encoding/: Adopt serde style encoding

Adopt encoding style similar to serde. `EncodeXXX` for a type that can be
encoded (see serde's `Serialize`) and `XXXEncoder` for a supported encoding i.e.
text and protobuf (see serde's `Serializer`).

- Compatible with Rust's additive features. Enabling the `protobuf` feature does
not change type signatures.
- `EncodeMetric` is trait object safe, and thus `Registry` can use dynamic dispatch.
- Implement a single encoding trait `EncodeMetric` per metric type instead of
one implementation per metric AND per encoding format.
- Leverage `std::fmt::Write` instead of `std::io::Write`. The OpenMetrics text
format has to be unicode compliant. The OpenMetrics Protobuf format requires
labels to be valid strings.

Signed-off-by: Max Inden <mail@max-inden.de>

CHANGELOG.md

@@ -16,11 +16,22 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed
 
-- Move`Encode` trait from `prometheus_client::encoding::text` to `prometheus_client::encoding`. See [PR 83].
+- Always use dynamic dispatch on `Registry`, i.e. remove generic type parameter `M` from `Registry`. See [PR 105].
+- Refactor encoding. See [PR 105].
+  - Introducing separate traits to encode
+    - value (e.g. `EncodeCounterValue`)
+    - label set (`EncodeLabelSet`), derivable for structs via `prometheus-client-derive-encode`
+    - label (`EncodeLabel`)
+    - label key (`EncodeLabelKey`)
+    - label value (`EncodeLabelValue`), derivable for enums via `prometheus-client-derive-encode`
+  - Encode as UTF-8 strings, not bytes. I.e. use `std::fmt::Write` instead of `std::io::Write`.
+- Use signed integers for `Gauge` for compliance with OpenMetrics protobuf
+  format. See [PR 105].
 
 [PR 83]: https://github.com/prometheus/client_rust/pull/83
 [PR 85]: https://github.com/prometheus/client_rust/pull/85
 [PR 96]: https://github.com/prometheus/client_rust/pull/96
+[PR 105]: https://github.com/prometheus/client_rust/pull/105
 
 ## [0.18.1]
 

Cargo.toml

@@ -11,7 +11,8 @@ homepage = "https://github.com/prometheus/client_rust"
 documentation = "https://docs.rs/prometheus-client"
 
 [features]
-protobuf = ["dep:prost", "dep:prost-types", "dep:prost-build", "dep:void", "prometheus-client-derive-encode/protobuf"]
+default = []
+protobuf = ["dep:prost", "dep:prost-types", "dep:prost-build"]
 
 [workspace]
 members = ["derive-encode"]
@@ -23,7 +24,6 @@ parking_lot = "0.12"
 prometheus-client-derive-encode = { version = "0.3.0", path = "derive-encode" }
 prost = { version = "0.11.0", optional = true }
 prost-types = { version = "0.11.0", optional = true }
-void = { version = "1.0", optional = true }
 
 [dev-dependencies]
 async-std = { version = "1", features = ["attributes"] }

benches/encoding/proto.rs

@@ -2,82 +2,80 @@
 // https://github.com/tikv/rust-prometheus/blob/ab1ca7285d3463504381a5025ae1951e020d6796/benches/text_encoder.rs:write
 
 use criterion::{black_box, criterion_group, criterion_main, Criterion};
-use prometheus_client::encoding::proto::{encode, EncodeMetric};
-use prometheus_client::encoding::Encode;
+use prometheus_client::encoding::protobuf;
 use prometheus_client::metrics::counter::Counter;
 use prometheus_client::metrics::family::Family;
 use prometheus_client::metrics::histogram::{exponential_buckets, Histogram};
 use prometheus_client::registry::Registry;
-use std::fmt::{Display, Formatter};
+use prometheus_client_derive_encode::{EncodeLabelSet, EncodeLabelValue};
 
 pub fn proto(c: &mut Criterion) {
     c.bench_function("encode", |b| {
-        #[derive(Clone, Hash, PartialEq, Eq, Encode)]
-        struct Labels {
+        #[derive(Clone, Hash, PartialEq, Eq, EncodeLabelSet, Debug)]
+        struct CounterLabels {
             path: String,
             method: Method,
             some_number: u64,
         }
 
-        #[derive(Clone, Hash, PartialEq, Eq, Encode)]
+        #[derive(Clone, Hash, PartialEq, Eq, EncodeLabelValue, Debug)]
         enum Method {
             Get,
             #[allow(dead_code)]
             Put,
         }
 
-        impl Display for Method {
-            fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
-                match self {
-                    Method::Get => write!(f, "Get"),
-                    Method::Put => write!(f, "Put"),
-                }
-            }
+        #[derive(Clone, Hash, PartialEq, Eq, EncodeLabelSet, Debug)]
+        struct HistogramLabels {
+            region: Region,
         }
 
-        #[derive(Clone, Hash, PartialEq, Eq, Encode)]
+        #[derive(Clone, Hash, PartialEq, Eq, EncodeLabelValue, Debug)]
         enum Region {
             Africa,
             #[allow(dead_code)]
             Asia,
         }
 
-        let mut registry = Registry::<Box<dyn EncodeMetric>>::default();
+        let mut registry = Registry::default();
 
         for i in 0..100 {
-            let counter_family = Family::<Labels, Counter>::default();
-            let histogram_family = Family::<Region, Histogram>::new_with_constructor(|| {
-                Histogram::new(exponential_buckets(1.0, 2.0, 10))
-            });
+            let counter_family = Family::<CounterLabels, Counter>::default();
+            let histogram_family =
+                Family::<HistogramLabels, Histogram>::new_with_constructor(|| {
+                    Histogram::new(exponential_buckets(1.0, 2.0, 10))
+                });
 
             registry.register(
                 format!("my_counter{}", i),
                 "My counter",
-                Box::new(counter_family.clone()),
+                counter_family.clone(),
             );
             registry.register(
                 format!("my_histogram{}", i),
                 "My histogram",
-                Box::new(histogram_family.clone()),
+                histogram_family.clone(),
             );
 
             for j in 0_u32..100 {
                 counter_family
-                    .get_or_create(&Labels {
+                    .get_or_create(&CounterLabels {
                         path: format!("/path/{}", i),
                         method: Method::Get,
                         some_number: j.into(),
                     })
                     .inc();
 
                 histogram_family
-                    .get_or_create(&Region::Africa)
+                    .get_or_create(&HistogramLabels {
+                        region: Region::Africa,
+                    })
                     .observe(j.into());
             }
         }
 
         b.iter(|| {
-            let metric_set = encode(&registry);
+            let metric_set = protobuf::encode(&registry).unwrap();
             black_box(metric_set);
         })
     });

benches/encoding/text.rs

@@ -1,31 +1,30 @@
 // Benchmark inspired by https://github.com/tikv/rust-prometheus/blob/ab1ca7285d3463504381a5025ae1951e020d6796/benches/text_encoder.rs
 
 use criterion::{black_box, criterion_group, criterion_main, Criterion};
-use prometheus_client::encoding::text::{encode, EncodeMetric};
-use prometheus_client::encoding::Encode;
+use prometheus_client::encoding::{self, EncodeLabelSet, EncodeLabelValue, LabelValueEncoder};
 use prometheus_client::metrics::counter::Counter;
 use prometheus_client::metrics::family::Family;
 use prometheus_client::metrics::histogram::{exponential_buckets, Histogram};
 use prometheus_client::registry::Registry;
-use std::io::Write;
+use std::fmt::Write;
 
 pub fn text(c: &mut Criterion) {
     c.bench_function("encode", |b| {
-        #[derive(Clone, Hash, PartialEq, Eq, Encode)]
+        #[derive(Clone, Hash, PartialEq, Eq, EncodeLabelSet, Debug)]
         struct Labels {
             method: Method,
             status: Status,
             some_number: u64,
         }
 
-        #[derive(Clone, Hash, PartialEq, Eq, Encode)]
+        #[derive(Clone, Hash, PartialEq, Eq, EncodeLabelValue, Debug)]
         enum Method {
             Get,
             #[allow(dead_code)]
             Put,
         }
 
-        #[derive(Clone, Hash, PartialEq, Eq)]
+        #[derive(Clone, Hash, PartialEq, Eq, Debug)]
         enum Status {
             Two,
             #[allow(dead_code)]
@@ -34,34 +33,19 @@ pub fn text(c: &mut Criterion) {
             Five,
         }
 
-        impl prometheus_client::encoding::text::Encode for Status {
-            fn encode(&self, writer: &mut dyn Write) -> Result<(), std::io::Error> {
+        impl prometheus_client::encoding::EncodeLabelValue for Status {
+            fn encode(&self, writer: &mut LabelValueEncoder) -> Result<(), std::fmt::Error> {
                 let status = match self {
-                    Status::Two => b"200",
-                    Status::Four => b"400",
-                    Status::Five => b"500",
+                    Status::Two => "200",
+                    Status::Four => "400",
+                    Status::Five => "500",
                 };
-                writer.write_all(status)?;
+                writer.write_str(status)?;
                 Ok(())
             }
         }
 
-        #[cfg(feature = "protobuf")]
-        impl prometheus_client::encoding::proto::EncodeLabels for Status {
-            fn encode(&self, labels: &mut Vec<prometheus_client::encoding::proto::Label>) {
-                let value = match self {
-                    Status::Two => "200".to_string(),
-                    Status::Four => "400".to_string(),
-                    Status::Five => "500".to_string(),
-                };
-                labels.push(prometheus_client::encoding::proto::Label {
-                    name: "status".to_string(),
-                    value,
-                });
-            }
-        }
-
-        let mut registry = Registry::<Box<dyn EncodeMetric>>::default();
+        let mut registry = Registry::default();
 
         for i in 0..100 {
             let counter_family = Family::<Labels, Counter>::default();
@@ -72,12 +56,12 @@ pub fn text(c: &mut Criterion) {
             registry.register(
                 format!("my_counter_{}", i),
                 "My counter",
-                Box::new(counter_family.clone()),
+                counter_family.clone(),
             );
             registry.register(
                 format!("my_histogram_{}", i),
                 "My histogram",
-                Box::new(histogram_family.clone()),
+                histogram_family.clone(),
             );
 
             for j in 0u32..100 {
@@ -98,10 +82,10 @@ pub fn text(c: &mut Criterion) {
             }
         }
 
-        let mut buffer = vec![];
+        let mut buffer = String::new();
 
         b.iter(|| {
-            encode(&mut buffer, &registry).unwrap();
+            encoding::text::encode(&mut buffer, &registry).unwrap();
             black_box(&mut buffer);
         })
     });

derive-encode/Cargo.toml

@@ -9,9 +9,6 @@ repository = "https://github.com/prometheus/client_rust"
 homepage = "https://github.com/prometheus/client_rust"
 documentation = "https://docs.rs/prometheus-client-derive-text-encode"
 
-[features]
-protobuf = []
-
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]