use PortManagementSupport mixin to reserve port in #register

lib/logstash/inputs/tcp.rb

@@ -6,6 +6,7 @@
 require "logstash/util/socket_peer"
 require "logstash-input-tcp_jars"
 require 'logstash/plugin_mixins/ecs_compatibility_support'
+require 'logstash/plugin_mixins/port_management_support'
 
 require "socket"
 require "openssl"
@@ -68,6 +69,8 @@ class LogStash::Inputs::Tcp < LogStash::Inputs::Base
   # ecs_compatibility option, provided by Logstash core or the support adapter.
   include LogStash::PluginMixins::ECSCompatibilitySupport(:disabled, :v1, :v8 => :v1)
 
+  include LogStash::PluginMixins::PortManagementSupport
+
   config_name "tcp"
 
   default :codec, "line"
@@ -177,15 +180,22 @@ def register
     validate_ssl_config!
 
     if server?
-      @loop = InputLoop.new(@id, @host, @port, DecoderImpl.new(@codec, self), @tcp_keep_alive, java_ssl_context)
+      @port_reservation = port_management.reserve(addr: @host, port: @port) do |reserved_addr, reserved_port|
+        # we create the loop for the *requested* host addr, because the *reserved* addr
+        # may be reported overly-broad (e.g, ipv4-only `0.0.0.0` can become ipv6-tolerating `::` depending on arch)
+        @loop = InputLoop.new(@id, @host, reserved_port, DecoderImpl.new(@codec, self), @tcp_keep_alive, java_ssl_context)
+      end
     end
   end
 
   def run(output_queue)
     @output_queue = output_queue
     if server?
-      @logger.info("Starting tcp input listener", :address => "#{@host}:#{@port}", :ssl_enabled => @ssl_enabled)
-      @loop.run
+      @port_reservation.convert do |_, reserved_port|
+        @logger.info("Starting tcp input listener", :address => "#{@host}:#{reserved_port}", :ssl_enabled => @ssl_enabled)
+        @loop.start
+      end
+      @loop.wait_until_closed
     else
       run_client()
     end

logstash-input-tcp.gemspec

@@ -22,6 +22,7 @@ Gem::Specification.new do |s|
   # Gem dependencies
   s.add_runtime_dependency "logstash-core-plugin-api", ">= 1.60", "<= 2.99"
   s.add_runtime_dependency 'logstash-mixin-ecs_compatibility_support', '~>1.2'
+  s.add_runtime_dependency 'logstash-mixin-port_management_support', '~>1.0'
 
   s.add_runtime_dependency 'logstash-core', '>= 8.1.0'
 

spec/inputs/tcp_spec.rb

@@ -21,19 +21,27 @@
 #Cabin::Channel.get(LogStash).level = :debug
 describe LogStash::Inputs::Tcp, :ecs_compatibility_support do
 
-  def get_port
-    begin
-      # Start high to better avoid common services
-      port = rand(10000..65535)
-      s = TCPServer.new("127.0.0.1", port)
-      s.close
-      return port
-    rescue Errno::EADDRINUSE
-      retry
-    end
+  ##
+  # yield the block with a port that is available
+  # @return [Integer]: a port that is available
+  def find_available_port(host)
+    with_bound_port(host: host, &:itself)
+  end
+
+  ##
+  # Yields block with a port that is unavailable
+  # @yieldparam port [Integer]
+  # @yieldreturn [Object]
+  # @return [Object]
+  def with_bound_port(host:"::", port:0, &block)
+    server = TCPServer.new(host, port)
+
+    return yield(server.local_address.ip_port)
+  ensure
+    server.close
   end
 
-  let(:port) { get_port }
+  let(:port) { find_available_port("127.0.0.1") }
 
   context "codec (PR #1372)" do
     it "switches from plain to line" do
@@ -373,6 +381,14 @@ def get_port
         expect { subject.register }.to_not raise_error
       end
 
+      context "when the port is unavailable" do
+        it 'raises a helpful exception' do
+          with_bound_port(host: "127.0.0.1", port: port) do |unavailable_port|
+            expect { subject.register }.to raise_error(Errno::EADDRINUSE)
+          end
+        end
+      end
+
       context "when using ssl" do
         let(:config) do
           {

src/main/java/org/logstash/tcp/InputLoop.java

@@ -26,7 +26,7 @@
 /**
  * Plain TCP Server Implementation.
  */
-public final class InputLoop implements Runnable, Closeable {
+public final class InputLoop implements Closeable {
 
     // historically this class was passing around the plugin's logger
     private static final Logger logger = LogManager.getLogger("logstash.inputs.tcp");
@@ -46,6 +46,11 @@ public final class InputLoop implements Runnable, Closeable {
      */
     private final ServerBootstrap serverBootstrap;
 
+    /**
+     * The channel after starting
+     */
+    private volatile Channel channel;
+
     /**
      * SSL configuration.
      */
@@ -82,11 +87,26 @@ public InputLoop(final String id, final String host, final int port, final Decod
             .childHandler(new InputLoop.InputHandler(decoder, sslContext));
     }
 
-    @Override
-    public void run() {
+    public synchronized void start() {
+        if (channel != null) {
+            throw new IllegalStateException("Already started");
+        }
         try {
-            serverBootstrap.bind(host, port).sync().channel().closeFuture().sync();
-        } catch (final InterruptedException ex) {
+            channel = serverBootstrap.bind(host, port).sync().channel();
+        }catch (final InterruptedException ex) {
+            throw new IllegalStateException(ex);
+        }
+    }
+
+    public void waitUntilClosed() {
+        synchronized (this) {
+            if (channel == null) {
+                throw new IllegalStateException("not started");
+            }
+        }
+        try {
+            channel.closeFuture().sync();
+        }catch (final InterruptedException ex) {
             throw new IllegalStateException(ex);
         }
     }