instances can be shared freely. There exist some overloads for HttpRequest.create
that simplify creating requests for common cases. Also, to aid readability, there are predefined alternatives for create
named after HTTP methods to create a request with a given method and URI directly.
There are certain environments where it is easy to inadvertently print, write or log entries built out of string representations of HttpRequest
HttpRequest
instances. On the other hand, it is not uncommon for HTTP headers and entities to contain Personal Identifying Information (PII) or Sensitive Personal Information (SPI) .
To avoid accidentally leaking such information, these fields are omitted from HttpRequest
HttpRequest
toString
output.
If needed, it is possible to define a custom string representation including all fields as shown in the following example:
- Scala
-
source
/* * Copyright (C) 2009-2023 Lightbend Inc. <https://www.lightbend.com> */ package docs.http.scaladsl import akka.http.scaladsl.model.{ HttpEntity, HttpRequest } import akka.http.scaladsl.model.headers.{ Authorization, BasicHttpCredentials } import akka.testkit.AkkaSpec import scala.collection.immutable class HttpRequestDetailedStringExampleSpec extends AkkaSpec { // Custom string representation which includes headers def toDetailedString(request: HttpRequest): String = { import request._ s"""HttpRequest(${_1},${_2},${_3},${_4},${_5})""" } "Include headers in custom string representation" in { // An HTTP header containing Personal Identifying Information val piiHeader = Authorization(BasicHttpCredentials("user", "password")) // An HTTP entity containing Personal Identifying Information val piiBody: HttpEntity.Strict = "This body contains information about [user]" val httpRequestWithHeadersAndBody = HttpRequest(entity = piiBody, headers = immutable.Seq(piiHeader)) // Our custom string representation includes body and headers string representations... assert( toDetailedString(httpRequestWithHeadersAndBody) .contains(piiHeader.toString) ) assert( toDetailedString(httpRequestWithHeadersAndBody).contains(piiBody.toString) ) // ... while default `toString` doesn't. assert(!s"$httpRequestWithHeadersAndBody".contains(piiHeader.unsafeToString)) assert(!s"$httpRequestWithHeadersAndBody".contains(piiBody.data.utf8String)) } }
- Java
-
source
/* * Copyright (C) 2009-2023 Lightbend Inc. <https://www.lightbend.com> */ package docs.http.javadsl; import akka.http.javadsl.model.*; import akka.http.javadsl.model.headers.Authorization; import org.junit.Test; import static org.junit.Assert.*; import java.util.Arrays; public class HttpRequestDetailedStringExampleTest { // Custom string representation which includes headers public String toDetailedString(HttpRequest request) { HttpMethod method = request.method(); Uri uri = request.getUri(); Iterable<HttpHeader> headers = request.getHeaders(); RequestEntity entity = request.entity(); HttpProtocol protocol = request.protocol(); return String.format("HttpRequest(%s, %s, %s, %s, %s)", method, uri, headers, entity, protocol); } @Test public void headersInCustomStringRepresentation() { // An HTTP header containing Personal Identifying Information Authorization piiHeader = Authorization.basic("user", "password"); // An HTTP entity containing Personal Identifying Information HttpEntity.Strict piiBody = HttpEntities.create("This body contains information about [user]"); HttpRequest httpRequestWithHeadersAndBody = HttpRequest.create() .withEntity(piiBody) .withHeaders(Arrays.asList(piiHeader)); // Our custom string representation includes body and headers string representations... assertTrue(toDetailedString(httpRequestWithHeadersAndBody).contains(piiHeader.toString())); assertTrue(toDetailedString(httpRequestWithHeadersAndBody).contains(piiBody.toString())); // ... while default `toString` doesn't. assertFalse(httpRequestWithHeadersAndBody.toString().contains(piiHeader.unsafeToString())); assertFalse(httpRequestWithHeadersAndBody.toString().contains(piiBody.getData().utf8String())); } }
Synthetic Headers
In some cases it may be necessary to deviate from fully RFC-Compliant behavior. For instance, Amazon S3 treats the +
character in the path part of the URL as a space, even though the RFC specifies that this behavior should be limited exclusively to the query portion of the URI.
In order to work around these types of edge cases, Akka HTTP provides for the ability to provide extra, non-standard information to the request via synthetic headers. These headers are not passed to the client but are instead consumed by the request engine and used to override default behavior.
For instance, in order to provide a raw request URI, bypassing the default URL normalization, you could do the following:
- Scala
-
source
import akka.http.scaladsl.model.headers.`Raw-Request-URI` val req = HttpRequest(uri = "/ignored", headers = List(`Raw-Request-URI`("/a/b%2Bc")))
- Java
-
source
// imports akka.http.javadsl.model.headers.RawRequestURI HttpRequest.create("/ignored").addHeader(RawRequestURI.create("/a/b%2Bc"));
HttpResponse
An HttpResponse
HttpResponse
consists of
- a status code
- a
Seq
list of headers - an entity (body data)
- a protocol
Here are some examples how to construct an HttpResponse
HttpResponse
:
- Scala
-
source
import StatusCodes._ // simple OK response without data created using the integer status code HttpResponse(200) // 404 response created using the named StatusCode constant HttpResponse(NotFound) // 404 response with a body explaining the error HttpResponse(404, entity = "Unfortunately, the resource couldn't be found.") // A redirecting response containing an extra header val locationHeader = headers.Location("http://example.com/other") HttpResponse(Found, headers = List(locationHeader))
- Java
-
source
// simple OK response without data created using the integer status code HttpResponse ok = HttpResponse.create().withStatus(200); // 404 response created using the named StatusCode constant HttpResponse notFound = HttpResponse.create().withStatus(StatusCodes.NOT_FOUND); // 404 response with a body explaining the error HttpResponse notFoundCustom = HttpResponse.create() .withStatus(404) .withEntity("Unfortunately, the resource couldn't be found."); // A redirecting response containing an extra header Location locationHeader = Location.create("http://example.com/other"); HttpResponse redirectResponse = HttpResponse.create() .withStatus(StatusCodes.FOUND) .addHeader(locationHeader);
In addition to the simple HttpEntity
HttpEntity
constructorsHttpEntities.create
methods which create an entity from a fixed String
or ByteString
ByteString
as shown here the Akka HTTP model defines a number of subclasses of HttpEntity
HttpEntity
which allow body data to be specified as a stream of bytes. All of these types can be created using the method on HttpEntites
.
There are certain environments where it is easy to inadvertently print, write or log entries built out of string representations of HttpResponse
HttpResponse
instances. On the other hand, it is not uncommon for HTTP headers and entities to contain Personal Identifying Information (PII) or Sensitive Personal Information (SPI) .
To avoid accidentally leaking such information, these fields are omitted from HttpResponse
HttpResponse
toString
output.
If needed, it is possible to define a custom string representation including all fields as shown in the following example:
- Scala
-
source
/* * Copyright (C) 2009-2023 Lightbend Inc. <https://www.lightbend.com> */ package docs.http.scaladsl import akka.http.scaladsl.model.{ HttpEntity, HttpResponse } import akka.http.scaladsl.model.headers.{ Authorization, BasicHttpCredentials } import akka.testkit.AkkaSpec import scala.collection.immutable class HttpResponseDetailedStringExampleSpec extends AkkaSpec { // Custom string representation which includes headers def toDetailedString(response: HttpResponse): String = { import response._ s"""HttpResponse(${_1},${_2},${_3},${_4})""" } "Include headers in custom string representation" in { // An HTTP header containing Personal Identifying Information val piiHeader = Authorization(BasicHttpCredentials("user", "password")) // An HTTP entity containing Personal Identifying Information val piiBody: HttpEntity.Strict = "This body contains information about [user]" val httpResponseWithHeadersAndBody = HttpResponse(entity = piiBody, headers = immutable.Seq(piiHeader)) // Our custom string representation includes body and headers string representations... assert( toDetailedString(httpResponseWithHeadersAndBody) .contains(piiHeader.toString) ) assert( toDetailedString(httpResponseWithHeadersAndBody) .contains(piiBody.toString) ) // ... while default `toString` doesn't. assert(!s"$httpResponseWithHeadersAndBody".contains(piiHeader.unsafeToString)) assert(!s"$httpResponseWithHeadersAndBody".contains(piiBody.data.utf8String)) } }
- Java
-
source
/* * Copyright (C) 2009-2023 Lightbend Inc. <https://www.lightbend.com> */ package docs.http.javadsl; import akka.http.javadsl.model.*; import akka.http.javadsl.model.headers.Authorization; import org.junit.Test; import java.util.Arrays; import static org.junit.Assert.assertFalse; import static org.junit.Assert.assertTrue; public class HttpResponseDetailedStringExampleTest { // Custom string representation which includes headers public String toDetailedString(HttpResponse response) { StatusCode status = response.status(); Iterable<HttpHeader> headers = response.getHeaders(); HttpEntity entity = response.entity(); HttpProtocol protocol = response.protocol(); return String.format("HttpResponse(%s, %s, %s, %s)", status, headers, entity, protocol); } @Test public void headersInCustomStringRepresentation() { // An HTTP header containing Personal Identifying Information Authorization piiHeader = Authorization.basic("user", "password"); // An HTTP entity containing Personal Identifying Information HttpEntity.Strict piiBody = HttpEntities.create("This body contains information about [user]"); HttpResponse httpResponseWithHeadersAndBody = HttpResponse.create() .withEntity(piiBody) .withHeaders(Arrays.asList(piiHeader)); // Our custom string representation includes body and headers string representations... assertTrue(toDetailedString(httpResponseWithHeadersAndBody).contains(piiHeader.toString())); assertTrue(toDetailedString(httpResponseWithHeadersAndBody).contains(piiBody.toString())); // ... while default `toString` doesn't. assertFalse(httpResponseWithHeadersAndBody.toString().contains(piiHeader.unsafeToString())); assertFalse(httpResponseWithHeadersAndBody.toString().contains(piiBody.getData().utf8String())); } }
HttpEntity
An HttpEntity
HttpEntity
carries the data bytes of a message together with its Content-Type and, if known, its Content-Length. In Akka HTTP there are five different kinds of entities which model the various ways that message content can be received or sent:
- HttpEntity.StrictHttpEntityStrict
- The simplest entity, which is used when all the entity are already available in memory. It wraps a plain
ByteString
ByteString
and represents a standard, unchunked entity with a knownContent-Length
. - HttpEntity.DefaultHttpEntityDefault
- The general, unchunked HTTP/1.1 message entity. It has a known length and presents its data as a
Source<ByteString, ?>
Source[ByteString, _]
which can be only materialized once. It is an error if the provided source doesn’t produce exactly as many bytes as specified. The distinction ofStrict
HttpEntityStrict
andDefault
HttpEntityDefault
is an API-only one. On the wire, both kinds of entities look the same. - HttpEntity.ChunkedHttpEntityChunked
- The model for HTTP/1.1 chunked content (i.e. sent with
Transfer-Encoding: chunked
). The content length is unknown and the individual chunks are presented as aSource[HttpEntity.ChunkStreamPart]
Source<ChunkStreamPart, ?>
Source[ChunkStreamPart, ?]
. AChunkStreamPart
is either a non-emptyChunk
chunk or aLastChunk
the empty last chunk containing optional trailer headers. The stream consists of zero or moreChunked
non-empty chunks parts and can be terminated by an optionalLastChunk
partlast chunk. - HttpEntity.CloseDelimitedHttpEntityCloseDelimited
- An unchunked entity of unknown length that is implicitly delimited by closing the connection (
Connection: close
). The content data are presented as aSource<ByteString, ?>
Source[ByteString, _]
. Since the connection must be closed after sending an entity of this type it can only be used on the server-side for sending a response. Also, the main purpose ofCloseDelimited
entities is compatibility with HTTP/1.0 peers, which do not support chunked transfer encoding. If you are building a new application and are not constrained by legacy requirements you shouldn’t rely onCloseDelimited
entities, since implicit terminate-by-connection-close is not a robust way of signaling response end, especially in the presence of proxies. Additionally this type of entity prevents connection reuse which can seriously degrade performance. UseHttpEntity.Chunked
HttpEntityChunked
instead! - HttpEntity.IndefiniteLengthHttpEntityIndefiniteLength
- A streaming entity of unspecified length for use in a
Multipart.BodyPart
.
Entity types Strict
HttpEntityStrict
, Default
HttpEntityDefault
, and Chunked
HttpEntityChunked
are a subtype of HttpEntity.Regular
RequestEntity
RequestEntity
which allows to use them for requests and responses. In contrast, HttpEntity.CloseDelimited
HttpEntityCloseDelimited
can only be used for responses.
Streaming entity types (i.e. all but Strict
HttpEntityStrict
) cannot be shared or serialized. To create a strict, shareable copy of an entity or message use HttpEntity.toStrict
or HttpMessage.toStrict
which returns a Future
CompletionStage
of the object with the body data collected into a ByteString
ByteString
.
The HttpEntity
HttpEntity
companion objectclass HttpEntities
contains several helper constructorsstatic methods to create entities from common types easily.
You can pattern match overuse the subtypesisX
methods of HttpEntity
HttpEntity
to find out of which subclass an entity is if you want to provide special handling for each of the subtypes. However, in many cases a recipient of an HttpEntity
HttpEntity
doesn’t care about of which subtype an entity is (and how data is transported exactly on the HTTP layer). Therefore, the general method HttpEntity.dataBytes
HttpEntity.getDataBytes()
is provided which returns a Source<ByteString, ?>
Source[ByteString, _]
that allows access to the data of an entity regardless of its concrete subtype.
- Use
Strict
HttpEntityStrict
if the amount of data is “small” and already available in memory (e.g. as aString
orByteString
ByteString
) - Use
Default
HttpEntityDefault
if the data is generated by a streaming data source and the size of the data is known - Use
Chunked
HttpEntityChunked
for an entity of unknown length - Use
CloseDelimited
HttpEntityCloseDelimited
for a response as a legacy alternative toChunked
HttpEntityChunked
if the client doesn’t support chunked transfer encoding. Otherwise useChunked
HttpEntityChunked
! - In a
Multipart.BodyPart
useIndefiniteLength
HttpEntityIndefiniteLength
for content of unknown length.
When you receive a non-strict message from a connection then additional data are only read from the network when you request them by consuming the entity data stream. This means that, if you don’t consume the entity stream then the connection will effectively be stalled. In particular no subsequent message (request or response) will be read from the connection as the entity of the current message “blocks” the stream. Therefore you must make sure that you always consume the entity data, even in the case that you are not actually interested in it!
Limiting message entity length
All message entities that Akka HTTP reads from the network automatically get a length verification check attached to them. This check makes sure that the total entity size is less than or equal to the configured max-content-length
[1], which is an important defense against certain Denial-of-Service attacks. However, a single global limit for all requests (or responses) is often too inflexible for applications that need to allow large limits for some requests (or responses) but want to clamp down on all messages not belonging into that group.
In order to give you maximum flexibility in defining entity size limits according to your needs the HttpEntity
HttpEntity
features a withSizeLimit
method, which lets you adjust the globally configured maximum size for this particular entity, be it to increase or decrease any previously set value. This means that your application will receive all requests (or responses) from the HTTP layer, even the ones whose Content-Length
exceeds the configured limit (because you might want to increase the limit yourself). Only when the actual data stream Source
Source
contained in the entity is materialized will the boundary checks be actually applied. In case the length verification fails the respective stream will be terminated with an EntityStreamSizeException
either directly at materialization time (if the Content-Length
is known) or whenever more data bytes than allowed have been read.
When called on Strict
entities the withSizeLimit
method will return the entity itself if the length is within the bound, otherwise a Default
entity with a single element data stream. This allows for potential refinement of the entity size limit at a later point (before materialization of the data stream).
By default all message entities produced by the HTTP layer automatically carry the limit that is defined in the application’s max-content-length
config setting. If the entity is transformed in a way that changes the content-length and then another limit is applied then this new limit will be evaluated against the new content-length. If the entity is transformed in a way that changes the content-length and no new limit is applied then the previous limit will be applied against the previous content-length. Generally this behavior should be in line with your expectations.
[1] akka.http.parsing.max-content-length (applying to server- as well as client-side), akka.http.server.parsing.max-content-length (server-side only), akka.http.client.parsing.max-content-length (client-side only) or akka.http.host-connection-pool.client.parsing.max-content-length (only host-connection-pools)
Special processing for HEAD requests
RFC 7230 defines very clear rules for the entity length of HTTP messages.
Especially this rule requires special treatment in Akka HTTP:
Any response to a HEAD request and any response with a 1xx (Informational), 204 (No Content), or 304 (Not Modified) status code is always terminated by the first empty line after the header fields, regardless of the header fields present in the message, and thus cannot contain a message body.
Responses to HEAD requests introduce the complexity that Content-Length or Transfer-Encoding headers can be present but the entity is empty. This is modeled by allowing HttpEntity.DefaultHttpEntityDefault and HttpEntity.ChunkedHttpEntityChunked to be used for HEAD responses with an empty data stream.
Also, when a HEAD response has an HttpEntity.CloseDelimitedHttpEntityCloseDelimited entity the Akka HTTP implementation will not close the connection after the response has been sent. This allows the sending of HEAD responses without Content-Length header across persistent HTTP connections.
Header Model
Akka HTTP contains a rich model of the most common HTTP headers. Parsing and rendering is done automatically so that applications don’t need to care for the actual syntax of headers. Headers not modelled explicitly are represented as a RawHeader
RawHeader
, which is essentially a String/String name/value pair.
See these examples of how to deal with headers:
- Scala
-
source
import akka.http.scaladsl.model.headers._ // create a ``Location`` header val loc = Location("http://example.com/other") // create an ``Authorization`` header with HTTP Basic authentication data val auth = Authorization(BasicHttpCredentials("joe", "josepp")) // custom type case class User(name: String, pass: String) // a method that extracts basic HTTP credentials from a request def credentialsOfRequest(req: HttpRequest): Option[User] = for { case Authorization(BasicHttpCredentials(user, pass)) <- req.header[Authorization] } yield User(user, pass)
- Java
-
source
// create a ``Location`` header Location locationHeader = Location.create("http://example.com/other"); // create an ``Authorization`` header with HTTP Basic authentication data Authorization authorization = Authorization.basic("user", "pass"); // a method that extracts basic HTTP credentials from a request private Optional<BasicHttpCredentials> getCredentialsOfRequest(HttpRequest request) { Optional<Authorization> auth = request.getHeader(Authorization.class); if (auth.isPresent() && auth.get().credentials() instanceof BasicHttpCredentials) return Optional.of((BasicHttpCredentials) auth.get().credentials()); else return Optional.empty(); }
HTTP Headers
When the Akka HTTP server receives an HTTP request it tries to parse all its headers into their respective model classes. Independently of whether this succeeds or not, the HTTP layer will always pass on all received headers to the application. Unknown headers as well as ones with invalid syntax (according to the header parser) will be made available as RawHeader
RawHeader
instances. For the ones exhibiting parsing errors a warning message is logged depending on the value of the illegal-header-warnings
config setting.
Some headers have special status in HTTP and are therefore treated differently from “regular” headers:
- Content-Type
- The Content-Type of an HTTP message is modeled as the
contentType
field of theHttpEntity
HttpEntity
. TheContent-Type
header therefore doesn’t appear in theheaders
sequence of a message. Also, aContent-Type
header instance that is explicitly added to theheaders
of a request or response will not be rendered onto the wire and trigger a warning being logged instead! - Transfer-Encoding
- Messages with
Transfer-Encoding: chunked
are represented via theHttpEntity.Chunked
as aHttpEntityChunked
entity. As such chunked messages that do not have another deeper nested transfer encoding will not have aTransfer-Encoding
header in theirheaders
sequencelist. Similarly, aTransfer-Encoding
header instance that is explicitly added to theheaders
of a request or response will not be rendered onto the wire and trigger a warning being logged instead! - Content-Length
- The content length of a message is modelled via its HttpEntity. As such no
Content-Length
header will ever be part of a message’sheader
sequence. Similarly, aContent-Length
header instance that is explicitly added to theheaders
of a request or response will not be rendered onto the wire and trigger a warning being logged instead! - Server
- A
Server
header is usually added automatically to any response and its value can be configured via theakka.http.server.server-header
setting. Additionally an application can override the configured header with a custom one by adding it to the response’sheader
sequence. - User-Agent
- A
User-Agent
header is usually added automatically to any request and its value can be configured via theakka.http.client.user-agent-header
setting. Additionally an application can override the configured header with a custom one by adding it to the request’sheader
sequence. - Date
- The
Date
Date
response header is added automatically but can be overridden by supplying it manually. - Connection
- On the server-side Akka HTTP watches for explicitly added
Connection: close
response headers and as such honors the potential wish of the application to close the connection after the respective response has been sent out. The actual logic for determining whether to close the connection is quite involved. It takes into account the request’s method, protocol and potentialConnection
Connection
header as well as the response’s protocol, entity and potentialConnection
Connection
header. See this test for a full table of what happens when. - Strict-Transport-Security
- HTTP Strict Transport Security (HSTS) is a web security policy mechanism which is communicated by the
Strict-Transport-Security
header. The most important security vulnerability that HSTS can fix is SSL-stripping man-in-the-middle attacks. The SSL-stripping attack works by transparently converting a secure HTTPS connection into a plain HTTP connection. The user can see that the connection is insecure, but crucially there is no way of knowing whether the connection should be secure. HSTS addresses this problem by informing the browser that connections to the site should always use TLS/SSL. See also RFC 6797.
Custom Headers
Sometimes you may need to model a custom header type which is not part of HTTP and still be able to use it as convenient as is possible with the built-in types.
Because of the number of ways one may interact with headers (i.e. try to matchconvert a CustomHeader
CustomHeader
againstto a RawHeader
RawHeader
or the other way around etc), a helper traitclasses for custom Header types and their companions classes are provided by Akka HTTP. Thanks to extending ModeledCustomHeader
ModeledCustomHeader
instead of the plain CustomHeader
CustomHeader
such header can be matchedthe following methods are at your disposal:
- Scala
-
source
final class ApiTokenHeader(token: String) extends ModeledCustomHeader[ApiTokenHeader] { override def renderInRequests = true override def renderInResponses = true override val companion = ApiTokenHeader override def value: String = token } object ApiTokenHeader extends ModeledCustomHeaderCompanion[ApiTokenHeader] { override val name = "apiKey" override def parse(value: String) = Try(new ApiTokenHeader(value)) }
- Java
-
source
public static class ApiTokenHeader extends ModeledCustomHeader { ApiTokenHeader(String name, String value) { super(name, value); } public boolean renderInResponses() { return false; } public boolean renderInRequests() { return false; } } static class ApiTokenHeaderFactory extends ModeledCustomHeaderFactory<ApiTokenHeader> { public String name() { return "apiKey"; } @Override public ApiTokenHeader parse(String value) { return new ApiTokenHeader(name(), value); } }
Which allows this CustomHeadermodeled custom header to be used in the following scenarios:
- Scala
-
source
val ApiTokenHeader(t1) = ApiTokenHeader("token") t1 should ===("token") val RawHeader(k2, v2) = ApiTokenHeader("token") k2 should ===("apiKey") v2 should ===("token") // will match, header keys are case insensitive val ApiTokenHeader(v3) = RawHeader("APIKEY", "token") v3 should ===("token") intercept[MatchError] { // won't match, different header name val ApiTokenHeader(v4) = DifferentHeader("token") } intercept[MatchError] { // won't match, different header name val RawHeader("something", v5) = DifferentHeader("token") } intercept[MatchError] { // won't match, different header name val ApiTokenHeader(v6) = RawHeader("different", "token") }
- Java
-
source
final ApiTokenHeaderFactory apiTokenHeaderFactory = new ApiTokenHeaderFactory(); final ApiTokenHeader token = apiTokenHeaderFactory.create("token"); assertEquals("token", token.value()); final HttpHeader header = apiTokenHeaderFactory.create("token"); assertEquals("apiKey", header.name()); assertEquals("token", header.value()); final Optional<ApiTokenHeader> fromRaw = apiTokenHeaderFactory .from(RawHeader.create("apiKey", "token")); assertTrue("Expected a header", fromRaw.isPresent()); assertEquals("apiKey", fromRaw.get().name()); assertEquals("token", fromRaw.get().value()); // will match, header keys are case insensitive final Optional<ApiTokenHeader> fromRawUpper = apiTokenHeaderFactory .from(RawHeader.create("APIKEY", "token")); assertTrue("Expected a header", fromRawUpper.isPresent()); assertEquals("apiKey", fromRawUpper.get().name()); assertEquals("token", fromRawUpper.get().value()); // won't match, different header name final Optional<ApiTokenHeader> wrong = apiTokenHeaderFactory .from(RawHeader.create("different", "token")); assertFalse(wrong.isPresent());
Including usage within the header directives like in the following headerValuePF example:
- Scala
-
source
def extractFromCustomHeader = headerValuePF { case t @ ApiTokenHeader(token) => s"extracted> $t" case raw: RawHeader => s"raw> $raw" } val routes = extractFromCustomHeader { s => complete(s) } Get().withHeaders(RawHeader("apiKey", "TheKey")) ~> routes ~> check { status should ===(StatusCodes.OK) responseAs[String] should ===("extracted> apiKey: TheKey") } Get().withHeaders(RawHeader("somethingElse", "TheKey")) ~> routes ~> check { status should ===(StatusCodes.OK) responseAs[String] should ===("raw> somethingElse: TheKey") } Get().withHeaders(ApiTokenHeader("TheKey")) ~> routes ~> check { status should ===(StatusCodes.OK) responseAs[String] should ===("extracted> apiKey: TheKey") }
- Java
-
source
import akka.http.javadsl.server.Directives; import static akka.http.javadsl.server.Directives.headerValuePF; final ApiTokenHeaderFactory apiTokenHeaderFactory = new ApiTokenHeaderFactory(); final PartialFunction<HttpHeader, String> extractFromCustomHeader = new JavaPartialFunction<HttpHeader, String>() { @Override public String apply(HttpHeader header, boolean isCheck) throws Exception { if (isCheck) return null; return apiTokenHeaderFactory.from(header) .map(apiTokenHeader -> "extracted> " + apiTokenHeader) .orElseGet(() -> "raw> " + header); } }; final Route route = headerValuePF(extractFromCustomHeader, Directives::complete); testRoute(route) .run(HttpRequest.GET("/").addHeader(RawHeader.create("apiKey", "TheKey"))) .assertStatusCode(StatusCodes.OK) .assertEntity("extracted> apiKey: TheKey"); testRoute(route) .run(HttpRequest.GET("/").addHeader(RawHeader.create("somethingElse", "TheKey"))) .assertStatusCode(StatusCodes.OK) .assertEntity("raw> somethingElse: TheKey"); testRoute(route) .run(HttpRequest.GET("/").addHeader(apiTokenHeaderFactory.create("TheKey"))) .assertStatusCode(StatusCodes.OK) .assertEntity("extracted> apiKey: TheKey");
Custom headers do not work with the header[T]
method on HttpMessage
HttpMessage
.
When defining custom headers, it is better to extend ModeledCustomHeader
ModeledCustomHeader
instead of its parent CustomHeader
CustomHeader
. Custom headers that extend ModeledCustomHeader
ModeledCustomHeader
automatically comply with the pattern matching semantics that usually apply to built-in types (such as matching a custom header against a RawHeader
RawHeader
in routing layers of Akka HTTP applications).
Custom headers do not work with the getHeader(Class)
method on HttpMessage
HttpMessage
.
Implement ModeledCustomHeader
ModeledCustomHeader
and ModeledCustomHeaderFactory
instead of CustomHeader
CustomHeader
to be able to use the convenience methods that allow parsing the custom user-defined header from HttpHeader
HttpHeader
.
Attributes
Sometimes it can be useful to keep track of some information associated with a request without explicitly closing over it. Such information can be attached to a request or response though message attributes:
- Scala
-
source
case class User(name: String) object User { val attributeKey = AttributeKey[User]("user") } def determineUser(req: HttpRequest): HttpRequest = { val user = // ... somehow determine the user for this request // Add the attribute req.addAttribute(User.attributeKey, user) } // Retrieve the attribute val user: Option[User] = requestWithAttribute.attribute(User.attributeKey)
- Java
-
source
class User { final String name; public User(String name) { this.name = name; } public static final AttributeKey<User> attributeKey = AttributeKey.create("user", User.class); } public HttpRequest determineUser(HttpRequest request) { User user = //... somehow determine the user for this request // Add the attribute return request.addAttribute(User.attributeKey, user); } // Retrieve the attribute Optional<User> user = requestWithAttribute.getAttribute(User.attributeKey);
Message attributes are only to be used within in your application, they are not present on the wire.
Parsing / Rendering
Parsing and rendering of HTTP data structures is heavily optimized and for most types there’s currently no public API provided to parse (or render to) Strings or byte arrays.
Various parsing and rendering settings are available to tweak in the configuration under akka.http.client[.parsing]
, akka.http.server[.parsing]
and akka.http.host-connection-pool[.client.parsing]
, with defaults for all of these being defined in the akka.http.parsing
configuration section.
For example, if you want to change a parsing setting for all components, you can set the akka.http.parsing.illegal-header-warnings = off
value. However this setting can be still overridden by the more specific sections, like for example akka.http.server.parsing.illegal-header-warnings = on
.
In this case both client
and host-connection-pool
APIs will see the setting off
, however the server will see on
.
In the case of akka.http.host-connection-pool.client
settings, they default to settings set in akka.http.client
, and can override them if needed. This is useful, since both client
and host-connection-pool
APIs, such as the Client API Http().outgoingConnection
Http.get(sys).outgoingConnection
or the Host Connection Pool APIs Http().singleRequest
Http.get(sys).singleRequest
or Http().superPool
Http.get(sys).superPool
, usually need the same settings, however the server
most likely has a very different set of settings.
Registering Custom Media Types
Akka HTTP predefines
predefines
most commonly encountered media types and emits them in their well-typed form while parsing http messages. Sometimes you may want to define a custom media type and inform the parser infrastructure about how to handle these custom media types, e.g. that application/custom
is to be treated as NonBinary
with WithFixedCharset
. To achieve this you need to register the custom media type in the server’s settings by configuring ParserSettings
ParserSettings
like this:
- Scala
-
source
// similarly in Java: `akka.http.javadsl.settings.[...]` import akka.http.scaladsl.settings.ParserSettings import akka.http.scaladsl.settings.ServerSettings // define custom media type: val utf8 = HttpCharsets.`UTF-8` val `application/custom`: WithFixedCharset = MediaType.customWithFixedCharset("application", "custom", utf8) // add custom media type to parser settings: val parserSettings = ParserSettings.forServer(system).withCustomMediaTypes(`application/custom`) val serverSettings = ServerSettings(system).withParserSettings(parserSettings) val routes = extractRequest { r => complete(r.entity.contentType.toString + " = " + r.entity.contentType.getClass) } val binding = Http().newServerAt("localhost", 0).withSettings(serverSettings).bind(routes) - Java
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source
import static akka.http.javadsl.server.Directives.complete; import static akka.http.javadsl.server.Directives.extractRequest; // Define custom media type: final MediaType.WithFixedCharset applicationCustom = MediaTypes.customWithFixedCharset("application", "custom", // The new Media Type name HttpCharsets.UTF_8, // The charset used new HashMap<>(), // Empty parameters false); // No arbitrary subtypes are allowed // Add custom media type to parser settings: final ParserSettings parserSettings = ParserSettings.forServer(system) .withCustomMediaTypes(applicationCustom); final ServerSettings serverSettings = ServerSettings.create(system) .withParserSettings(parserSettings); final Route route = extractRequest(req -> complete(req.entity().getContentType().toString() + " = " + req.entity().getContentType().getClass()) ); final CompletionStage<ServerBinding> binding = Http.get(system) .newServerAt(host, 0) .withSettings(serverSettings) .bind(route);
You may also want to read about MediaType Registration trees, in order to register your vendor specific media types in the right style / place.
Registering Custom Status Codes
Similarly to media types, Akka HTTP predefines
predefines
well-known status codes, however sometimes you may need to use a custom one (or are forced to use an API which returns custom status codes). Similarly to the media types registration, you can register custom status codes by configuring ParserSettings
ParserSettings
like this:
- Scala
-
source
// similarly in Java: `akka.http.javadsl.settings.[...]` import akka.http.scaladsl.settings.{ ParserSettings, ServerSettings } // define custom status code: val LeetCode = StatusCodes.custom(777, "LeetCode", "Some reason", isSuccess = true, allowsEntity = false) // add custom method to parser settings: val parserSettings = ParserSettings.forServer(system).withCustomStatusCodes(LeetCode) val serverSettings = ServerSettings(system).withParserSettings(parserSettings) val clientConSettings = ClientConnectionSettings(system).withParserSettings(parserSettings) val clientSettings = ConnectionPoolSettings(system).withConnectionSettings(clientConSettings) val routes = complete(HttpResponse(status = LeetCode)) // use serverSettings in server: val binding = Http().newServerAt("127.0.0.1", 0).withSettings(serverSettings).bind(routes).futureValue // use clientSettings in client: val request = HttpRequest(uri = s"http://127.0.0.1:${binding.localAddress.getPort}/") val response = Http().singleRequest(request, settings = clientSettings) // futureValue is a ScalaTest helper: response.futureValue.status should ===(LeetCode)
- Java
-
source
import static akka.http.javadsl.server.Directives.complete; import static akka.http.javadsl.server.Directives.extractRequest; // Define custom status code: final StatusCode leetCode = StatusCodes.custom(777, // Our custom status code "LeetCode", // Our custom reason "Some reason", // Our custom default message true, // It should be considered a success response false);// Does not allow entities // Add custom method to parser settings: final ParserSettings parserSettings = ParserSettings.forServer(system) .withCustomStatusCodes(leetCode); final ServerSettings serverSettings = ServerSettings.create(system) .withParserSettings(parserSettings); final ClientConnectionSettings clientConSettings = ClientConnectionSettings.create(system) .withParserSettings(parserSettings); final ConnectionPoolSettings clientSettings = ConnectionPoolSettings.create(system) .withConnectionSettings(clientConSettings); final Route route = extractRequest(req -> complete(HttpResponse.create().withStatus(leetCode)) ); // Use serverSettings in server: final CompletionStage<ServerBinding> binding = Http.get(system) .newServerAt(host, 0) .withSettings(serverSettings) .bind(route); final ServerBinding serverBinding = binding.toCompletableFuture().get(); final int port = serverBinding.localAddress().getPort(); // Use clientSettings in client: final HttpResponse response = Http.get(system) .singleRequest(HttpRequest .GET("http://" + host + ":" + port + "/"), ConnectionContext.httpsClient(SSLContext.getDefault()), clientSettings, system.log()) .toCompletableFuture() .get(); // Check we get the right code back assertEquals(leetCode, response.status());
Registering Custom HTTP Method
Akka HTTP also allows you to define custom HTTP methods, other than the well-known methods predefined
predefined
in Akka HTTP. To use a custom HTTP method, you need to define it, and then add it to parser settings like below:
- Scala
-
source
import akka.http.scaladsl.settings.{ ParserSettings, ServerSettings } // define custom method type: val BOLT = HttpMethod.custom("BOLT", safe = false, idempotent = true, requestEntityAcceptance = Expected, contentLengthAllowed = true) // add custom method to parser settings: val parserSettings = ParserSettings.forServer(system).withCustomMethods(BOLT) val serverSettings = ServerSettings(system).withParserSettings(parserSettings) val routes = extractMethod { method => complete(s"This is a ${method.name} method request.") } val binding = Http().newServerAt(host, port).withSettings(serverSettings).bind(routes) val request = HttpRequest(BOLT, s"http://$host:$port/", protocol = `HTTP/1.1`)
- Java
-
source
import static akka.http.javadsl.server.Directives.complete; import static akka.http.javadsl.server.Directives.extractMethod; // define custom method type: HttpMethod BOLT = HttpMethods.custom("BOLT", false, true, Expected); // add custom method to parser settings: final ParserSettings parserSettings = ParserSettings.forServer(system).withCustomMethods(BOLT); final ServerSettings serverSettings = ServerSettings.create(system).withParserSettings(parserSettings); final Route routes = concat( extractMethod( method -> complete( "This is a " + method.name() + " request.") ) ); final Http http = Http.get(system); final CompletionStage<ServerBinding> binding = http.newServerAt(host, port) .withSettings(serverSettings) .logTo(loggingAdapter) .bind(routes); HttpRequest request = HttpRequest.create() .withUri("http://" + host + ":" + Integer.toString(port)) .withMethod(BOLT) .withProtocol(HTTP_1_1); CompletionStage<HttpResponse> response = http.singleRequest(request);