sys/ubjson: Do not invert bool when writing it

[fhessel]

Contribution description

The UBJSON writer inverts boolean values when writing the output. This does not seem to be the intended behavior. This PR reverts the inversion.

UBJSON in general uses a <type-marker>[value] syntax, and for boolean values, there are two dedicated markers for true (T) and false (F). Those are interchanged when writing.

Testing procedure

The following demo application can be run on native to examine the issue in isolation:

main.c

#include <ctype.h>
#include <stdio.h>
#include "ubjson.h"

/** Callback to print the data to the console. */
int write_cb(ubjson_cookie_t *cookie, const void *buf, size_t len);

int main(void)
{
    ubjson_cookie_t cookie;
    ubjson_write_init(&cookie, write_cb);
    ubjson_open_object(&cookie);
    ubjson_write_key(&cookie, "bool_true", 9);
    ubjson_write_bool(&cookie, true);
    ubjson_write_key(&cookie, "bool_false", 10);
    ubjson_write_bool(&cookie, false);
    ubjson_close_object(&cookie);
    return 0;
}

int write_cb(ubjson_cookie_t *cookie, const void *buf, size_t len)
{
    (void)cookie;
    const uint8_t *tbuf = buf;
    for(size_t idx = 0; idx < len; idx++) {
        printf("0x%02x ", tbuf[idx]);
        putchar(isprint(tbuf[idx]) ? tbuf[idx] : '.');
        printf("\n");
    }
    return len;
}

Makefile

APPLICATION = ubjson-test-bool
BOARD ?= native
RIOTBASE ?= $(CURDIR)/../..
DEVELHELP ?= 1
QUIET ?= 1
USEMODULE += ubjson
include $(RIOTBASE)/Makefile.include

Before applying the fix, it will output:

0x7b 0x69 0x09 0x62 0x6f 0x6f 0x6c 0x5f 0x74 0x72 0x75 0x65 0x46 0x69 0x0a 0x62 0x6f 0x6f 0x6c 0x5f 0x66 0x61 0x6c 0x73 0x65 0x54 0x7d
{    i    .    b    o    o    l    _    t    r    u    e    F    i    .    b    o    o    l    _    f    a    l    s    e    T    }

With the fix, the values will be correct (note the different markers after bool_true and bool_false):

0x7b 0x69 0x09 0x62 0x6f 0x6f 0x6c 0x5f 0x74 0x72 0x75 0x65 0x54 0x69 0x0a 0x62 0x6f 0x6f 0x6c 0x5f 0x66 0x61 0x6c 0x73 0x65 0x46 0x7d
{    i    .    b    o    o    l    _    t    r    u    e    T    i    .    b    o    o    l    _    f    a    l    s    e    F    }

Issues/PRs references

None.

[leandrolanzieri]

Good catch, thanks for fixing this. The change makes sense. ACK!