Add Header Enricher function

function/header-enricher-function/src/main/java/org/springframework/cloud/fn/header/enricher/HeaderEnricherFunctionConfiguration.java

@@ -0,0 +1,72 @@
+/*
+ * Copyright 2020-2020 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.cloud.fn.header.enricher;
+
+import java.util.Enumeration;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Properties;
+import java.util.function.Function;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.beans.factory.config.ConfigurableBeanFactory;
+import org.springframework.boot.context.properties.EnableConfigurationProperties;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.context.annotation.Scope;
+import org.springframework.integration.transformer.HeaderEnricher;
+import org.springframework.integration.transformer.support.ExpressionEvaluatingHeaderValueMessageProcessor;
+import org.springframework.messaging.Message;
+
+/**
+ * @author Gary Russell
+ * @author Christian Tzolov
+ * @author Soby Chacko
+ */
+@Configuration
+@EnableConfigurationProperties(HeaderEnricherFunctionProperties.class)
+public class HeaderEnricherFunctionConfiguration {
+
+	@Autowired
+	private HeaderEnricherFunctionProperties properties;
+
+	@Bean
+	public Function<Message<?>, Message<?>> headerEnricherFunction() {
+		return headerEnricher()::transform;
+	}
+
+	@Bean
+	public HeaderEnricher headerEnricher() {
+		Map<String, ExpressionEvaluatingHeaderValueMessageProcessor<?>> headersToAdd = new HashMap<>();
+		Properties props = this.properties.getHeaders();
+		Enumeration<?> enumeration = props.propertyNames();
+		while (enumeration.hasMoreElements()) {
+			String propertyName = (String) enumeration.nextElement();
+			headersToAdd.put(propertyName, processor(props.getProperty(propertyName)));
+		}
+		HeaderEnricher headerEnricher = new HeaderEnricher(headersToAdd);
+		headerEnricher.setDefaultOverwrite(this.properties.isOverwrite());
+		return headerEnricher;
+	}
+
+	@Bean
+	@Scope(ConfigurableBeanFactory.SCOPE_PROTOTYPE) // Need a new processor for each header
+	public ExpressionEvaluatingHeaderValueMessageProcessor<?> processor(String expression) {
+		return new ExpressionEvaluatingHeaderValueMessageProcessor<>(expression, null);
+	}
+
+}

function/header-enricher-function/src/main/java/org/springframework/cloud/fn/header/enricher/HeaderEnricherFunctionProperties.java

@@ -0,0 +1,66 @@
+/*
+ * Copyright 2020-2020 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.cloud.fn.header.enricher;
+
+
+import java.util.Properties;
+
+import javax.validation.constraints.NotNull;
+
+import org.springframework.boot.context.properties.ConfigurationProperties;
+import org.springframework.validation.annotation.Validated;
+
+/**
+ * Configuration properties for the Header Enricher Processor application.
+ *
+ * @author Gary Russell
+ * @author Artem Bilan
+ * @author Soby Chacko
+ */
+@ConfigurationProperties("header.enricher")
+@Validated
+public class HeaderEnricherFunctionProperties {
+
+	/**
+	 * \n separated properties representing headers in which values are SpEL expressions,
+	 * e.g foo='bar' \n baz=payload.baz.
+	 */
+	private Properties headers;
+
+	/**
+	 *  set to true to overwrite any existing message headers.
+	 */
+	private boolean overwrite = false;
+
+	@NotNull
+	public Properties getHeaders() {
+		return this.headers;
+	}
+
+	public void setHeaders(Properties headers) {
+		this.headers = headers;
+	}
+
+	public boolean isOverwrite() {
+		return this.overwrite;
+	}
+
+	public void setOverwrite(boolean overwrite) {
+		this.overwrite = overwrite;
+	}
+
+}