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http-verbs

http-verbs is a Scala library providing an interface to make asynchronous HTTP calls.

It encapsulates some common concerns for calling other HTTP services on the HMRC Tax Platform, including:

  • Http Transport
  • Core Http function interfaces
  • Logging
  • Propagation of common headers
  • Executing hooks, for example Auditing
  • Request & Response de-serializations
  • Response handling, converting failure status codes into a consistent set of exceptions - allows failures to be automatically propagated to the caller

Migration

See CHANGELOG for changes and migrations.

Adding to your build

In your SBT build add:

resolvers += MavenRepository("HMRC-open-artefacts-maven2", "https://open.artefacts.tax.service.gov.uk/maven2")

libraryDependencies += "uk.gov.hmrc" %% "http-verbs-play-xx" % "x.x.x"

Where play-xx is your version of Play (e.g. play-30).

Usage

There are two HttpClients available, but HttpClient and related API have been deprecated. Please use uk.gov.hmrc.http.client.HttpClientV2 instead.

uk.gov.hmrc.http.client.HttpClientV2

This client has more features than the original HttpClient and is simpler to use.

It requires a HeaderCarrier to represent the context of the caller, and an HttpReads to process the http response.

It also :

  • Supports streaming
  • Exposes the underlying play.api.libs.ws.WSRequest with transform, making it easier to customise the request.
  • Only accepts the URL as java.net.URL; you can make use of the provided URL interpolator.

Examples can be found here and here

uk.gov.hmrc.http.HttpClient

This client has been deprecated. You can migrate as follows:

httpClient.GET[ResponseType](url)

becomes

httpClientV2.get(url"$url").execute[ResponseType]

and

httpClient.POST[ResponseType](url, payload, headers)

becomes

httpClientV2.post(url"$url").withBody(Json.toJson(payload)).setHeader(headers).execute[ResponseType]

If you were previously creating multiple HttpClients to configure proxies or change the user-agent, this will no-longer be necessary since these can all be controlled with the HttpClientV2 API per call.

Header manipulation

The HeaderCarrier should largely be treated as an immutable representation of the caller. If you need to manipulate the headers being sent in requests, you can do this with the HttpClientV2 API.

For example to override the default User-Agent or the Authorization header defined in the HeaderCarrier, you can use setHeader which will replace any existing ones.

httpClientV2.get(url"$url")
  .setHeader("User-Agent" -> userAgent)
  .setHeader("Authorization" -> authorization)
  .execute[ResponseType]

If you want to append to default headers, then you can access addHttpHeaders on the underlying WSClient with transform. e.g.

httpClientV2.get(url"$url")
  .transform(_.addHttpHeaders("User-Agent" -> userAgent))
  .execute[ResponseType]

Be aware that "Content-Type" cannot be changed once set with WSRequest so if you want a different one to that defined by the implicit BodyWriter, you will need to set it before providing the body. e.g.

httpClientV2.post(url"$url")
  .setHeader("Content-Type" -> "application/xml")
  .withBody(<foo>bar</foo>)

Using proxy

With HttpClient, to use a proxy required creating a new instance of HttpClient to mix in WSProxy and configure. With HttpClientV2 this can be done with the same client, calling withProxy per call. e.g.

httpClientV2.get(url"$url").withProxy.execute[ResponseType]
  • It uses WSProxyConfiguration.buildWsProxyServer which is enabled with http-verbs.proxy.enabled in configuration. It is disabled by default, which is appropriate for local development and tests, but will need enabling when deployed (if not already enabled by environmental configuration).

Streaming

Streaming is supported with HttpClientV2, and will be audited in the same way as non-streamed calls. Note that payloads will be truncated in audit logs if they exceed the max supported (as configured by http-verbs.auditing.maxBodyLength).

Streamed requests can simply be passed to withBody:

val reqStream: Source[ByteString, _] = ???
httpClientV2.post(url"$url").withBody(reqStream).execute[ResponseType]

For streamed responses, use stream rather than execute:

httpClientV2.get(url"$url").stream[Source[ByteString, _]]

Auditing

HttpClientV2 truncates payloads for audit logs if they exceed the max supported (as configured by http-verbs.auditing.maxBodyLength).

This means audits that were rejected for being too large with HttpClient will probably be accepted with HttpClientV2.

⚠️ Please check any potential impact this may have on auditing behaviour.

URL interpolator

A URL interpolator has been provided to help with escaping query and path parameters correctly.

import uk.gov.hmrc.http.StringContextOps

url"http://localhost:8080/users/${user.id}?email=${user.email}"

Headers

Creating HeaderCarrier

The HeaderCarrier should be created with HeaderCarrierConverter when a request is available, this will ensure that the appropriate headers are forwarded to internal hosts.

E.g. for backends:

HeaderCarrierConverter.fromRequest(request)

and for frontends:

HeaderCarrierConverter.fromRequestAndSession(request, request.session)

If a frontend endpoint is servicing an API call, it should probably use fromRequest since fromRequestAndSession will only look for an Authorization token in the session, and ignore any provided as a request header.

For asynchronous calls, where no request is available, a new HeaderCarrier can be created with default params:

HeaderCarrier()

Propagation of headers

Headers are forwarded differently to hosts depending on whether they are internal or external. This distinction is made by the internalServiceHostPatterns configuration.

External hosts

For external hosts, only the User-Agent header is sent. Any other headers should be provided explicitly to the VERB function (get, post etc).

httpClientV2
  .get(url"https://externalhost/api")(hc)
  .setHeader("Authorization" -> "Bearer token") // explicit Authorization header for external request
Internal hosts

In addition to the User agent, all headers that are modelled explicitly in the HeaderCarrier are forwarded to internal hosts. It will also forward any other headers in the HeaderCarrier if listed in the bootstrap.http.headersAllowlist configuration.

You can replace any of these implicitly forwarded headers or add any others by providing them to the setHeader function.

Note, for the original HttpClient, headers provided to the VERB function are sent in addition to those in the HeaderCarrier, so if you want to replace one, you will have to manipulate the HeaderCarrier e.g.:

client.GET("https://internalhost/api")(hc.copy(authorization = Some(Authorization("Basic 1234"))))

Deserialising Response

The Response is deserialised by an instance of HttpReads.

You can either create your own instances or use the provided instances with

import uk.gov.hmrc.http.HttpReads.Implicits._

The default implicits (without explicit import) have been deprecated. See here for more details.

The HttpReads describes how to convert a HttpResponse into your model using the status code and response body.

The provided instances, brought into scope with the above import, allow you to:

  • Request raw HttpResponse: 
    client.GET[HttpResponse](url)
  • Convert the response body from Json using a play json reads: 
    implicit val reads: Reads[MyModel] = ???
client.get[MyModel](url)
    Note this instance will return failed Futures with UpstreamErrorResponse for non-success status codes. Json parsing failures will similarly be returned as JsValidationException These exceptions can be recovered from if required.
  • Handle 404s with None 
    implict val reads: Reads[MyModel] = ???
client.get[Option[MyModel]](url)
  • Return non-success status codes as UpstreamErrorResponse in Either 
    implict val reads: Reads[MyModel] = ???
client.get[Either[UpstreamErrorResponse, MyModel]](url)

Testing

In your SBT build add the following in your test dependencies:

libraryDependencies += "uk.gov.hmrc" %% "http-verbs-test-play-xx" % "x.x.x" % Test

We recommend that Wiremock is used for testing http-verbs code, with extensive assertions on the URL, Headers, and Body fields for both requests and responses. This will test most things, doesn't involve "mocking what you don't own", and ensures that changes to this library will be caught. I.e. that the result of using this library is what was intended, not just if the library was invoked as expected.

The WireMockSupport trait helps set up WireMock for your tests. It provides wireMockHost, wireMockPort and wireMockUrl which can be used to configure your client appropriately.

e.g. with an application:

class MyConnectorSpec extends WireMockSupport with GuiceOneAppPerSuite {
  override def fakeApplication(): Application =
    new GuiceApplicationBuilder()
      .configure(
        "connector.host" -> wireMockHost,
        "connector.port" -> wireMockPort
      ).build()

  private val connector = app.injector.instanceOf[MyConnector]
}

The HttpClientV2Support trait can provide an instance of HttpClientV2 as an alternative to instanciating the application:

class MyConnectorSpec extends WireMockSupport with HttpClientV2Support {
  private val connector = new MyConnector(
      httpClientV2,
      Configuration("connector.url" -> wireMockUrl)
  )
}

The ExternalWireMockSupport trait is an alternative to WireMockSupport which uses 127.0.0.1 instead of localhost for the hostname which is treated as an external host for header forwarding rules. This should be used for tests of connectors which call endpoints external to the platform. The variable externalWireMockHost (or externalWireMockUrl) should be used to provide the hostname in configuration.

Both WireMockSupport and ExternalWireMockSupport can be used together for integration tests if required.

The ResponseMatchers trait provides some useful helpers for testing responses.

License

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