INT-4067: Cover empty file case in FileSplitter

JIRA: https://jira.spring.io/browse/INT-4067

When `FileSplitter` is configured with `markers = true` and file is empty, an `iterator` for file throws `IOException: Stream closed`,
because we close the `buffer` just after the first `readLine()` attempt, but still return `true` from the first `hasNext()` call
where the `this.sof` and `this.eof` are `true` for markers.

Add logic to mark internal splitter `iterator` as `done` where we don't have content and still in `sof` state.

build.gradle

@@ -3,22 +3,20 @@ buildscript {
 		maven { url 'https://repo.spring.io/plugins-release' }
 	}
 	dependencies {
-		classpath 'io.spring.gradle:spring-io-plugin:0.0.4.RELEASE'
+		classpath 'io.spring.gradle:spring-io-plugin:0.0.5.RELEASE'
 		classpath 'io.spring.gradle:docbook-reference-plugin:0.3.1'
 		classpath 'org.asciidoctor:asciidoctor-gradle-plugin:1.5.0'
 	}
 }
 
 plugins {
-	id "org.sonarqube" version "1.2"
+	id 'java'
+	id 'base'
+	id 'org.sonarqube' version '1.2'
 }
 
 description = 'Spring Integration'
 
-apply plugin: 'base'
-apply plugin: 'idea'
-
-
 def docsDir = 'src/reference/asciidoc' // Will be default with newer asciidoctor plugin
 
 ext {
@@ -141,7 +139,7 @@ subprojects { subproject ->
 		springSecurityVersion = '4.1.0.RELEASE'
 		springSocialTwitterVersion = '1.1.2.RELEASE'
 		springRetryVersion = '1.1.2.RELEASE'
-		springVersion = project.hasProperty('springVersion') ? project.springVersion : '4.3.1.BUILD-SNAPSHOT'
+		springVersion = project.hasProperty('springVersion') ? project.springVersion : '4.3.1.RELEASE'
 		springWsVersion = '2.3.0.RELEASE'
 		xmlUnitVersion = '1.6'
 		xstreamVersion = '1.4.7'

spring-integration-file/src/main/java/org/springframework/integration/file/splitter/FileSplitter.java

@@ -235,6 +235,9 @@ public class FileSplitter extends AbstractMessageSplitter {
 					if (!ready) {
 						if (this.markers) {
 							this.eof = true;
+							if (this.sof) {
+								this.done = true;
+							}
 						}
 						bufferedReader.close();
 					}

spring-integration-file/src/test/java/org/springframework/integration/file/splitter/FileSplitterTests.java

@@ -207,6 +207,34 @@ public class FileSplitterTests {
 		assertEquals(2, fileMarker.getLineCount());
 	}
 
+	@Test
+	public void testMarkersEmptyFile() throws IOException {
+		QueueChannel outputChannel = new QueueChannel();
+		FileSplitter splitter = new FileSplitter(true, true);
+		splitter.setOutputChannel(outputChannel);
+		File file = File.createTempFile("empty", ".txt");
+		splitter.handleMessage(new GenericMessage<File>(file));
+		Message<?> received = outputChannel.receive(0);
+		assertNotNull(received);
+		assertNull(received.getHeaders().get(IntegrationMessageHeaderAccessor.SEQUENCE_SIZE));
+		assertEquals("START", received.getHeaders().get(FileHeaders.MARKER));
+		assertThat(received.getPayload(), instanceOf(FileSplitter.FileMarker.class));
+		FileMarker fileMarker = (FileSplitter.FileMarker) received.getPayload();
+		assertEquals(FileMarker.Mark.START, fileMarker.getMark());
+		assertEquals(file.getAbsolutePath(), fileMarker.getFilePath());
+		assertEquals(0, fileMarker.getLineCount());
+
+		received = outputChannel.receive(0);
+		assertNotNull(received);
+
+		assertEquals("END", received.getHeaders().get(FileHeaders.MARKER));
+		assertThat(received.getPayload(), instanceOf(FileSplitter.FileMarker.class));
+		fileMarker = (FileSplitter.FileMarker) received.getPayload();
+		assertEquals(FileMarker.Mark.END, fileMarker.getMark());
+		assertEquals(file.getAbsolutePath(), fileMarker.getFilePath());
+		assertEquals(0, fileMarker.getLineCount());
+	}
+
 	@Test
 	public void testMarkersJson() throws Exception {
 		JsonObjectMapper<?, ?> objectMapper = JsonObjectMapperProvider.newInstance();

src/reference/asciidoc/file.adoc

@@ -820,7 +820,8 @@ Markers are messages with `FileSplitter.FileMarker` payloads (with `START` and `
 Markers might be used when sequentially processing files in a downstream flow where some lines are filtered.
 They enable the downstream processing to know when a file has been completely processed.
 In addition, a header `file_marker` containing `START` or `END` are added to these messages.
-The 'END' marker includes a line count.
+The `END` marker includes a line count.
+If the file is empty, only `START` and `END` markers are emitted with `0` as the `lineCount`.
 Default: `false`.
 When `true`, `apply-sequence` is `false` by default.
 Also see `markers-json`.