WIP: crate: Added Ping method

crate.go

@@ -2,6 +2,7 @@ package crate
 
 import (
 	"bytes"
+	"context"
 	"database/sql"
 	"database/sql/driver"
 	"encoding/json"
@@ -10,11 +11,25 @@ import (
 	"io"
 	"net/http"
 	"net/url"
+	"strings"
+	"time"
+)
+
+var (
+	// DefaultTimeout is the default timeout for CrateDriver if one is
+	// not specified.
+	DefaultTimeout = 10 * time.Second
 )
 
 // Crate conn structure
 type CrateDriver struct {
-	Url string // Crate http endpoint url
+	URL  string // Crate http endpoint url
+	http *http.Client
+	// Timeout is set with a URL query value.
+	// Example:
+	//		sql.Open("crate", "http://127.0.0.1:4200/?timeout=1s")
+	//			Makes the timeout on connections one second.
+	Timeout time.Duration
 }
 
 // Init a new "Connection" to a Crate Data Storage instance.
@@ -28,11 +43,33 @@ func (c *CrateDriver) Open(crate_url string) (driver.Conn, error) {
 
 	sanUrl := fmt.Sprintf("%s://%s", u.Scheme, u.Host)
 
-	c.Url = sanUrl
+	c.URL = sanUrl
+
+	c.Timeout = DefaultTimeout
+	if u.Query().Get("timeout") != "" {
+		c.Timeout, err = time.ParseDuration(u.Query().Get("timeout"))
+		if err != nil {
+			return nil, err
+		}
+	}
+	c.http = &http.Client{
+		Transport: http.DefaultTransport,
+		Timeout:   c.Timeout,
+	}
 
 	return c, nil
 }
 
+// Ping checks if we can connect to the cluster by selecting its name
+// from sys.cluster. If the select fails we return an error.
+func (c *CrateDriver) Ping(ctx context.Context) error {
+	_, err := c.Exec("SELECT name FROM sys.cluster", nil)
+	if err != nil && strings.Contains(err.Error(), "dial tcp") {
+		return fmt.Errorf("Could not connect to crate at %s", c.URL)
+	}
+	return err
+}
+
 // JSON endpoint response struct
 // We expect error to be null or ommited
 type endpointResponse struct {
@@ -59,7 +96,7 @@ type endpointQuery struct {
 // "Parameter Substitution" is also supported, read, https://crate.io/docs/stable/sql/rest.html#parameter-substitution
 // This is the internal query function
 func (c *CrateDriver) query(stmt string, args []driver.Value) (*endpointResponse, error) {
-	endpoint := c.Url + "/_sql?types"
+	endpoint := c.URL + "/_sql?types"
 
 	query := &endpointQuery{
 		Stmt: stmt,
@@ -77,7 +114,7 @@ func (c *CrateDriver) query(stmt string, args []driver.Value) (*endpointResponse
 
 	data := bytes.NewReader(buf)
 
-	resp, err := http.Post(endpoint, "application/json", data)
+	resp, err := c.http.Post(endpoint, "application/json", data)
 
 	if err != nil {
 		return nil, err