add "field_tags" to json parser config

plugins/parsers/json/parser.go

@@ -20,6 +20,7 @@ var (
 type JSONParser struct {
 	MetricName  string
 	TagKeys     []string
+	FieldKeys   []string
 	DefaultTags map[string]string
 }
 
@@ -86,6 +87,17 @@ func (p *JSONParser) switchFieldToTag(tags map[string]string, fields map[string]
 		}
 	}
 
+	//if field_keys is specified, only those values should be reported as fields
+	if len(p.FieldKeys) > 0 {
+		nFields := make(map[string]interface{})
+		for _, name := range p.FieldKeys {
+			if fields[name] != nil {
+				nFields[name] = fields[name]
+			}
+		}
+		return tags, nFields
+	}
+
 	//remove any additional string/bool values from fields
 	for k := range fields {
 		switch fields[k].(type) {

plugins/parsers/json/parser_test.go

@@ -448,19 +448,24 @@ func TestJSONParseNestedArray(t *testing.T) {
 	"total_devices": 5,
 	"total_threads": 10,
 	"shares": {
-	"total": 5,
-	"accepted": 5,
-	"rejected": 0,
-	"avg_find_time": 4,
-	"tester": "work",
-	"tester2": "don't want this",
-	"tester3": 7.93
+		"total": 5,
+		"accepted": 5,
+		"rejected": 0,
+		"avg_find_time": 4,
+		"tester": "work",
+		"tester2": "don't want this",
+		"tester3": {
+			"hello":"sup",
+			"fun":"money",
+			"break":9
+		}
 	}
 	}`
 
 	parser := JSONParser{
 		MetricName: "json_test",
-		TagKeys:    []string{"total_devices", "total_threads", "shares_tester", "shares_tester3"},
+		TagKeys:    []string{"total_devices", "total_threads", "shares_tester3_fun"},
+		FieldKeys:  []string{"shares_tester", "shares_tester3_break"},
 	}
 
 	metrics, err := parser.Parse([]byte(testString))