ENCODING JSON PAYLOADSΒΆ

Flux API functions that are based on Jansson's json_pack() accept the following tokens in their format string. The type in parenthesis denotes the resulting JSON type, and the type in brackets (if any) denotes the C type that is expected as the corresponding argument or arguments.

s (string)['const char *']

Convert a null terminated UTF-8 string to a JSON string.

s# (string)['const char *', 'int']

Convert a UTF-8 buffer of a given length to a JSON string.

s% (string)['const char *', 'size_t']

Like s# but the length argument is of type size_t.

+ ['const char *']

Like s, but concatenate to the previous string. Only valid after a string.

+# ['const char *', 'int']

Like s#, but concatenate to the previous string. Only valid after a string.

+% ['const char *', 'size_t']

Like +#, but the length argument is of type size_t.

n (null)

Output a JSON null value. No argument is consumed.

b (boolean)['int']

Convert a C int to JSON boolean value. Zero is converted to false and non-zero to true.

i (integer)['int']

Convert a C int to JSON integer.

I (integer)['int64_t']

Convert a C int64_t to JSON integer. Note: Jansson expects a json_int_t here without committing to a size, but Flux guarantees that this is a 64-bit integer.

f (real)['double']

Convert a C double to JSON real.

o (any value)['json_t *']

Output any given JSON value as-is. If the value is added to an array or object, the reference to the value passed to o is stolen by the container.

O (any value)['json_t *']

Like o, but the argument's reference count is incremented. This is useful if you pack into an array or object and want to keep the reference for the JSON value consumed by O to yourself.

[fmt] (array)

Build an array with contents from the inner format string. fmt may contain objects and arrays, i.e. recursive value building is supported.

{fmt} (object)

Build an object with contents from the inner format string fmt. The first, third, etc. format specifier represent a key, and must be a string as object keys are always strings. The second, fourth, etc. format specifier represent a value. Any value may be an object or array, i.e. recursive value building is supported.

Whitespace, : (colon) and , (comma) are ignored.

These descriptions came from the Jansson 2.6 manual.

See also: Jansson API: Building Values