INT-4171: Document Solution for FTPS Shared SSL

JIRA: https://jira.spring.io/browse/INT-4171

Since the solution requires reflection on `sun` classes, document only.

Also fix some PDF text overflows in (S)FTP.

spring-integration-ftp/src/main/java/org/springframework/integration/ftp/session/AbstractFtpSessionFactory.java

@@ -40,7 +40,7 @@ import org.springframework.util.Assert;
  */
 public abstract class AbstractFtpSessionFactory<T extends FTPClient> implements SessionFactory<FTPFile> {
 
-	private final Log logger = LogFactory.getLog(this.getClass());
+	protected final Log logger = LogFactory.getLog(this.getClass()); // NOSONAR
 
 	protected FTPClientConfig config;
 

spring-integration-ftp/src/test/java/org/springframework/integration/ftp/outbound/FtpServerOutboundTests-context.xml

@@ -52,12 +52,12 @@
 							  command="mget"
 							  expression="payload"
 							  command-options="-R"
-							  filter="startDotTxtFilter"
+							  filter="starDotTxtFilter"
 							  local-directory-expression="@extraConfig.targetLocalDirectoryName + #remoteDirectory"
 							  local-filename-generator-expression="#remoteFileName.replaceFirst('ftpSource', 'localTarget')"
 							  reply-channel="output"/>
 
-	<bean id="startDotTxtFilter" class="org.springframework.integration.ftp.filters.FtpSimplePatternFileListFilter">
+	<bean id="starDotTxtFilter" class="org.springframework.integration.ftp.filters.FtpSimplePatternFileListFilter">
 		<constructor-arg value="*.txt" />
 		<property name="alwaysAcceptDirectories" value="true" />
 	</bean>

src/reference/asciidoc/ftp.adoc

@@ -27,6 +27,8 @@ xsi:schemaLocation="http://www.springframework.org/schema/integration/ftp
 [[ftp-session-factory]]
 === FTP Session Factory
 
+==== Default Factories
+
 IMPORTANT: Starting with version 3.0, sessions are no longer cached by default.
 See <<ftp-session-caching>>.
 
@@ -121,6 +123,74 @@ public class AdvancedFtpSessionFactory extends DefaultFtpSessionFactory {
 }
 ----
 
+==== FTPS and Shared SSLSession
+
+When using FTP over SSL/TLS, some servers require the same `SSLSession` to be used on the control and data connections; this is to prevent "stealing" data connections; see https://scarybeastsecurity.blogspot.cz/2009/02/vsftpd-210-released.html[here for more information].
+
+Currently, the Apache FTPSClient does not support this feature - see https://issues.apache.org/jira/browse/NET-408[NET-408].
+
+The following solution, courtesy of http://stackoverflow.com/questions/32398754/how-to-connect-to-ftps-server-with-data-connection-using-same-tls-session[Stack Overflow], uses reflection on the `sun.security.ssl.SSLSessionContextImpl` so may not work on other JVMs.
+The stack overflow answer was submitted in 2015 and the solution has been tested by the Spring Integration team recently on JDK 1.8.0_112.
+
+[source, java]
+----
+@Bean
+public DefaultFtpsSessionFactory sf() {
+    DefaultFtpsSessionFactory sf = new DefaultFtpsSessionFactory() {
+
+        @Override
+        protected FTPSClient createClientInstance() {
+            return new SharedSSLFTPSClient();
+        }
+
+    };
+    sf.setHost("...");
+    sf.setPort(21);
+    sf.setUsername("...");
+    sf.setPassword("...");
+    sf.setNeedClientAuth(true);
+    return sf;
+}
+
+private static final class SharedSSLFTPSClient extends FTPSClient {
+
+    @Override
+    protected void _prepareDataSocket_(final Socket socket) throws IOException {
+        if (socket instanceof SSLSocket) {
+            // Control socket is SSL
+            final SSLSession session = ((SSLSocket) _socket_).getSession();
+            final SSLSessionContext context = session.getSessionContext();
+            context.setSessionCacheSize(0); // you might want to limit the cache
+            try {
+                final Field sessionHostPortCache = context.getClass()
+                        .getDeclaredField("sessionHostPortCache");
+                sessionHostPortCache.setAccessible(true);
+                final Object cache = sessionHostPortCache.get(context);
+                final Method method = cache.getClass().getDeclaredMethod("put", Object.class,
+                        Object.class);
+                method.setAccessible(true);
+                String key = String.format("%s:%s", socket.getInetAddress().getHostName(),
+                        String.valueOf(socket.getPort())).toLowerCase(Locale.ROOT);
+                method.invoke(cache, key, session);
+                key = String.format("%s:%s", socket.getInetAddress().getHostAddress(),
+                        String.valueOf(socket.getPort())).toLowerCase(Locale.ROOT);
+                method.invoke(cache, key, session);
+            }
+            catch (NoSuchFieldException e) {
+                // Not running in expected JRE
+                logger.warn("No field sessionHostPortCache in SSLSessionContext", e);
+            }
+            catch (Exception e) {
+                // Not running in expected JRE
+                logger.warn(e.getMessage());
+            }
+        }
+
+    }
+
+}
+----
+
 [[ftp-dsf]]
 === Delegating Session Factory
 
@@ -804,7 +874,8 @@ This allows recursion for a simple pattern; examples follow:
 
 [source, xml]
 ----
-<bean id="startDotTxtFilter" class="org.springframework.integration.ftp.filters.FtpSimplePatternFileListFilter">
+<bean id="starDotTxtFilter"
+        class="org.springframework.integration.ftp.filters.FtpSimplePatternFileListFilter">
     <constructor-arg value="*.txt" />
     <property name="alwaysAcceptDirectories" value="true" />
 </bean>

src/reference/asciidoc/sftp.adoc

@@ -893,7 +893,8 @@ This allows recursion for a simple pattern; examples follow:
 
 [source, xml]
 ----
-<bean id="startDotTxtFilter" class="org.springframework.integration.sftp.filters.SftpSimplePatternFileListFilter">
+<bean id="starDotTxtFilter"
+            class="org.springframework.integration.sftp.filters.SftpSimplePatternFileListFilter">
     <constructor-arg value="*.txt" />
     <property name="alwaysAcceptDirectories" value="true" />
 </bean>