1 files changed, 260 insertions, 0 deletions
diff --git a/plugins/metrics/rpc.go b/plugins/metrics/rpc.go
new file mode 100644
index 00000000..2dd6d4ef
--- /dev/null
+++ b/plugins/metrics/rpc.go
@@ -0,0 +1,260 @@
+package metrics
+
+import (
+	"fmt"
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+type rpcServer struct {
+	svc *Plugin
+}
+
+// Metric represent single metric produced by the application.
+type Metric struct {
+	// Collector name.
+	Name string
+
+	// Collector value.
+	Value float64
+
+	// Labels associated with metric. Only for vector metrics. Must be provided in a form of label values.
+	Labels []string
+}
+
+// Add new metric to the designated collector.
+func (rpc *rpcServer) Add(m *Metric, ok *bool) (err error) {
+	defer func() {
+		if r, fail := recover().(error); fail {
+			err = r
+		}
+	}()
+
+	c := rpc.svc.Collector(m.Name)
+	if c == nil {
+		return fmt.Errorf("undefined collector `%s`", m.Name)
+	}
+
+	switch c := c.(type) {
+	case prometheus.Gauge:
+		c.Add(m.Value)
+
+	case *prometheus.GaugeVec:
+		if len(m.Labels) == 0 {
+			return fmt.Errorf("required labels for collector `%s`", m.Name)
+		}
+
+		c.WithLabelValues(m.Labels...).Add(m.Value)
+
+	case prometheus.Counter:
+		c.Add(m.Value)
+
+	case *prometheus.CounterVec:
+		if len(m.Labels) == 0 {
+			return fmt.Errorf("required labels for collector `%s`", m.Name)
+		}
+
+		c.WithLabelValues(m.Labels...).Add(m.Value)
+
+	default:
+		return fmt.Errorf("collector `%s` does not support method `Add`", m.Name)
+	}
+
+	// RPC, set ok to true as return value. Need by rpc.Call reply argument
+	*ok = true
+	return nil
+}
+
+// Sub subtract the value from the specific metric (gauge only).
+func (rpc *rpcServer) Sub(m *Metric, ok *bool) (err error) {
+	defer func() {
+		if r, fail := recover().(error); fail {
+			err = r
+		}
+	}()
+
+	c := rpc.svc.Collector(m.Name)
+	if c == nil {
+		return fmt.Errorf("undefined collector `%s`", m.Name)
+	}
+
+	switch c := c.(type) {
+	case prometheus.Gauge:
+		c.Sub(m.Value)
+
+	case *prometheus.GaugeVec:
+		if len(m.Labels) == 0 {
+			return fmt.Errorf("required labels for collector `%s`", m.Name)
+		}
+
+		c.WithLabelValues(m.Labels...).Sub(m.Value)
+	default:
+		return fmt.Errorf("collector `%s` does not support method `Sub`", m.Name)
+	}
+
+	// RPC, set ok to true as return value. Need by rpc.Call reply argument
+	*ok = true
+	return nil
+}
+
+// Observe the value (histogram and summary only).
+func (rpc *rpcServer) Observe(m *Metric, ok *bool) (err error) {
+	defer func() {
+		if r, fail := recover().(error); fail {
+			err = r
+		}
+	}()
+
+	c := rpc.svc.Collector(m.Name)
+	if c == nil {
+		return fmt.Errorf("undefined collector `%s`", m.Name)
+	}
+
+	switch c := c.(type) {
+	case *prometheus.SummaryVec:
+		if len(m.Labels) == 0 {
+			return fmt.Errorf("required labels for collector `%s`", m.Name)
+		}
+
+		c.WithLabelValues(m.Labels...).Observe(m.Value)
+
+	case prometheus.Histogram:
+		c.Observe(m.Value)
+
+	case *prometheus.HistogramVec:
+		if len(m.Labels) == 0 {
+			return fmt.Errorf("required labels for collector `%s`", m.Name)
+		}
+
+		c.WithLabelValues(m.Labels...).Observe(m.Value)
+	default:
+		return fmt.Errorf("collector `%s` does not support method `Observe`", m.Name)
+	}
+
+	// RPC, set ok to true as return value. Need by rpc.Call reply argument
+	*ok = true
+	return nil
+}
+// Declare is used to register new collector in prometheus
+// THE TYPES ARE:
+// 	NamedCollector -> Collector with the name
+// 	bool -> RPC reply value
+// RETURNS:
+// 	error
+func (rpc *rpcServer) Declare(c *NamedCollector, ok *bool) (err error) {
+	// MustRegister could panic, so, to return error and not shutdown whole app
+	// we recover and return error
+	defer func() {
+		if r, fail := recover().(error); fail {
+			err = r
+		}
+	}()
+
+	if rpc.svc.Collector(c.Name) != nil {
+		*ok = false
+		// alternative is to return error
+		// fmt.Errorf("tried to register existing collector with the name `%s`", c.Name)
+		return nil
+	}
+
+	var collector prometheus.Collector
+	switch c.Type {
+	case Histogram:
+		opts := prometheus.HistogramOpts{
+			Name:      c.Name,
+			Namespace: c.Namespace,
+			Subsystem: c.Subsystem,
+			Help:      c.Help,
+			Buckets:   c.Buckets,
+		}
+
+		if len(c.Labels) != 0 {
+			collector = prometheus.NewHistogramVec(opts, c.Labels)
+		} else {
+			collector = prometheus.NewHistogram(opts)
+		}
+	case Gauge:
+		opts := prometheus.GaugeOpts{
+			Name:      c.Name,
+			Namespace: c.Namespace,
+			Subsystem: c.Subsystem,
+			Help:      c.Help,
+		}
+
+		if len(c.Labels) != 0 {
+			collector = prometheus.NewGaugeVec(opts, c.Labels)
+		} else {
+			collector = prometheus.NewGauge(opts)
+		}
+	case Counter:
+		opts := prometheus.CounterOpts{
+			Name:      c.Name,
+			Namespace: c.Namespace,
+			Subsystem: c.Subsystem,
+			Help:      c.Help,
+		}
+
+		if len(c.Labels) != 0 {
+			collector = prometheus.NewCounterVec(opts, c.Labels)
+		} else {
+			collector = prometheus.NewCounter(opts)
+		}
+	case Summary:
+		opts := prometheus.SummaryOpts{
+			Name:      c.Name,
+			Namespace: c.Namespace,
+			Subsystem: c.Subsystem,
+			Help:      c.Help,
+		}
+
+		if len(c.Labels) != 0 {
+			collector = prometheus.NewSummaryVec(opts, c.Labels)
+		} else {
+			collector = prometheus.NewSummary(opts)
+		}
+
+	default:
+		return fmt.Errorf("unknown collector type `%s`", c.Type)
+
+	}
+
+	// add collector to sync.Map
+	rpc.svc.collectors.Store(c.Name, collector)
+	// that method might panic, we handle it by recover
+	rpc.svc.MustRegister(collector)
+
+	*ok = true
+	return nil
+}
+
+// Set the metric value (only for gaude).
+func (rpc *rpcServer) Set(m *Metric, ok *bool) (err error) {
+	defer func() {
+		if r, fail := recover().(error); fail {
+			err = r
+		}
+	}()
+
+	c := rpc.svc.Collector(m.Name)
+	if c == nil {
+		return fmt.Errorf("undefined collector `%s`", m.Name)
+	}
+
+	switch c := c.(type) {
+	case prometheus.Gauge:
+		c.Set(m.Value)
+
+	case *prometheus.GaugeVec:
+		if len(m.Labels) == 0 {
+			return fmt.Errorf("required labels for collector `%s`", m.Name)
+		}
+
+		c.WithLabelValues(m.Labels...).Set(m.Value)
+
+	default:
+		return fmt.Errorf("collector `%s` does not support method `Set`", m.Name)
+	}
+
+	// RPC, set ok to true as return value. Need by rpc.Call reply argument
+	*ok = true
+	return nil
+}