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AWS C MQTT

C99 implementation of the MQTT 3.1.1 and MQTT 5 specifications.

License

This library is licensed under the Apache 2.0 License.

Usage

Building

CMake 3.9+ is required to build.

<install-path> must be an absolute path in the following instructions.

Linux-Only Dependencies

If you are building on Linux, you will need to build aws-lc and s2n-tls first.

git clone [email protected]:awslabs/aws-lc.git
cmake -S aws-lc -B aws-lc/build -DCMAKE_INSTALL_PREFIX=<install-path>
cmake --build aws-lc/build --target install

git clone [email protected]:aws/s2n-tls.git
cmake -S s2n-tls -B s2n-tls/build -DCMAKE_INSTALL_PREFIX=<install-path> -DCMAKE_PREFIX_PATH=<install-path>
cmake --build s2n-tls/build --target install

Building aws-c-mqtt and Remaining Dependencies

git clone [email protected]:awslabs/aws-c-common.git
cmake -S aws-c-common -B aws-c-common/build -DCMAKE_INSTALL_PREFIX=<install-path>
cmake --build aws-c-common/build --target install

git clone [email protected]:awslabs/aws-c-cal.git
cmake -S aws-c-cal -B aws-c-cal/build -DCMAKE_INSTALL_PREFIX=<install-path> -DCMAKE_PREFIX_PATH=<install-path>
cmake --build aws-c-cal/build --target install

git clone [email protected]:awslabs/aws-c-io.git
cmake -S aws-c-io -B aws-c-io/build -DCMAKE_INSTALL_PREFIX=<install-path> -DCMAKE_PREFIX_PATH=<install-path>
cmake --build aws-c-io/build --target install

git clone [email protected]:awslabs/aws-c-compression.git
cmake -S aws-c-compression -B aws-c-compression/build -DCMAKE_INSTALL_PREFIX=<install-path> -DCMAKE_PREFIX_PATH=<install-path>
cmake --build aws-c-compression/build --target install

git clone [email protected]:awslabs/aws-c-http.git
cmake -S aws-c-http -B aws-c-http/build -DCMAKE_INSTALL_PREFIX=<install-path> -DCMAKE_PREFIX_PATH=<install-path>
cmake --build aws-c-http/build --target install

git clone [email protected]:awslabs/aws-c-mqtt.git
cmake -S aws-c-mqtt -B aws-c-mqtt/build -DCMAKE_INSTALL_PREFIX=<install-path> -DCMAKE_PREFIX_PATH=<install-path>
cmake --build aws-c-mqtt/build --target install

Overview

This library contains an MQTT implementation that is simple and easy to use, but also quite powerful and low on unnecessary copies. Here is a general overview of the API:

struct aws_mqtt_client;

aws_mqtt_client is meant to be created once per application to pool common resources required for opening MQTT connections. The instance does not need to be allocated, and may be managed by the user.

int aws_mqtt_client_init(
    struct aws_mqtt_client *client,
    struct aws_allocator *allocator,
    struct aws_event_loop_group *elg);

Initializes an instance of aws_mqtt_client with the required parameters.

  • client is effectively the this parameter.
  • allocator will be used to initialize the client (note that the client itself is NOT allocated). This resource must outlive client.
  • bootstrap will be used to initiate new socket connections MQTT. This resource must outlive client. See aws-c-io for more information about aws_client_bootstrap.
void aws_mqtt_client_clean_up(struct aws_mqtt_client *client);

Cleans up a client and frees all owned resources.

NOTE: DO NOT CALL THIS FUNCTION UNTIL ALL OUTSTANDING CONNECTIONS ARE CLOSED.

struct aws_mqtt_client_connection;

struct aws_mqtt_client_connection *aws_mqtt_client_connection_new(
    struct aws_mqtt_client *client,
    struct aws_mqtt_client_connection_callbacks callbacks,
    const struct aws_byte_cursor *host_name,
    uint16_t port,
    struct aws_socket_options *socket_options,
    struct aws_tls_ctx_options *tls_options);

Allocates and initializes a new connection object (does NOT actually connect). You may use the returned object to configure connection parameters, and then call aws_mqtt_client_connection_connect to actually open the connection.

  • client is required in order to use an existing DNS resolver, event loop group, and allocator.
  • callbacks provides the connection-level (not operation level) callbacks and the userdata to be given back.
  • host_name lists the end point to connect to. This may be a DNS address or an IP address. This resource may be freed immediately after return.
  • port the port to connect to on host_name.
  • socket_options describes how to open the connection. See aws-c-io for more information about aws_socket_options.
  • tls_options provides TLS credentials to connect with. Pass NULL to not use TLS (NOT RECOMMENDED). See aws-c-io for more information about aws_tls_ctx_options.
void aws_mqtt_client_connection_destroy(struct aws_mqtt_client_connection *connection);

Destroys a connection and frees all outstanding resources.

NOTE: DO NOT CALL THIS FUNCTION UNTIL THE CONNECTION IS CLOSED.

int aws_mqtt_client_connection_set_will(
    struct aws_mqtt_client_connection *connection,
    const struct aws_byte_cursor *topic,
    enum aws_mqtt_qos qos,
    bool retain,
    const struct aws_byte_cursor *payload);

Sets the last will and testament to be distributed by the server upon client disconnection. Must be called before aws_mqtt_client_connection_connect. See aws_mqtt_client_connection_publish for information on the parameters. topic and payload must persist past the call to aws_mqtt_client_connection_connect.

int aws_mqtt_client_connection_set_login(
    struct aws_mqtt_client_connection *connection,
    const struct aws_byte_cursor *username,
    const struct aws_byte_cursor *password);

Sets the username and password to be sent to the server on connection. Must be called before aws_mqtt_client_connection_connect. username and password must persist past the call to aws_mqtt_client_connection_connect.

int aws_mqtt_client_connection_set_reconnect_timeout(
    struct aws_mqtt_client_connection *connection,
    uint64_t min_timeout,
    uint64_t max_timeout);

Sets the minimum and maximum reconnect timeouts. The time between reconnect attempts will start at min and multipy by 2 until max is reached.

int aws_mqtt_client_connection_connect(
    struct aws_mqtt_client_connection *connection,
    const struct aws_byte_cursor *client_id,
    bool clean_session,
    uint16_t keep_alive_time);

Connects to the remote endpoint. The parameters here are set in the MQTT CONNECT packet directly. client_id must persist until the on_connack connection callback is called.

int aws_mqtt_client_connection_disconnect(struct aws_mqtt_client_connection *connection);

Closes an open connection. Does not clean up any resources, that's to be done by aws_mqtt_client_connection_destroy, probably from the on_disconnected connection callback.

uint16_t aws_mqtt_client_connection_subscribe_single(
    struct aws_mqtt_client_connection *connection,
    const struct aws_byte_cursor *topic_filter,
    enum aws_mqtt_qos qos,
    aws_mqtt_client_publish_received_fn *on_publish,
    void *on_publish_ud,
    aws_mqtt_suback_single_fn *on_suback,
    void *on_suback_ud);

Subscribes to the topic filter given with the given QoS. on_publish will be called whenever a packet matching topic_filter arrives. on_suback will be called when the SUBACK packet has been received. topic_filter must persist until on_suback is called. The packet_id of the SUBSCRIBE packet will be returned, or 0 on error.

uint16_t aws_mqtt_client_connection_unsubscribe(
    struct aws_mqtt_client_connection *connection,
    const struct aws_byte_cursor *topic_filter,
    aws_mqtt_op_complete_fn *on_unsuback,
    void *on_unsuback_ud);

Unsubscribes from the topic filter given. topic_filter must persist until on_unsuback is called. The packet_id of the UNSUBSCRIBE packet will be returned, or 0 on error.

uint16_t aws_mqtt_client_connection_publish(
    struct aws_mqtt_client_connection *connection,
    const struct aws_byte_cursor *topic,
    enum aws_mqtt_qos qos,
    bool retain,
    const struct aws_byte_cursor *payload,
    aws_mqtt_op_complete_fn *on_complete,
    void *userdata);

Publish a payload to the topic specified. For QoS 0, on_complete will be called as soon as the packet is sent over the wire. For QoS 1, as soon as PUBACK comes back. For QoS 2, PUBCOMP. topic and payload must persist until on_complete.

int aws_mqtt_client_connection_ping(struct aws_mqtt_client_connection *connection);

Sends a PINGREQ packet to the server.