From 8068b8a38a967d98b07c657852721161170341a2 Mon Sep 17 00:00:00 2001
From: katelyn martin <me+cratelyn@katelyn.world>
Date: Tue, 15 Oct 2024 00:00:00 +0000
Subject: [PATCH] feat(metrics/family): `contains()` checks if metrics exist

this commit introduces a small accessor to the `Family<S, M, C>` metric
family type. this new `contains()` method allows callers to check
whether or not a metric with the provided set of labels exists.

if no metric has been created via e.g. `get_or_create()`, this method
will return `false`.

Signed-off-by: katelyn martin <me+cratelyn@katelyn.world>
---
 src/metrics/family.rs | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/src/metrics/family.rs b/src/metrics/family.rs
index 2f23b198..330e23e9 100644
--- a/src/metrics/family.rs
+++ b/src/metrics/family.rs
@@ -288,6 +288,26 @@ impl<S: Clone + std::hash::Hash + Eq, M, C: MetricConstructor<M>> Family<S, M, C
         self.metrics.write().clear()
     }
 
+    /// Returns `true` if the given label set exists within the metric family.
+    ///
+    /// ```
+    /// # use prometheus_client::metrics::counter::{Atomic, Counter};
+    /// # use prometheus_client::metrics::family::Family;
+    /// #
+    /// let family = Family::<Vec<(String, String)>, Counter>::default();
+    /// let get = vec![("method".to_owned(), "GET".to_owned())];
+    /// let post = vec![("method".to_owned(), "POST".to_owned())];
+    ///
+    /// // Create the metric with labels `method="GET"`.
+    /// family.get_or_create(&get).inc();
+    ///
+    /// assert!(family.contains(&get), "a `method=\"GET\"`-labeled metric exists");
+    /// assert!(!family.contains(&post), "a `method=\"POST\"`-labeled metric does NOT exist");
+    /// ```
+    pub fn contains(&self, label_set: &S) -> bool {
+        self.metrics.read().get(label_set).is_some()
+    }
+
     pub(crate) fn read(&self) -> RwLockReadGuard<HashMap<S, M>> {
         self.metrics.read()
     }