Added header-filter function and processor.

functions/function/header-filter-function/README.adoc

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+= Header Enricher Function
+
+This module provides a header enricher function that can be reused and composed in other applications.
+
+== Beans for injection
+
+You can import the `HeaderEnricherFunctionConfiguration` in a Spring Boot application and then inject the following bean.
+
+`headerFilterFunction`
+
+You can use `headerFilterFunction` as a qualifier when injecting.
+
+Once injected, you can use the `apply` method of the `Function` to invoke it and get the result.
+
+== Configuration Options
+
+For more information on the various options available, please see link:src/main/java/org/springframework/cloud/fn/header/filter/HeaderFilterFunctionProperties.java[HeaderFilterFunctionProperties.java]
+
+== Tests
+
+See this link:src/test/java/org/springframework/cloud/fn/header/filter/HeaderFilterFunctionApplicationTests.java[test suite] for examples of how this function is used.
+
+== Other usage
+
+See this link:../../../applications/processor/header-filter-processor/README.adoc[README] where this function is used to create a Spring Cloud Stream application.

functions/function/header-filter-function/pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <parent>
+        <groupId>org.springframework.cloud.fn</groupId>
+        <artifactId>spring-functions-parent</artifactId>
+        <version>4.0.0-SNAPSHOT</version>
+        <relativePath>../../spring-functions-parent/pom.xml</relativePath>
+    </parent>
+
+    <artifactId>header-filter-function</artifactId>
+    <name>header-filter-function</name>
+    <description>Spring Native Function for applying message filters</description>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.springframework.cloud.fn</groupId>
+            <artifactId>payload-converter-function</artifactId>
+            <version>${project.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+</project>

functions/function/header-filter-function/src/main/java/org/springframework/cloud/fn/header/filter/HeaderFilterFunctionConfiguration.java

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+/*
+ * Copyright 2023-2023 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.filter;
+
+import java.util.HashSet;
+import java.util.function.Function;
+
+import org.springframework.boot.autoconfigure.AutoConfiguration;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnExpression;
+import org.springframework.boot.context.properties.EnableConfigurationProperties;
+import org.springframework.context.annotation.Bean;
+import org.springframework.integration.IntegrationMessageHeaderAccessor;
+import org.springframework.integration.transformer.HeaderFilter;
+import org.springframework.messaging.Message;
+import org.springframework.util.StringUtils;
+
+/**
+ * Configure a function using {@link HeaderFilter}.
+ *
+ * @author Corneil du Plessis
+ */
+@AutoConfiguration
+@EnableConfigurationProperties(HeaderFilterFunctionProperties.class)
+@ConditionalOnExpression("'${header.filter.remove}'!='' or '${header.filter.delete-all}' != ''")
+public class HeaderFilterFunctionConfiguration {
+	private final HeaderFilterFunctionProperties properties;
+	public HeaderFilterFunctionConfiguration(HeaderFilterFunctionProperties properties) {
+		this.properties = properties;
+	}
+
+	@Bean
+	public Function<Message<?>, Message<?>> headerFilterFunction() {
+		if (properties.isDeleteAll()) {
+			return (message) -> {
+				var  accessor = new IntegrationMessageHeaderAccessor(message);
+				var headers = new HashSet<>(message.getHeaders().keySet());
+				headers.removeIf(accessor::isReadOnly);
+				HeaderFilter filter = new HeaderFilter(headers.toArray(new String[0]));
+				return filter.transform(message);
+			};
+		}
+		else {
+			return headerFilter()::transform;
+		}
+	}
+
+	@Bean
+	public HeaderFilter headerFilter() {
+		if (properties.getRemove() != null) {
+			String[] remove = StringUtils.tokenizeToStringArray(properties.getRemove(), ", ", true, true);
+			HeaderFilter filter = new HeaderFilter(remove);
+			if (properties.getRemove().contains("*")) {
+				filter.setPatternMatch(true);
+			}
+			return filter;
+		}
+		else {
+			return new HeaderFilter("");
+		}
+	}
+
+}

functions/function/header-filter-function/src/main/java/org/springframework/cloud/fn/header/filter/HeaderFilterFunctionProperties.java

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+/*
+ * Copyright 2023-2023 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.filter;
+
+import org.springframework.boot.context.properties.ConfigurationProperties;
+
+/**
+ * Properties for configuration of header-filter-function.
+ * @author Corneil du Plessis
+ */
+@ConfigurationProperties("header.filter")
+public class HeaderFilterFunctionProperties {
+	/**
+	 * Indicates the need to remove all headers.
+	 */
+	private boolean deleteAll = false;
+
+	/**
+	 * Remove all headers named. A comma, space separated list of header names.
+	 * The names may contain patterns.
+	 */
+	private String remove;
+
+	public boolean isDeleteAll() {
+		return deleteAll;
+	}
+
+	public void setDeleteAll(boolean deleteAll) {
+		this.deleteAll = deleteAll;
+	}
+
+	public String getRemove() {
+		return remove;
+	}
+
+	public void setRemove(String remove) {
+		this.remove = remove;
+	}
+}

functions/function/header-filter-function/src/test/java/org/springframework/cloud/fn/header/filter/HeaderFilterFunctionApplicationDeleteAllTests.java

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+/*
+ * Copyright 2023-2023 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.filter;
+
+import java.util.Set;
+import java.util.function.Function;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.messaging.Message;
+import org.springframework.messaging.support.MessageBuilder;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+@SpringBootTest(classes = {
+	HeaderFilterFunctionApplicationDeleteAllTests.HeaderFilterFunctionTestApplication.class,
+	HeaderFilterFunctionConfiguration.class
+},
+	properties = {"header.filter.delete-all=true"}
+)
+public class HeaderFilterFunctionApplicationDeleteAllTests {
+	@Autowired
+	protected Function<Message<?>, Message<?>> headerFilter;
+
+	@Test
+	public void testRemoveLeavesIdTimestampAll() {
+		// given
+		final Message<?> message = MessageBuilder.withPayload("hello")
+			.setHeader("foo", "bar")
+			.setHeader("bar", "foo")
+			.build();
+		Message<?> result = headerFilter.apply(message);
+		var headers = result.getHeaders().keySet();
+		assertThat(headers).isEqualTo(Set.of("id", "timestamp"));
+	}
+
+	@SpringBootApplication
+	static class HeaderFilterFunctionTestApplication {
+		public static void main(String[] args) throws Exception {
+			SpringApplication.main(args);
+		}
+	}
+
+}

functions/function/header-filter-function/src/test/java/org/springframework/cloud/fn/header/filter/HeaderFilterFunctionApplicationTests.java

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+/*
+ * Copyright 2023-2023 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.filter;
+
+import java.util.Set;
+import java.util.function.Function;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.messaging.Message;
+import org.springframework.messaging.support.MessageBuilder;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+@SpringBootTest(classes = {
+	HeaderFilterFunctionApplicationTests.HeaderFilterFunctionTestApplication.class,
+	HeaderFilterFunctionConfiguration.class
+},
+	properties = {"header.filter.remove=foo,bar,pf-*"}
+)
+public class HeaderFilterFunctionApplicationTests {
+	@Autowired
+	protected Function<Message<?>, Message<?>> headerFilter;
+
+	@Test
+	public void testRemoveAll() {
+		// given
+		final Message<?> message = MessageBuilder.withPayload("hello")
+			.setHeader("foo", "bar")
+			.setHeader("bar", "foo")
+			.build();
+		Message<?> result = headerFilter.apply(message);
+		var headers = HeaderUtils.getNonReadOnlyHeaders(result);
+		assertThat(headers).isEmpty();
+	}
+
+	@Test
+	public void testRemoveSome() {
+		// given
+		final Message<?> message = MessageBuilder.withPayload("hello")
+			.setHeader("foo", "bar")
+			.setHeader("foo-bar", "bar")
+			.setHeader("bar", "foo")
+			.build();
+		Message<?> result = headerFilter.apply(message);
+		var headers = HeaderUtils.getNonReadOnlyHeaders(result);
+		assertThat(headers).isEqualTo(Set.of("foo-bar"));
+	}
+
+	@Test
+	public void testRemoveSomeWithWildcard() {
+		// given
+		final Message<?> message = MessageBuilder.withPayload("hello")
+			.setHeader("foo", "bar")
+			.setHeader("pf-foo", "bar")
+			.setHeader("pf-bar", "bar")
+			.setHeader("pfBar", "bar")
+			.setHeader("bar", "foo")
+			.build();
+		Message<?> result = headerFilter.apply(message);
+		var headers = HeaderUtils.getNonReadOnlyHeaders(result);
+		assertThat(result.getHeaders().keySet()).isEqualTo(Set.of("pfBar"));
+	}
+
+	@Test
+	public void testRemoveLeavesIdTimestampAll() {
+		// given
+		final Message<?> message = MessageBuilder.withPayload("hello")
+			.setHeader("foo", "bar")
+			.setHeader("bar", "foo")
+			.build();
+		Message<?> result = headerFilter.apply(message);
+
+		assertThat(result.getHeaders().keySet()).isEqualTo(Set.of("id", "timestamp"));
+	}
+
+	@SpringBootApplication
+	static class HeaderFilterFunctionTestApplication {
+		public static void main(String[] main) {
+
+		}
+	}
+
+}

functions/function/header-filter-function/src/test/java/org/springframework/cloud/fn/header/filter/HeaderUtils.java

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+/*
+ * Copyright 2023-2023 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.filter;
+
+import java.util.HashSet;
+import java.util.Set;
+
+import org.jetbrains.annotations.NotNull;
+
+import org.springframework.integration.IntegrationMessageHeaderAccessor;
+import org.springframework.messaging.Message;
+
+final public class HeaderUtils {
+	private HeaderUtils() {
+	}
+
+	@NotNull
+	public static Set<String> getNonReadOnlyHeaders(Message<?> message) {
+		var headers = new HashSet<>(message.getHeaders().keySet());
+		var accessor = new IntegrationMessageHeaderAccessor(message);
+		headers.removeIf(accessor::isReadOnly);
+		return headers;
+	}
+}

functions/function/header-filter-function/src/test/resources/test.properties

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+logging.level.root=debug