Remote plugins plumbing.

Signed-off-by: David Calavera <david.calavera@gmail.com>

plugins/discovery.go

@@ -0,0 +1,78 @@
+package plugins
+
+import (
+	"errors"
+	"fmt"
+	"io/ioutil"
+	"net/url"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+const defaultLocalRegistry = "/usr/share/docker/plugins"
+
+var (
+	ErrNotFound = errors.New("Plugin not found")
+)
+
+type Registry interface {
+	Plugins() ([]*Plugin, error)
+	Plugin(name string) (*Plugin, error)
+}
+
+type LocalRegistry struct {
+	path string
+}
+
+func newLocalRegistry(path string) *LocalRegistry {
+	if len(path) == 0 {
+		path = defaultLocalRegistry
+	}
+
+	return &LocalRegistry{path}
+}
+
+func (l *LocalRegistry) Plugin(name string) (*Plugin, error) {
+	filepath := filepath.Join(l.path, name)
+	specpath := filepath + ".spec"
+	if fi, err := os.Stat(specpath); err == nil {
+		return readPluginInfo(specpath, fi)
+	}
+	socketpath := filepath + ".sock"
+	if fi, err := os.Stat(socketpath); err == nil {
+		return readPluginInfo(socketpath, fi)
+	}
+	return nil, ErrNotFound
+}
+
+func readPluginInfo(path string, fi os.FileInfo) (*Plugin, error) {
+	name := strings.Split(fi.Name(), ".")[0]
+
+	if fi.Mode()&os.ModeSocket != 0 {
+		return &Plugin{
+			Name: name,
+			Addr: "unix://" + path,
+		}, nil
+	}
+
+	content, err := ioutil.ReadFile(path)
+	if err != nil {
+		return nil, err
+	}
+	addr := strings.TrimSpace(string(content))
+
+	u, err := url.Parse(addr)
+	if err != nil {
+		return nil, err
+	}
+
+	if len(u.Scheme) == 0 {
+		return nil, fmt.Errorf("Unknown protocol")
+	}
+
+	return &Plugin{
+		Name: name,
+		Addr: addr,
+	}, nil
+}