Add Plugin.ID()

ast/ast.go

@@ -2,6 +2,7 @@ package ast
 
 import (
 	"bytes"
+	"errors"
 	"fmt"
 )
 
@@ -160,6 +161,24 @@ func (p Plugin) String() string {
 	return s.String()
 }
 
+// ID returns the id of a Logstash plugin.
+// The id attribute is one of the common options, that is optionally available
+// on every Logstash plugin. In generall, it is highly recommended for a Logstash
+// plugin to have an id.
+func (p Plugin) ID() (string, error) {
+	for _, attr := range p.Attributes {
+		if attr != nil && attr.Name() == "id" {
+			switch stringAttr := attr.(type) {
+			case StringAttribute:
+				return stringAttr.value, nil
+			default:
+				return "", errors.New("attribut id is not of type string attribute")
+			}
+		}
+	}
+	return "", fmt.Errorf("plugin %s does not contain an id attribute", p.name)
+}
+
 // Attribute interface combines Logstash plugin attribute types.
 type Attribute interface {
 	Name() string

ast/ast_test.go

@@ -582,6 +582,79 @@ output {
 	}
 }
 
+func TestPluginID(t *testing.T) {
+	cases := []struct {
+		name   string
+		plugin Plugin
+
+		wantID  string
+		wantErr bool
+	}{
+		{
+			name: "double quoted id",
+			plugin: NewPlugin("stdin",
+				NewStringAttribute("id", "123", DoubleQuoted),
+			),
+
+			wantID: "123",
+		},
+		{
+			name: "bareword id",
+			plugin: NewPlugin("stdin",
+				NewStringAttribute("id", "123", Bareword),
+			),
+
+			wantID: "123",
+		},
+		{
+			name: "bareword id",
+			plugin: NewPlugin("stdin",
+				NewNumberAttribute("id", 123),
+			),
+
+			wantID:  "",
+			wantErr: true,
+		},
+		{
+			name: "multiple attributes with id",
+			plugin: NewPlugin("stdin",
+				NewStringAttribute("name", "fobar", Bareword),
+				NewStringAttribute("id", "123", Bareword),
+				NewStringAttribute("description", "the description", DoubleQuoted),
+			),
+
+			wantID: "123",
+		},
+		{
+			name: "multiple attributes without id",
+			plugin: NewPlugin("stdin",
+				NewStringAttribute("name", "fobar", Bareword),
+				NewStringAttribute("alternative", "baz", Bareword),
+				NewStringAttribute("description", "the description", DoubleQuoted),
+			),
+
+			wantID:  "",
+			wantErr: true,
+		},
+	}
+
+	for _, test := range cases {
+		t.Run(test.name, func(t *testing.T) {
+			id, err := test.plugin.ID()
+
+			if test.wantErr && err == nil {
+				t.Error("Expected an error, but go none.")
+			}
+			if !test.wantErr && err != nil {
+				t.Errorf("Expected no error but got: %v", err)
+			}
+			if test.wantID != id {
+				t.Errorf("Expected id to be %q, but got %q", test.wantID, id)
+			}
+		})
+	}
+}
+
 func TestPluginType(t *testing.T) {
 	cases := []struct {
 		name     string