all: imp adguard_legacy log, docs

README.md

@@ -130,8 +130,6 @@ Option `--version` makes AdGuard DNS Client print out the version of the `AdGuar
 
 ## <a href="#conf" id="conf" name="conf">Configuration</a>
 
-### <a href="#conf-file" id="conf-file" name="conf-file">File</a>
-
 The YAML configuration file is described in the [`doc/configuration.md`] file, and there is also a sample configuration file `config.dist.yaml`. Some configuration parameters can also be overridden using the environment, see [`doc/environment.md`].
 
 [`doc/configuration.md`]: doc/configuration.md

doc/configuration.md

@@ -208,16 +208,19 @@ the following properties:
 
 ##  <a href="#log" id="log" name="log">Logging</a>
 
-**NOTE:** In its current state, the log system is only intended for debugging
-startup errors.
+> [!NOTE]
+> In its current state, the log system is only intended for debugging startup errors.
 
 The `log` object configures the logging.  It has the following properties:
 
  *  <a href="#log-output" id="log-output" name="log-output">`output`</a>:
     The output to which logs are written.
 
-    **NOTE:** Log entries written to the system log are in text format and use
-    the system timestamp.
+    > [!NOTE]
+    > Log entries written to the system log are in text format and use the system timestamp.
+
+    > [!NOTE]
+    > If `log.format` is set to `adguard_legacy`, output is set to `stderr`.
 
     Possible values:
 
@@ -239,6 +242,9 @@ The `log` object configures the logging.  It has the following properties:
  *  <a href="#log-format" id="log-format" name="log-format">`format`</a>:
     Specifies format of the log entries.
 
+    > [!NOTE]
+    > If `log.format` is set to `adguard_legacy`, output is set to `stderr`.
+
     Possible values:
 
      *  `adguard_legacy`;

doc/environment.md

@@ -24,6 +24,9 @@ AdGuard DNS Client uses [environment variables][wiki-env] to store some of the c
 
 The log destination, must be an absolute path to the file or one of the special values.
 
+> [!NOTE]
+> If `LOG_FORMAT` is set to `adguard_legacy`, output is set to `stderr`.
+
 - `syslog` means that the platform-specific system log is used, which is syslog for Linux and Event Log for Windows.
 
     > [!NOTE]
@@ -49,6 +52,9 @@ This environment variable has priority over [log.output][conf-log-output] field
 
 The format for log entries.
 
+> [!NOTE]
+> If `LOG_FORMAT` is set to `adguard_legacy`, output is set to `stderr`.
+
 - `adguard_legacy`;
 - `default`;
 - `json`;

internal/cmd/program.go

@@ -41,13 +41,14 @@ func (prog *program) Start(_ osservice.Service) (err error) {
 	ctx := context.Background()
 	l := prog.log.With(slogutil.KeyPrefix, serviceProgramPrefix)
 
-	// Disable the dnsproxy logging for now, unless asked for debug output.
+	// Disable the dnsproxy logging for now, unless asked for debug output or
+	// using the "adguard_legacy" format.
 	//
 	// TODO(e.burkov):  Use [log/slog] in [dnsproxy] and make it configurable.
 	isVerbose := l.Enabled(ctx, slog.LevelDebug)
 	if isVerbose {
 		log.SetLevel(log.DEBUG)
-	} else {
+	} else if _, ok := l.Handler().(*slogutil.AdGuardLegacyHandler); !ok {
 		log.SetLevel(log.OFF)
 	}