JavaScript CoAPRequest API

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1 JavaScript CoAPRequest API Abstract The CoAPRequest specification defines an API that provides scripted client functionality for transferring data between a CoAP client and a CoAP server. Table of Contents Abstract Introduction Interface CoAPRequest Event Handlers States The constructor The open() method The send() method The abort() method The setrequestheader() method The timeout attribute The responsetext attribute The responsetype attribute The responselocationpath attribute The response attribute References... 6

2 1 Introduction CoAPRequest is an API similar to the XMLHttpRequest [XHR], known from web browser scripting languages such as JavaScript. It is used to send CoAP [COAPD] requests (instead of HTTP) directly to a CoAP resource and loads the response back into the script. The object supports any text based format, including XML. A simple code demonstration to fetch data from a CoAP resource over the network var client = new CoAPRequest(); client.onreadystatechange = handler; client.open("get", "coap://mydomain.myresource"); client.send(); function handler() { if (this.readystate==this.done) { if (this.status==this.content) { processdata(this.responsetext); To send a POST message to a CoAP resource function sendmessage(message) { var client = new CoAPRequest(); client.open("post", "coap://mydomain.myresource"); client.setrequestheader("content-type", "text/plain"); client.send(message); Send a POST request using a timeout and react to network problems var client = new CoAPRequest(); client.open("post", "coap://mydomain.myresource"); client.timeout = 1000; // one second client.onload = successhandler; // called if we get response in time client.onerror = errorhandler; // called if there is a network error client.ontimeout = timeouthandler; // called if no response in time client.send(data); The CoAPRequest object was initially defined by Martin Lanter and Matthias Kovatsch at ETH Zürich in 2011.

3 2 Interface CoAPRequest interface CoAPRequest { // event handler Attribute Function? onreadystatechange; Attribute Function? onerror; Attribute Function? onload; Attribute Function? ontimeout; // states const signed int UNSEND = 0; const signed int OPENED = 1; const signed int DONE = 4; signed int readystate; boolean send; boolean error; // request fields String method; String uri; String locationpath; boolean async; long timeout; // request methods void open(string method, String uri, optional boolean async); void setrequestheader(string header, String value); void send(); void send(string data); void abort(); // response status signed int status; // CoAP status signed int httpstatus; String statustext; // CoAP status as text String getresponseheader(string header); String getresponseheader(int headernr); String getallresponseheaders(); // response Response response; String responsetext; String responsetype; String responselocationpath ; 2.1 Event Handlers onreadystatechange: Invoked, when readystate has been changed ontimeout: Invoked, when a timeout has occured onload: Invoked, when a response has been received onerror: Invoked, when a request error has occured 2.2 States UNSENT: (numeric value 0) OPENED: (numeric value 1) HEADERS_RECEIVED: (numeric value 2) DONE: (numeric value 4) The send flag indicates that the send() method has been invoked. It is initially unset. The error flag indicates some type of network error or request abortion. It is initially unset.

4 2.3 The constructor client = new CoAPRequest() The CoAPRequest() constructor must return new CoAPRequest object. 2.4 The open() method client.open(method, uri, async) The open(method, uri, async) method must run therse steps. 1. If method is invalid, throw an exception and terminate these steps 2. Resolve uri. Relative URIs are not allowed. If uri is invalid, throw an exception and terminate these steps 3. If async has been omitted, let it be true 4. Terminate the abort() algorithm 5. Terminate the send() algorithm 6. Set variables associated with the object as follows: a. Set the request method to method b. Set the request uri to uri c. Set the async flag to async d. Set the send flag to false e. Set response entity body to null 7. Change the state to OPENED 8. Fire an event named onreadystatechange 2.5 The send() method client.send(data) The send(data) method must run these steps. This algorithm can be terminated by invoking the open() or abort() method. 1. If the state is not OPENED, throw an exception and terminate these steps 2. If the send flag is set, throw an exception and terminate these steps 3. Unset the error flag 4. Set the send flag 5. If the request is synchronous wait for the response 6. If the request is asynchronous return the send() method call, but continue the steps in this algorithm If there is a problem with the transmission this is a network error. If timeout is not 0 and since the request started the amount of milliseconds specified by timeout has passed this is a timeout error. If the user cancels the request this is an abort error. Network errors, timeout errors and abort errors are request errors with a NetworkErrorException, TimeoutErrorException and AbortErrorException respectively as exception. When something is said to be a request error with exception e run these steps. 1. Set the error flag 2. Change the state to DONE 3. Fire onreadystatechange 4. If the error is a network error call onerror 5. If the error is a timeout error call ontimeout 6. If the request is synchronous throw the exception e

5 Once the whole response has been received successfully run these steps 1. Change the state to DONE 2. Fire onreadystatechange 3. Fire onload 2.6 The abort() method The abort() method must run there steps. This algorithm can be terminated by invoking the open() method. 1. Terminate the send() algorithm 2. Set the error flag 3. If the state is UNSENT, OPENED without the send flag or DONE (the request has not been sent) skip this step. Otherwise a. Change the state to DONE b. Unset the send flag c. Fire onreadystatechange Change the state to UNSENT (no onreadystatechange event is dispatched) 2.7 The setrequestheader() method client.setrequestheader(header, value) The setrequestheader(header, value) method must run these steps: 1. If the state is not OPENED, throw an exception and terminate these steps 2. If the send flag is set, throw an exception and terminate these steps 3. If the header is not in the list of request headers yet append header with the associated value to the list 4. If the header is already in the list of request headers combine the values 2.8 The timeout attribute client.timeout The timeout attribute must return its value. Initially its value must be zero. 2.9 The responsetext attribute client.responsetext Returns the text response entity body. Initially its value must be null The responsetype attribute client.responsetype Returns the response s type. Initially its value must be the empty string The responselocationpath attribute client.responselocationpath Returns the response s location path if defined. Initially its value must be null The response attribute client.response Returns the response object. Initially its value must be null.

6 3 References [XHR] XMLHttpRequest: [COAPD] IETF CoAP Draft:

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