Value parser, for parsing a single value into a metric

closes #849

docs/DATA_FORMATS_INPUT.md

@@ -1,5 +1,12 @@
 # Telegraf Input Data Formats
 
+Telegraf is able to parse the following input data formats into metrics:
+
+1. InfluxDB Line Protocol
+1. JSON
+1. Graphite
+1. Value, ie 45 or "booyah"
+
 Telegraf metrics, like InfluxDB
 [points](https://docs.influxdata.com/influxdb/v0.10/write_protocols/line/),
 are a combination of four basic parts:
@@ -134,6 +141,38 @@ Your Telegraf metrics would get tagged with "my_tag_1"
 exec_mycollector,my_tag_1=foo a=5,b_c=6
 ```
 
+## Value:
+
+The "value" data format translates single values into Telegraf metrics. This
+is done by assigning a measurement name (which can be overridden using the
+`name_override` config option), and setting a single field ("value") as the
+parsed metric.
+
+#### Value Configuration:
+
+You can tell Telegraf what type of metric to collect by using the `data_type`
+configuration option.
+
+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 name of the
+plugin.
+
+```toml
+[[inputs.exec]]
+  ## Commands array
+  commands = ["cat /proc/sys/kernel/random/entropy_avail"]
+
+  ## override the default metric name of "exec"
+  name_override = "entropy_available"
+
+  ## Data format to consume. This can be "json", "value", influx" or "graphite"
+  ## Each data format has it's own unique set of configuration options, read
+  ## more about them here:
+  ## https://github.com/influxdata/telegraf/blob/master/docs/DATA_FORMATS_INPUT.md
+  data_format = "value"
+  data_type = "integer"
+```
+
 ## Graphite:
 
 The Graphite data format translates graphite _dot_ buckets directly into

internal/config/config.go

@@ -701,12 +701,21 @@ func buildParser(name string, tbl *ast.Table) (parsers.Parser, error) {
 		}
 	}
 
+	if node, ok := tbl.Fields["data_type"]; ok {
+		if kv, ok := node.(*ast.KeyValue); ok {
+			if str, ok := kv.Value.(*ast.String); ok {
+				c.DataType = str.Value
+			}
+		}
+	}
+
 	c.MetricName = name
 
 	delete(tbl.Fields, "data_format")
 	delete(tbl.Fields, "separator")
 	delete(tbl.Fields, "templates")
 	delete(tbl.Fields, "tag_keys")
+	delete(tbl.Fields, "data_type")
 
 	return parsers.NewParser(c)
 }

plugins/parsers/registry.go

@@ -8,6 +8,7 @@ import (
 	"github.com/influxdata/telegraf/plugins/parsers/graphite"
 	"github.com/influxdata/telegraf/plugins/parsers/influx"
 	"github.com/influxdata/telegraf/plugins/parsers/json"
+	"github.com/influxdata/telegraf/plugins/parsers/value"
 )
 
 // ParserInput is an interface for input plugins that are able to parse
@@ -38,7 +39,7 @@ type Parser interface {
 // Config is a struct that covers the data types needed for all parser types,
 // and can be used to instantiate _any_ of the parsers.
 type Config struct {
-	// Dataformat can be one of: json, influx, graphite
+	// Dataformat can be one of: json, influx, graphite, value
 	DataFormat string
 
 	// Separator only applied to Graphite data.
@@ -48,9 +49,12 @@ type Config struct {
 
 	// TagKeys only apply to JSON data
 	TagKeys []string
-	// MetricName only applies to JSON data. This will be the name of the measurement.
+	// MetricName applies to JSON & value. This will be the name of the measurement.
 	MetricName string
 
+	// DataType only applies to value, this will be the type to parse value to
+	DataType string
+
 	// DefaultTags are the default tags that will be added to all parsed metrics.
 	DefaultTags map[string]string
 }
@@ -63,6 +67,9 @@ func NewParser(config *Config) (Parser, error) {
 	case "json":
 		parser, err = NewJSONParser(config.MetricName,
 			config.TagKeys, config.DefaultTags)
+	case "value":
+		parser, err = NewValueParser(config.MetricName,
+			config.DataType, config.DefaultTags)
 	case "influx":
 		parser, err = NewInfluxParser()
 	case "graphite":
@@ -98,3 +105,15 @@ func NewGraphiteParser(
 ) (Parser, error) {
 	return graphite.NewGraphiteParser(separator, templates, defaultTags)
 }
+
+func NewValueParser(
+	metricName string,
+	dataType string,
+	defaultTags map[string]string,
+) (Parser, error) {
+	return &value.ValueParser{
+		MetricName:  metricName,
+		DataType:    dataType,
+		DefaultTags: defaultTags,
+	}, nil
+}

plugins/parsers/value/parser.go

@@ -0,0 +1,68 @@
+package value
+
+import (
+	"bytes"
+	"fmt"
+	"strconv"
+	"time"
+
+	"github.com/influxdata/telegraf"
+)
+
+type ValueParser struct {
+	MetricName  string
+	DataType    string
+	DefaultTags map[string]string
+}
+
+func (v *ValueParser) Parse(buf []byte) ([]telegraf.Metric, error) {
+	// separate out any fields in the buffer, ignore anything but the first.
+	values := bytes.Fields(buf)
+	if len(values) < 1 {
+		return []telegraf.Metric{}, nil
+	}
+	valueStr := string(values[0])
+
+	var value interface{}
+	var err error
+	switch v.DataType {
+	case "", "int", "integer":
+		value, err = strconv.Atoi(valueStr)
+	case "float", "long":
+		value, err = strconv.ParseFloat(valueStr, 64)
+	case "str", "string":
+		value = valueStr
+	case "bool", "boolean":
+		value, err = strconv.ParseBool(valueStr)
+	}
+	if err != nil {
+		return nil, err
+	}
+
+	fields := map[string]interface{}{"value": value}
+	metric, err := telegraf.NewMetric(v.MetricName, v.DefaultTags,
+		fields, time.Now().UTC())
+	if err != nil {
+		return nil, err
+	}
+
+	return []telegraf.Metric{metric}, nil
+}
+
+func (v *ValueParser) ParseLine(line string) (telegraf.Metric, error) {
+	metrics, err := v.Parse([]byte(line))
+
+	if err != nil {
+		return nil, err
+	}
+
+	if len(metrics) < 1 {
+		return nil, fmt.Errorf("Can not parse the line: %s, for data format: value", line)
+	}
+
+	return metrics[0], nil
+}
+
+func (v *ValueParser) SetDefaultTags(tags map[string]string) {
+	v.DefaultTags = tags
+}