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NAME | C SYNOPSIS | DESCRIPTION | EXAMPLE | RETURN CODE | SEE ALSO | COLOPHON |
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PMJSONGET(3) Library Functions Manual PMJSONGET(3)
pmjsonGet, pmjsonPrint, pmjsonInit, pmjsonInitIndom - JSON string
helpers and metrics extraction
#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
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.
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}, ""},
};
The functions return zero on success, otherwise an error code
suitable for passing to pmErrStr_r(3) is returned.
PMDA(3), pmErrStr_r(3), pmdaCacheAdd(3), http://json.org/ ,
https://tools.ietf.org/html/rfc7159 , and
https://tools.ietf.org/html/rfc6901 .
This page is part of the PCP (Performance Co-Pilot) project.
Information about the project can be found at ⟨http://www.pcp.io/⟩.
If you have a bug report for this manual page, send it to
pcp@groups.io. This page was obtained from the project's upstream
Git repository ⟨https://github.com/performancecopilot/pcp.git⟩ on
2018-02-02. (At that time, the date of the most recent commit that
was found in the repository was 2018-02-02.) If you discover any
rendering problems in this HTML version of the page, or you believe
there is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
Performance Co-Pilot PCP PMJSONGET(3)
Pages that refer to this page: pmhttpnewclient(3)
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