MQTTPublisher.lf

target C

/**
 * Reactor that publishes strings (or arbitrary byte arrays cast to `char*`) to a specified MQTT
 * topic.
 *
 * This publisher ensures in-order delivery messages to subscribers. If an attempt is made to send a
 * message before the delivery of the previous message has completed, then the reaction that sends
 * the message (the reaction to an input 'in') will block until the previous delivery has completed.
 *
 * If `include_timestamp` is true (the default is `false`), then two things happen:
 *
 * 1. The publisher ensures that the message is null terminated by adding a null terminator if
 * needed. This ensures that the message can be treated as a string at the receiving end. 2. The
 * publisher appends to the end of the message the current logical time at which the publishing
 * occurs.
 *
 * This can be useful if the receiving end will be an instance of `MQTTSubscriber` in another Lingua
 * Franca program. Note that `include_timestamp` *must* be true if an `MQTTSubcriber` that
 * subscribes to this topic has its `use_physical_time` parameter set to false (its default is
 * `true`). Otherwise, the subscriber will issue a warning.
 *
 * @param address The IP address of the MQTT broker.
 * @param timeout Timeout for completion of message sending in milliseconds.
 * @see MQTTSubscriber.
 *
 * @author Ravi Akella
 * @author Edward A. Lee
 */
reactor MQTTPublisher(
    topic: string = "DefaultTopic",
    address: string = "tcp://localhost:1883",
    include_timestamp: bool = false,
    timeout: time = 10 sec) {
  preamble {=
    #include "MQTTClient.h"
    #include "core/federated/net_util.h"

    // Count of instances of this reactor so that unique client IDs are generated.
    static size_t _lf_MQTTPublisher_count = 0;

    // Connection options for the client.
    // Making this global means that all instances of this reactor have
    // the same connection options.
    MQTTClient_connectOptions pub_connect_options = MQTTClient_connectOptions_initializer;

    // Struct type used to keep track of messages in flight between reactions.
    typedef struct inflight_t {
      bool message_in_flight;
      MQTTClient_deliveryToken delivery_token;
      char* message;
    } inflight_t;

    // Callback invoked once delivery is complete.
    void pub_delivered(void *inflight, MQTTClient_deliveryToken dt) {
      LF_PRINT_LOG("MQTTPublisher: Message with token value %d delivery confirmed\n", dt);
      ((inflight_t*)inflight)->message_in_flight = false;
      free(((inflight_t*)inflight)->message);
      ((inflight_t*)inflight)->delivery_token = 0;
      ((inflight_t*)inflight)->message = NULL;
    }
    // Callback invoked if the connection is lost.
    void pub_connection_lost(void *context, char *cause) {
      lf_print_error("\nMQTTPublisher: Connection lost. Cause: %s\n", cause);
    }
  =}

  /**
   * Input type char* instead of string is used for dynamically allocated character arrays (as
   * opposed to static constant strings).
   */
  input in: char*

  /** State variable that keeps track of a message in flight. */
  state inflight: inflight_t = {= {false, 0, NULL} =}

  /** Client ID. This is automatically generated. */
  state clientID: char* = {= NULL =}

  /** The client object. */
  state client: MQTTClient = {= NULL =}

  /** The message object. */
  state mqtt_msg: MQTTClient_message = {= MQTTClient_message_initializer =}

  /** Connect to the broker. Exit if this fails. */
  reaction(startup) {=
    // In case there are multiple instances of this or the subscriber, enter
    // a critical section. The Paho MQTT functions are not thread safe.
    lf_critical_section_enter();

    // Create a unique ID.
    if (asprintf(&self->clientID, "LF_MQTTPublisher_%zu", _lf_MQTTPublisher_count++) < 0) {
      lf_print_error_and_exit("MQTTPublisher: Failed to create client ID.");
    }

    MQTTClient_create(&self->client, self->address, self->clientID, MQTTCLIENT_PERSISTENCE_NONE, NULL);
    pub_connect_options.keepAliveInterval = 20;
    pub_connect_options.cleansession = 1;

    // Set up callback functions.
    // Second to last argument should be a pointer to a function
    // to handle notification of delivery of a message.
    // But this reactor isn't sending any messages.
    // Second argument is a pointer to context that will be passed to pub_delivered,
    // which in this case is a pointer to the inflight state variable.
    MQTTClient_setCallbacks(self->client, &self->inflight, pub_connection_lost, NULL, pub_delivered);

    // Connect to the broker.
    int rc; // response code.
    if ((rc = MQTTClient_connect(self->client, &pub_connect_options)) != MQTTCLIENT_SUCCESS) {
      lf_print_error_and_exit("MQTTPublisher: Failed to connect to MQTT broker.\n"
          "Perhaps one is not running? Return code: %d", rc);
    }

    lf_critical_section_exit();

    LF_PRINT_LOG("MQTTPublisher: connected to broker.");
  =}

  /**
   * React to an input by sending a message with the value of the input as the payload. If delivery
   * has not yet completed for a previously sent message, then wait for it to complete before
   * proceeding (blocking this reaction). This copies the message from the input into a buffer, so
   * the input can freed upon return from this reaction.
   */
  reaction(in) {=
    // In case there are multiple instances of this or the subscriber, enter
    // a critical section. The Paho MQTT functions are not thread safe.
    lf_critical_section_enter();

    if(self->inflight.message_in_flight) {
      // Wait for message delivery to be complete.
      LF_PRINT_LOG("MQTTPublisher: Waiting for confirmation of publication of previous message");
      int rc = MQTTClient_waitForCompletion(
          self->client, self->inflight.delivery_token, self->timeout
      );
      if (rc != MQTTCLIENT_SUCCESS) {
        lf_print_error("MQTTPublisher: Message delivery failed with error code %d.\n", rc);
        lf_print_error("  Message: %s\n", in->value);
        lf_print_error("  On topic '%s' for publisher with ClientID: %s\n", self->topic, self->clientID);
      }
    }
    LF_PRINT_LOG("MQTTPublisher: Publishing message: %s", in->value);
    LF_PRINT_LOG("MQTTPublisher: on topic '%s' for publisher with ClientID: %s", self->topic, self->clientID);

    // Allocate memory for a copy of the message.
    // The default length is just the length of the incoming message.
    int length = in->length;
    // If a timestamp is to be included, the length is bigger.
    if (self->include_timestamp) {
      // If the input message is not null terminated, then add a null terminator.
      if (in->value[in->length - 1] != '\0') length++;
      // Allow space (4 bytes) for the magic string "LFts".
      length += 4 + sizeof(instant_t);
    }

    self->inflight.message = (char*) malloc(sizeof(char) * length);
    memcpy(self->inflight.message, in->value, in->length);
    // Append null terminator and timestamp, if appropriate.
    if (self->include_timestamp) {
      // If the input message is not null terminated, then add a null terminator.
      if (in->value[in->length - 1] != '\0') {
        self->inflight.message[in->length] = '\0';
        // Add magic string.
        memcpy(&self->inflight.message[in->length + 1], "LFts", 4);
      } else {
        // Add magic string.
        memcpy(&self->inflight.message[in->length], "LFts", 4);
      }

      // Append the current timestamp to the message.
      instant_t timestamp = lf_time_logical();
      encode_int64(timestamp,
        (unsigned char*)(self->inflight.message + length - sizeof(instant_t))
      );
      LF_PRINT_LOG("MQTTPublisher: Timestamp (elapsed) of sending message: " PRINTF_TIME,
        timestamp - lf_time_start()
      );
    }
    self->mqtt_msg.payload = self->inflight.message;
    self->mqtt_msg.payloadlen = length;

    // QoS 2 means that the message will be delivered exactly once.
    self->mqtt_msg.qos = 2;

    // Retained messages are held by the server and sent to future new subscribers.
    // Specify that this message should not be retained.
    // It will be sent only to subscribers currently subscribed.
    self->mqtt_msg.retained = 0;

    MQTTClient_publishMessage(self->client, self->topic, &self->mqtt_msg, &self->inflight.delivery_token);
    self->inflight.message_in_flight = true;

    lf_critical_section_exit();

    // It is not clear why the following is needed, but the message
    // does not go out until the next invocation without it.
    MQTTClient_yield();
  =}

  /** Disconnect the client. */
  reaction(shutdown) {=
    LF_PRINT_LOG("MQTTPublisher: Client ID %s disconnecting.", self->clientID);
    if (self->clientID) free(self->clientID);
    MQTTClient_disconnect(self->client, 10000);
    MQTTClient_destroy(&self->client);
  =}
}