add metric

crates/obs/src/metrics/entry/descriptor.rs

@@ -0,0 +1,44 @@
+use crate::metrics::{MetricName, MetricType};
+use std::collections::HashSet;
+
+/// MetricDescriptor - Indicates the metric descriptor
+#[derive(Debug, Clone)]
+pub struct MetricDescriptor {
+    pub name: MetricName,
+    pub metric_type: MetricType,
+    pub help: String,
+    pub variable_labels: Vec<String>,
+
+    // internal values for management：
+    label_set: Option<HashSet<String>>,
+}
+
+impl MetricDescriptor {
+    /// Create a new metric descriptor
+    pub fn new(name: MetricName, metric_type: MetricType, help: String, variable_labels: Vec<String>) -> Self {
+        Self {
+            name,
+            metric_type,
+            help,
+            variable_labels,
+            label_set: None,
+        }
+    }
+
+    /// Check whether the label is in the label set
+    pub fn has_label(&mut self, label: &str) -> bool {
+        self.get_label_set().contains(label)
+    }
+
+    /// Gets a collection of tags, and creates if it doesn't exist
+    pub fn get_label_set(&mut self) -> &HashSet<String> {
+        if self.label_set.is_none() {
+            let mut set = HashSet::with_capacity(self.variable_labels.len());
+            for label in &self.variable_labels {
+                set.insert(label.clone());
+            }
+            self.label_set = Some(set);
+        }
+        self.label_set.as_ref().unwrap()
+    }
+}