10. Using the Pluggable Architecture

The ContractConverter interface lets you register your own implementation of a contract structure converter. The following code listing shows the ContractConverter interface:

package org.springframework.cloud.contract.spec

/**
 * Converter to be used to convert FROM {@link File} TO {@link Contract}
 * and from {@link Contract} to {@code T}
 *
 * @param <T> - type to which we want to convert the contract
 *
 * @author Marcin Grzejszczak
 * @since 1.1.0
 */
interface ContractConverter<T> {

	/**
	 * Should this file be accepted by the converter. Can use the file extension
	 * to check if the conversion is possible.
	 *
	 * @param file - file to be considered for conversion
	 * @return - {@code true} if the given implementation can convert the file
	 */
	boolean isAccepted(File file)

	/**
	 * Converts the given {@link File} to its {@link Contract} representation
	 *
	 * @param file - file to convert
	 * @return - {@link Contract} representation of the file
	 */
	Collection<Contract> convertFrom(File file)

	/**
	 * Converts the given {@link Contract} to a {@link T} representation
	 *
	 * @param contract - the parsed contract
	 * @return - {@link T} the type to which we do the conversion
	 */
	T convertTo(Collection<Contract> contract)
}

Your implementation must define the condition on which it should start the conversion. Also, you must define how to perform that conversion in both directions.

	Important
	Once you create your implementation, you must create a /META-INF/spring.factories file in which you provide the fully qualified name of your implementation.

The following example shows a typical spring.factories file:

org.springframework.cloud.contract.spec.ContractConverter=\
org.springframework.cloud.contract.verifier.converter.YamlContractConverter

{
  "provider": {
    "name": "Provider"
  },
  "consumer": {
    "name": "Consumer"
  },
  "interactions": [
    {
      "description": "",
      "request": {
        "method": "PUT",
        "path": "/fraudcheck",
        "headers": {
          "Content-Type": "application/vnd.fraud.v1+json"
        },
        "body": {
          "clientId": "1234567890",
          "loanAmount": 99999
        },
        "generators": {
          "body": {
            "$.clientId": {
              "type": "Regex",
              "regex": "[0-9]{10}"
            }
          }
        },
        "matchingRules": {
          "header": {
            "Content-Type": {
              "matchers": [
                {
                  "match": "regex",
                  "regex": "application/vnd\\.fraud\\.v1\\+json.*"
                }
              ],
              "combine": "AND"
            }
          },
          "body" : {
            "$.clientId": {
              "matchers": [
                {
                  "match": "regex",
                  "regex": "[0-9]{10}"
                }
              ],
              "combine": "AND"
            }
          }
        }
      },
      "response": {
        "status": 200,
        "headers": {
          "Content-Type": "application/vnd.fraud.v1+json;charset=UTF-8"
        },
        "body": {
          "fraudCheckStatus": "FRAUD",
          "rejectionReason": "Amount too high"
        },
        "matchingRules": {
          "header": {
            "Content-Type": {
              "matchers": [
                {
                  "match": "regex",
                  "regex": "application/vnd\\.fraud\\.v1\\+json.*"
                }
              ],
              "combine": "AND"
            }
          },
          "body": {
            "$.fraudCheckStatus": {
              "matchers": [
                {
                  "match": "regex",
                  "regex": "FRAUD"
                }
              ],
              "combine": "AND"
            }
          }
        }
      }
    }
  ],
  "metadata": {
    "pact-specification": {
      "version": "3.0.0"
    },
    "pact-jvm": {
      "version": "3.5.13"
    }
  }
}

<plugin>
	<groupId>org.springframework.cloud</groupId>
	<artifactId>spring-cloud-contract-maven-plugin</artifactId>
	<version>${spring-cloud-contract.version}</version>
	<extensions>true</extensions>
	<configuration>
		<packageWithBaseClasses>com.example.fraud</packageWithBaseClasses>
	</configuration>
	<dependencies>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-contract-pact</artifactId>
			<version>${spring-cloud-contract.version}</version>
		</dependency>
	</dependencies>
</plugin>

classpath "org.springframework.cloud:spring-cloud-contract-pact:${findProperty('verifierVersion') ?: verifierVersion}"

@Test
public void validate_shouldMarkClientAsFraud() throws Exception {
	// given:
		MockMvcRequestSpecification request = given()
				.header("Content-Type", "application/vnd.fraud.v1+json")
				.body("{\"clientId\":\"1234567890\",\"loanAmount\":99999}");

	// when:
		ResponseOptions response = given().spec(request)
				.put("/fraudcheck");

	// then:
		assertThat(response.statusCode()).isEqualTo(200);
		assertThat(response.header("Content-Type")).matches("application/vnd\\.fraud\\.v1\\+json.*");
	// and:
		DocumentContext parsedJson = JsonPath.parse(response.getBody().asString());
		assertThatJson(parsedJson).field("['rejectionReason']").isEqualTo("Amount too high");
	// and:
		assertThat(parsedJson.read("$.fraudCheckStatus", String.class)).matches("FRAUD");
}

{
  "id" : "996ae5ae-6834-4db6-8fac-358ca187ab62",
  "uuid" : "996ae5ae-6834-4db6-8fac-358ca187ab62",
  "request" : {
    "url" : "/fraudcheck",
    "method" : "PUT",
    "headers" : {
      "Content-Type" : {
        "matches" : "application/vnd\\.fraud\\.v1\\+json.*"
      }
    },
    "bodyPatterns" : [ {
      "matchesJsonPath" : "$[?(@.['loanAmount'] == 99999)]"
    }, {
      "matchesJsonPath" : "$[?(@.clientId =~ /([0-9]{10})/)]"
    } ]
  },
  "response" : {
    "status" : 200,
    "body" : "{\"fraudCheckStatus\":\"FRAUD\",\"rejectionReason\":\"Amount too high\"}",
    "headers" : {
      "Content-Type" : "application/vnd.fraud.v1+json;charset=UTF-8"
    },
    "transformers" : [ "response-template" ]
  },
}

<dependency>
	<groupId>org.springframework.cloud</groupId>
	<artifactId>spring-cloud-contract-pact</artifactId>
	<scope>test</scope>
</dependency>

testCompile "org.springframework.cloud:spring-cloud-contract-pact"

If you want to generate tests for languages other than Java or you are not happy with the way the verifier builds Java tests, you can register your own implementation.

The SingleTestGenerator interface lets you register your own implementation. The following code listing shows the SingleTestGenerator interface:

package org.springframework.cloud.contract.verifier.builder

import org.springframework.cloud.contract.verifier.config.ContractVerifierConfigProperties
import org.springframework.cloud.contract.verifier.file.ContractMetadata
/**
 * Builds a single test.
 *
 * @since 1.1.0
 */
interface SingleTestGenerator {

	/**
	 * Creates contents of a single test class in which all test scenarios from
	 * the contract metadata should be placed.
	 *
	 * @param properties - properties passed to the plugin
	 * @param listOfFiles - list of parsed contracts with additional metadata
	 * @param className - the name of the generated test class
	 * @param classPackage - the name of the package in which the test class should be stored
	 * @param includedDirectoryRelativePath - relative path to the included directory
	 * @return contents of a single test class
	 */
	String buildClass(ContractVerifierConfigProperties properties, Collection<ContractMetadata> listOfFiles,
					  String className, String classPackage, String includedDirectoryRelativePath)

	/**
	 * Extension that should be appended to the generated test class. E.g. {@code .java} or {@code .php}
	 *
	 * @param properties - properties passed to the plugin
	 */
	String fileExtension(ContractVerifierConfigProperties properties)
}

Again, you must provide a spring.factories file, such as the one shown in the following example:

org.springframework.cloud.contract.verifier.builder.SingleTestGenerator=/
com.example.MyGenerator

If you want to generate stubs for stub servers other than WireMock, you can plug in your own implementation of the StubGenerator interface. The following code listing shows the StubGenerator interface:

package org.springframework.cloud.contract.verifier.converter

import groovy.transform.CompileStatic
import org.springframework.cloud.contract.spec.Contract
import org.springframework.cloud.contract.verifier.file.ContractMetadata

/**
 * Converts contracts into their stub representation.
 *
 * @since 1.1.0
 */
@CompileStatic
interface StubGenerator {

	/**
	 * Returns {@code true} if the converter can handle the file to convert it into a stub.
	 */
	boolean canHandleFileName(String fileName)

	/**
	 * Returns the collection of converted contracts into stubs. One contract can
	 * result in multiple stubs.
	 */
	Map<Contract, String> convertContents(String rootName, ContractMetadata content)

	/**
	 * Returns the name of the converted stub file. If you have multiple contracts
	 * in a single file then a prefix will be added to the generated file. If you
	 * provide the {@link Contract#name} field then that field will override the
	 * generated file name.
	 *
	 * Example: name of file with 2 contracts is {@code foo.groovy}, it will be
	 * converted by the implementation to {@code foo.json}. The recursive file
	 * converter will create two files {@code 0_foo.json} and {@code 1_foo.json}
	 */
	String generateOutputFileNameForInput(String inputFileName)
}

Again, you must provide a spring.factories file, such as the one shown in the following example:

# Stub converters
org.springframework.cloud.contract.verifier.converter.StubGenerator=\
org.springframework.cloud.contract.verifier.wiremock.DslToWireMockClientConverter

The default implementation is the WireMock stub generation.

	Tip
	You can provide multiple stub generator implementations. For example, from a single DSL, you can produce both WireMock stubs and Pact files.

If you decide to use a custom stub generation, you also need a custom way of running stubs with your different stub provider.

Assume that you use Moco to build your stubs and that you have written a stub generator and placed your stubs in a JAR file.

In order for Stub Runner to know how to run your stubs, you have to define a custom HTTP Stub server implementation, which might resemble the following example:

package org.springframework.cloud.contract.stubrunner.provider.moco

import com.github.dreamhead.moco.bootstrap.arg.HttpArgs
import com.github.dreamhead.moco.runner.JsonRunner
import com.github.dreamhead.moco.runner.RunnerSetting
import groovy.util.logging.Commons

import org.springframework.cloud.contract.stubrunner.HttpServerStub
import org.springframework.util.SocketUtils

@Commons
class MocoHttpServerStub implements HttpServerStub {

	private boolean started
	private JsonRunner runner
	private int port

	@Override
	int port() {
		if (!isRunning()) {
			return -1
		}
		return port
	}

	@Override
	boolean isRunning() {
		return started
	}

	@Override
	HttpServerStub start() {
		return start(SocketUtils.findAvailableTcpPort())
	}

	@Override
	HttpServerStub start(int port) {
		this.port = port
		return this
	}

	@Override
	HttpServerStub stop() {
		if (!isRunning()) {
			return this
		}
		this.runner.stop()
		return this
	}

	@Override
	HttpServerStub registerMappings(Collection<File> stubFiles) {
		List<RunnerSetting> settings = stubFiles.findAll { it.name.endsWith("json") }
				.collect {
			log.info("Trying to parse [${it.name}]")
			try {
				return RunnerSetting.aRunnerSetting().withStream(it.newInputStream()).build()
			} catch (Exception e) {
				log.warn("Exception occurred while trying to parse file [${it.name}]", e)
				return null
			}
		}.findAll { it }
		this.runner = JsonRunner.newJsonRunnerWithSetting(settings,
				HttpArgs.httpArgs().withPort(this.port).build())
		this.runner.run()
		this.started = true
		return this
	}

	@Override
	String registeredMappings() {
		return ""
	}

	@Override
	boolean isAccepted(File file) {
		return file.name.endsWith(".json")
	}
}

Then, you can register it in your spring.factories file, as shown in the following example:

org.springframework.cloud.contract.stubrunner.HttpServerStub=\
org.springframework.cloud.contract.stubrunner.provider.moco.MocoHttpServerStub

Now you can run stubs with Moco.

	Important
	If you do not provide any implementation, then the default (WireMock) implementation is used. If you provide more than one, the first one on the list is used.

You can customize the way your stubs are downloaded by creating an implementation of the StubDownloaderBuilder interface, as shown in the following example:

package com.example;

class CustomStubDownloaderBuilder implements StubDownloaderBuilder {

	@Override
	public StubDownloader build(final StubRunnerOptions stubRunnerOptions) {
		return new StubDownloader() {
			@Override
			public Map.Entry<StubConfiguration, File> downloadAndUnpackStubJar(
					StubConfiguration config) {
				File unpackedStubs = retrieveStubs();
				return new AbstractMap.SimpleEntry<>(
						new StubConfiguration(config.getGroupId(), config.getArtifactId(), version,
								config.getClassifier()), unpackedStubs);
			}

			File retrieveStubs() {
			    // here goes your custom logic to provide a folder where all the stubs reside
			}
}

Then you can register it in your spring.factories file, as shown in the following example:

# Example of a custom Stub Downloader Provider
org.springframework.cloud.contract.stubrunner.StubDownloaderBuilder=\
com.example.CustomStubDownloaderBuilder

Now you can pick a folder with the source of your stubs.

	Important
	If you do not provide any implementation, then the default is used (scan classpath). If you provide the stubsMode = StubRunnerProperties.StubsMode.LOCAL or , stubsMode = StubRunnerProperties.StubsMode.REMOTE then the Aether implementation will be used If you provide more than one, then the first one on the list is used.

Whenever the repositoryRoot starts with a SCM protocol (currently we support only git://), the stub downloader will try to clone the repository and use it as a source of contracts to generate tests or stubs.

Either via environment variables, system properties, properties set inside the plugin or contracts repository configuration you can tweak the downloader’s behaviour. Below you can find the list of properties

Whenever the repositoryRoot starts with a Pact protocol (starts with pact://), the stub downloader will try to fetch the Pact contract definitions from the Pact Broker. Whatever is set after pact:// will be parsed as the Pact Broker URL.

Either via environment variables, system properties, properties set inside the plugin or contracts repository configuration you can tweak the downloader’s behaviour. Below you can find the list of properties