From 5cc16a4722172106671cfdd08cd567ca04152cc4 Mon Sep 17 00:00:00 2001
From: "Roger A. Light" <roger@atchoo.org>
Date: Thu, 12 Dec 2019 13:19:51 +0000
Subject: [PATCH] Basic publishing example.

---
 examples/publish/basic-1.c | 128 +++++++++++++++++++++++++++++++++++++
 1 file changed, 128 insertions(+)
 create mode 100644 examples/publish/basic-1.c

diff --git a/examples/publish/basic-1.c b/examples/publish/basic-1.c
new file mode 100644
index 00000000..a330db1d
--- /dev/null
+++ b/examples/publish/basic-1.c
@@ -0,0 +1,128 @@
+/*
+ * This example shows how to publish messages from outside of the Mosquitto network loop.
+ */
+
+#include <mosquitto.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+
+/* Callback called when the client receives a CONNACK message from the broker. */
+void on_connect(struct mosquitto *mosq, void *obj, int reason_code)
+{
+	/* Print out the connection result. mosquitto_connack_string() produces an
+	 * appropriate string for MQTT v3.x clients, the equivalent for MQTT v5.0
+	 * clients is mosquitto_reason_string().
+	 */
+	printf("on_connect: %s\n", mosquitto_connack_string(reason_code));
+
+	/* You may wish to set a flag here to indicate to your application that the
+	 * client is now connected. */
+}
+
+
+/* Callback called when the client knows to the best of its abilities that a
+ * PUBLISH has been successfully sent. For QoS 0 this means the message has
+ * been completely written to the operating system. For QoS 1 this means we
+ * have received a PUBACK from the broker. For QoS 2 this means we have
+ * received a PUBCOMP from the broker. */
+void on_publish(struct mosquitto *mosq, void *obj, int mid)
+{
+	printf("Message with mid %d has been published.\n", mid);
+}
+
+
+int get_temperature(void)
+{
+	sleep(1); /* Prevent a storm of messages - this pretend sensor works at 1Hz */
+	return random()%100;
+}
+
+/* This function pretends to read some data from a sensor and publish it.*/
+void publish_sensor_data(struct mosquitto *mosq)
+{
+	char payload[20];
+	int temp;
+	int rc;
+
+	/* Get our pretend data */
+	temp = get_temperature();
+	/* Print it to a string for easy human reading - payload format is highly
+	 * application dependent. */
+	snprintf(payload, sizeof(payload), "%d", temp);
+
+	/* Publish the message
+	 * mosq - our client instance
+	 * *mid = NULL - we don't want to know what the message id for this message is
+	 * topic = "example/temperature" - the topic on which this message will be published
+	 * payloadlen = strlen(payload) - the length of our payload in bytes
+	 * payload - the actual payload
+	 * qos = 2 - publish with QoS 2 for this example
+	 * retain = false - do not use the retained message feature for this message
+	 */
+	rc = mosquitto_publish(mosq, NULL, "example/temperature", strlen(payload), payload, 2, false);
+	if(rc != MOSQ_ERR_SUCCESS){
+		fprintf(stderr, "Error publishing: %s\n", mosquitto_strerror(rc));
+	}
+}
+
+
+int main(int argc, char *argv[])
+{
+	struct mosquitto *mosq;
+	int rc;
+
+	/* Required before calling other mosquitto functions */
+	mosquitto_lib_init();
+
+	/* Create a new client instance.
+	 * id = NULL -> ask the broker to generate a client id for us
+	 * clean session = true -> the broker should remove old sessions when we connect
+	 * obj = NULL -> we aren't passing any of our private data for callbacks
+	 */
+	mosq = mosquitto_new(NULL, true, NULL);
+	if(mosq == NULL){
+		fprintf(stderr, "Error: Out of memory.\n");
+		return 1;
+	}
+
+	/* Configure callbacks. This should be done before connecting ideally. */
+	mosquitto_connect_callback_set(mosq, on_connect);
+	mosquitto_publish_callback_set(mosq, on_publish);
+
+	/* Connect to test.mosquitto.org on port 1883, with a keepalive of 60 seconds.
+	 * This call makes the socket connection only, it does not complete the MQTT
+	 * CONNECT/CONNACK flow, you should use mosquitto_loop_start() or
+	 * mosquitto_loop_forever() for processing net traffic. */
+	rc = mosquitto_connect(mosq, "test.mosquitto.org", 1883, 60);
+	if(rc != MOSQ_ERR_SUCCESS){
+		mosquitto_destroy(mosq);
+		fprintf(stderr, "Error: %s\n", mosquitto_strerror(rc));
+		return 1;
+	}
+
+	/* Run the network loop in a background thread, this call returns quickly. */
+	rc = mosquitto_loop_start(mosq);
+	if(rc != MOSQ_ERR_SUCCESS){
+		mosquitto_destroy(mosq);
+		fprintf(stderr, "Error: %s\n", mosquitto_strerror(rc));
+		return 1;
+	}
+
+	/* At this point the client is connected to the network socket, but may not
+	 * have completed CONNECT/CONNACK.
+	 * It is fairly safe to start queuing messages at this point, but if you
+	 * want to be really sure you should wait until after a successful call to
+	 * the connect callback.
+	 * In this case we know it is 1 second before we start publishing.
+	 */
+	while(1){
+		publish_sensor_data(mosq);
+	}
+
+	mosquitto_lib_cleanup();
+	return 0;
+}
+