Added support for the protobuf format for prometheus

this is a pre-req for #601, because native histograms are only supported with protobufs

Author: alex

Cargo.lock

@@ -21,6 +21,7 @@ async-runtime = ["tokio", "hyper-util/tokio"]
 http-listener = ["async-runtime", "ipnet", "tracing", "_hyper-server"]
 uds-listener = ["http-listener"]
 push-gateway = ["async-runtime", "tracing", "_hyper-client"]
+protobuf = ["mime", "prost", "prost-types", "prost-build"]
 _hyper-server = ["http-body-util", "hyper/server", "hyper-util/server-auto"]
 _hyper-client = [
     "http-body-util",
@@ -52,12 +53,20 @@ thiserror = { workspace = true }
 tokio = { workspace = true, optional = true }
 tracing = { workspace = true, optional = true }
 
+# Protobuf support
+mime = { version = "0.3", optional = true }
+prost = { workspace = true, optional = true }
+prost-types = { workspace = true, optional = true }
+
 [dev-dependencies]
 proptest = { workspace = true }
 rand = { workspace = true }
 tracing = { workspace = true }
 tracing-subscriber = { workspace = true, features = ["fmt"] }
 
+[build-dependencies]
+prost-build = { workspace = true, optional = true }
+
 [[example]]
 name = "prometheus_push_gateway"
 required-features = ["push-gateway"]

metrics-exporter-prometheus/Cargo.toml

@@ -0,0 +1,6 @@
+fn main() {
+    #[cfg(feature = "protobuf")]
+    {
+        prost_build::compile_protos(&["proto/metrics.proto"], &["proto/"]).unwrap();
+    }
+}