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MQTT connection error handling #3495

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MQTT connection error handling #3495

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5 changes: 5 additions & 0 deletions include/libwebsockets/lws-mqtt.h
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Original file line number Diff line number Diff line change
Expand Up @@ -33,6 +33,11 @@ struct lws_mqtt_str_st;
typedef struct lws_mqtt_str_st lws_mqtt_str_t;

#define MQTT_VER_3_1_1 4
#if MQTT_VER_3_1_1 == 4
#define MQTT_VER_STRING "3.1.1"
#else
#define MQTT_VER_STRING "unknown"
#endif

#define LWS_MQTT_FINAL_PART 1

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24 changes: 22 additions & 2 deletions lib/roles/mqtt/client/client-mqtt.c
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Expand Up @@ -338,8 +338,28 @@ lws_mqtt_client_socket_service(struct lws *wsi, struct lws_pollfd *pollfd,
else
n = lws_read_mqtt(wsi, ebuf.token, (unsigned int)ebuf.len);
if (n < 0) {
lwsl_err("%s: Parsing packet failed\n", __func__);
goto fail;
lws_mqttc_t *c = &wsi->mqtt->client;
char msgBuffer[128];
switch (c->par.reason) {
case LMQCP_REASON_UNSUPPORTED_PROTOCOL:
snprintf(msgBuffer, sizeof(msgBuffer), "reason: %s %s\n", "server does not support MQTT protocol", MQTT_VER_STRING);
break;
case LMQCP_REASON_CLIENT_ID_INVALID:
snprintf(msgBuffer, sizeof(msgBuffer), "reason: %s %.*s\n", "server does not accept client ID", c->id->len, c->id->buf);
break;
case LMQCP_REASON_BAD_CREDENTIALS:
snprintf(msgBuffer, sizeof(msgBuffer), "reason: %s\n", "invalid credentials");
break;
case LMQCP_REASON_NOT_AUTHORIZED:
snprintf(msgBuffer, sizeof(msgBuffer), "reason: %s\n", "not authorized");
break;
default:
snprintf(msgBuffer, sizeof(msgBuffer), "reason: %s\n", "unknown MQTT connection failure");
break;
}
lws_inform_client_conn_fail(wsi, (void *)msgBuffer, strlen(msgBuffer));
lws_close_free_wsi(wsi, LWS_CLOSE_STATUS_NOSTATUS, __func__);
return -1;
}

m = ebuf.len - n;
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16 changes: 13 additions & 3 deletions lib/roles/mqtt/mqtt.c
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Expand Up @@ -1029,17 +1029,27 @@ _lws_mqtt_rx_parser(struct lws *wsi, lws_mqtt_parser_t *par,
switch (par->conn_rc) {
case 0:
goto cmd_completion;
/* 3.1.1 errors [MQTT-3.2.3] */
case 1:
par->reason = LMQCP_REASON_UNSUPPORTED_PROTOCOL;
goto send_reason_and_close;
case 2:
par->reason = LMQCP_REASON_CLIENT_ID_INVALID;
goto send_reason_and_close;
case 3:
par->reason = LMQCP_REASON_SERVER_UNAVAILABLE;
goto send_reason_and_close;
case 4:
par->reason = LMQCP_REASON_BAD_CREDENTIALS;
goto send_reason_and_close;
case 5:
par->reason = LMQCP_REASON_UNSUPPORTED_PROTOCOL +
par->conn_rc - 1;
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@johnhe4 johnhe4 Nov 12, 2025

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I'm guessing this logic used to work at one point? Maybe the MQTT error code enum was updated to support 5.0 errors and that's where this broke.

par->reason = LMQCP_REASON_NOT_AUTHORIZED;
goto send_reason_and_close;
/* 5.0 and all other errors [MQTT-3.2.2.2] */
default:
par->reason = (lws_mqtt_reason_t)par->conn_rc;
lwsl_notice("%s: bad connack retcode\n", __func__);
goto send_protocol_error_and_close;
goto send_reason_and_close;
}
break;

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