Preserve request body state when retrying

When POST request was retried it threw a „Body length 0“ error. See janeczku/docker-machine-vultr#26

Signed-off-by: janeczku <jan@rancher.com>

lib/client.go

@@ -1,6 +1,7 @@
 package lib
 
 import (
+	"bytes"
 	"crypto/tls"
 	"encoding/json"
 	"errors"
@@ -168,8 +169,25 @@ func (c *Client) do(req *http.Request, data interface{}) error {
 	// Throttle http requests to avoid hitting Vultr's API rate-limit
 	c.bucket.Wait(1)
 
+	// Request body gets drained on each read so we
+	// need to save it's content for retrying requests
+	var err error
+	var requestBody []byte
+	if req.Body != nil {
+		requestBody, err = ioutil.ReadAll(req.Body)
+		if err != nil {
+			return fmt.Errorf("Error reading request body: %v", err)
+		}
+		req.Body.Close()
+	}
+
 	var apiError error
 	for tryCount := 1; tryCount <= c.MaxAttempts; tryCount++ {
+		// Restore request body to the original state
+		if requestBody != nil {
+			req.Body = ioutil.NopCloser(bytes.NewBuffer(requestBody))
+		}
+
 		resp, err := c.client.Do(req)
 		if err != nil {
 			return err

lib/client_test.go

@@ -132,3 +132,27 @@ func Test_Client_Retry(t *testing.T) {
 
 	wg.Wait()
 }
+
+// Test that body state is preserved when retrying POST requests
+func Test_Client_Retry_Post(t *testing.T) {
+	server := getTestServerThrottled(`{"SUBID":"5671234"}`)
+	defer server.Close()
+
+	options := Options{
+		Endpoint:   server.URL,
+		MaxRetries: 5,
+	}
+	client := NewClient("test-key", &options)
+
+	var wg sync.WaitGroup
+	wg.Add(10)
+	for i := 0; i < 10; i++ {
+		go func() {
+			defer wg.Done()
+			_, err := client.CreateBlockStorage("delta", 33, 150)
+			assert.NoError(t, err)
+		}()
+	}
+
+	wg.Wait()
+}