Persistent banner to ./bin/elasticsearch on the terminal

distribution/src/bin/elasticsearch

@@ -17,6 +17,7 @@ source "`dirname "$0"`"/elasticsearch-env
 
 CHECK_KEYSTORE=true
 DAEMONIZE=false
+QUIET=false
 for option in "$@"; do
   case "$option" in
     -h|--help|-V|--version)
@@ -25,6 +26,9 @@ for option in "$@"; do
     -d|--daemonize)
       DAEMONIZE=true
       ;;
+    -q|--quiet)
+      QUIET=true
+      ;;
   esac
 done
 
@@ -56,6 +60,17 @@ ES_JAVA_OPTS=`export ES_TMPDIR; "$JAVA" "$XSHARE" -cp "$ES_CLASSPATH" org.elasti
 
 # manual parsing to find out, if process should be detached
 if [[ $DAEMONIZE = false ]]; then
+  if [[ "$QUIET" = false ]]; then
+    # redirects the stdout of the following `exec` to the stdin of this special sort-of `cat` with a bottom banner
+    # the banner contents sit in a file (this uses bash process substitution), and are not available initially
+    exec > >("$JAVA" "$XSHARE" -cp "$ES_CLASSPATH" org.elasticsearch.tools.launchers.OutputBottomBanner "EOF"\
+      <(sleep 15; echo -ne "DEMO BANNER\n"\
+"SECURITY HAS BEEN AUTO-CONFIGURED\n"\
+"\"elastic\" user password: *******\n"\
+"ES node enrollment token (expires in 30 mins): *******\n"\
+"Kibana enrollment token (expires in 30 mins): *******\n"\
+"EOF"))
+  fi
   exec \
     "$JAVA" \
     "$XSHARE" \

distribution/tools/launchers/src/main/java/org/elasticsearch/tools/launchers/OutputBottomBanner.java

@@ -0,0 +1,123 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0 and the Server Side Public License, v 1; you may not use this file except
+ * in compliance with, at your election, the Elastic License 2.0 or the Server
+ * Side Public License, v 1.
+ */
+
+package org.elasticsearch.tools.launchers;
+
+import org.elasticsearch.tools.java_version_checker.SuppressForbidden;
+
+import java.io.BufferedReader;
+import java.io.FileReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.io.UncheckedIOException;
+import java.nio.charset.Charset;
+import java.util.Arrays;
+import java.util.Locale;
+import java.util.concurrent.atomic.AtomicReference;
+
+/**
+ * Prints the text lines, that are coming through the standard input, to the standard output
+ * (like the no-arg `cat` command), but followed by a multi-line text "banner" that persists as the last text
+ * that is printed to the terminal.
+ * The "banner" persists because it is printed out after every line of text, and is then cleared
+ * before the next line is printed. Clearing and moving the cursor only works if the output is a terminal
+ * (this redirection should not be used otherwise).
+ * The banner is read from an input file, and mustn't necessarily be available before the stdin input is.
+ * Once the content of the banner becomes available it cannot be changed.
+ */
+final class OutputBottomBanner {
+
+    @SuppressForbidden(reason = "System#out")
+    public static void main(final String[] args) throws IOException {
+        if (args.length != 2) {
+            throw new IllegalArgumentException("expected two arguments, but provided " + Arrays.toString(args));
+        }
+        // TODO validate args
+        final String bannerEndMarker = args[0];
+        final String bannerFileName = args[1];
+        final AtomicReference<Banner> bannerReference = new AtomicReference<>();
+        // asynchronously read the whole banner; the banner is only used when complete
+        final Thread bannerThread = new Thread(() -> {
+            StringBuilder bannerBuilder = new StringBuilder();
+            int lineCount = 0;
+            // read banner from file using platform's charset
+            try (BufferedReader reader = new BufferedReader(new FileReader(bannerFileName, Charset.defaultCharset()))) {
+                while (true) {
+                    String bannerLine;
+                    while ((bannerLine = reader.readLine()) != null) {
+                        if (bannerEndMarker.equals(bannerLine)) {
+                            break;
+                        }
+                        if (lineCount != 0) {
+                            bannerBuilder.append(System.lineSeparator());
+                        }
+                        bannerBuilder.append(bannerLine);
+                        lineCount++;
+                    }
+                    // the banner is now complete (marker on its own line)
+                    if (bannerEndMarker.equals(bannerLine)) {
+                        break;
+                    }
+                    // this is EOF without the banner end marker. Keep reading until encountering the end marker.
+                    Thread.sleep(1000);
+                }
+            } catch (IOException e) {
+                throw new UncheckedIOException(e);
+            } catch (InterruptedException ignore) {
+                Thread.currentThread().interrupt();
+            }
+            bannerReference.set(new Banner(bannerBuilder.toString(), lineCount));
+        });
+        bannerThread.setDaemon(true);
+        bannerThread.start();
+
+        // forward stdin to stdout
+        try (BufferedReader reader = new BufferedReader(new InputStreamReader(System.in, Charset.defaultCharset()))) {
+            String line;
+            // no banner yet
+            while (bannerReference.get() == null) {
+                // avoid blocking if no input, because banner can become available and it must be shown even if no input lines
+                if (reader.ready()) {
+                    // this might block if only part of line is available
+                    // this is reasonable because the assumption is that the input is a stream of lines
+                    // so it only blocks for a short while
+                    line = reader.readLine();
+                    System.out.printf(Locale.ROOT, "%s%n", line);
+                } else {
+                    // avoid busy looping when no input lines and no banner
+                    Thread.sleep(1000);
+                }
+            }
+            Banner banner = bannerReference.get();
+            // print banner
+            System.out.printf(Locale.ROOT, "%s%n", banner.banner);
+            // we can block indefinitely for input lines since the banner has already been printed
+            while ((line = reader.readLine()) != null) {
+                // clear banner
+                System.out.printf(Locale.ROOT, "\u001b[%dF\u001b[J", banner.lineCount);
+                // line overwrites banner
+                System.out.printf(Locale.ROOT, "%s%n", line);
+                // append another banner
+                System.out.printf(Locale.ROOT, "%s%n", banner.banner);
+            }
+        } catch (InterruptedException e) {
+            Thread.currentThread().interrupt();
+        }
+    }
+
+    private static class Banner {
+        String banner;
+        Integer lineCount;
+
+        Banner(String banner, Integer lineCount) {
+            this.banner = banner;
+            this.lineCount = lineCount;
+        }
+    }
+
+}

docs/changelog/74516.yaml

@@ -0,0 +1,5 @@
+pr: 74516
+summary: Persistent banner to ./bin/elasticsearch on the terminal
+area: Infra/CLI
+type: feature
+issues: []