From 62dd5a0023dc25365e30595f77e38e2a3d61dd38 Mon Sep 17 00:00:00 2001
From: David Arroyo <droyo@aqwari.net>
Date: Sat, 30 Jul 2016 19:46:45 -0400
Subject: [PATCH] Add log.Logger's Output method to Logger&Entry

The standard library's *log.Logger type has the method

	Output(calldepth int, s string) error

Because it is so minimal, many libraries chose to target
it as an interface, which users could implement to receive
additional log messages:

	type Logger {
		Output(int, string) error
	}

While it is not overwhelmingly used, it is out there. Implementing
this interface allows us to use logrus.Logger and logrus.Entry
types to receive log messages from such libraries. I chose to log
such messages at the "Info" level, copying the Print* methods. The
"calldepth" argument is ignored.
---
 entry.go       | 5 +++++
 logger.go      | 5 +++++
 logrus_test.go | 9 +++++++++
 3 files changed, 19 insertions(+)

diff --git a/entry.go b/entry.go
index 54bfc57d7..92584aa2d 100644
--- a/entry.go
+++ b/entry.go
@@ -254,6 +254,11 @@ func (entry *Entry) Panicln(args ...interface{}) {
 	}
 }
 
+func (entry *Entry) Output(calldepth int, s string) error {
+	entry.Infoln(s)
+	return nil
+}
+
 // Sprintlnn => Sprint no newline. This is to get the behavior of how
 // fmt.Sprintln where spaces are always added between operands, regardless of
 // their type. Instead of vendoring the Sprintln implementation to spare a
diff --git a/logger.go b/logger.go
index 9052a8065..0ac2f67f5 100644
--- a/logger.go
+++ b/logger.go
@@ -210,3 +210,8 @@ func (logger *Logger) Panicln(args ...interface{}) {
 		NewEntry(logger).Panicln(args...)
 	}
 }
+
+func (logger *Logger) Output(calldepth int, s string) error {
+	NewEntry(logger).Println(s)
+	return nil
+}
diff --git a/logrus_test.go b/logrus_test.go
index bfc478055..5d3915da3 100644
--- a/logrus_test.go
+++ b/logrus_test.go
@@ -83,6 +83,15 @@ func TestWarn(t *testing.T) {
 	})
 }
 
+func TestOutput(t *testing.T) {
+	LogAndAssertJSON(t, func(log *Logger) {
+		log.Output(2, "test")
+	}, func(fields Fields) {
+		assert.Equal(t, fields["msg"], "test")
+		assert.Equal(t, fields["level"], "info")
+	})
+}
+
 func TestInfolnShouldAddSpacesBetweenStrings(t *testing.T) {
 	LogAndAssertJSON(t, func(log *Logger) {
 		log.Infoln("test", "test")