Re: JSON Encoding and Decoding

[Aditya Xavier <ad...@me.com>]

Hi Mynewt Team,

I have been trying to decode JSON using the provided json decoding library.

This particular library seems quite similar to mJSON, however there are difference regarding json_read_object etc.

Also unlike mJSON, there is a requirement to write few more methods :-

char jbuf_read_next(struct json_buffer *jb);
char jbuf_read_prev(struct json_buffer *jb);
int jbuf_readn(struct json_buffer *jb, char *buf, int size);
int write(void *buf, char* data, int len);
void buf_init(struct jbuf *ptjb, char *string);

At least thats what I gathered as per the test example. (Am I correct in this thought ?)

However, am unable to get the following code working.
/*-----------
#define MAXCHANNELS 72

long long int PRN[MAXCHANNELS];
long long int elevation[MAXCHANNELS];
long long int azimuth[MAXCHANNELS];

int visible;
struct jbuf tjb;

const struct json_attr_t sat_attrs[] = {
    {	.attribute = "PRN",
    	.type = t_integer,
    	.addr.integer = PRN
    },
    {	.attribute = "el",     
    	.type = t_integer,
    	.addr.integer = elevation
    },
    {
    	.attribute = "az",     
    	.type = t_integer,
    	.addr.integer = azimuth
    },
    {NULL},
};

const struct json_attr_t json_attrs_sky[] = {
    {	
    	.attribute = "class",
        .type = t_check,
        .dflt.check = "SKY"
    },
    {
    	.attribute = "satellites",     
    	.type = t_array,
    	.addr.array = {
            .element_type = t_structobject,
            .arr.objects.subtype=sat_attrs,
            .maxlen = MAXCHANNELS,
            .count = &visible
        }
    },
    {NULL},
};
    
int fetch_map(const char *map){
	
// 	int i;
	
	buf_init(&tjb,(char *) map);
	console_printf("Buffer Initiated\n");
	
    json_read_object(&tjb.json_buf, json_attrs_sky);

	console_printf("JSON Read %d!\n", visible);    
	
//     for (i = 0; i < visible; i++){
        console_printf("PRN = %lld, elevation = %lld, azimuth = %lld\n", PRN[0], elevation[0], azimuth[0]);
	console_printf("PRN = %lld, elevation = %lld, azimuth = %lld\n", PRN[1], elevation[1], azimuth[1]);
//     }
    printf(“Completed\n");
    return 1;

}
*/————

Calling this method using 
	fetch_map(R"=====({"class":"SKY","satellites":[{"PRN":10,"el":45,"az":196,"used":true},{"PRN":29,"el":67,"az":310,"used":true}]})=====“);

Am getting the following response :-

000001 Buffer Initiated
000002 JSON Read 0!
000003 PRN = 10, elevation = 45, azimuth = 196
000004 PRN = 0, elevation = 0, azimuth = 0
Completed

Which means its not populating the count value in the array as it should. 

It is also quite possible am completely wrong about it :)

Thanks,
Aditya Xavier.


> On 28-Feb-2018, at 10:49 PM, Aditya Xavier <ad...@me.com> wrote:
> 
> I have been trying to use the same example as is; assuming that apache was also utilizing mJSON.
> 
> However, it seems there are quite some differences from that library. For e.g. 
> 
> .addr.integer = PRN  is no longer valid.
> 
> It is now 
> .arr.integers.store = PRN
> 
> And json_read_object requires a struct json_buffer *jb instead of a char array.
> 
> This struct has to be populated using user method etc. There are multiple differences from the MicroJSON implementation.
> 
> Isn’t there some good documentation on this ?
> 
> 
>> On 28-Feb-2018, at 10:39 PM, Christopher Collins <ch...@runtime.io> wrote:
>> 
>> Hi Aditya,
>> 
>> On Wed, Feb 28, 2018 at 06:35:04PM +0530, Aditya Xavier wrote:
>>> Thanks got Encoding working for the required JSON.
>>> 
>>> Any pointers on how to get the decoding working ?
>>> 
>>> From the example https://github.com/apache/mynewt-core/blob/master/encoding/json/test/src/testcases/json_simple_decode.c <https://github.com/apache/mynewt-core/blob/master/encoding/json/test/src/testcases/json_simple_decode.c>
>>> 
>>> Am able to decode upto name2 only.
>>> 
>>> {“name1": 1,”name2": “value2”, “name3”: [{“name4”: 2, “name5”: 3}]};
>>> 
>>> Please let me know the Structure for Array of objects.
>> 
>> Example 2 in the microjson document
>> (http://www.catb.org/~esr/microjson/microjson.html) does something
>> similar, so I would take a look at that.  This example is under the
>> "Compound Value Types" heading.
>> 
>> Chris
>