INT-1770 Support Client Mode For TCP Endpoints

Add client mode for inbound endpoints, and for the
outbound adapter.

INT-1770 Allow Inbound Adapter to Open Connection

Normally, inbound adapters use server sockets and wait for incoming
connection. There are use cases where the adapter should establish
the connection and wait for inbound messages.

INT-1770 Open Connection on Start

Allow configuration of outbound adapter to permit
connection establishment when the adapter is started
rather than when the first message arrives.

INT-1770 Allow Inbound Gateway to Open Connection

Normally, inbound gateways listen for connections. There are
use cases where an inbound gateway might open the connection
and then wait for incoming requests.

INT-1770 Parsers

Update parsers and tests to support attributes for setting
endpoints in client-mode.

INT-1770 Docs

Update reference with client-mode information.

INT-1770 Add Control Bus for Client Mode

Enable control bus commands to check status and to attempt
connection establishment.

spring-integration-ip/src/main/resources/org/springframework/integration/ip/config/spring-integration-ip-2.1.xsd

@@ -156,6 +156,17 @@ task executors such as a WorkManagerTaskExecutor.
 							</xsd:documentation>
 						</xsd:annotation>
 					</xsd:attribute>
+					<xsd:attribute name="client-mode" type="xsd:string" use="optional" default="false">
+						<xsd:annotation>
+							<xsd:documentation>
+							 If set to true, causes the adapter to act as a client with respect to
+							 establishing the connection, rather than listening for incoming connections.
+							 Requires a type="client" connection factory, with single-use set to false.
+							 Defaults to true.
+							</xsd:documentation>
+						</xsd:annotation>
+					</xsd:attribute>
+					<xsd:attributeGroup ref="clientModeAttributeGroup" />
 				</xsd:extension>
 			</xsd:complexContent>
 		</xsd:complexType>
@@ -198,6 +209,17 @@ task executors such as a WorkManagerTaskExecutor.
 							</xsd:documentation>
 						</xsd:annotation>
 					</xsd:attribute>
+					<xsd:attribute name="client-mode" type="xsd:string" use="optional" default="false">
+						<xsd:annotation>
+							<xsd:documentation>
+							 If set to true, causes the adapter to establish a connection when started,
+							 rather than when the first message is sent.
+							 Requires a type="client" connection factory, with single-use set to false.
+							 Defaults to true.
+							</xsd:documentation>
+						</xsd:annotation>
+					</xsd:attribute>
+					<xsd:attributeGroup ref="clientModeAttributeGroup" />
 				</xsd:extension>
 			</xsd:complexContent>
 		</xsd:complexType>
@@ -256,6 +278,17 @@ task executors such as a WorkManagerTaskExecutor.
 							</xsd:documentation>
 						</xsd:annotation>
 					</xsd:attribute>
+					<xsd:attribute name="client-mode" type="xsd:string" use="optional" default="false">
+						<xsd:annotation>
+							<xsd:documentation>
+							 If set to true, causes the gateway to act as a client with respect to
+							 establishing the connection, rather than listening for incoming connections.
+							 Requires a type="client" connection factory, with single-use set to false.
+							 Defaults to true.
+							</xsd:documentation>
+						</xsd:annotation>
+					</xsd:attribute>
+					<xsd:attributeGroup ref="clientModeAttributeGroup" />
 				</xsd:extension>
 			</xsd:complexContent>
 		</xsd:complexType>
@@ -523,4 +556,29 @@ default is 0. Values can be negative. See SmartLifeCycle.
 		</xsd:attribute>
 	</xsd:complexType>
 
+	<xsd:attributeGroup name="clientModeAttributeGroup">
+		<xsd:attribute name="retry-interval" type="xsd:string" use="optional" default="60000">
+			<xsd:annotation>
+				<xsd:documentation>
+				 When in client mode, specifies the retry interval, in milliseconds, if a connection
+				 cannot be established. Defaults to 60000.
+				</xsd:documentation>
+			</xsd:annotation>
+		</xsd:attribute>
+		<xsd:attribute name="scheduler" type="xsd:string">
+			<xsd:annotation>
+				<xsd:documentation>
+				    When in client mode,
+					provide a reference to the TaskScheduler instance to
+					be used for establishing connections. If not provided, the default
+					will use a thread pool of size 1.
+				</xsd:documentation>
+				<xsd:appinfo>
+					<tool:annotation kind="ref">
+						<tool:expected-type type="org.springframework.scheduling.TaskScheduler" />
+					</tool:annotation>
+				</xsd:appinfo>
+			</xsd:annotation>
+		</xsd:attribute>
+	</xsd:attributeGroup>
 </xsd:schema>