net: prometheus: Use const pointer for string data

Instead of allocating space for description and label name + value,
have a const pointer for it. The data is set typically statically
when the metric is defined, so there should be no need to allocate
separate buffer for those strings.

Signed-off-by: Jukka Rissanen <[email protected]>

Author: jukkar

include/zephyr/net/prometheus/label.h

@@ -16,10 +16,6 @@
  * @{
  */
 
-/* maximum length of label key */
-#define MAX_PROMETHEUS_LABEL_KEY_LENGTH   16
-/* maximum length of label value */
-#define MAX_PROMETHEUS_LABEL_VALUE_LENGTH 16
 /* maximum namber of labels per metric */
 #define MAX_PROMETHEUS_LABELS_PER_METRIC  5
 
@@ -30,9 +26,9 @@
  */
 struct prometheus_label {
 	/** Prometheus metric label key */
-	char key[MAX_PROMETHEUS_LABEL_KEY_LENGTH];
+	const char *key;
 	/** Prometheus metric label value */
-	char value[MAX_PROMETHEUS_LABEL_VALUE_LENGTH];
+	const char *value;
 };
 
 /**

include/zephyr/net/prometheus/metric.h

@@ -37,9 +37,6 @@ enum prometheus_metric_type {
 	PROMETHEUS_HISTOGRAM,
 };
 
-#define MAX_METRIC_NAME_LENGTH        32
-#define MAX_METRIC_DESCRIPTION_LENGTH 64
-
 /**
  * @brief Type used to represent a Prometheus metric base.
  *
@@ -52,9 +49,9 @@ struct prometheus_metric {
 	/** Type of the Prometheus metric. */
 	enum prometheus_metric_type type;
 	/** Name of the Prometheus metric. */
-	char name[MAX_METRIC_NAME_LENGTH];
+	const char *name;
 	/** Description of the Prometheus metric. */
-	char description[MAX_METRIC_DESCRIPTION_LENGTH];
+	const char *description;
 	/** Labels associated with the Prometheus metric. */
 	struct prometheus_label labels[MAX_PROMETHEUS_LABELS_PER_METRIC];
 	/** Number of labels associated with the Prometheus metric. */