add log file

README.md

@@ -30,6 +30,15 @@ gradle
 
 ## 参数
 ```
+-Dauthlibinjector.noLogFile
+    不要将日志输出到文件.
+    默认情况下, authlib-injector 会将日志输出到控制台以及当前目录下的 authlib-injector.log 文件.
+    开启此选项后, 日志仅会输出到控制台.
+
+    需要注意的是, authlib-injector 的日志是不会输出到 Minecraft 服务端/客户端的日志文件中的.
+
+    每次启动时，日志文件都会被清空. 如果有多个进程使用同一个日志文件, 则只有最早启动的会成功打开日志文件.
+
 -Dauthlibinjector.mojangNamespace={default|enabled|disabled}
     设置是否启用 Mojang 命名空间 (@mojang 后缀).
     若验证服务器未设置 feature.no_mojang_namespace 选项, 则该功能默认启用.

src/main/java/moe/yushi/authlibinjector/util/Logging.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2020  Haowei Wen <yushijinhun@gmail.com> and contributors
+ * Copyright (C) 2021  Haowei Wen <yushijinhun@gmail.com> and contributors
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU Affero General Public License as published by
@@ -16,15 +16,50 @@
  */
 package moe.yushi.authlibinjector.util;
 
+import static java.nio.file.StandardOpenOption.CREATE;
+import static java.nio.file.StandardOpenOption.WRITE;
+import static moe.yushi.authlibinjector.util.Logging.Level.INFO;
+import static moe.yushi.authlibinjector.util.Logging.Level.WARNING;
+import java.io.IOException;
 import java.io.PrintStream;
 import java.io.PrintWriter;
 import java.io.StringWriter;
+import java.nio.channels.FileChannel;
+import java.nio.charset.Charset;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.time.Instant;
 import moe.yushi.authlibinjector.Config;
 
 public final class Logging {
 	private Logging() {}
 
 	private static final PrintStream out = System.err;
+	private static final FileChannel logfile = openLogFile();
+
+	private static FileChannel openLogFile() {
+		if (System.getProperty("authlibinjector.noLogFile") != null) {
+			log(INFO, "Logging to file is disabled");
+			return null;
+		}
+
+		Path logfilePath = Paths.get("authlib-injector.log").toAbsolutePath();
+		try {
+			FileChannel channel = FileChannel.open(logfilePath, CREATE, WRITE);
+			if (channel.tryLock() == null) {
+				log(WARNING, "Couldn't lock log file [" + logfilePath + "]");
+				return null;
+			}
+			channel.truncate(0);
+			String logHeader = "Logging started at " + Instant.now() + System.lineSeparator();
+			channel.write(Charset.defaultCharset().encode(logHeader));
+			log(INFO, "Logging file: " + logfilePath);
+			return channel;
+		} catch (IOException e) {
+			log(WARNING, "Couldn't open log file [" + logfilePath + "]");
+			return null;
+		}
+	}
 
 	public static enum Level {
 		DEBUG, INFO, WARNING, ERROR;
@@ -50,5 +85,14 @@ public final class Logging {
 		// remove control characters to prevent messing up the console
 		log = log.replaceAll("[\\p{Cc}&&[^\r\n\t]]", "");
 		out.println(log);
+
+		if (logfile != null) {
+			try {
+				logfile.write(Charset.defaultCharset().encode(log + System.lineSeparator()));
+				logfile.force(true);
+			} catch (IOException ex) {
+				out.println("[authlib-injector] [ERROR] Error writing to log file: " + ex);
+			}
+		}
 	}
 }