From 2ce6c0cb44b88b3cf9b97e7513269d00c7eee11c Mon Sep 17 00:00:00 2001
From: Przemyslaw Wegrzyn <pwegrzyn@codepainters.com>
Date: Tue, 19 Jun 2018 14:31:57 +0200
Subject: [PATCH] Support for Entry data under nested JSON dictionary.

---
 json_formatter.go      | 10 ++++++++++
 json_formatter_test.go | 42 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 52 insertions(+)

diff --git a/json_formatter.go b/json_formatter.go
index 7064947..dab1761 100644
--- a/json_formatter.go
+++ b/json_formatter.go
@@ -33,6 +33,9 @@ type JSONFormatter struct {
 	// DisableTimestamp allows disabling automatic timestamps in output
 	DisableTimestamp bool
 
+	// DataKey allows users to put all the log entry parameters into a nested dictionary at a given key.
+	DataKey string
+
 	// FieldMap allows users to customize the names of keys for default fields.
 	// As an example:
 	// formatter := &JSONFormatter{
@@ -58,6 +61,13 @@ func (f *JSONFormatter) Format(entry *Entry) ([]byte, error) {
 			data[k] = v
 		}
 	}
+
+	if f.DataKey != "" {
+		newData := make(Fields, 4)
+		newData[f.DataKey] = data
+		data = newData
+	}
+
 	prefixFieldClashes(data, f.FieldMap)
 
 	timestampFormat := f.TimestampFormat
diff --git a/json_formatter_test.go b/json_formatter_test.go
index 1c140d0..0dde300 100644
--- a/json_formatter_test.go
+++ b/json_formatter_test.go
@@ -161,6 +161,48 @@ func TestFieldClashWithRemappedFields(t *testing.T) {
 	}
 }
 
+func TestFieldsInNestedDictionary(t *testing.T) {
+	formatter := &JSONFormatter{
+		DataKey: "args",
+	}
+
+	logEntry := WithFields(Fields{
+		"level":      "level",
+		"test":		  "test",
+	})
+	logEntry.Level = InfoLevel
+
+	b, err := formatter.Format(logEntry)
+	if err != nil {
+		t.Fatal("Unable to format entry: ", err)
+	}
+
+	entry := make(map[string]interface{})
+	err = json.Unmarshal(b, &entry)
+	if err != nil {
+		t.Fatal("Unable to unmarshal formatted entry: ", err)
+	}
+
+	args := entry["args"].(map[string]interface{})
+
+	for _, field := range []string{"test", "level"} {
+		if value, present := args[field]; !present || value != field {
+			t.Errorf("Expected field %v to be present under 'args'; untouched", field)
+		}
+	}
+
+	for _, field := range []string{"test", "fields.level"} {
+		if _, present := entry[field]; present {
+			t.Errorf("Expected field %v not to be present at top level", field)
+		}
+	}
+
+	// with nested object, "level" shouldn't clash
+	if entry["level"] != "info" {
+		t.Errorf("Expected 'level' field to contain 'info'")
+	}
+}
+
 func TestJSONEntryEndsWithNewline(t *testing.T) {
 	formatter := &JSONFormatter{}