spring-projectsGH-3247: Fix SftpSession.exists for error code

Fixes spring-projects#3247

When there is no path on the SFTP server, a `ChannelSftp.SSH_FX_NO_SUCH_FILE`
error is returned in the thrown `SftpException`.

* Fix `SftpSession.exists()` to check for the `SSH_FX_NO_SUCH_FILE` to
return `false` and re-throw an exception otherwise
* Add mock test for `SftpSession.exists()`
* Add `org.mockito.AdditionalMatchers` to `checkstyle.xml` exclusions

**Cherry-pick to 5.2.x & 5.1.x**

spring-integration-sftp/src/main/java/org/springframework/integration/sftp/session/SftpSession.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -127,16 +127,15 @@ public LsEntry[] list(String path) throws IOException {
 	@Override
 	public String[] listNames(String path) throws IOException {
 		LsEntry[] entries = this.list(path);
-		List<String> names = new ArrayList<String>();
-		for (int i = 0; i < entries.length; i++) {
-			String fileName = entries[i].getFilename();
-			SftpATTRS attrs = entries[i].getAttrs();
+		List<String> names = new ArrayList<>();
+		for (LsEntry entry : entries) {
+			String fileName = entry.getFilename();
+			SftpATTRS attrs = entry.getAttrs();
 			if (!attrs.isDir() && !attrs.isLink()) {
 				names.add(fileName);
 			}
 		}
-		String[] fileNames = new String[names.size()];
-		return names.toArray(fileNames);
+		return names.toArray(new String[0]);
 	}
 
 
@@ -270,15 +269,19 @@ public boolean rmdir(String remoteDirectory) throws IOException {
 	}
 
 	@Override
-	public boolean exists(String path) {
+	public boolean exists(String path) throws IOException {
 		try {
 			this.channel.lstat(path);
 			return true;
 		}
-		catch (@SuppressWarnings("unused") SftpException e) {
-			// ignore
+		catch (SftpException ex) {
+			if (ex.id == ChannelSftp.SSH_FX_NO_SUCH_FILE) {
+				return false;
+			}
+			else {
+				throw new NestedIOException("Cannot check 'lstat' for path " + path, ex);
+			}
 		}
-		return false;
 	}
 
 	void connect() {

spring-integration-sftp/src/test/java/org/springframework/integration/sftp/outbound/SftpOutboundTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -17,8 +17,14 @@
 package org.springframework.integration.sftp.outbound;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
+import static org.mockito.AdditionalMatchers.and;
+import static org.mockito.AdditionalMatchers.not;
 import static org.mockito.ArgumentMatchers.anyString;
+import static org.mockito.ArgumentMatchers.eq;
 import static org.mockito.BDDMockito.willAnswer;
+import static org.mockito.BDDMockito.willReturn;
+import static org.mockito.BDDMockito.willThrow;
 import static org.mockito.Mockito.doAnswer;
 import static org.mockito.Mockito.doNothing;
 import static org.mockito.Mockito.doReturn;
@@ -30,6 +36,7 @@
 
 import java.io.File;
 import java.io.FileOutputStream;
+import java.io.IOException;
 import java.io.InputStream;
 import java.lang.reflect.Constructor;
 import java.util.ArrayList;
@@ -38,12 +45,13 @@
 import java.util.Vector;
 import java.util.concurrent.atomic.AtomicInteger;
 
-import org.junit.Test;
+import org.junit.jupiter.api.Test;
 import org.mockito.Mockito;
 
 import org.springframework.beans.DirectFieldAccessor;
 import org.springframework.beans.factory.BeanFactory;
 import org.springframework.context.support.ClassPathXmlApplicationContext;
+import org.springframework.core.NestedIOException;
 import org.springframework.expression.common.LiteralExpression;
 import org.springframework.integration.file.DefaultFileNameGenerator;
 import org.springframework.integration.file.remote.FileInfo;
@@ -67,6 +75,7 @@
 import com.jcraft.jsch.JSch;
 import com.jcraft.jsch.JSchException;
 import com.jcraft.jsch.SftpATTRS;
+import com.jcraft.jsch.SftpException;
 
 /**
  * @author Oleg Zhurakousky
@@ -76,15 +85,15 @@
  */
 public class SftpOutboundTests {
 
-	private static com.jcraft.jsch.Session jschSession = mock(com.jcraft.jsch.Session.class);
+	private static final com.jcraft.jsch.Session jschSession = mock(com.jcraft.jsch.Session.class);
 
 	@Test
 	public void testHandleFileMessage() throws Exception {
 		File targetDir = new File("remote-target-dir");
 		assertThat(targetDir.exists()).as("target directory does not exist: " + targetDir.getName()).isTrue();
 
 		SessionFactory<LsEntry> sessionFactory = new TestSftpSessionFactory();
-		FileTransferringMessageHandler<LsEntry> handler = new FileTransferringMessageHandler<LsEntry>(sessionFactory);
+		FileTransferringMessageHandler<LsEntry> handler = new FileTransferringMessageHandler<>(sessionFactory);
 		handler.setRemoteDirectoryExpression(new LiteralExpression(targetDir.getName()));
 		DefaultFileNameGenerator fGenerator = new DefaultFileNameGenerator();
 		fGenerator.setBeanFactory(mock(BeanFactory.class));
@@ -133,7 +142,7 @@ public void testHandleBytesMessage() throws Exception {
 			file.delete();
 		}
 		SessionFactory<LsEntry> sessionFactory = new TestSftpSessionFactory();
-		FileTransferringMessageHandler<LsEntry> handler = new FileTransferringMessageHandler<LsEntry>(sessionFactory);
+		FileTransferringMessageHandler<LsEntry> handler = new FileTransferringMessageHandler<>(sessionFactory);
 		DefaultFileNameGenerator fGenerator = new DefaultFileNameGenerator();
 		fGenerator.setBeanFactory(mock(BeanFactory.class));
 		fGenerator.setExpression("'foo.txt'");
@@ -142,7 +151,7 @@ public void testHandleBytesMessage() throws Exception {
 		handler.setBeanFactory(mock(BeanFactory.class));
 		handler.afterPropertiesSet();
 
-		handler.handleMessage(new GenericMessage<byte[]>("byte[] data".getBytes()));
+		handler.handleMessage(new GenericMessage<>("byte[] data".getBytes()));
 		assertThat(new File("remote-target-dir", "foo.txt").exists()).isTrue();
 		byte[] inFile = FileCopyUtils.copyToByteArray(file);
 		assertThat(new String(inFile)).isEqualTo("byte[] data");
@@ -171,7 +180,7 @@ public void testSftpOutboundChannelAdapterInsideChain() throws Exception {
 	}
 
 	@Test //INT-2275
-	public void testFtpOutboundGatewayInsideChain() throws Exception {
+	public void testFtpOutboundGatewayInsideChain() {
 		ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext(
 				"SftpOutboundInsideChainTests-context.xml", getClass());
 
@@ -202,17 +211,17 @@ public void testMkDir() throws Exception {
 		@SuppressWarnings("unchecked")
 		SessionFactory<LsEntry> sessionFactory = mock(SessionFactory.class);
 		when(sessionFactory.getSession()).thenReturn(session);
-		FileTransferringMessageHandler<LsEntry> handler = new FileTransferringMessageHandler<LsEntry>(sessionFactory);
+		FileTransferringMessageHandler<LsEntry> handler = new FileTransferringMessageHandler<>(sessionFactory);
 		handler.setAutoCreateDirectory(true);
 		handler.setRemoteDirectoryExpression(new LiteralExpression("/foo/bar/baz"));
 		handler.setBeanFactory(mock(BeanFactory.class));
 		handler.afterPropertiesSet();
-		final List<String> madeDirs = new ArrayList<String>();
+		final List<String> madeDirs = new ArrayList<>();
 		doAnswer(invocation -> {
 			madeDirs.add(invocation.getArgument(0));
 			return null;
 		}).when(session).mkdir(anyString());
-		handler.handleMessage(new GenericMessage<String>("qux"));
+		handler.handleMessage(new GenericMessage<>("qux"));
 		assertThat(madeDirs.size()).isEqualTo(3);
 		assertThat(madeDirs.get(0)).isEqualTo("/foo");
 		assertThat(madeDirs.get(1)).isEqualTo("/foo/bar");
@@ -380,6 +389,34 @@ public void testSharedSessionCachedReset() throws Exception {
 		verify(jschSession2).disconnect();
 	}
 
+	@Test
+	public void testExists() throws SftpException, IOException {
+		ChannelSftp channelSftp = mock(ChannelSftp.class);
+
+		willReturn(mock(SftpATTRS.class))
+				.given(channelSftp)
+				.lstat(eq("exist"));
+
+		willThrow(new SftpException(ChannelSftp.SSH_FX_NO_SUCH_FILE, "Path does not exist."))
+				.given(channelSftp)
+				.lstat(eq("notExist"));
+
+		willThrow(new SftpException(ChannelSftp.SSH_FX_CONNECTION_LOST, "Connection lost."))
+				.given(channelSftp)
+				.lstat(and(not(eq("exist")), not(eq("notExist"))));
+
+		SftpSession sftpSession = new SftpSession(mock(com.jcraft.jsch.Session.class));
+		DirectFieldAccessor fieldAccessor = new DirectFieldAccessor(sftpSession);
+		fieldAccessor.setPropertyValue("channel", channelSftp);
+
+		assertThat(sftpSession.exists("exist")).isTrue();
+
+		assertThat(sftpSession.exists("notExist")).isFalse();
+
+		assertThatExceptionOfType(NestedIOException.class).
+				isThrownBy(() -> sftpSession.exists("foo"));
+	}
+
 	private void noopConnect(ChannelSftp channel1) throws JSchException {
 		doNothing().when(channel1).connect(5000);
 	}

src/checkstyle/checkstyle.xml

@@ -84,6 +84,7 @@
 				org.mockito.BDDMockito.*,
 				org.mockito.AdditionalAnswers.*,
 				org.mockito.ArgumentMatchers.*,
+				org.mockito.AdditionalMatchers.*,
 				org.springframework.integration.gemfire.config.xml.ParserTestUtil.*,
 				org.springframework.integration.test.mock.MockIntegration.*,
 				org.springframework.integration.test.util.TestUtils.*,