From 9a65e7ccd2bad9082586a4de21f914648416c90f Mon Sep 17 00:00:00 2001
From: Ravi Raju <ravir@employees.org>
Date: Wed, 8 Nov 2017 10:47:56 -0800
Subject: [PATCH] Fix Output with existing context (fix #20)

Also includes tests for Output()
---
 log.go      |  6 ++++--
 log_test.go | 28 ++++++++++++++++++++++++++++
 2 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/log.go b/log.go
index a9b4121..66c8410 100644
--- a/log.go
+++ b/log.go
@@ -155,8 +155,10 @@ func (l Logger) Output(w io.Writer) Logger {
 	l2 := New(w)
 	l2.level = l.level
 	l2.sampler = l.sampler
-	l2.context = make([]byte, len(l.context), cap(l.context))
-	copy(l2.context, l.context)
+	if l.context != nil {
+		l2.context = make([]byte, len(l.context), cap(l.context))
+		copy(l2.context, l.context)
+	}
 	return l2
 }
 
diff --git a/log_test.go b/log_test.go
index a5a51e5..ed9e498 100644
--- a/log_test.go
+++ b/log_test.go
@@ -406,3 +406,31 @@ func TestEventTimestamp(t *testing.T) {
 		t.Errorf("invalid log output:\ngot:  %v\nwant: %v", got, want)
 	}
 }
+
+func TestOutputWithoutTimestamp(t *testing.T) {
+	ignoredOut := &bytes.Buffer{}
+	out := &bytes.Buffer{}
+	log := New(ignoredOut).Output(out).With().Str("foo", "bar").Logger()
+	log.Log().Msg("hello world")
+
+	if got, want := out.String(), `{"foo":"bar","message":"hello world"}`+"\n"; got != want {
+		t.Errorf("invalid log output:\ngot:  %v\nwant: %v", got, want)
+	}
+}
+
+func TestOutputWithTimestamp(t *testing.T) {
+	TimestampFunc = func() time.Time {
+		return time.Date(2001, time.February, 3, 4, 5, 6, 7, time.UTC)
+	}
+	defer func() {
+		TimestampFunc = time.Now
+	}()
+	ignoredOut := &bytes.Buffer{}
+	out := &bytes.Buffer{}
+	log := New(ignoredOut).Output(out).With().Timestamp().Str("foo", "bar").Logger()
+	log.Log().Msg("hello world")
+
+	if got, want := out.String(), `{"time":"2001-02-03T04:05:06Z","foo":"bar","message":"hello world"}`+"\n"; got != want {
+		t.Errorf("invalid log output:\ngot:  %v\nwant: %v", got, want)
+	}
+}