Adding Prometheus serialization format

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "prometheus-client"
-version = "0.24.0"
+version = "0.24.1"
 authors = ["Max Inden <mail@max-inden.de>"]
 edition = "2021"
 description = "Open Metrics client library allowing users to natively instrument applications."

src/encoding.rs

@@ -98,6 +98,16 @@ impl<'a> From<protobuf::DescriptorEncoder<'a>> for DescriptorEncoder<'a> {
     }
 }
 
+/// Select the pattern of metric serialization
+#[derive(Debug, PartialEq, Eq, Default, Clone, Copy)]
+pub enum OutputFormat {
+    /// Used for the Prometheus format which does not add the suffix to the metric names.
+    Prometheus,
+    /// Used for the OpenMetrics format which adds the suffix for the metric names.
+    #[default]
+    OpenMetrics,
+}
+
 impl DescriptorEncoder<'_> {
     pub(crate) fn with_prefix_and_labels<'s>(
         &'s mut self,
@@ -120,12 +130,16 @@ impl DescriptorEncoder<'_> {
         help: &str,
         unit: Option<&'s Unit>,
         metric_type: MetricType,
+        output_format: OutputFormat,
     ) -> Result<MetricEncoder<'s>, std::fmt::Error> {
         for_both_mut!(
             self,
             DescriptorEncoderInner,
             e,
-            Ok(e.encode_descriptor(name, help, unit, metric_type)?.into())
+            Ok(
+                e.encode_descriptor(name, help, unit, metric_type, output_format)?
+                    .into()
+            )
         )
     }
 }
@@ -203,13 +217,22 @@ impl MetricEncoder<'_> {
         &'s mut self,
         label_set: &'s S,
     ) -> Result<MetricEncoder<'s>, std::fmt::Error> {
+        let output_format = self.output_format();
         for_both_mut!(
             self,
             MetricEncoderInner,
             e,
-            e.encode_family(label_set).map(Into::into)
+            e.encode_family(label_set, output_format).map(Into::into)
         )
     }
+
+    /// Returns the `OutputFormat` selected for the encoder.
+    pub fn output_format(&self) -> OutputFormat {
+        match &self.0 {
+            MetricEncoderInner::Text(metric_encoder) => metric_encoder.output_format,
+            MetricEncoderInner::Protobuf(_) => Default::default(),
+        }
+    }
 }
 
 /// An encodable label set.

src/encoding/protobuf.rs

@@ -32,6 +32,7 @@ pub mod openmetrics_data_model {
 
 use std::{borrow::Cow, collections::HashMap};
 
+use crate::encoding::OutputFormat;
 use crate::metrics::MetricType;
 use crate::registry::{Registry, Unit};
 use crate::{metrics::exemplar::Exemplar, registry::Prefix};
@@ -43,7 +44,7 @@ use super::{EncodeCounterValue, EncodeExemplarValue, EncodeGaugeValue, EncodeLab
 pub fn encode(registry: &Registry) -> Result<openmetrics_data_model::MetricSet, std::fmt::Error> {
     let mut metric_set = openmetrics_data_model::MetricSet::default();
     let mut descriptor_encoder = DescriptorEncoder::new(&mut metric_set.metric_families).into();
-    registry.encode(&mut descriptor_encoder)?;
+    registry.encode(&mut descriptor_encoder, OutputFormat::OpenMetrics)?;
     Ok(metric_set)
 }
 
@@ -98,6 +99,7 @@ impl DescriptorEncoder<'_> {
         help: &str,
         unit: Option<&Unit>,
         metric_type: MetricType,
+        _output_format: OutputFormat,
     ) -> Result<MetricEncoder<'s>, std::fmt::Error> {
         let family = openmetrics_data_model::MetricFamily {
             name: {
@@ -232,6 +234,7 @@ impl MetricEncoder<'_> {
     pub fn encode_family<S: EncodeLabelSet>(
         &mut self,
         label_set: &S,
+        _output_format: OutputFormat,
     ) -> Result<MetricEncoder<'_>, std::fmt::Error> {
         let mut labels = self.labels.clone();
         label_set.encode(