From 9ee2b35eaa585d85e587a092f85d598d8765c826 Mon Sep 17 00:00:00 2001
From: Leander Beernaert <leander.beernaert@proton.ch>
Date: Thu, 16 Feb 2023 10:31:56 +0100
Subject: [PATCH] fix(GODT-2021): Indefinite parser stall after new line

Can't consume new line or we will be stuck waiting on more data which
does not arrive until the client has received the response.
---
 imap/command/parser.go      | 10 ++++++--
 imap/command/parser_test.go | 51 +++++++++++++++++++++++++++++++++++++
 2 files changed, 59 insertions(+), 2 deletions(-)

diff --git a/imap/command/parser.go b/imap/command/parser.go
index 3d1a424f..a602aa07 100644
--- a/imap/command/parser.go
+++ b/imap/command/parser.go
@@ -115,8 +115,14 @@ func (p *Parser) Parse() (Command, error) {
 
 	result.Payload = payload
 
-	if err := p.parser.ConsumeNewLine(); err != nil {
-		return result, err
+	if err := p.parser.Consume(rfcparser.TokenTypeCR, "expected CR"); err != nil {
+		return Command{}, err
+	}
+
+	// Can't fully consume the last new line here or we will hang forever as the clients don't send the next token.
+	// In the next loop, the call to advance will ensure the next token in the stream gets loaded properly.
+	if !p.parser.Check(rfcparser.TokenTypeLF) {
+		return Command{}, p.parser.MakeError("expected LF after CR")
 	}
 
 	return result, nil
diff --git a/imap/command/parser_test.go b/imap/command/parser_test.go
index 9c97e270..48afc755 100644
--- a/imap/command/parser_test.go
+++ b/imap/command/parser_test.go
@@ -120,3 +120,54 @@ func TestParser_LiteralWithContinuationSubmission(t *testing.T) {
 	require.NoError(t, err)
 	require.Equal(t, expected, cmd)
 }
+
+func TestParser_TwoCommandsInSuccession(t *testing.T) {
+	// Run one go routine that submits bytes until the continuation call has been received
+	continueCh := make(chan struct{})
+	reader, writer := io.Pipe()
+
+	go func() {
+		defer writer.Close()
+
+		firstLine := toIMAPLine(`A003 CAPABILITY`)
+
+		secondLine := toIMAPLine(`B002 LIST "" %`)
+
+		if l, err := writer.Write(firstLine); err != nil || l != len(firstLine) {
+			writer.CloseWithError(fmt.Errorf("failed to write first line: %w", err))
+			return
+		}
+
+		<-continueCh
+
+		if l, err := writer.Write(secondLine); err != nil || l != len(secondLine) {
+			writer.CloseWithError(fmt.Errorf("failed to write second line: %w", err))
+			return
+		}
+	}()
+
+	s := rfcparser.NewScanner(reader)
+	p := NewParser(s)
+
+	// First command
+	{
+		expected := Command{Tag: "A003", Payload: &Capability{}}
+
+		cmd, err := p.Parse()
+		require.NoError(t, err)
+		require.Equal(t, expected, cmd)
+	}
+
+	// Submit next command.
+	close(continueCh)
+	{
+		expected := Command{Tag: "B002", Payload: &List{
+			Mailbox:     "",
+			ListMailbox: "%",
+		}}
+
+		cmd, err := p.Parse()
+		require.NoError(t, err)
+		require.Equal(t, expected, cmd)
+	}
+}