MQTT features

[egekorkan]

Added features:

• Before the expose() returns, the TD is published to the broker, addresses issue [question] How to get the TD with MQTT Subscribe #144. This is also published with retain set to true
• readOnly and writeOnly properties are handled. Before even writeOnly properties were readable and there was no way to write to properties via MQTT. Now, only readable properties are published to and there is handling of subscribed topics to handle writing, like with actions. Addresses issue [proposal][binding-mqtt] Adding writeable property feature #152

I am not able to write tests for this due to 2 reasons:

1. See [testing] mqtt test is not working/old #161
2. A test for this would require to fetch the TD from the broker. This is not possible with the fetch() function since it always maps to readResource() which is not implemented in the mqtt binding. Then I have tried the following but was blocked by the same reason as in the point 1:

                            let broker = mqtt.connect("test.mosquitto.org");
                            broker.on("connect", () => {
                                broker.subscribe("TestWoTMQTT");
                                broker.on("message", (receivedTopic: string, payload: string) => {
                                    if (receivedTopic == "TestWoTMQTT"){
                                        expect(payload).contain("TestWoTMQTT")
                                        console.log(payload)
                                    }
                                });

However, I have tested using mosquitto_sub and mosquitto_pub and gotten the TD, even multiple times or published before subscription. Only writeable properties are written to and their form show up in the TD. Same for readable properties.
Signed-off-by: Ege Korkan egekorkan@gmail.com

[egekorkan]

I am not fully understanding the error produced by Travis but it seems that it is failing since it is taking too long to build node.js from the sources. There are the following lines in the raw log file:

Downloading https://nodejs.org/dist/v13.6.0/node-v13.6.0.tar.xz...
Computing checksum with sha256sum
Checksums matched!
$>./configure --prefix=/home/travis/.nvm/versions/node/v13.6.0 <
Node.js configure: Found Python 2.7.12...
�[1m�[93mWARNING�[0m: C++ compiler (CXX=g++, 5.4.0) too old, need g++ 6.3.0 or clang++ 8.0.0
�[1m�[93mWARNING�[0m: warnings were emitted in the configure phase
�[1m�[32mINFO�[0m: configure completed successfully
make -C out BUILDTYPE=Release V=0

... (lots of difficult to understand lines)
The job exceeded the maximum time limit for jobs, and has been terminated.

[danielpeintner]

1 out of 4 Travis builds failed. I guess there was another issue since the Travis build was stopped after 50 minutes while all other builds finished after around 4-6 minutes (see https://travis-ci.org/eclipse/thingweb.node-wot/builds/638673659)

I will restart the build and let's see whether the issue is resolved...