[core.logging] recreate outputStream if sighup doesn't dispose append…

…er within 500ms

src/core/server/logging/appenders/file/file_appender.ts

@@ -17,8 +17,12 @@
  * under the License.
  */
 
+import { EventEmitter } from 'events';
+
 import { schema } from '@kbn/config-schema';
 import { createWriteStream, WriteStream } from 'fs';
+import { fromEvent } from 'rxjs';
+import { delay } from 'rxjs/operators';
 
 import { Layout, Layouts } from '../../layouts/layouts';
 import { LogRecord } from '../../log_record';
@@ -35,11 +39,25 @@ export class FileAppender implements DisposableAppender {
     path: schema.string(),
   });
 
+  /**
+   * Simple buffer that will capture log records written while the writable stream
+   * is recreated
+   */
+  private buffer?: LogRecord[];
+
   /**
    * Writable file stream to write formatted `LogRecord` to.
    */
   private outputStream?: WriteStream;
 
+  private refreshFileDescriptorSub? = fromEvent(process as EventEmitter, 'SIGHUP')
+    .pipe(delay(500))
+    .subscribe(() =>
+      this.recreateOutputStream().catch(error => {
+        // TODO: what do we do with errors here?
+      })
+    );
+
   /**
    * Creates FileAppender instance with specified layout and file path.
    * @param layout Instance of `Layout` sub-class responsible for `LogRecord` formatting.
@@ -52,23 +70,33 @@ export class FileAppender implements DisposableAppender {
    * @param record `LogRecord` instance to be logged.
    */
   public append(record: LogRecord) {
-    if (this.outputStream === undefined) {
-      this.outputStream = createWriteStream(this.path, {
-        encoding: 'utf8',
-        flags: 'a',
-      });
+    if (this.buffer) {
+      this.buffer.push(record);
+      return;
+    }
+
+    if (!this.outputStream) {
+      this.createOutputStream();
     }
 
-    this.outputStream.write(`${this.layout.format(record)}\n`);
+    this.outputStream!.write(`${this.layout.format(record)}\n`);
   }
 
   /**
    * Disposes `FileAppender`. Waits for the underlying file stream to be completely flushed and closed.
    */
   public async dispose() {
+    await this.endOutputStream();
+    if (this.refreshFileDescriptorSub) {
+      this.refreshFileDescriptorSub.unsubscribe();
+      this.refreshFileDescriptorSub = undefined;
+    }
+  }
+
+  private async endOutputStream() {
     await new Promise(resolve => {
-      if (this.outputStream === undefined) {
-        return resolve();
+      if (!this.outputStream) {
+        return;
       }
 
       this.outputStream.end(undefined, undefined, () => {
@@ -77,4 +105,22 @@ export class FileAppender implements DisposableAppender {
       });
     });
   }
+
+  private createOutputStream() {
+    this.outputStream = createWriteStream(this.path, {
+      encoding: 'utf8',
+      flags: 'a',
+    });
+  }
+
+  private async recreateOutputStream() {
+    this.buffer = [];
+    await this.endOutputStream();
+
+    const records = this.buffer;
+    this.buffer = undefined;
+    for (const record of records) {
+      this.append(record);
+    }
+  }
 }