feat: add an influxql service that communicates with influxdb 1.x

It creates a simple client that follows the QueryService interface and
uses the `influxql.Compiler` type to determine where the query should be
routed to and to return the query as a `flux.ResultIterator`.

This will be useful for replaying transpiler queries against influxdb
1.x servers to verify correctness.

query/influxql/service.go

@@ -0,0 +1,82 @@
+package influxql
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"net/url"
+
+	"github.com/influxdata/flux"
+	"github.com/influxdata/platform/query"
+)
+
+// Endpoint contains the necessary information to connect to a specific cluster.
+type Endpoint struct {
+	URL      string `json:"url"`
+	Username string `json:"username,omitempty"`
+	Password string `json:"password,omitempty"`
+}
+
+// Service is a client for the influxdb 1.x endpoint that implements the QueryService
+// for the influxql compiler type.
+type Service struct {
+	// Endpoints maps a cluster name to the influxdb 1.x endpoint.
+	Endpoints map[string]Endpoint
+}
+
+// Query will execute a query for the influxql.Compiler type against an influxdb 1.x endpoint.
+func (s *Service) Query(ctx context.Context, req *query.Request) (flux.ResultIterator, error) {
+	// Verify that this is an influxql query in the compiler.
+	compiler, ok := req.Compiler.(*Compiler)
+	if !ok {
+		return nil, fmt.Errorf("influxql query service does not support the '%s' compiler type", req.Compiler.CompilerType())
+	}
+
+	// Lookup the endpoint information for the cluster.
+	endpoint, ok := s.Endpoints[compiler.Cluster]
+	if !ok {
+		return nil, fmt.Errorf("no endpoint found for cluster %s", compiler.Cluster)
+	}
+
+	// Prepare the HTTP request.
+	u, err := url.Parse(endpoint.URL)
+	if err != nil {
+		return nil, err
+	}
+	u.Path += "/query"
+
+	params := url.Values{}
+	params.Set("q", compiler.Query)
+	if compiler.DB != "" {
+		params.Set("db", compiler.DB)
+	}
+	if compiler.RP != "" {
+		params.Set("rp", compiler.RP)
+	}
+	u.RawQuery = params.Encode()
+
+	hreq, err := http.NewRequest("POST", u.String(), nil)
+	if err != nil {
+		return nil, err
+	}
+	hreq.WithContext(ctx)
+	hreq.SetBasicAuth(endpoint.Username, endpoint.Password)
+
+	// Perform the request and look at the status code.
+	resp, err := http.DefaultClient.Do(hreq)
+	if err != nil {
+		return nil, err
+	} else if resp.StatusCode/100 != 2 {
+		return nil, fmt.Errorf("unexpected http status: %s", resp.Status)
+	}
+
+	// Decode the response into the JSON structure.
+	var results Response
+	if err := json.NewDecoder(resp.Body).Decode(&results); err != nil {
+		return nil, err
+	}
+
+	// Return a result iterator using the response.
+	return NewResponseIterator(&results), nil
+}

query/influxql/service_test.go

@@ -0,0 +1,65 @@
+package influxql_test
+
+import (
+	"context"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/influxdata/platform/query"
+	"github.com/influxdata/platform/query/influxql"
+)
+
+func TestService(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		// Verify the parameters were passed correctly.
+		if want, got := "POST", r.Method; want != got {
+			t.Errorf("unexpected method -want/+got\n\t- %q\n\t+ %q", want, got)
+		}
+		if want, got := "SHOW DATABASES", r.FormValue("q"); want != got {
+			t.Errorf("unexpected query -want/+got\n\t- %q\n\t+ %q", want, got)
+		}
+		if want, got := "db0", r.FormValue("db"); want != got {
+			t.Errorf("unexpected database -want/+got\n\t- %q\n\t+ %q", want, got)
+		}
+		if want, got := "rp0", r.FormValue("rp"); want != got {
+			t.Errorf("unexpected retention policy -want/+got\n\t- %q\n\t+ %q", want, got)
+		}
+		user, pass, ok := r.BasicAuth()
+		if !ok {
+			w.WriteHeader(http.StatusUnauthorized)
+			return
+		}
+		if want, got := "me", user; want != got {
+			t.Errorf("unexpected username -want/+got\n\t- %q\n\t+ %q", want, got)
+		}
+		if want, got := "secretpassword", pass; want != got {
+			t.Errorf("unexpected password -want/+got\n\t- %q\n\t+ %q", want, got)
+		}
+		io.WriteString(w, `{"results":[{"statement_id":0,"series":[{"name":"databases","columns":["name"],"values":[["db0"]]}]}]}`)
+	}))
+	defer server.Close()
+
+	service := &influxql.Service{
+		Endpoints: map[string]influxql.Endpoint{
+			"myserver": {
+				URL:      server.URL,
+				Username: "me",
+				Password: "secretpassword",
+			},
+		},
+	}
+	results, err := service.Query(context.Background(), &query.Request{
+		Compiler: &influxql.Compiler{
+			Cluster: "myserver",
+			DB:      "db0",
+			RP:      "rp0",
+			Query:   "SHOW DATABASES",
+		},
+	})
+	if err != nil {
+		t.Fatalf("unexpected error: %s", err)
+	}
+	defer results.Cancel()
+}