simplejson

Overview ¶

Package simplejson provides a Go implementation for Grafana's SimpleJSON datasource: https://grafana.com/grafana/plugins/grafana-simple-json-datasource

Overview ¶

A simplejson server is an HTTP server that supports one or more handlers. Each handler can support multiple targets, each of which can be supported by a timeseries or table query. Optionally tags can be used to alter the behaviour of the query (e.g. filtering what data should be returned). Finally, a handler can support annotation, i.e. a set of timestamps with associated text.

Server ¶

To create a SimpleJSON server, create a Server and run it:

s := simplejson.Server{
	Handlers: map[string]simplejson.Handler{
		"my-target": myHandler,
	},
}
err := s.Run(8080)

This starts a server, listening on port 8080, with one target "my-target", served by myHandler.

Handler ¶

A handler serves incoming requests from Grafana, e.g. queries, requests for annotations or tags. The Handler interface contains all functions a handler needs to implement. It contains only one function (Endpoints). This function returns the Grafana SimpleJSON endpoints that the handler supports. Those can be:

• Query() implements the /query endpoint for timeseries targets
• TableQuery() implements the /query endpoint for table targets
• Annotations() implements the /annotation endpoint
• TagKeys() implements the /tag-keys endpoint
• TagValues() implements the /tag-values endpoint

Here's an example of a handler that supports timeseries queries:

type myHandler struct {
}

func (handler myHandler) Endpoints() simplejson.Endpoints {
	return simplejson.Endpoints{
		Query:  handler.Query
	}
}

func (handler *myHandler) Query(ctx context.Context, target string, target *simplejson.TimeSeriesQueryArgs) (response *simplejson.QueryResponse, err error) {
	// build response
	return
}

Timeseries Queries ¶

Timeseries queries return values as a list of timestamp/value tuples. Here's an example of a timeseries query handler:

func (handler *myHandler) Query(_ context.Context, _ string, _ *simplejson.TimeSeriesQueryArgs) (response *simplejson.QueryResponse, err error) {
	response = &simplejson.QueryResponse{
		Target: "A",
		DataPoints: []simplejson.QueryResponseDataPoint{
			{Timestamp: time.Date(2020, 1, 1, 0, 0, 0, 0, time.UTC), Value: 100},
			{Timestamp: time.Date(2020, 1, 1, 0, 1, 0, 0, time.UTC), Value: 101},
			{Timestamp: time.Date(2020, 1, 1, 0, 2, 0, 0, time.UTC), Value: 103},
		},
	}
	return
}

Table Queries ¶

Table Queries, on the other hand, return data organized in columns and rows. Each column needs to have the same number of rows:

func (handler *myHandler) TableQuery(_ context.Context, _ string, _ *simplejson.TableQueryArgs) (response *simplejson.QueryResponse, err error) {
	response = &simplejson.TableQueryResponse{
		Columns: []simplejson.TableQueryResponseColumn{
			{ Text: "Time",     Data: simplejson.TableQueryResponseTimeColumn{time.Date(2020, 1, 1, 0, 0, 0, 0, time.UTC), time.Date(2020, 1, 1, 0, 1, 0, 0, time.UTC)} },
			{ Text: "Label",    Data: simplejson.TableQueryResponseStringColumn{"foo", "bar"}},
			{ Text: "Series A", Data: simplejson.TableQueryResponseNumberColumn{42, 43}},
			{ Text: "Series B", Data: simplejson.TableQueryResponseNumberColumn{64.5, 100.0}},
		},
	}
	return
}

Metrics ¶

simplejson exports two Prometheus metrics for performance analytics:

simplejson_query_duration_seconds: duration of query requests by target, in seconds
simplejson_query_failed_count:     number of failed query requests

Other topics ¶

For information on query arguments, annotation and tags, refer to the documentation for those data structures.

package main

import (
	"context"
	"github.com/clambin/simplejson"
	"time"
)

type handler struct{}

func (h handler) Endpoints() simplejson.Endpoints {
	return simplejson.Endpoints{
		Query:      h.Query,
		TableQuery: h.TableQuery,
	}
}

func (h *handler) Query(_ context.Context, _ *simplejson.TimeSeriesQueryArgs) (response *simplejson.TimeSeriesResponse, err error) {
	response = &simplejson.TimeSeriesResponse{
		DataPoints: make([]simplejson.DataPoint, 60),
	}

	timestamp := time.Now().Add(-1 * time.Hour)
	for i := 0; i < 60; i++ {
		response.DataPoints[i] = simplejson.DataPoint{
			Timestamp: timestamp,
			Value:     int64(i),
		}
		timestamp = timestamp.Add(1 * time.Minute)
	}
	return
}

func (h *handler) TableQuery(_ context.Context, _ *simplejson.TableQueryArgs) (response *simplejson.TableQueryResponse, err error) {
	timestamps := make(simplejson.TableQueryResponseTimeColumn, 60)
	seriesA := make(simplejson.TableQueryResponseNumberColumn, 60)
	seriesB := make(simplejson.TableQueryResponseNumberColumn, 60)

	timestamp := time.Now().Add(-1 * time.Hour)
	for i := 0; i < 60; i++ {
		timestamps[i] = timestamp
		seriesA[i] = float64(i)
		seriesB[i] = float64(-i)
		timestamp = timestamp.Add(1 * time.Minute)
	}

	response = &simplejson.TableQueryResponse{
		Columns: []simplejson.TableQueryResponseColumn{
			{Text: "timestamp", Data: timestamps},
			{Text: "series A", Data: seriesA},
			{Text: "series B", Data: seriesB},
		},
	}

	return
}

func main() {
	s := simplejson.Server{
		Handlers: map[string]simplejson.Handler{
			"A": &handler{},
		},
	}

	_ = s.Run(8088)
}

Output: