From 7908e412123daf91fc07e8ce6f04ed6e26950fb7 Mon Sep 17 00:00:00 2001
From: James Hillyerd <james@hillyerd.com>
Date: Thu, 14 Dec 2017 18:51:35 -0800
Subject: [PATCH] Fixes #61 - monitor.history=0 panic

---
 CHANGELOG.md       |  1 +
 msghub/hub.go      | 16 +++++++++-------
 msghub/hub_test.go | 11 +++++++++++
 3 files changed, 21 insertions(+), 7 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5817b71..7d6e8e5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -17,6 +17,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 - `rest/client.NewV1` renamed to `New`
 - `rest/client` package now embeds the shared `rest/model` structs into its own
   types
+- Fixed panic when `monitor.history` set to 0
 
 [1.2.0-rc1] - 2017-01-29
 ------------------------
diff --git a/msghub/hub.go b/msghub/hub.go
index afc32b5..77e06ee 100644
--- a/msghub/hub.go
+++ b/msghub/hub.go
@@ -63,13 +63,15 @@ func New(ctx context.Context, historyLen int) *Hub {
 // history buffer and then relayed to all registered listeners.
 func (hub *Hub) Dispatch(msg Message) {
 	hub.opChan <- func(h *Hub) {
-		// Add to history buffer
-		h.history.Value = msg
-		h.history = h.history.Next()
-		// Deliver message to all listeners, removing listeners if they return an error
-		for l := range h.listeners {
-			if err := l.Receive(msg); err != nil {
-				delete(h.listeners, l)
+		if h.history != nil {
+			// Add to history buffer
+			h.history.Value = msg
+			h.history = h.history.Next()
+			// Deliver message to all listeners, removing listeners if they return an error
+			for l := range h.listeners {
+				if err := l.Receive(msg); err != nil {
+					delete(h.listeners, l)
+				}
 			}
 		}
 	}
diff --git a/msghub/hub_test.go b/msghub/hub_test.go
index f5da3ad..db77c7f 100644
--- a/msghub/hub_test.go
+++ b/msghub/hub_test.go
@@ -60,6 +60,17 @@ func TestHubNew(t *testing.T) {
 	}
 }
 
+func TestHubZeroLen(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	hub := New(ctx, 0)
+	m := Message{}
+	for i := 0; i < 100; i++ {
+		hub.Dispatch(m)
+	}
+	// Just making sure Hub doesn't panic
+}
+
 func TestHubZeroListeners(t *testing.T) {
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()