No matching format found error when sending CoAP GET about node-wot

[cdh4u]

Ok, I found the reason. When looking in Wireshark, the CoAP response indicates a Content-Format value that node-wot does not understand.

To solve this, the CoAP request sent from node-wot would have to indicate that it accepts text/plain.

[6d77]

Hi,

I think you can just do that by specifying text/plain as mediaType in the forms of your property specification in the TD. Default is application/json AFAIK.

[cdh4u]

I have the following in my TD:

"forms":[{"href":"coap://193.234.219.199:5683/3303/0/5700","mediaType":"text/plain"}]

But, it does not have any impact on the request.

[6d77]

I just have seen that @mkovatsc commented line https://github.com/eclipse/thingweb.node-wot/blob/20fdc5b2ea0f95e6e2d24d73dd0100e5f7b39e5f/packages/binding-coap/src/coap-client.ts#L191 a month ago. This line had set the Accept option before. We would have to ask him for the reason of this change.

[6d77]

Just talked to him. There was another CoAP server implementation which could not cope with Accept headers, so he removed it to make this working. Until a final solution is found to fit both requirements you might just uncomment the line again locally.

[cdh4u]

I think the master branch should be based on endpoints behaving correctly - in this case being able to process the Accept header :)

Anyway, I will see Matthias this weekend, so I can discuss it with him then. Short term I will uncomment the line.

[danielpeintner]

The code
req.setOption("Accept", form.mediaType);
is activated again.

@cdh4u Can we close the issue?

[danielpeintner]

as mentioned the option is in by default now, see https://github.com/eclipse/thingweb.node-wot/blob/6dad9786152e40f939caa7f63ef1abf1769ef316/packages/binding-coap/src/coap-client.ts#L212