| <!-- | |
| Copyright (C) Daniel Stenberg, <[email protected]>, et al. | |
| SPDX-License-Identifier: curl | |
| --> | |
| # MQTT in curl | |
| ## Usage | |
| A plain "GET" subscribes to the topic and prints all published messages. | |
| Doing a "POST" publishes the post data to the topic and exits. | |
| ### Subscribing | |
| Command usage: | |
| curl mqtt://host/topic | |
| Example subscribe: | |
| curl mqtt://host.home/bedroom/temp | |
| This will send an MQTT SUBSCRIBE packet for the topic `bedroom/temp` and listen in for incoming PUBLISH packets. | |
| ### Publishing | |
| Command usage: | |
| curl -d payload mqtt://host/topic | |
| Example publish: | |
| curl -d 75 mqtt://host.home/bedroom/dimmer | |
| This will send an MQTT PUBLISH packet to the topic `bedroom/dimmer` with the payload `75`. | |
| ## What does curl deliver as a response to a subscribe | |
| Whenever a PUBLISH packet is received, curl outputs two bytes topic length (MSB | LSB), the topic followed by the | |
| payload. | |
| ## Caveats | |
| Remaining limitations: | |
| - Only QoS level 0 is implemented for publish | |
| - No way to set retain flag for publish | |
| - No TLS (mqtts) support | |
| - Naive EAGAIN handling does not handle split messages | |