From 03378da81bc68cf5c0544f1e797eac19fcb42de6 Mon Sep 17 00:00:00 2001
From: Shivaram Lingamneni <slingamn@cs.stanford.edu>
Date: Thu, 20 Feb 2020 23:47:13 -0500
Subject: [PATCH] CHATHISTORY with no results SHOULD send an empty batch

---
 irc/channel.go  |  9 ++++-----
 irc/client.go   | 16 ++++++++--------
 irc/handlers.go |  4 ++--
 irc/znc.go      |  2 +-
 4 files changed, 15 insertions(+), 16 deletions(-)

diff --git a/irc/channel.go b/irc/channel.go
index 4eedd07a..eec9355a 100644
--- a/irc/channel.go
+++ b/irc/channel.go
@@ -944,7 +944,9 @@ func (channel *Channel) replayHistoryForResume(session *Session, after time.Time
 		items, complete, _ = seq.Between(afterS, beforeS, channel.server.Config().History.ZNCMax)
 	}
 	rb := NewResponseBuffer(session)
-	channel.replayHistoryItems(rb, items, false)
+	if len(items) != 0 {
+		channel.replayHistoryItems(rb, items, false)
+	}
 	if !complete && !session.resumeDetails.HistoryIncomplete {
 		// warn here if we didn't warn already
 		rb.Add(nil, histServMask, "NOTICE", channel.Name(), session.client.t("Some additional message history may have been lost"))
@@ -961,10 +963,7 @@ func stripMaskFromNick(nickMask string) (nick string) {
 }
 
 func (channel *Channel) replayHistoryItems(rb *ResponseBuffer, items []history.Item, autoreplay bool) {
-	if len(items) == 0 {
-		return
-	}
-
+	// send an empty batch if necessary, as per the CHATHISTORY spec
 	chname := channel.Name()
 	client := rb.target
 	eventPlayback := rb.session.capabilities.Has(caps.EventPlayback)
diff --git a/irc/client.go b/irc/client.go
index 49d9b2db..85fc19c5 100644
--- a/irc/client.go
+++ b/irc/client.go
@@ -832,9 +832,11 @@ func (session *Session) playResume() {
 	if !timestamp.IsZero() && privmsgSeq != nil {
 		after := history.Selector{Time: timestamp}
 		items, complete, _ := privmsgSeq.Between(after, history.Selector{}, config.History.ZNCMax)
-		rb := NewResponseBuffer(session)
-		client.replayPrivmsgHistory(rb, items, "", complete)
-		rb.Send(true)
+		if len(items) != 0 {
+			rb := NewResponseBuffer(session)
+			client.replayPrivmsgHistory(rb, items, "", complete)
+			rb.Send(true)
+		}
 	}
 
 	session.resumeDetails = nil
@@ -844,12 +846,10 @@ func (client *Client) replayPrivmsgHistory(rb *ResponseBuffer, items []history.I
 	var batchID string
 	details := client.Details()
 	nick := details.nick
-	if 0 < len(items) {
-		if target == "" {
-			target = nick
-		}
-		batchID = rb.StartNestedHistoryBatch(target)
+	if target == "" {
+		target = nick
 	}
+	batchID = rb.StartNestedHistoryBatch(target)
 
 	allowTags := rb.session.capabilities.Has(caps.MessageTags)
 	for _, item := range items {
diff --git a/irc/handlers.go b/irc/handlers.go
index 2546dddf..373c1a1a 100644
--- a/irc/handlers.go
+++ b/irc/handlers.go
@@ -525,7 +525,7 @@ func chathistoryHandler(server *Server, client *Client, msg ircmsg.IrcMessage, r
 	var err error
 	defer func() {
 		// successful responses are sent as a chathistory or history batch
-		if err == nil && 0 < len(items) {
+		if err == nil {
 			if channel != nil {
 				channel.replayHistoryItems(rb, items, false)
 			} else {
@@ -958,7 +958,7 @@ func historyHandler(server *Server, client *Client, msg ircmsg.IrcMessage, rb *R
 		items, _, err = sequence.Between(start, end, limit)
 	}
 
-	if err == nil {
+	if err == nil && len(items) != 0 {
 		if channel != nil {
 			channel.replayHistoryItems(rb, items, false)
 		} else {
diff --git a/irc/znc.go b/irc/znc.go
index cd3ff783..c90e7144 100644
--- a/irc/znc.go
+++ b/irc/znc.go
@@ -124,7 +124,7 @@ func zncPlayPrivmsgs(client *Client, rb *ResponseBuffer, after, before time.Time
 	}
 	zncMax := client.server.Config().History.ZNCMax
 	items, _, err := sequence.Between(history.Selector{Time: after}, history.Selector{Time: before}, zncMax)
-	if err == nil {
+	if err == nil && len(items) != 0 {
 		client.replayPrivmsgHistory(rb, items, "", true)
 	}
 }