Implement initial Influx Enterprise client

This is an initial implementation of the Influx Enterprise client. It
incorporates introspection of a cluster to determine available data
nodes and issues requests in a round-robin fasion to those nodes.

Currently all nodes are assumed to be healthy, so there is no pruning of
the available data node pool.

enterprise/enterprise.go

@@ -0,0 +1,56 @@
+package enterprise
+
+import (
+	"container/ring"
+
+	"github.com/influxdata/mrfusion"
+	"github.com/influxdata/mrfusion/influx"
+	"github.com/influxdata/plutonium/meta/control"
+	"golang.org/x/net/context"
+)
+
+var _ mrfusion.TimeSeries = &Client{}
+
+// Client is a device for retrieving time series data from an Influx Enterprise
+// cluster. It is configured using the addresses of one or more meta node URLs.
+// Data node URLs are retrieved automatically from the meta nodes and queries
+// are appropriately load balanced across the cluster.
+type Client struct {
+	Ctrl interface {
+		ShowCluster() (*control.Cluster, error)
+	}
+
+	dataNodes *ring.Ring
+}
+
+// NewClient initializes and returns a Client.
+func (c *Client) Open() error {
+	cluster, err := c.Ctrl.ShowCluster()
+	if err != nil {
+		return err
+	}
+
+	c.dataNodes = ring.New(len(cluster.DataNodes))
+	for _, dn := range cluster.DataNodes {
+		cl, err := influx.NewClient(dn.HTTPAddr)
+		if err != nil {
+			continue
+		} else {
+			c.dataNodes.Value = cl
+			c.dataNodes = c.dataNodes.Next()
+		}
+	}
+	return nil
+}
+
+// Query retrieves timeseries information pertaining to a specified query. It
+// can be cancelled by using a provided context.
+func (c *Client) Query(ctx context.Context, q mrfusion.Query) (mrfusion.Response, error) {
+	cl := c.dataNodes.Next().Value.(mrfusion.TimeSeries)
+	return cl.Query(ctx, q)
+}
+
+// MonitoredServices returns the services monitored by this Enterprise cluster.
+func (c *Client) MonitoredServices(ctx context.Context) ([]mrfusion.MonitoredService, error) {
+	return []mrfusion.MonitoredService{}, nil
+}

enterprise/enterprise_test.go

@@ -0,0 +1,68 @@
+package enterprise_test
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"golang.org/x/net/context"
+
+	"github.com/influxdata/mrfusion"
+	"github.com/influxdata/mrfusion/enterprise"
+	"github.com/influxdata/mrfusion/mock"
+	"github.com/influxdata/plutonium/meta/control"
+)
+
+func Test_Enterprise_FetchesDataNodes(t *testing.T) {
+	t.Parallel()
+
+	ctrl := &mock.ControlClient{
+		Cluster: &control.Cluster{},
+	}
+	cl := &enterprise.Client{
+		Ctrl: ctrl,
+	}
+
+	err := cl.Open()
+
+	if err != nil {
+		t.Fatal("Unexpected error while creating enterprise client. err:", err)
+	}
+
+	if ctrl.ShowClustersCalled != true {
+		t.Fatal("Expected request to meta node but none was issued")
+	}
+}
+
+func Test_Enterprise_IssuesQueries(t *testing.T) {
+	t.Parallel()
+
+	called := false
+	ts := httptest.NewServer(http.HandlerFunc(func(rw http.ResponseWriter, r *http.Request) {
+		called = true
+		if r.URL.Path != "/query" {
+			t.Fatal("Expected request to '/query' but was", r.URL.Path)
+		}
+		rw.Write([]byte(`{}`))
+	}))
+	defer ts.Close()
+
+	cl := &enterprise.Client{
+		Ctrl: mock.NewMockControlClient(ts.URL),
+	}
+
+	err := cl.Open()
+	if err != nil {
+		t.Fatal("Unexpected error initializing client: err:", err)
+	}
+
+	_, err = cl.Query(context.Background(), mrfusion.Query{"show shards", "_internal", "autogen"})
+
+	if err != nil {
+		t.Fatal("Unexpected error while querying data node: err:", err)
+	}
+
+	if called == false {
+		t.Fatal("Expected request to data node but none was received")
+	}
+}

mock/plutonium.go

@@ -0,0 +1,34 @@
+package mock
+
+import (
+	"net/url"
+
+	"github.com/influxdata/plutonium/meta/control"
+)
+
+type ControlClient struct {
+	Cluster            *control.Cluster
+	ShowClustersCalled bool
+}
+
+func NewMockControlClient(addr string) *ControlClient {
+	_, err := url.Parse(addr)
+	if err != nil {
+		panic(err)
+	}
+
+	return &ControlClient{
+		Cluster: &control.Cluster{
+			DataNodes: []control.DataNode{
+				control.DataNode{
+					HTTPAddr: addr,
+				},
+			},
+		},
+	}
+}
+
+func (cc *ControlClient) ShowCluster() (*control.Cluster, error) {
+	cc.ShowClustersCalled = true
+	return cc.Cluster, nil
+}