1 files changed, 91 insertions, 9 deletions

diff --git a/std/log/handlers.ts b/std/log/handlers.ts
index 32b0525e7..eea7f32ff 100644
--- a/std/log/handlers.ts
+++ b/std/log/handlers.ts
@@ -1,13 +1,15 @@
 // Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
-const { open } = Deno;
+const { open, openSync, close, renameSync, statSync } = Deno;
 type File = Deno.File;
 type Writer = Deno.Writer;
 import { getLevelByName, LogLevel } from "./levels.ts";
 import { LogRecord } from "./logger.ts";
 import { red, yellow, blue, bold } from "../fmt/colors.ts";
+import { existsSync, exists } from "../fs/exists.ts";
 
 const DEFAULT_FORMATTER = "{levelName} {msg}";
 type FormatterFunction = (logRecord: LogRecord) => string;
+type LogMode = "a" | "w" | "x";
 
 interface HandlerOptions {
   formatter?: string | FormatterFunction;
@@ -85,33 +87,113 @@ export class ConsoleHandler extends BaseHandler {
 
 export abstract class WriterHandler extends BaseHandler {
   protected _writer!: Writer;
-  private _encoder = new TextEncoder();
+  #encoder = new TextEncoder();
 
-  log(msg: string): void {
-    this._writer.write(this._encoder.encode(msg + "\n"));
-  }
+  abstract log(msg: string): void;
 }
 
 interface FileHandlerOptions extends HandlerOptions {
   filename: string;
+  mode?: LogMode;
 }
 
 export class FileHandler extends WriterHandler {
-  private _file!: File;
-  private _filename: string;
+  protected _file!: File;
+  protected _filename: string;
+  protected _mode: LogMode;
+  #encoder = new TextEncoder();
 
   constructor(levelName: string, options: FileHandlerOptions) {
     super(levelName, options);
     this._filename = options.filename;
+    // default to append mode, write only
+    this._mode = options.mode ? options.mode : "a";
   }
 
   async setup(): Promise<void> {
-    // open file in append mode - write only
-    this._file = await open(this._filename, "a");
+    this._file = await open(this._filename, this._mode);
     this._writer = this._file;
   }
 
+  log(msg: string): void {
+    Deno.writeSync(this._file.rid, this.#encoder.encode(msg + "\n"));
+  }
+
   async destroy(): Promise<void> {
     await this._file.close();
   }
 }
+
+interface RotatingFileHandlerOptions extends FileHandlerOptions {
+  maxBytes: number;
+  maxBackupCount: number;
+}
+
+export class RotatingFileHandler extends FileHandler {
+  #maxBytes: number;
+  #maxBackupCount: number;
+
+  constructor(levelName: string, options: RotatingFileHandlerOptions) {
+    super(levelName, options);
+    this.#maxBytes = options.maxBytes;
+    this.#maxBackupCount = options.maxBackupCount;
+  }
+
+  async setup(): Promise<void> {
+    if (this.#maxBytes < 1) {
+      throw new Error("maxBytes cannot be less than 1");
+    }
+    if (this.#maxBackupCount < 1) {
+      throw new Error("maxBackupCount cannot be less than 1");
+    }
+    await super.setup();
+
+    if (this._mode === "w") {
+      // Remove old backups too as it doesn't make sense to start with a clean
+      // log file, but old backups
+      for (let i = 1; i <= this.#maxBackupCount; i++) {
+        if (await exists(this._filename + "." + i)) {
+          await Deno.remove(this._filename + "." + i);
+        }
+      }
+    } else if (this._mode === "x") {
+      // Throw if any backups also exist
+      for (let i = 1; i <= this.#maxBackupCount; i++) {
+        if (await exists(this._filename + "." + i)) {
+          Deno.close(this._file.rid);
+          throw new Deno.errors.AlreadyExists(
+            "Backup log file " + this._filename + "." + i + " already exists"
+          );
+        }
+      }
+    }
+  }
+
+  handle(logRecord: LogRecord): void {
+    if (this.level > logRecord.level) return;
+
+    const msg = this.format(logRecord);
+    const currentFileSize = statSync(this._filename).size;
+    if (currentFileSize + msg.length > this.#maxBytes) {
+      this.rotateLogFiles();
+    }
+
+    return this.log(msg);
+  }
+
+  rotateLogFiles(): void {
+    close(this._file.rid);
+
+    for (let i = this.#maxBackupCount - 1; i >= 0; i--) {
+      const source = this._filename + (i === 0 ? "" : "." + i);
+      const dest = this._filename + "." + (i + 1);
+
+      if (existsSync(source)) {
+        renameSync(source, dest);
+      }
+    }
+
+    this._file = openSync(this._filename, this._mode);
+    this._writer = this._file;
+  }
+}