feat: custom address/date parser based on rfc5322 abnf

pkg/message/rfc5322/walker.go

@@ -0,0 +1,62 @@
+// Copyright (c) 2020 Proton Technologies AG
+//
+// This file is part of ProtonMail Bridge.
+//
+// ProtonMail Bridge is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// ProtonMail Bridge is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with ProtonMail Bridge.  If not, see <https://www.gnu.org/licenses/>.
+
+package rfc5322
+
+import (
+	"fmt"
+
+	"github.com/ProtonMail/proton-bridge/pkg/message/rfc5322/parser"
+	"github.com/antlr/antlr4/runtime/Go/antlr"
+)
+
+// walker implements parser.BaseRFC5322ParserListener, defining what to do at
+// each node while traversing the syntax tree.
+// It also implements antlr.DefaultErrorListener, allowing us to react to
+// errors encountered while trying to determine the syntax tree of the input.
+type walker struct {
+	parser.BaseRFC5322ParserListener
+	antlr.DefaultErrorListener
+
+	// nodes acts as a stack; when entering a node, it is pushed here, and when
+	// exiting a node, it is popped from here.
+	nodes []interface{}
+
+	// res holds the result of walking the parse tree.
+	res interface{}
+
+	// err holds the error encountered during parsing, if any.
+	err error
+}
+
+func (w *walker) enter(b interface{}) {
+	w.nodes = append(w.nodes, b)
+}
+
+func (w *walker) exit() interface{} {
+	b := w.nodes[len(w.nodes)-1]
+	w.nodes = w.nodes[:len(w.nodes)-1]
+	return b
+}
+
+func (w *walker) parent() (b interface{}) {
+	return w.nodes[len(w.nodes)-1]
+}
+
+func (w *walker) SyntaxError(_ antlr.Recognizer, _ interface{}, _, _ int, msg string, _ antlr.RecognitionException) {
+	w.err = fmt.Errorf("error parsing rfc5322 input: %v", msg)
+}