From 73f5be4e5c6ed2a9b98f81d5cf00d77bb3a2e935 Mon Sep 17 00:00:00 2001
From: Matthijs Kooijman <matthijs@stdin.nl>
Date: Thu, 2 Jul 2015 12:59:46 +0200
Subject: [PATCH] Use const pointers for payload

The payload data is never modified by the library, so using const is
possible without any further changes. Using const allows using a string
literal, or String::c_str() as the payload.
---
 Adafruit_MQTT.cpp | 6 +++---
 Adafruit_MQTT.h   | 6 +++---
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/Adafruit_MQTT.cpp b/Adafruit_MQTT.cpp
index 5d98279..d7963dc 100644
--- a/Adafruit_MQTT.cpp
+++ b/Adafruit_MQTT.cpp
@@ -140,7 +140,7 @@ int8_t Adafruit_MQTT::connect() {
   return 0;
 }
 
-bool Adafruit_MQTT::publish(const char *topic, char *data, uint8_t qos) {
+bool Adafruit_MQTT::publish(const char *topic, const char *data, uint8_t qos) {
   // Construct and send publish packet.
   uint8_t len = publishPacket(buffer, topic, data, qos);
   if (!sendPacket(buffer, len))
@@ -294,7 +294,7 @@ uint8_t Adafruit_MQTT::connectPacket(uint8_t *packet) {
 }
 
 uint8_t Adafruit_MQTT::publishPacket(uint8_t *packet, const char *topic, 
-                                     char *data, uint8_t qos) {
+                                     const char *data, uint8_t qos) {
   uint8_t *p = packet;
   uint16_t len;
 
@@ -375,7 +375,7 @@ bool Adafruit_MQTT_Publish::publish(uint32_t i) {
   return mqtt->publish(topic, payload, qos);
 }
 
-bool Adafruit_MQTT_Publish::publish(char *payload) {
+bool Adafruit_MQTT_Publish::publish(const char *payload) {
   return mqtt->publish(topic, payload, qos);
 }
 
diff --git a/Adafruit_MQTT.h b/Adafruit_MQTT.h
index c5c76aa..7d89801 100644
--- a/Adafruit_MQTT.h
+++ b/Adafruit_MQTT.h
@@ -116,7 +116,7 @@ class Adafruit_MQTT {
 
   // Publish a message to a topic using the specified QoS level.  Returns true
   // if the message was published, false otherwise.
-  bool publish(const char *topic, char *payload, uint8_t qos);
+  bool publish(const char *topic, const char *payload, uint8_t qos);
 
   // Add a subscription to receive messages for a topic.  Returns true if the
   // subscription could be added, false otherwise.
@@ -161,7 +161,7 @@ class Adafruit_MQTT {
 
   // Functions to generate MQTT packets.
   uint8_t connectPacket(uint8_t *packet);
-  uint8_t publishPacket(uint8_t *packet, const char *topic, char *payload, uint8_t qos);
+  uint8_t publishPacket(uint8_t *packet, const char *topic, const char *payload, uint8_t qos);
   uint8_t subscribePacket(uint8_t *packet, const char *topic, uint8_t qos);
   uint8_t pingPacket(uint8_t *packet);
 };
@@ -171,7 +171,7 @@ class Adafruit_MQTT_Publish {
  public:
   Adafruit_MQTT_Publish(Adafruit_MQTT *mqttserver, const char *feed, uint8_t qos = 0);
 
-  bool publish(char *s);
+  bool publish(const char *s);
   bool publish(double f, uint8_t precision=2);  // Precision controls the minimum number of digits after decimal.
                                                 // This might be ignored and a higher precision value sent.
   bool publish(int32_t i);