Use an 'auto' parser by default for value input format

docs/DATA_FORMATS_INPUT.md

@@ -150,8 +150,14 @@ as the parsed metric.
 
 #### Value Configuration:
 
-You **must** tell Telegraf what type of metric to collect by using the
-`data_type` configuration option.
+You **should** tell Telegraf what type of metric to collect by using the
+`data_type` configuration option. The options are:
+
+1. integer
+1. float
+1. string
+1. boolean
+1. auto (this will try parsing into the above types, in order)
 
 **Note:** It is also recommended that you set `name_override` to a measurement
 name that makes sense for your metric, otherwise it will just be set to the
@@ -170,7 +176,7 @@ name of the plugin.
   ## more about them here:
   ## https://github.com/influxdata/telegraf/blob/master/docs/DATA_FORMATS_INPUT.md
   data_format = "value"
-  data_type = "integer" # required
+  data_type = "integer"
 ```
 
 # Graphite:

plugins/parsers/value/parser.go

@@ -26,7 +26,9 @@ func (v *ValueParser) Parse(buf []byte) ([]telegraf.Metric, error) {
 	var value interface{}
 	var err error
 	switch v.DataType {
-	case "", "int", "integer":
+	case "", "auto":
+		value, err = autoParse(valueStr)
+	case "int", "integer":
 		value, err = strconv.Atoi(valueStr)
 	case "float", "long":
 		value, err = strconv.ParseFloat(valueStr, 64)
@@ -49,6 +51,30 @@ func (v *ValueParser) Parse(buf []byte) ([]telegraf.Metric, error) {
 	return []telegraf.Metric{metric}, nil
 }
 
+// autoParse tries to parse the given string into (in order):
+//   1. integer
+//   2. float
+//   3. boolean
+//   4. string
+func autoParse(valueStr string) (interface{}, error) {
+	var value interface{}
+	var err error
+	// 1st try integer:
+	if value, err = strconv.Atoi(valueStr); err == nil {
+		return value, err
+	}
+	// 2nd try float:
+	if value, err = strconv.ParseFloat(valueStr, 64); err == nil {
+		return value, err
+	}
+	// 3rd try boolean:
+	if value, err = strconv.ParseBool(valueStr); err == nil {
+		return value, err
+	}
+	// 4th, none worked, so string
+	return valueStr, nil
+}
+
 func (v *ValueParser) ParseLine(line string) (telegraf.Metric, error) {
 	metrics, err := v.Parse([]byte(line))
 

plugins/parsers/value/parser_test.go

@@ -60,6 +60,60 @@ func TestParseValidValues(t *testing.T) {
 	assert.Equal(t, map[string]string{}, metrics[0].Tags())
 }
 
+func TestParseAutoValues(t *testing.T) {
+	parser := ValueParser{
+		MetricName: "value_test",
+		DataType:   "auto",
+	}
+	metrics, err := parser.Parse([]byte("55"))
+	assert.NoError(t, err)
+	assert.Len(t, metrics, 1)
+	assert.Equal(t, "value_test", metrics[0].Name())
+	assert.Equal(t, map[string]interface{}{
+		"value": int64(55),
+	}, metrics[0].Fields())
+	assert.Equal(t, map[string]string{}, metrics[0].Tags())
+
+	parser = ValueParser{
+		MetricName: "value_test",
+		DataType:   "auto",
+	}
+	metrics, err = parser.Parse([]byte("64.1"))
+	assert.NoError(t, err)
+	assert.Len(t, metrics, 1)
+	assert.Equal(t, "value_test", metrics[0].Name())
+	assert.Equal(t, map[string]interface{}{
+		"value": float64(64.1),
+	}, metrics[0].Fields())
+	assert.Equal(t, map[string]string{}, metrics[0].Tags())
+
+	parser = ValueParser{
+		MetricName: "value_test",
+		DataType:   "auto",
+	}
+	metrics, err = parser.Parse([]byte("foobar"))
+	assert.NoError(t, err)
+	assert.Len(t, metrics, 1)
+	assert.Equal(t, "value_test", metrics[0].Name())
+	assert.Equal(t, map[string]interface{}{
+		"value": "foobar",
+	}, metrics[0].Fields())
+	assert.Equal(t, map[string]string{}, metrics[0].Tags())
+
+	parser = ValueParser{
+		MetricName: "value_test",
+		DataType:   "auto",
+	}
+	metrics, err = parser.Parse([]byte("true"))
+	assert.NoError(t, err)
+	assert.Len(t, metrics, 1)
+	assert.Equal(t, "value_test", metrics[0].Name())
+	assert.Equal(t, map[string]interface{}{
+		"value": true,
+	}, metrics[0].Fields())
+	assert.Equal(t, map[string]string{}, metrics[0].Tags())
+}
+
 func TestParseMultipleValues(t *testing.T) {
 	parser := ValueParser{
 		MetricName: "value_test",