Perform LSP tracing server-side.

java/java.lsp.server/src/org/netbeans/modules/java/lsp/server/protocol/Server.java

@@ -159,6 +159,10 @@
  */
 public final class Server {
     private static final Logger LOG = Logger.getLogger(Server.class.getName());
+    /**
+     * Special logger that logs LSP in/out messages.
+     */
+    private static final Logger LSP_LOG = Logger.getLogger("org.netbeans.modules.java.lsp.server.lsptrace"); // NOI18N
     private static final LspServerTelemetryManager LSP_SERVER_TELEMETRY = new LspServerTelemetryManager();
     private static final ErrorsNotifier ERR_NOTIFIER = new ErrorsNotifier();
 
@@ -266,7 +270,17 @@ public MessageConsumer attachLookup(MessageConsumer delegate) {
             // PENDING: allow for message consumer wrappers to be registered to add pre/post processing for
             // the request plus build the request's default Lookup contents.
             if (!(delegate instanceof Endpoint)) {
-                return delegate; 
+                return new MessageConsumer() {
+                    @Override
+                    public void consume(Message msg) throws MessageIssueException, JsonRpcException {
+                        if (LSP_LOG.isLoggable(Level.FINEST)) {
+                            LSP_LOG.log(Level.FINEST, "OUT: {0}", 
+                                    msg.toString().replace("\n", "\n\t"));
+                        }
+                        delegate.consume(msg);
+                    }
+
+                };
             }
             return new MessageConsumer() {
                 @Override
@@ -275,6 +289,10 @@ public void consume(Message msg) throws MessageIssueException, JsonRpcException
                     ProxyLookup ll = new ProxyLookup(new AbstractLookup(ic), sessionLookup);
                     final OperationContext ctx;
 
+                    if (LSP_LOG.isLoggable(Level.FINEST)) {
+                        LSP_LOG.log(Level.FINEST, "IN : {0}", 
+                                msg.toString().replace("\n", "\n\t"));
+                    }
                     // Intercept client REQUESTS; take the progress token from them, if it is
                     // attached.
                     Runnable r;

java/java.lsp.server/vscode/BUILD.md

@@ -163,7 +163,11 @@ The default userdir location is inside the **global** vscode settings location:
 When the environment variable `nbcode_userdir` (to e.g. `/tmp/foo`) is set when starting vscode or nbcode (npm run nbcode), the userdir will point to `/tmp/foo/userdir`.
 
 ### Debug output 
-_Standalone NBLS_ can be instructed to print messages (stderr, out) to the console: add `-J-Dnetbeans.logger.console=true` to the npm commandline. This has the same effect as `netbeans.verbose = true` settings in the vscode. Messages from the LSP protocol can be displayed in vscode by setting `java.trace.server = verbose` setting in vscode JSON settings.
+_Standalone NBLS_ can be instructed to print messages (stderr, out) to the console: add `-J-Dnetbeans.logger.console=true` to the npm commandline. This has the same effect as `netbeans.verbose = true` settings in the vscode. 
+
+### LSP protocol tracing
+Messages from the LSP protocol can be displayed in vscode by setting `java.trace.server = verbose` setting in vscode JSON settings. Sometimes it may be needed to record LSP requests and responses in the debug output log stream from the Apache NetBeans language server so that requests are properly ordered with logs from executed actions. This can be enabled on language server startup by adding `-J-Dorg.netbeans.modules.java.lsp.server.lsptrace.level=FINEST`
+to the NBLS commandline.
 
 ### Debugging separately from global NBLS
 By default the extension uses **global** userdir of the **global** vscode instance and uses NBLS data in there. In case this is not desired, the `launch.json` must be changed: