From fe564af756cf67fd29f9b6957d2080aa5031eb5a Mon Sep 17 00:00:00 2001
From: Simon Ser <contact@emersion.fr>
Date: Fri, 10 Dec 2021 10:44:40 +0100
Subject: [PATCH] Handle upstream multi-line SASL

References: https://todo.sr.ht/~emersion/soju/173
---
 downstream.go |  2 +-
 irc.go        |  1 +
 upstream.go   | 28 +++++++++++++++++++---------
 3 files changed, 21 insertions(+), 10 deletions(-)

diff --git a/downstream.go b/downstream.go
index 026b04b..ad4c352 100644
--- a/downstream.go
+++ b/downstream.go
@@ -983,7 +983,7 @@ func (dc *downstreamConn) handleAuthenticateCommand(msg *irc.Message) (result *d
 
 		dc.sasl.pendingResp.WriteString(chunk)
 
-		if len(chunk) == 400 {
+		if len(chunk) == maxSASLLength {
 			return nil, nil // Multi-line response, wait for the next command
 		}
 
diff --git a/irc.go b/irc.go
index 5355f1a..1da97a2 100644
--- a/irc.go
+++ b/irc.go
@@ -25,6 +25,7 @@ const (
 const (
 	maxMessageLength = 512
 	maxMessageParams = 15
+	maxSASLLength    = 400
 )
 
 // The server-time layout, as defined in the IRCv3 spec.
diff --git a/upstream.go b/upstream.go
index 4863ba2..ae30c2d 100644
--- a/upstream.go
+++ b/upstream.go
@@ -619,16 +619,26 @@ func (uc *upstreamConn) handleMessage(ctx context.Context, msg *irc.Message) err
 			return err
 		}
 
-		// TODO: send response in multiple chunks if >= 400 bytes
-		var respStr = "+"
-		if len(resp) != 0 {
-			respStr = base64.StdEncoding.EncodeToString(resp)
-		}
+		// <= instead of < because we need to send a final empty response if
+		// the last chunk is exactly 400 bytes long
+		for i := 0; i <= len(resp); i += maxSASLLength {
+			j := i + maxSASLLength
+			if j > len(resp) {
+				j = len(resp)
+			}
 
-		uc.SendMessage(ctx, &irc.Message{
-			Command: "AUTHENTICATE",
-			Params:  []string{respStr},
-		})
+			chunk := resp[i:j]
+
+			var respStr = "+"
+			if len(chunk) != 0 {
+				respStr = base64.StdEncoding.EncodeToString(chunk)
+			}
+
+			uc.SendMessage(ctx, &irc.Message{
+				Command: "AUTHENTICATE",
+				Params:  []string{respStr},
+			})
+		}
 	case irc.RPL_LOGGEDIN:
 		if err := parseMessageParams(msg, nil, nil, &uc.account); err != nil {
 			return err