json.hpp

ROS/acres_sim/include/acres_sim/json.hpp Generated

JSON helpers shared by the game's line protocols (the RL / drive-by-wire bridge and the simulator control channel).

The text the bridge writes is byte for byte what the Python bridge (acres_ros, json.dumps) wrote: the same float spelling (Python's shortest repr), the same separators and the same ASCII escaping, so the game sees identical commands whichever bridge runs, and the implement state published on ROS is the same string.

Name	Type	Unit	Default	Description
Json	using		nlohmann::ordered_json	JSON value that keeps the key order of its source (Python dicts do too).

python_float_repr

Python's repr() of a float: the shortest decimal that round-trips, fixed notation for exponents -4..15, with a trailing ".0" for integral values; "NaN", "Infinity" and "-Infinity" as json.dumps writes them.

Argument	Description
value	The number.

Returns: Its spelling, e.g. "0.1", "1.0", "1e-05", "1e+16".

std::string python_float_repr(double value);

python_dumps

json.dumps(value) (compact = false: separators ", " and ": ") or json.dumps(value, separators=(",", ":")).

Argument	Description
value	The JSON value.
compact	Separators without spaces.

Returns: The text, ASCII only (other characters as \uXXXX escapes, as ensure_ascii does).

std::string python_dumps(const Json& value, bool compact);

finite

A finite number for the game's JSON parser, which has no NaN or Infinity literals: NaN becomes 0 and an infinity +-1e9 (ds_dbw_msgs uses INFINITY for "unlimited"), as acres_ros stream._finite.

Argument	Description
value	The number.

Returns: The finite number.

double finite(double value);

finite_message

Applies finite() to the top-level values of a message and to the values of its nested objects, one level deep, as the Python JsonBridge.send did before writing a command.

Argument	Description
message	A command object, e.g. {"steering_cmd": {...}}.

Returns: The message with every such float finite.

Json finite_message(const Json& message);

get_number

float(obj.get(key, fallback)) of the Python bridge: numbers and booleans convert, anything else gives fallback.

Argument	Description
object	A JSON object (anything else gives fallback).
key	The key.
fallback	Value when the key is missing or not a number.

Returns: The number.

double get_number(const Json& object, const char* key, double fallback = 0.0);

get_int

int(obj.get(key, fallback)): numbers truncate toward zero, booleans give 0 or 1.

Argument	Description
object	A JSON object.
key	The key.
fallback	Value when the key is missing or not a number.

Returns: The integer.

int64_t get_int(const Json& object, const char* key, int64_t fallback = 0);

get_truthy

bool(obj.get(key)): Python truthiness (missing or null false, numbers non-zero, strings, arrays and objects non-empty).

Argument	Description
object	A JSON object.
key	The key.

Returns: The truth value.

bool get_truthy(const Json& object, const char* key);

get_object

obj.get(key, {}) for a nested object: a reference to the member if it is an object, else to an empty object.

Argument	Description
object	A JSON object.
key	The key.

Returns: The nested object or an empty one.

const Json& get_object(const Json& object, const char* key);