flux_request_decode(3)

SYNOPSIS

#include <flux/core.h>

int flux_request_decode (const flux_msg_t *msg,
                         const char **topic,
                         const char **s);

int flux_request_unpack (const flux_msg_t *msg,
                         const char **topic,
                         const char *fmt,
                         ...);

int flux_request_decode_raw (const flux_msg_t *msg,
                             const char **topic,
                             const void **data,
                             size_t *len);

Link with -lflux-core.

DESCRIPTION

flux_request_decode() decodes a request message msg.

topic, if non-NULL, will be set the message's topic string. The storage for this string belongs to msg and should not be freed.

s, if non-NULL, will be set to the message's NULL-terminated string payload. If no payload exists, it is set to NULL. The storage for this string belongs to msg and should not be freed.

flux_request_unpack() decodes a request message with a JSON payload as above, parsing the payload using variable arguments with a format string in the style of jansson's json_unpack() (used internally). Decoding fails if the message doesn't have a JSON payload.

flux_request_decode_raw() decodes a request message with a raw payload, setting data and len to the payload data and length. The storage for the raw payload belongs to msg and should not be freed.

DECODING JSON PAYLOADS

Flux API functions that are based on Jansson's json_unpack() 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 JSON string to a pointer to a null terminated UTF-8 string. The resulting string is extracted by using 'json_string_value()' internally, so it exists as long as there are still references to the corresponding JSON string.

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

Convert a JSON string to a pointer to a null terminated UTF-8 string and its length.

n (null)

Expect a JSON null value. Nothing is extracted.

b (boolean)['int']

Convert a JSON boolean value to a C int, so that true is converted to 1 and false to 0.

i (integer)['int']

Convert a JSON integer to a C int.

I (integer)['int64_t']

Convert a JSON integer to a C int64_t. 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 JSON real to a C double.

F (real)['double']

Convert JSON number (integer or real) to a C double.

o (any value)['json_t *']

Store a JSON value, with no conversion, to a json_t pointer.

O (any value)['json_t *']

Like o, but the JSON value's reference count is incremented.

[fmt] (array)

Convert each item in the JSON array according to the inner format string. fmt may contain objects and arrays, i.e. recursive value extraction is supported.

{fmt} (object)

Convert each item in the JSON object according to the inner format string fmt. The first, third, etc. format specifier represent a key, and must by s. The corresponding argument to unpack functions is read as the object key. The second, fourth, etc. format specifier represent a value and is written to the address given as the corresponding argument. Note that every other argument is read from and every other is written to. fmt may contain objects and arrays as values, i.e. recursive value extraction is supported. Any s representing a key may be suffixed with ? to make the key optional. If the key is not found, nothing is extracted.

!

This special format specifier is used to enable the check that all object and array items are accessed, on a per-value basis. It must appear inside an array or object as the last format specifier before the closing bracket or brace.

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

These descriptions came from the Jansson 2.9 manual.

See also: Jansson API: Parsing and Validating Values: http://jansson.readthedocs.io/en/2.9/apiref.html#parsing-and-validating-values

RETURN VALUE

These functions return 0 on success. On error, -1 is returned, and errno is set appropriately.

ERRORS

EINVAL

The msg argument was NULL.

EPROTO

Message decoding failed, such as due to incorrect message type, missing topic string, etc.

RESOURCES

Flux: http://flux-framework.org

Flux RFC: https://flux-framework.readthedocs.io/projects/flux-rfc

Issue Tracker: https://github.com/flux-framework/flux-core/issues

SEE ALSO

flux_respond(3), flux_rpc(3)