Initial support for plugins

pkg/plugin/plugin.go

@@ -0,0 +1,83 @@
+package plugin
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"plugin"
+	"strings"
+)
+
+type (
+	// Set of plugins
+	Set []*item
+
+	// item represents a plugin
+	item struct {
+		src string
+		def interface{}
+	}
+)
+
+// Resolve string with colon separated paths
+func Resolve(paths string) (out []string, err error) {
+	var (
+		matches []string
+	)
+
+	for _, part := range strings.Split(paths, ":") {
+		matches, err = filepath.Glob(part)
+
+		if err != nil {
+			return
+		}
+
+		out = append(out, matches...)
+	}
+
+	return
+}
+
+// Load loads plugins from all given paths
+func Load(paths ...string) (Set, error) {
+	var set = Set{}
+
+	for _, path := range paths {
+
+		if info, err := os.Lstat(path); err != nil {
+			return nil, err
+		} else if info.IsDir() {
+			return nil, fmt.Errorf("can not use directory %s as a plugin", path)
+		}
+
+		if i, err := load(path); err != nil {
+			return nil, err
+		} else {
+			set = append(set, i)
+		}
+	}
+
+	return set, nil
+}
+
+// load single plugin from the given path
+func load(path string) (i *item, err error) {
+	i = &item{}
+	p, err := plugin.Open(path)
+	if err != nil {
+		return
+	}
+
+	aux, err := p.Lookup("CortezaPlugin")
+	if err != nil {
+		return
+	}
+
+	fn, is := aux.(func() interface{})
+	if !is {
+		return nil, fmt.Errorf("incompatible plugin definition")
+	}
+
+	i.def = fn()
+	return
+}