Add influx client

This adds a simple HTTP influx client to fetch time series results. It
implements the TimeSeries interface. Also included is an implementation
of the mrfusion.Results interface that wraps results returned from the
influx client.

We only support HTTP connections (there's also a UDP influx client). We
also require that all Queries to Influx be fully-qualified--they should
include the database and retention policies in the query.

This also makes Resuls a json.Marshaler. In order to hand results back
to clients, we need to guarantee that those results can be serialized to
json in some form. json.Marshaller is just such a guarantee!

influx/influx.go

@@ -0,0 +1,37 @@
+package influx
+
+import (
+	ixClient "github.com/influxdata/influxdb/client/v2"
+	"github.com/influxdata/mrfusion"
+
+	"golang.org/x/net/context"
+)
+
+// Client is a device for retrieving time series data from an InfluxDB instance
+type Client struct {
+	ix ixClient.Client
+}
+
+// NewClient initializes a Client
+func NewClient(host string) (*Client, error) {
+	cl, err := ixClient.NewHTTPClient(ixClient.HTTPConfig{
+		Addr: host,
+	})
+
+	if err != nil {
+		return nil, err
+	}
+
+	return &Client{
+		ix: cl,
+	}, nil
+}
+
+// Query issues a request to a configured InfluxDB instance for time series
+// information specified by query. Queries must be "fully-qualified," and
+// include both the database and retention policy.
+func (c *Client) Query(ctx context.Context, query mrfusion.Query) (mrfusion.Response, error) {
+	q := ixClient.NewQuery(string(query), "", "")
+	resp, err := c.ix.Query(q)
+	return response{resp}, err
+}

influx/influx_test.go

@@ -0,0 +1,40 @@
+package influx_test
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/influxdata/mrfusion"
+	"github.com/influxdata/mrfusion/influx"
+	"golang.org/x/net/context"
+)
+
+func Test_MakesRequestsToQueryEndpoint(t *testing.T) {
+	t.Parallel()
+	called := false
+	ts := httptest.NewServer(http.HandlerFunc(func(rw http.ResponseWriter, r *http.Request) {
+		rw.WriteHeader(http.StatusOK)
+		rw.Write([]byte(`{}`))
+		called = true
+		if path := r.URL.Path; path != "/query" {
+			t.Error("Expected the path to contain `/query` but was", path)
+		}
+	}))
+	defer ts.Close()
+
+	var series mrfusion.TimeSeries
+	series, err := influx.NewClient(ts.URL)
+	if err != nil {
+		t.Fatal("Unexpected error initializing client: err:", err)
+	}
+
+	_, err = series.Query(context.Background(), "show databases")
+	if err != nil {
+		t.Fatal("Expected no error but was", err)
+	}
+
+	if called == false {
+		t.Error("Expected http request to Influx but there was none")
+	}
+}

influx/response.go

@@ -0,0 +1,20 @@
+package influx
+
+import (
+	"encoding/json"
+
+	"github.com/influxdata/influxdb/client/v2"
+	"github.com/influxdata/mrfusion"
+)
+
+type response struct {
+	*client.Response
+}
+
+func (r response) MarshalJSON() ([]byte, error) {
+	return json.Marshal(r.Results)
+}
+
+func (r response) Results() ([]mrfusion.Result, error) {
+	return []mrfusion.Result{}, nil
+}

timeseries.go

@@ -1,6 +1,10 @@
 package mrfusion
 
-import "golang.org/x/net/context"
+import (
+	"encoding/json"
+
+	"golang.org/x/net/context"
+)
 
 // Used to retrieve a Response from a TimeSeries.
 type Query string
@@ -28,6 +32,7 @@ type Result interface {
 // Response is the result of a query against a TimeSeries
 type Response interface {
 	Results() ([]Result, error)
+	json.Marshaler
 }
 
 // Represents a queryable time series database.