enable long message&topic data

[Sild]

Hi, I have written to you email a few time ago, and ask you about the limitation on topic/message size. Now I find the reason of this behavior and fix it. Please make a new release to make it available to install by ArduinoIDE.

[256dpi]

Maybe that could be constant, like:

#define MAX_WRITE_SIZE 90

[Sild]

updated

[256dpi]

Thanks for your contribution!

Have you tested the patch extensively? And with what Hardware?

[256dpi]

I like to prevent changes to the underlying library as that gets updated automatically by a script.

I just pulled the latest library and saw that they have been also working on a fix, for I guess the same problem: https://github.com/256dpi/arduino-mqtt/pull/6/files

Maybe you could take a look and check if that would also help in your situation?

[Sild]

I have tested my patch for my particular use case with arduinoUNO and wifi shield, however there is no reason to break something on other devices.

About following:

rc = ipstack.write(&sendbuf[sent], length - sent, timer.left_ms());

This is not enough to clear work with my device. If we try to write more then 90 symbols, ipstack.write() will return 0, so we get infinity loop ( while !timer.expired() ). I have tried this way and it's fail.

[256dpi]

I'll try to loop in @icraggs as he is the maintainer of the underlying library.

@icraggs: Is this really a bug in the embedded C client, or are we missing something here? I would appreciate it, if you could take a look at the code briefly: https://github.com/256dpi/arduino-mqtt/pull/5/files

[Sild]

Also I found out that if length is more then 128, we can not publish anything. Moreover, we do not call sendPacket function. Is it expected behavior? Serial output:

sending row: 'series e:zzzzzzzz-zzzz-zzzz-zzzz-zzzzzzzzzzzz m:millis=329.11IIIIIIIIIIIIIIIIII' ...
length: 127
sended.
sending row: 'series e:zzzzzzzz-zzzz-zzzz-zzzz-zzzzzzzzzzzz m:millis=329.11IIIIIIIIIIIIIIIIIII' ...
length: 128
sended.
sending row: 'series e:zzzzzzzz-zzzz-zzzz-zzzz-zzzzzzzzzzzz m:millis=329.11IIIIIIIIIIIIIIIIIIII' ...
sended.
sending row: 'series e:zzzzzzzz-zzzz-zzzz-zzzz-zzzzzzzzzzzz m:millis=329.11IIIIIIIIIIIIIIIIIIIII' ...

I just have added debug message in MQTTClient.h:

...
int MQTT::Client<Network, Timer, a, b>::sendPacket(int length, Timer& timer)
{    
int writeSize = 0;
Serial.print("length: ");
Serial.println(length);  
...
}

part of sketch code:

if(client.connected()) {
String data = "series e:" + entityID + " m:millis=" + (String)getData();
    while(true) {
        Serial.println("sending row: '" + data + "' ...");
        client.publish(pubTopic,data);
        Serial.println("sended.");
        data+="I";
        delay(5000);
    }

Full code to reproduce this bug you can find here

[icraggs]

Hello all. In MQTTClient.h there is a MQTT_BUFFER_SIZE constant, which defaults to 128. I did this to void dynamic memory allocation, which maximizes portability and makes the memory use more predictable. If you want to send or receive packets longer than 128, you need to increase the size of that constant.

[Sild]

Thanks for explanation. And what about ipstack.write() function? Why does it return 0 if I try to call with length > 90?

[256dpi]

@Sild I guess Ian is right. You need to increase the constants here directly: https://github.com/256dpi/arduino-mqtt/blob/master/src/MQTTClient.h#L5

Unfortunately you can't set it in your sketch as the libraries are compiled separately.