Coap Learning Note--nodejs NODE-COAP return JSON packet

0 PrefaceThis article explains how to use NODE-COAP to return JSON packets. COAP is a network-oriented application layer protocol stack developed specifically for IoT systems, and COAP is built on the UDP protocol to minimize network overhead and features of HTTP restful types. The NODE-COAP uses Nodejs to implement the COAP client and server side."test Environment"--ubuntu/linux"Related blog posts"
"CoAP Protocol Documentation--the Constrained application Protocol (CoAP)""Coap Agreement Learning--coap Foundation" "Coap Learning Notes--coap resource Discovery" "COAP Learning Notes-Process request flow when server-side busy" Coap Learning notes--nodejs Node-coap installation and use (Linux platform) "Coap Learning notes--nodejs Node-coap Installation and use (Windows platform)" "Raspberry Pi Learning Notes--webiopi installation and Getting Started" Webiopi integrates Coap Server, which allows you to conveniently control the Raspberry Pi Gpio via the COAP protocol.
1 server Code

var coap = require (' Coap '); var server = Coap.createserver (); Server.on (' Request ', function (req, res) {    Console.log ( Req.headers);    The request header must include Application/json    if (req.headers[' Accept ']! = ' Application/json ') {        res.code = ' 4.06 ';        return Res.end ();    }    Res.setoption (' Content-format ', ' Application/json ');    Res.end (json.stringify ({        Hello: "World"    })); Server.listen (function () {    console.log (' server started ');});

"Simple description" "1" req.headers[' Accept ']! = ' Application/json ' due to the return of the JSON packet, it is advisable to include Accept:application/json "2" in the request header res.setoption ( ' Content-format ', ' Application/json '); Set the response header "3" Res.end (json.stringify ({hello: "World"}); Returns a JSON packet with a fixed content {"Hello": "World"}
2 Client Code

var coap = require (' Coap '); var bl = require (' bl '); var req = coap.request ({    pathname: '/',    options: {        ' Accept ') : ' Application/json '}    ); Req.on (' Response ', function (res) {    console.log (' Response code ', Res.code);    if (Res.code!== ' 2.05 ') return Process.exit (1);    Res.pipe (BL (err, data) {        var json = json.parse (data);        Console.log (JSON);        Process.exit (0);    })); Req.end ();

"Execution Return"Response Code 2.05
{Hello: ' World '}"Brief description" "1" var req = coap.request ({pathname: '/', options: {' Accept ': ' Application/json '}}); The request header includes Accept:application/json. 3 Browser TestingIf Accept:application/json is not included in the request header, the server returns a 4.06 error equivalent to 404 in HTTP.
Figure 1 return error results start debug mode, set the Accept option to Application/json.
Figure 2 returning the correct result
4 Wireshark Grab Bag4.1 Using the Tcpdump toolsudo tcpdump-i lo-w ~/temp/coap-json.cap"Simple description" "1"-I parameter make Nic, lo represents loopback
"2"-W set the output file path and file name, saved here in the CAP format file

4.2 Cap file Import in Wireshark
Figure 3 Wireshark Grab Bag5 SummaryFeeling that the COAP protocol is not enough in depth, the protocol itself still needs to spend some time to digest.

Coap Learning Note--nodejs NODE-COAP return JSON packet