Create extpoint for graphdrivers

Allows people to create out-of-process graphdrivers that can be used
with Docker.

Extensions must be started before Docker otherwise Docker will fail to
start.

Signed-off-by: Brian Goff <cpuguy83@gmail.com>

plugins/client.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"encoding/json"
 	"fmt"
+	"io"
 	"io/ioutil"
 	"net/http"
 	"strings"
@@ -52,19 +53,41 @@ type Client struct {
 // Call calls the specified method with the specified arguments for the plugin.
 // It will retry for 30 seconds if a failure occurs when calling.
 func (c *Client) Call(serviceMethod string, args interface{}, ret interface{}) error {
-	return c.callWithRetry(serviceMethod, args, ret, true)
-}
-
-func (c *Client) callWithRetry(serviceMethod string, args interface{}, ret interface{}, retry bool) error {
 	var buf bytes.Buffer
 	if err := json.NewEncoder(&buf).Encode(args); err != nil {
 		return err
 	}
-
+	body, err := c.callWithRetry(serviceMethod, &buf, true)
-	req, err := http.NewRequest("POST", "/"+serviceMethod, &buf)
 	if err != nil {
 		return err
 	}
+	defer body.Close()
+	return json.NewDecoder(body).Decode(&ret)
+}
+
+// Stream calls the specified method with the specified arguments for the plugin and returns the response body
+func (c *Client) Stream(serviceMethod string, args interface{}) (io.ReadCloser, error) {
+	var buf bytes.Buffer
+	if err := json.NewEncoder(&buf).Encode(args); err != nil {
+		return nil, err
+	}
+	return c.callWithRetry(serviceMethod, &buf, true)
+}
+
+// SendFile calls the specified method, and passes through the IO stream
+func (c *Client) SendFile(serviceMethod string, data io.Reader, ret interface{}) error {
+	body, err := c.callWithRetry(serviceMethod, data, true)
+	if err != nil {
+		return err
+	}
+	return json.NewDecoder(body).Decode(&ret)
+}
+
+func (c *Client) callWithRetry(serviceMethod string, data io.Reader, retry bool) (io.ReadCloser, error) {
+	req, err := http.NewRequest("POST", "/"+serviceMethod, data)
+	if err != nil {
+		return nil, err
+	}
 	req.Header.Add("Accept", versionMimetype)
 	req.URL.Scheme = "http"
 	req.URL.Host = c.addr
@@ -76,12 +99,12 @@ func (c *Client) callWithRetry(serviceMethod string, args interface{}, ret inter
 		resp, err := c.http.Do(req)
 		if err != nil {
 			if !retry {
-				return err
+				return nil, err
 			}
 
 			timeOff := backoff(retries)
 			if abort(start, timeOff) {
-				return err
+				return nil, err
 			}
 			retries++
 			logrus.Warnf("Unable to connect to plugin: %s, retrying in %v", c.addr, timeOff)
@@ -89,16 +112,14 @@ func (c *Client) callWithRetry(serviceMethod string, args interface{}, ret inter
 			continue
 		}
 
-		defer resp.Body.Close()
 		if resp.StatusCode != http.StatusOK {
 			remoteErr, err := ioutil.ReadAll(resp.Body)
 			if err != nil {
-				return &remoteError{err.Error(), serviceMethod}
+				return nil, &remoteError{err.Error(), serviceMethod}
 			}
-			return &remoteError{string(remoteErr), serviceMethod}
+			return nil, &remoteError{string(remoteErr), serviceMethod}
 		}
-
+		return resp.Body, nil
-		return json.NewDecoder(resp.Body).Decode(&ret)
 	}
 }
 

plugins/client_test.go

@@ -30,7 +30,7 @@ func teardownRemotePluginServer() {
 
 func TestFailedConnection(t *testing.T) {
 	c, _ := NewClient("tcp://127.0.0.1:1", tlsconfig.Options{InsecureSkipVerify: true})
-	err := c.callWithRetry("Service.Method", nil, nil, false)
+	_, err := c.callWithRetry("Service.Method", nil, false)
 	if err == nil {
 		t.Fatal("Unexpected successful connection")
 	}