GH-3: Add tail support for spring-file-supplier (#42)

This commit adds `tail` support to the `spring-file-supplier`.

Additionally, move `FileMessageSource` specific beans into separate inner 
`FileMessageSourceConfiguration` class for easier conditional config 

Fixes: #3

supplier/spring-file-supplier/README.adoc

@@ -1,12 +1,16 @@
-# File Supplier
+= File Supplier
 
 This module provides a File supplier that can be reused and composed in other applications.
 The `Supplier` uses the `FileInboundChannelAdapter` from Spring Integration.
 `FileSupplier` is implemented as a `java.util.function.Supplier`.
 This supplier gives you a reactive stream of files from the provided directory as the supplier has a signature of `Supplier<Flux<Message<?>>>`.
 Users have to subscribe to this `Flux` and receive the data.
 
-## Beans for injection
+This module also can be configured for file tailing functionality.
+The implementation and logic is fully based on respective Spring Integration https://docs.spring.io/spring-integration/reference/file/reading.html#file-tailing[Tailing Message Producer].
+The `Supplier<Flux<Message<?>>>` emits messages for each tailed line from the file.
+
+== Beans for injection
 
 The `FileSupplierConfiguration` auto-configuration provides the following bean:
 
@@ -18,7 +22,7 @@ You can use `fileSupplier` as a qualifier when injecting.
 
 Once injected, you can use the `get` method of the `Supplier` to invoke it and then subscribe to the returned `Flux`.
 
-## Configuration Options
+== Configuration Options
 
 All configuration properties are prefixed with `file.supplier`.
 There are also properties that need to be used with the prefix `file.consumer`.
@@ -28,10 +32,14 @@ See `FileConsumerProperties` also.
 
 A `ComponentCustomizer<FileInboundChannelAdapterSpec>` bean can be added in the target project to provide any custom options for the `FileInboundChannelAdapterSpec` configuration used by the `fileSupplier`.
 
-## Tests
+If `file.supplier.tail` option is provided, this supplier works in a tailing file mode.
+See `FileSupplierProperties.Tailer` container for more information.
+In `tail` mode, all other options for directory polling are ignored.
+
+== Tests
 
 See this link:src/test/java/org/springframework/cloud/fn/supplier/file[test suite] for the various ways, this supplier is used.
 
-## Other usage
+== Other usage
 
 See this https://github.com/spring-cloud/stream-applications/blob/master/applications/source/file-source/README.adoc[README] where this supplier is used to create a Spring Cloud Stream application where it makes a File Source.

supplier/spring-file-supplier/src/main/java/org/springframework/cloud/fn/supplier/file/FileSupplierConfiguration.java

@@ -26,17 +26,21 @@
 import org.springframework.beans.factory.BeanInitializationException;
 import org.springframework.boot.autoconfigure.AutoConfiguration;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnExpression;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
 import org.springframework.boot.context.properties.EnableConfigurationProperties;
 import org.springframework.cloud.fn.common.config.ComponentCustomizer;
 import org.springframework.cloud.fn.common.file.FileConsumerProperties;
 import org.springframework.cloud.fn.common.file.FileReadingMode;
 import org.springframework.cloud.fn.common.file.FileUtils;
 import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.integration.JavaUtils;
 import org.springframework.integration.dsl.IntegrationFlow;
 import org.springframework.integration.dsl.IntegrationFlowBuilder;
 import org.springframework.integration.file.FileReadingMessageSource;
 import org.springframework.integration.file.dsl.FileInboundChannelAdapterSpec;
 import org.springframework.integration.file.dsl.Files;
+import org.springframework.integration.file.dsl.TailAdapterSpec;
 import org.springframework.integration.file.filters.ChainFileListFilter;
 import org.springframework.integration.file.filters.FileListFilter;
 import org.springframework.integration.file.filters.FileSystemPersistentAcceptOnceFileListFilter;
@@ -58,78 +62,113 @@
 @EnableConfigurationProperties({ FileSupplierProperties.class, FileConsumerProperties.class })
 public class FileSupplierConfiguration {
 
-	private static final String METADATA_STORE_PREFIX = "local-file-system-metadata-";
-
-	private final FileSupplierProperties fileSupplierProperties;
-
-	private final FileConsumerProperties fileConsumerProperties;
-
-	public FileSupplierConfiguration(FileSupplierProperties fileSupplierProperties,
-			FileConsumerProperties fileConsumerProperties) {
-
-		this.fileSupplierProperties = fileSupplierProperties;
-		this.fileConsumerProperties = fileConsumerProperties;
+	@Bean
+	@ConditionalOnProperty(prefix = "file.supplier", name = "tail")
+	public Publisher<Message<String>> fileTailingFlow(FileSupplierProperties fileSupplierProperties) {
+		FileSupplierProperties.Tailer tail = fileSupplierProperties.getTailer();
+		TailAdapterSpec tailAdapterSpec = Files.tailAdapter(fileSupplierProperties.getTail())
+			// TODO until Spring Integration 6.2.3
+			.autoStartup(false)
+			.fileDelay(tail.getAttemptsDelay().toMillis())
+			// OS native tail command
+			.nativeOptions(tail.getNativeOptions())
+			.enableStatusReader(tail.isStatusReader());
+
+		JavaUtils.INSTANCE
+			.acceptIfNotNull(tail.getIdleEventInterval(),
+					(duration) -> tailAdapterSpec.idleEventInterval(duration.toMillis()))
+			// Apache Commons Tailer
+			.acceptIfNotNull(tail.isEnd(), tailAdapterSpec::end)
+			.acceptIfNotNull(tail.isReopen(), tailAdapterSpec::reopen)
+			.acceptIfNotNull(tail.getPollingDelay(), (duration) -> tailAdapterSpec.delay(duration.toMillis()));
+
+		return IntegrationFlow.from(tailAdapterSpec).toReactivePublisher(true);
 	}
 
 	@Bean
-	public ChainFileListFilter<File> filter(ConcurrentMetadataStore metadataStore) {
-		ChainFileListFilter<File> chainFilter = new ChainFileListFilter<>();
-		if (StringUtils.hasText(this.fileSupplierProperties.getFilenamePattern())) {
-			chainFilter.addFilter(new SimplePatternFileListFilter(this.fileSupplierProperties.getFilenamePattern()));
+	public Supplier<Flux<Message<?>>> fileSupplier(FileConsumerProperties fileConsumerProperties,
+			@Nullable Flux<Message<?>> fileMessageFlux, @Nullable Publisher<Message<Object>> fileReadingFlow,
+			@Nullable Publisher<Message<String>> fileTailingFlow) {
+
+		if (fileConsumerProperties.getMode() == FileReadingMode.ref) {
+			return () -> fileMessageFlux;
 		}
-		else if (this.fileSupplierProperties.getFilenameRegex() != null) {
-			chainFilter.addFilter(new RegexPatternFileListFilter(this.fileSupplierProperties.getFilenameRegex()));
+		else if (fileReadingFlow != null) {
+			return () -> Flux.from(fileReadingFlow);
 		}
-
-		if (this.fileSupplierProperties.isPreventDuplicates()) {
-			chainFilter
-				.addFilter(new FileSystemPersistentAcceptOnceFileListFilter(metadataStore, METADATA_STORE_PREFIX));
+		else if (fileTailingFlow != null) {
+			return () -> Flux.from(fileTailingFlow);
+		}
+		else {
+			throw new BeanInitializationException("Cannot creat 'fileSupplier' bean: no 'fileReadingFlow', "
+					+ "or 'fileTailingFlow' dependency, and is not 'FileReadingMode.ref'.");
 		}
-
-		return chainFilter;
 	}
 
-	@Bean
-	public FileInboundChannelAdapterSpec fileMessageSource(FileListFilter<File> fileListFilter,
-			@Nullable ComponentCustomizer<FileInboundChannelAdapterSpec> fileInboundChannelAdapterSpecCustomizer) {
+	@Configuration(proxyBeanMethods = false)
+	@ConditionalOnExpression("environment['file.supplier.tail'] == null")
+	protected static class FileMessageSourceConfiguration {
 
-		FileInboundChannelAdapterSpec adapterSpec = Files.inboundAdapter(this.fileSupplierProperties.getDirectory())
-			.filter(fileListFilter);
-		if (fileInboundChannelAdapterSpecCustomizer != null) {
-			fileInboundChannelAdapterSpecCustomizer.customize(adapterSpec);
-		}
-		return adapterSpec;
-	}
+		private static final String METADATA_STORE_PREFIX = "local-file-system-metadata-";
 
-	@Bean
-	public Flux<Message<File>> fileMessageFlux(FileReadingMessageSource fileReadingMessageSource) {
-		return IntegrationReactiveUtils.messageSourceToFlux(fileReadingMessageSource)
-			.contextWrite(Context.of(IntegrationReactiveUtils.DELAY_WHEN_EMPTY_KEY,
-					this.fileSupplierProperties.getDelayWhenEmpty()))
-			.doOnRequest((r) -> fileReadingMessageSource.start());
-	}
+		private final FileSupplierProperties fileSupplierProperties;
 
-	@Bean
-	@ConditionalOnExpression("environment['file.consumer.mode'] != 'ref'")
-	public Publisher<Message<Object>> fileReadingFlow(Flux<Message<?>> fileMessageFlux) {
-		IntegrationFlowBuilder flowBuilder = IntegrationFlow.from(fileMessageFlux);
-		return FileUtils.enhanceFlowForReadingMode(flowBuilder, this.fileConsumerProperties).toReactivePublisher(true);
-	}
+		private final FileConsumerProperties fileConsumerProperties;
 
-	@Bean
-	public Supplier<Flux<Message<?>>> fileSupplier(Flux<Message<?>> fileMessageFlux,
-			@Nullable Publisher<Message<Object>> fileReadingFlow) {
+		FileMessageSourceConfiguration(FileSupplierProperties fileSupplierProperties,
+				FileConsumerProperties fileConsumerProperties) {
 
-		if (this.fileConsumerProperties.getMode() == FileReadingMode.ref) {
-			return () -> fileMessageFlux;
+			this.fileSupplierProperties = fileSupplierProperties;
+			this.fileConsumerProperties = fileConsumerProperties;
 		}
-		else if (fileReadingFlow != null) {
-			return () -> Flux.from(fileReadingFlow);
+
+		@Bean
+		public ChainFileListFilter<File> filter(ConcurrentMetadataStore metadataStore) {
+			ChainFileListFilter<File> chainFilter = new ChainFileListFilter<>();
+			if (StringUtils.hasText(this.fileSupplierProperties.getFilenamePattern())) {
+				chainFilter
+					.addFilter(new SimplePatternFileListFilter(this.fileSupplierProperties.getFilenamePattern()));
+			}
+			else if (this.fileSupplierProperties.getFilenameRegex() != null) {
+				chainFilter.addFilter(new RegexPatternFileListFilter(this.fileSupplierProperties.getFilenameRegex()));
+			}
+
+			if (this.fileSupplierProperties.isPreventDuplicates()) {
+				chainFilter
+					.addFilter(new FileSystemPersistentAcceptOnceFileListFilter(metadataStore, METADATA_STORE_PREFIX));
+			}
+
+			return chainFilter;
 		}
-		else {
-			throw new BeanInitializationException(
-					"Cannot creat 'fileSupplier' bean: no 'fileReadingFlow' dependency and is not 'FileReadingMode.ref'.");
+
+		@Bean
+		public FileInboundChannelAdapterSpec fileMessageSource(FileListFilter<File> fileListFilter,
+				@Nullable ComponentCustomizer<FileInboundChannelAdapterSpec> fileInboundChannelAdapterSpecCustomizer) {
+
+			FileInboundChannelAdapterSpec adapterSpec = Files.inboundAdapter(this.fileSupplierProperties.getDirectory())
+				.filter(fileListFilter);
+			if (fileInboundChannelAdapterSpecCustomizer != null) {
+				fileInboundChannelAdapterSpecCustomizer.customize(adapterSpec);
+			}
+			return adapterSpec;
+		}
+
+		@Bean
+		public Flux<Message<File>> fileMessageFlux(FileReadingMessageSource fileReadingMessageSource) {
+			return IntegrationReactiveUtils.messageSourceToFlux(fileReadingMessageSource)
+				.contextWrite(Context.of(IntegrationReactiveUtils.DELAY_WHEN_EMPTY_KEY,
+						this.fileSupplierProperties.getDelayWhenEmpty()))
+				.doOnRequest((r) -> fileReadingMessageSource.start());
+		}
+
+		@Bean
+		@ConditionalOnExpression("environment['file.consumer.mode'] != 'ref'")
+		public Publisher<Message<Object>> fileReadingFlow(Flux<Message<?>> fileMessageFlux) {
+			IntegrationFlowBuilder flowBuilder = IntegrationFlow.from(fileMessageFlux);
+			return FileUtils.enhanceFlowForReadingMode(flowBuilder, this.fileConsumerProperties)
+				.toReactivePublisher(true);
 		}
+
 	}
 
 }

supplier/spring-file-supplier/src/main/java/org/springframework/cloud/fn/supplier/file/FileSupplierProperties.java

@@ -21,6 +21,7 @@
 import java.util.regex.Pattern;
 
 import org.springframework.boot.context.properties.ConfigurationProperties;
+import org.springframework.integration.file.tail.FileTailingMessageProducerSupport;
 import org.springframework.validation.annotation.Validated;
 
 /**
@@ -41,6 +42,11 @@ public class FileSupplierProperties {
 	 */
 	private File directory = new File(DEFAULT_DIR);
 
+	/**
+	 * The file to tail.
+	 */
+	private File tail;
+
 	/**
 	 * Set to true to include an AcceptOnceFileListFilter which prevents duplicates.
 	 */
@@ -61,6 +67,11 @@ public class FileSupplierProperties {
 	 */
 	private Duration delayWhenEmpty = Duration.ofSeconds(1);
 
+	/**
+	 * File tailing options.
+	 */
+	private final Tailer tailer = new Tailer();
+
 	public File getDirectory() {
 		return this.directory;
 	}
@@ -107,4 +118,113 @@ public void setDelayWhenEmpty(Duration delayWhenEmpty) {
 		this.delayWhenEmpty = delayWhenEmpty;
 	}
 
+	public File getTail() {
+		return this.tail;
+	}
+
+	public void setTail(File tail) {
+		this.tail = tail;
+	}
+
+	public Tailer getTailer() {
+		return this.tailer;
+	}
+
+	public static class Tailer {
+
+		/**
+		 * Options string for native tail command.
+		 */
+		private String nativeOptions;
+
+		/**
+		 * Whether to capture stderr output in the separate thread.
+		 */
+		private boolean statusReader;
+
+		/**
+		 * Delay between attempts to tail a non-existent file, or between attempts to
+		 * execute a process if it fails for any reason.
+		 */
+		private Duration attemptsDelay = Duration
+			.ofMillis(FileTailingMessageProducerSupport.DEFAULT_TAIL_ATTEMPTS_DELAY);
+
+		/**
+		 * How often to emit FileTailingIdleEvents.
+		 */
+		private Duration idleEventInterval;
+
+		/**
+		 * Delay between checks of the file for new content.
+		 */
+		private Duration pollingDelay;
+
+		/**
+		 * Whether to tail from the end of the file.
+		 */
+		private Boolean end;
+
+		/**
+		 * Whether to close and reopen the file between reading chunks.
+		 */
+		private Boolean reopen;
+
+		public String getNativeOptions() {
+			return this.nativeOptions;
+		}
+
+		public void setNativeOptions(String nativeOptions) {
+			this.nativeOptions = nativeOptions;
+		}
+
+		public boolean isStatusReader() {
+			return this.statusReader;
+		}
+
+		public void setStatusReader(boolean statusReader) {
+			this.statusReader = statusReader;
+		}
+
+		public Duration getAttemptsDelay() {
+			return this.attemptsDelay;
+		}
+
+		public void setAttemptsDelay(Duration attemptsDelay) {
+			this.attemptsDelay = attemptsDelay;
+		}
+
+		public Duration getIdleEventInterval() {
+			return this.idleEventInterval;
+		}
+
+		public void setIdleEventInterval(Duration idleEventInterval) {
+			this.idleEventInterval = idleEventInterval;
+		}
+
+		public Duration getPollingDelay() {
+			return this.pollingDelay;
+		}
+
+		public void setPollingDelay(Duration pollingDelay) {
+			this.pollingDelay = pollingDelay;
+		}
+
+		public Boolean isEnd() {
+			return this.end;
+		}
+
+		public void setEnd(Boolean end) {
+			this.end = end;
+		}
+
+		public Boolean isReopen() {
+			return this.reopen;
+		}
+
+		public void setReopen(Boolean reopen) {
+			this.reopen = reopen;
+		}
+
+	}
+
 }

supplier/spring-file-supplier/src/test/java/org/springframework/cloud/fn/supplier/file/AbstractFileSupplierTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2020-2022 the original author or authors.
+ * Copyright 2020-2024 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.
@@ -42,7 +42,7 @@
  */
 @SpringBootTest
 @DirtiesContext
-public class AbstractFileSupplierTests {
+public abstract class AbstractFileSupplierTests {
 
 	@TempDir
 	static Path tempDir;