помощники по строкам JSON и извлечение метрик (JSON string helpers and metrics extraction)
Дубль
(статьи:
pmjsonget - помощники по строкам JSON и извлечение метрик )
Имя (Name)
pmjsonGet, pmjsonPrint, pmjsonInit, pmjsonInitIndom - JSON string
helpers and metrics extraction
Синопсис C (C Synopsis)
#include <pcp/pmapi.h>
#include <pcp/pmjson.h>
typedef int (*json_get)(void *buffer, int length, void *data);
int pmjsonGet(json_metric_desc *json_metrics, int nmetrics,
pmInDom indom, json_get callback, void *data);
int pmjsonPrint(FILE *fp, json_flag *output_flags, const char
*json_pointer, json_get callback, void *data);
int pmjsonInit(int fd, json_metric_desc *json_metrics, int
nmetrics);
int pmjsonInitIndom(int fd, json_metric_desc *json_metrics, int
nmetrics, pmInDom indom);
cc ... -lpcp_web
Описание (Description)
pmjsonGet performs metric value extraction from JSON strings for
a Performance Metric Domain Agent (PMDA(3)). Metrics and
instances are defined by the json_metrics parameter. The result
of parsing is the extraction of values for the requested metrics
(as defined in the json_pointer field) in the values field.
A simple diagnostic utility for reporting JSON strings iss
provided as a convenience as well. Its output_flags argument
allows it to support a variety of alternate output formats,
including minimal JSON (no optional whitespace), pretty-printed,
and a simple YAML subset.
json_metrics is the array of json_metric_desc struct which
contains the json pointer to the metric data, possible flags to
check the data against, number of values (in the case of an
array), pmAtomValue where the data is stored, as well as the
instance domain in the event the PMDA has multiple instance
domains. The number of elements in the json_metrics array is
indicated by the nmetrics parameter.
Interfaces for common cases are provided - pmjsonInit specifies a
call to the JSON parsing and metric value extraction
functionality where there are no instance domains (or the PMDA
wishes to perform instance domain operations itself) and where
data can be read directly from an open file descriptor.
pmjsonInitIndom is similar, but makes use of the pmdaCacheAdd(3)
function where possible.
The JSON string must be provided by the callback function. This
function is passed a memory buffer of length bytes and an opaque
user data pointer which is unchanged from the original call to
pmjsonGet or pmjsonPrint. The returned result must be the number
of bytes written into buffer, zero when no more data is available
or less than zero on error conditions.
indom is the instance domain to be passed to pmdaCacheAdd.
typedef struct json_metrics_desc {
char *json_pointer; /* json pointer to metric */
int flags; /* flags to check if set */
int num_values; /* number of values */
pmAtomValue values; /* metric value */
char *dom; /* instance domain */
} json_metric_desc;
The JSON Pointer syntax current follows RFC6901 in specifying a
metrics location within the JSON document.
Примеры (Examples)
For the sample JSON document:
{
"Name": "/clever_almeida",
"State": {
"Dead": false,
"Error": "",
"ExitCode": 0,
"FinishedAt": "2016-07-18T21:21:20.332488706Z",
"OOMKilled": false,
"Paused": false,
"Pid": 0,
"Restarting": false,
"Running": false,
"StartedAt": "2016-07-18T14:10:58.52487316Z"
}
}
A possible corresponding json_metric array would be as follows
for the Pid, Name, and metrics to indicate whether the container
is Running, Paused, or Restarting.
static json_metric_desc json_metrics[] = {
{ "State/Pid", 0, 1, {0}, ""},
{ "Name", 0, 1, {0}, ""},
{ "State/Running", CONTAINER_FLAG_RUNNING, 1, {0}, ""},
{ "State/Paused", CONTAINER_FLAG_PAUSED, 1, {0}, ""},
{ "State/Restarting", CONTAINER_FLAG_RESTARTING, 1, {0}, ""},
};
Возвращаемое значение (Return value)
The functions return zero on success, otherwise an error code
suitable for passing to pmErrStr_r(3) is returned.
Смотри также (See also)
PMDA(3), pmErrStr_r(3), pmdaCacheAdd(3), http://json.org/ ,
https://tools.ietf.org/html/rfc7159 , and
https://tools.ietf.org/html/rfc6901 .
