Clients: improve error msgs when connecting v3.x broker with v5 client

Closes #1344. Thanks to HowJMay.

ChangeLog.txt

@@ -20,10 +20,15 @@ Client library:
 - `mosquitto_string_option(mosq, MOSQ_OPT_TLS_KEYFORM, ...)` was incorrectly
  returning `MOSQ_ERR_INVAL` with valid input. This has been fixed.
  Closes #1360.
+- on_connect callback is now called with the correct v5 reason code if a v5
+ client connects to a v3.x broker and is sent a CONNACK with the
+ "unacceptable protocol version" connack reason code.
 
 Clients:
 - mosquitto_pub: fix error codes not being returned when mosquitto_pub exits.
  Closes #1354.
+- All clients: improve error messages when connecting to a v3.x broker when in
+ v5 mode. Closes #1344.
 
 Other:
 - Various documentation fixes.

client/pub_client.c

@@ -168,10 +168,15 @@ void my_connect_callback(struct mosquitto *mosq, void *obj, int result, int flag
  }else{
  if(result){
  if(cfg.protocol_version == MQTT_PROTOCOL_V5){
- err_printf(&cfg, "%s\n", mosquitto_reason_string(result));
+ if(result == MQTT_RC_UNSUPPORTED_PROTOCOL_VERSION){
+ err_printf(&cfg, "Connection error: %s. Try connecting to an MQTT v5 broker, or use MQTT v3.x mode.\n", mosquitto_reason_string(result));
+ }else{
+ err_printf(&cfg, "Connection error: %s\n", mosquitto_reason_string(result));
+ }
  }else{
- err_printf(&cfg, "%s\n", mosquitto_connack_string(result));
+ err_printf(&cfg, "Connection error: %s\n", mosquitto_connack_string(result));
  }
+ mosquitto_disconnect_v5(mosq, 0, cfg.disconnect_props);
  }
  }
 }

client/rr_client.c

@@ -122,7 +122,11 @@ void my_connect_callback(struct mosquitto *mosq, void *obj, int result, int flag
  }else{
  client_state = rr_s_disconnect;
  if(result){
- err_printf(&cfg, "%s\n", mosquitto_connack_string(result));
+ if(result == MQTT_RC_UNSUPPORTED_PROTOCOL_VERSION){
+ err_printf(&cfg, "Connection error: %s. mosquitto_rr only supports connecting to an MQTT v5 broker\n", mosquitto_reason_string(result));
+ }else{
+ err_printf(&cfg, "Connection error: %s\n", mosquitto_reason_string(result));
+ }
  }
  mosquitto_disconnect_v5(mosq, 0, cfg.disconnect_props);
  }
@@ -356,7 +360,7 @@ int main(int argc, char *argv[])
  }
  client_config_cleanup(&cfg);
  if(rc){
- fprintf(stderr, "Error: %s\n", mosquitto_strerror(rc));
+ err_printf(&cfg, "Error: %s\n", mosquitto_strerror(rc));
  }
  return rc;
 

client/sub_client.c

@@ -126,9 +126,13 @@ void my_connect_callback(struct mosquitto *mosq, void *obj, int result, int flag
  }else{
  if(result){
  if(cfg.protocol_version == MQTT_PROTOCOL_V5){
- err_printf(&cfg, "%s\n", mosquitto_reason_string(result));
+ if(result == MQTT_RC_UNSUPPORTED_PROTOCOL_VERSION){
+ err_printf(&cfg, "Connection error: %s. Try connecting to an MQTT v5 broker, or use MQTT v3.x mode.\n", mosquitto_reason_string(result));
+ }else{
+ err_printf(&cfg, "Connection error: %s\n", mosquitto_reason_string(result));
+ }
  }else{
- err_printf(&cfg, "%s\n", mosquitto_connack_string(result));
+ err_printf(&cfg, "Connection error: %s\n", mosquitto_connack_string(result));
  }
  }
  mosquitto_disconnect_v5(mosq, 0, cfg.disconnect_props);
@@ -353,7 +357,7 @@ int main(int argc, char *argv[])
  }
  client_config_cleanup(&cfg);
  if(rc){
- fprintf(stderr, "Error: %s\n", mosquitto_strerror(rc));
+ err_printf(&cfg, "Error: %s\n", mosquitto_strerror(rc));
  }
  return rc;
 

lib/handle_connack.c

@@ -28,6 +28,29 @@ and the Eclipse Distribution License is available at
 #include "property_mosq.h"
 #include "read_handle.h"
 
+static void connack_callback(struct mosquitto *mosq, uint8_t reason_code, uint8_t connect_flags, const mosquitto_property *properties)
+{
+ log__printf(mosq, MOSQ_LOG_DEBUG, "Client %s received CONNACK (%d)", mosq->id, reason_code);
+ pthread_mutex_lock(&mosq->callback_mutex);
+ if(mosq->on_connect){
+ mosq->in_callback = true;
+ mosq->on_connect(mosq, mosq->userdata, reason_code);
+ mosq->in_callback = false;
+ }
+ if(mosq->on_connect_with_flags){
+ mosq->in_callback = true;
+ mosq->on_connect_with_flags(mosq, mosq->userdata, reason_code, connect_flags);
+ mosq->in_callback = false;
+ }
+ if(mosq->on_connect_v5){
+ mosq->in_callback = true;
+ mosq->on_connect_v5(mosq, mosq->userdata, reason_code, connect_flags, properties);
+ mosq->in_callback = false;
+ }
+ pthread_mutex_unlock(&mosq->callback_mutex);
+}
+
+
 int handle__connack(struct mosquitto *mosq)
 {
  uint8_t connect_flags;
@@ -44,7 +67,17 @@ int handle__connack(struct mosquitto *mosq)
 
  if(mosq->protocol == mosq_p_mqtt5){
  rc = property__read_all(CMD_CONNACK, &mosq->in_packet, &properties);
- if(rc) return rc;
+
+ if(rc == MOSQ_ERR_PROTOCOL && reason_code == CONNACK_REFUSED_PROTOCOL_VERSION){
+ /* This could occur because we are connecting to a v3.x broker and
+ * it has replied with "unacceptable protocol version", but with a
+ * v3 CONNACK. */
+
+ connack_callback(mosq, MQTT_RC_UNSUPPORTED_PROTOCOL_VERSION, connect_flags, NULL);
+ return rc;
+ }else if(rc){
+ return rc;
+ }
  }
 
  mosquitto_property_read_string(properties, MQTT_PROP_ASSIGNED_CLIENT_IDENTIFIER, &clientid, false);
@@ -68,24 +101,7 @@ int handle__connack(struct mosquitto *mosq)
 
  mosq->msgs_out.inflight_quota = mosq->msgs_out.inflight_maximum;
 
- log__printf(mosq, MOSQ_LOG_DEBUG, "Client %s received CONNACK (%d)", mosq->id, reason_code);
- pthread_mutex_lock(&mosq->callback_mutex);
- if(mosq->on_connect){
- mosq->in_callback = true;
- mosq->on_connect(mosq, mosq->userdata, reason_code);
- mosq->in_callback = false;
- }
- if(mosq->on_connect_with_flags){
- mosq->in_callback = true;
- mosq->on_connect_with_flags(mosq, mosq->userdata, reason_code, connect_flags);
- mosq->in_callback = false;
- }
- if(mosq->on_connect_v5){
- mosq->in_callback = true;
- mosq->on_connect_v5(mosq, mosq->userdata, reason_code, connect_flags, properties);
- mosq->in_callback = false;
- }
- pthread_mutex_unlock(&mosq->callback_mutex);
+ connack_callback(mosq, reason_code, connect_flags, properties);
  mosquitto_property_free_all(&properties);
 
  switch(reason_code){

lib/loop.c

@@ -314,7 +314,6 @@ static int mosquitto__loop_rc_handle(struct mosquitto *mosq, int rc)
  mosq->in_callback = false;
  }
  pthread_mutex_unlock(&mosq->callback_mutex);
- return rc;
  }
  return rc;
 }