Examples

Basic Example

Contains a basic use example for jsmn parser. This application parses json messages. Message structure shown below.

// JSON Message
{
	"request": "moveElement",
	"msgID": 1
}

// Callback function used to stored JSON string data in user defined data structure.
signed short parseCallback(myMessage_typ *data, jsmn_callback_data *data2) {
	if(data2->Size == 0) {
        // Identify the correct structure to use based on the active request.  
		if(!brsstrcmp(&data2->Structure[1], &"request")) {
			if(!brsstrcmp(&data2->Structure[0], &"moveElement")) {
				data->request= JSON_REQUEST_MOVE_ELEMENT;
			}
			else if(!brsstrcmp(&data2->Structure[0], &"stopElement")) {
				data->request= JSON_REQUEST_STOP_ELEMENT;
			} else {
                //Initiate an error for invalid request assignment and add error string to structure
				data->error = 1;
				brsstrcmp(data->errorString, &"Invalid request for element");
			}

		} else if(!brsstrcmp(&data2->Structure[1], &"msgID")) {
			brsstrcpy(&data->msgID, &data2->Structure[0]);

		} else {
            // Ignore all other parameters

		}
	}

	return 0;
}

// Cyclic function
void _CYCLIC ProgramCyclic(void) {
	// newMessage - BOOL - is populated somewhere in application
	// msg - STRING - is populated somewhere in application

	if(newMessage) {
		// Declare the data, tokens, and parser
		jsmn_parser parser;
		jsmntok_t tokens[32];
		myMessage_typ data; // myMessage_typ = {request: 0}
		
		// Clear all variables
		brsmemset(&parser, 0, sizeof(parser));
		brsmemset(&tokens, 0, sizeof(tokens));
		brsmemset(&data, 0, sizeof(data));

		JsmnInit(&parser);

		// Assign user defined callback function & data
		parser.callback.pFunction= (UDINT)parseCallback;
		parser.callback.pUserData = (UDINT)&data;
		
		// Parse message
		returnVar = JsmnParse((UDINT)&parser, (UDINT)msg, strlen((char*)msg), (UDINT)&tokens, sizeof(tokens)/sizeof(tokens[0]));

		if(returnVar < 0) {
			// Handle errors
		}

		if(data.request >= 0) {
			// Handle request
		}
	}
}
// For:
// Json Message: {"request": "moveElement", "msgID": 1}
// Result:
// data: {request: JSON_REQUEST_MOVE_ELEMENT}

Reentry

Example shows how to use jsmn parse reentry feature. Application parses json data gotten from function getJsonChunk(). Json will be given in chunks, example object shown below.

// JSON Data
{
	"command": 1,
	"variable": [
		"Motor1",
		"Motor2"
	]
}

char* getJsonChunk(char* json, unsigned long pos) {
	// Function returns next chunk of internal json string
	// next chunk is determined from current chunk (json) and how far
	// parser made it through the chunk (pos)
}

// Cyclic function
void _CYCLIC ProgramCyclic(void) {

	if(parseJson) {
		// Declare variables
		jsmn_parser parser;
		jsmntok_t tokens[32];
		myData_typ data; // myData_typ = {command: 0, variable: []}
		char* json;

		// Initialize variables
		brsmemset(&parser, 0, sizeof(parser));
		brsmemset(&tokens, 0, sizeof(tokens));
		brsmemset(&data, 0, sizeof(data));
		json = 0;

		JsmnInit(&parser);

		// Assign user defined callback function & data
		parser.callback.pFunction= (UDINT)parseCallback; // parseCallback declared in application
		parser.callback.pUserData = (UDINT)&data;

		do {
			json = getJsonChunk(json, parser.endPos); // Populates json variable
			parser.pos = 0; // Reset parser position to start of string
			returnVar = JsmnParse((UDINT)&parser, (UDINT)json, strlen((char*)json), (UDINT)&tokens, sizeof(tokens)/sizeof(tokens[0]));
		} while(returnVar == JSMN_ERROR_PART)
	}

	for(i = 0; i < MAX_VARIABLES; i++;) {
		// Do something with each variable
		// data.variables[i]
	}
}

// For a complete json of {"command": 1, "variable": ['Motor1', 'Motor2']}
// Iteration 1
// 	json = '{"command": 1, "vari'
// 	parser will successfully parse to position 14. After that JsmnParse will return JSMN_ERROR_PART.
// Iteration 2
// 	json = '"variable": ['Motor1', 'Motor2']}'
// 	parser will finish parsing json string and return 7

Callback iterations

This section shows what jsmn_callback_data will be populated with for each iteration given a some common situations.

JSON Primitives

{
    "mem1": 1,
    "mem2": "2",
    "mem3": 3
}
Iterations

JSON Objects

{
    "object": {
        "subObject" : {
            "mem1": 1
        },
        "mem2": 2
    },
    "mem3": 3
}
Iterations

JSON Arrays

Info

Due to a bug currently arrays will provide 2 callbacks per a token. This can be seen in the iterations below and is not intended.

{
    "array": [
        1,
        2
    ],
    "mem3": 3
}
Iterations