[JENKINS-48766] - Create restricted API for getting info about Remoting versions

core/src/filter/resources/jenkins/slaves/remoting-info.properties

+# Remoting version, which is embedded into the core
+# This version MAY differ from what is really classloaded (see the "Pluggable Core Components", JENKINS-41196)
+remoting.embedded.version=${remoting.version}
+
+# Minimal Remoting version on external agents which is supported by the core
+remoting.minimal.supported.version=${remoting.minimal.supported.version}

core/src/main/java/hudson/TcpSlaveAgentListener.java

@@ -290,6 +290,7 @@ public final class TcpSlaveAgentListener extends Thread {
             try {
                 Writer o = new OutputStreamWriter(s.getOutputStream(), "UTF-8");
 
+                //TODO: expose version about minimal supported Remoting version (JENKINS-48766)
                 if (header.startsWith("GET / ")) {
                     o.write("HTTP/1.0 200 OK\r\n");
                     o.write("Content-Type: text/plain;charset=UTF-8\r\n");

core/src/main/java/jenkins/slaves/RemotingVersionInfo.java

+/*
+ * The MIT License
+ *
+ * Copyright (c) 2018, CloudBees, Inc.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package jenkins.slaves;
+
+import hudson.util.VersionNumber;
+import org.kohsuke.accmod.Restricted;
+import org.kohsuke.accmod.restrictions.NoExternalUse;
+
+import javax.annotation.CheckForNull;
+import javax.annotation.Nonnull;
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.Properties;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+
+// TODO: Make the API public (JENKINS-48766)
+/**
+ * Provides information about Remoting versions used withing the core.
+ * @author Oleg Nenashev
+ * @since TODO
+ */
+@Restricted(NoExternalUse.class)
+public class RemotingVersionInfo {
+
+    private static final Logger LOGGER = Logger.getLogger(RemotingVersionInfo.class.getName());
+    private static final String RESOURCE_NAME="remoting-info.properties";
+
+    @CheckForNull
+    private static VersionNumber EMBEDDED_VERSION;
+
+    @CheckForNull
+    private static VersionNumber MINIMAL_SUPPORTED_VERSION;
+
+    private RemotingVersionInfo() {}
+
+    static {
+        Properties props = new Properties();
+        try (InputStream is = RemotingVersionInfo.class.getResourceAsStream(RESOURCE_NAME)) {
+            if(is!=null) {
+                props.load(is);
+            }
+        } catch (IOException e) {
+            LOGGER.log(Level.WARNING, "Failed to load Remoting Info from " + RESOURCE_NAME, e);
+        }
+
+        EMBEDDED_VERSION = tryExtractVersion(props, "remoting.embedded.version");
+        MINIMAL_SUPPORTED_VERSION = tryExtractVersion(props, "remoting.minimal.supported.version");
+    }
+
+    @CheckForNull
+    private static VersionNumber tryExtractVersion(@Nonnull Properties props, @Nonnull String propertyName) {
+        String prop = props.getProperty(propertyName);
+        if (prop == null) {
+            LOGGER.log(Level.FINE, "Property {0} is not defined in {1}", new Object[] {propertyName, RESOURCE_NAME});
+            return null;
+        }
+
+        if(prop.contains("${")) { // Due to whatever reason, Maven does not nullify them
+            LOGGER.log(Level.WARNING, "Property {0} in {1} has unresolved variable(s). Raw value: {2}",
+                    new Object[] {propertyName, RESOURCE_NAME, prop});
+            return null;
+        }
+
+        try {
+            return new VersionNumber(prop);
+        } catch (RuntimeException ex) {
+            LOGGER.log(Level.WARNING, String.format("Failed to parse version for for property %s in %s. Raw Value: %s",
+                    propertyName, RESOURCE_NAME, prop), ex);
+            return null;
+        }
+    }
+
+    @CheckForNull
+    public static VersionNumber getEmbeddedVersion() {
+        return EMBEDDED_VERSION;
+    }
+
+    @CheckForNull
+    public static VersionNumber getMinimalSupportedVersion() {
+        return MINIMAL_SUPPORTED_VERSION;
+    }
+}

core/src/test/java/jenkins/slaves/RemotingVersionInfoTest.java

+/*
+ * The MIT License
+ *
+ * Copyright (c) 2018, CloudBees, Inc.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package jenkins.slaves;
+
+import org.junit.Test;
+
+import static org.hamcrest.CoreMatchers.*;
+import static org.junit.Assert.assertThat;
+
+/**
+ * Tests for {@link RemotingVersionInfo}.
+ */
+public class RemotingVersionInfoTest {
+
+    @Test
+    public void shouldLoadEmbeddedVersionByDefault() {
+        assertThat("Remoting Embedded version is not defined",
+                RemotingVersionInfo.getEmbeddedVersion(), notNullValue());
+    }
+
+    @Test
+    public void shouldLoadMinimalSupportedVersionByDefault() {
+        assertThat("Remoting Minimal supported version is not defined",
+                RemotingVersionInfo.getMinimalSupportedVersion(), notNullValue());
+    }
+}

pom.xml

@@ -104,6 +104,10 @@ THE SOFTWARE.
 
     <maven-war-plugin.version>3.0.0</maven-war-plugin.version> <!-- JENKINS-47127 bump when 3.2.0 is out. Cf. MWAR-407 -->
 
+    <!-- Minimal Remoting version, which is tested for API compatibility -->
+    <remoting.version>3.15</remoting.version>
+    <remoting.minimal.supported.version>2.60</remoting.minimal.supported.version>
+
   </properties>
 
   <!-- Note that the 'repositories' and 'pluginRepositories' blocks below are actually copy-pasted
@@ -175,7 +179,7 @@ THE SOFTWARE.
       <dependency>
         <groupId>org.jenkins-ci.main</groupId>
         <artifactId>remoting</artifactId>
-        <version>3.15</version>
+        <version>${remoting.version}</version>
       </dependency>
 
       <dependency>