Capture stdout and stderr to log4j log (#50259)

This commit overrides the stdout and stderr print streams to be
redirected to the main elasticsearch.log file. While the Elasticsearch
project ensures stdout and stderr are not written to, the jdk or 3rd
party libs may do this, which can be unexepected for users used to
looking the elasticsearch log.

closes #50156

server/src/main/java/org/elasticsearch/common/logging/LogConfigurator.java

@@ -48,6 +48,8 @@ import org.elasticsearch.node.Node;
 
 import java.io.IOException;
 import java.io.InputStream;
+import java.io.PrintStream;
+import java.nio.charset.StandardCharsets;
 import java.nio.file.FileVisitOption;
 import java.nio.file.FileVisitResult;
 import java.nio.file.Files;
@@ -242,6 +244,11 @@ public class LogConfigurator {
                     + "log4j2.properties but will stop this behavior in 7.0. You should manually replace `%node_name` with "
                     + "`[%node_name]%marker ` in these locations:\n  {}", deprecatedLocationsString);
         }
+
+        // Redirect stdout/stderr to log4j. While we ensure Elasticsearch code does not write to those streams,
+        // third party libraries may do that
+        System.setOut(new PrintStream(new LoggingOutputStream(LogManager.getLogger("stdout"), Level.INFO), false, StandardCharsets.UTF_8));
+        System.setOut(new PrintStream(new LoggingOutputStream(LogManager.getLogger("stderr"), Level.WARN), false, StandardCharsets.UTF_8));
     }
 
     private static void configureStatusLogger() {

server/src/main/java/org/elasticsearch/common/logging/LoggingOutputStream.java

@@ -0,0 +1,111 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.elasticsearch.common.logging;
+
+import org.apache.logging.log4j.Level;
+import org.apache.logging.log4j.Logger;
+
+import java.io.IOException;
+import java.io.OutputStream;
+import java.nio.charset.StandardCharsets;
+import java.util.Arrays;
+
+/**
+ * A stream whose output is sent to the configured logger, line by line.
+ */
+class LoggingOutputStream extends OutputStream {
+    /** The starting length of the buffer */
+    static final int DEFAULT_BUFFER_LENGTH = 1024;
+
+    // limit a single log message to 64k
+    static final int MAX_BUFFER_LENGTH = DEFAULT_BUFFER_LENGTH * 64;
+
+    class Buffer {
+
+        /** The buffer of bytes sent to the stream */
+        byte[] bytes = new byte[DEFAULT_BUFFER_LENGTH];
+
+        /** Number of used bytes in the buffer */
+        int used = 0;
+    }
+
+    // each thread gets its own buffer so messages don't get garbled
+    ThreadLocal<Buffer> threadLocal = ThreadLocal.withInitial(Buffer::new);
+
+    private final Logger logger;
+
+    private final Level level;
+
+    LoggingOutputStream(Logger logger, Level level) {
+        this.logger = logger;
+        this.level = level;
+    }
+
+    @Override
+    public void write(int b) throws IOException {
+        if (threadLocal == null) {
+            throw new IOException("buffer closed");
+        }
+        if (b == 0) return;
+        if (b == '\n') {
+            // always flush with newlines instead of adding to the buffer
+            flush();
+            return;
+        }
+
+        Buffer buffer = threadLocal.get();
+
+        if (buffer.used == buffer.bytes.length) {
+            if (buffer.bytes.length >= MAX_BUFFER_LENGTH) {
+                // don't let the buffer get infinitely big
+                flush();
+                // we reset the buffer in flush so get the new instance
+                buffer = threadLocal.get();
+            } else {
+                // extend the buffer
+                buffer.bytes = Arrays.copyOf(buffer.bytes, 2 * buffer.bytes.length);
+            }
+        }
+
+        buffer.bytes[buffer.used++] = (byte) b;
+    }
+
+    @Override
+    public void flush() {
+        Buffer buffer = threadLocal.get();
+        if (buffer.used == 0) return;
+        log(new String(buffer.bytes, 0, buffer.used, StandardCharsets.UTF_8));
+        if (buffer.bytes.length != DEFAULT_BUFFER_LENGTH) {
+            threadLocal.set(new Buffer()); // reset size
+        } else {
+            buffer.used = 0;
+        }
+    }
+
+    @Override
+    public void close() {
+        threadLocal = null;
+    }
+
+    // pkg private for testing
+    void log(String msg) {
+        logger.log(level, msg);
+    }
+}

server/src/test/java/org/elasticsearch/common/logging/LoggingOutputStreamTests.java

@@ -0,0 +1,114 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.elasticsearch.common.logging;
+
+import org.elasticsearch.test.ESTestCase;
+import org.junit.Before;
+
+import java.io.IOException;
+import java.io.PrintStream;
+import java.nio.charset.StandardCharsets;
+import java.util.ArrayList;
+import java.util.List;
+
+import static org.elasticsearch.common.logging.LoggingOutputStream.DEFAULT_BUFFER_LENGTH;
+import static org.elasticsearch.common.logging.LoggingOutputStream.MAX_BUFFER_LENGTH;
+import static org.hamcrest.Matchers.contains;
+import static org.hamcrest.Matchers.containsString;
+import static org.hamcrest.Matchers.equalTo;
+
+public class LoggingOutputStreamTests extends ESTestCase {
+
+    class TestLoggingOutputStream extends LoggingOutputStream {
+        List<String> lines = new ArrayList<>();
+
+        TestLoggingOutputStream() {
+            super(null, null);
+        }
+
+        @Override
+        void log(String msg) {
+            lines.add(msg);
+        }
+    }
+
+    TestLoggingOutputStream loggingStream;
+    PrintStream printStream;
+
+    @Before
+    public void createStream() {
+        loggingStream = new TestLoggingOutputStream();
+        printStream = new PrintStream(loggingStream, false, StandardCharsets.UTF_8);
+    }
+
+    public void testEmptyLine() {
+        printStream.println("");
+        assertTrue(loggingStream.lines.isEmpty());
+        printStream.flush();
+        assertTrue(loggingStream.lines.isEmpty());
+    }
+
+    public void testNull() {
+        printStream.write(0);
+        printStream.flush();
+        assertTrue(loggingStream.lines.isEmpty());
+    }
+
+    public void testFlushOnNewline() {
+        printStream.println("hello");
+        printStream.println("world");
+        assertThat(loggingStream.lines, contains("hello", "world"));
+    }
+
+    public void testBufferExtension() {
+        String longStr = randomAlphaOfLength(DEFAULT_BUFFER_LENGTH);
+        String extraLongStr = randomAlphaOfLength(DEFAULT_BUFFER_LENGTH + 1);
+        printStream.println(longStr);
+        assertThat(loggingStream.threadLocal.get().bytes.length, equalTo(DEFAULT_BUFFER_LENGTH));
+        printStream.println(extraLongStr);
+        assertThat(loggingStream.lines, contains(longStr, extraLongStr));
+        assertThat(loggingStream.threadLocal.get().bytes.length, equalTo(DEFAULT_BUFFER_LENGTH));
+    }
+
+    public void testMaxBuffer() {
+        String longStr = randomAlphaOfLength(MAX_BUFFER_LENGTH);
+        String extraLongStr = longStr + "OVERFLOW";
+        printStream.println(longStr);
+        printStream.println(extraLongStr);
+        assertThat(loggingStream.lines, contains(longStr, longStr, "OVERFLOW"));
+    }
+
+    public void testClosed() {
+        loggingStream.close();
+        IOException e = expectThrows(IOException.class, () -> loggingStream.write('a'));
+        assertThat(e.getMessage(), containsString("buffer closed"));
+    }
+
+    public void testThreadIsolation() throws Exception {
+        printStream.print("from thread 1");
+        Thread thread2 = new Thread(() -> {
+            printStream.println("from thread 2");
+        });
+        thread2.start();
+        thread2.join();
+        printStream.flush();
+        assertThat(loggingStream.lines, contains("from thread 2", "from thread 1"));
+    }
+}