Add LogAppender for log crate

Cargo.toml

@@ -8,6 +8,7 @@ members = [
     "opentelemetry-dynatrace",
     "opentelemetry-http",
     "opentelemetry-jaeger",
+    "opentelemetry-appender-log",
     "opentelemetry-otlp",
     "opentelemetry-prometheus",
     "opentelemetry-proto",
@@ -32,6 +33,7 @@ members = [
     "examples/http",
     "examples/hyper-prometheus",
     "examples/metrics-basic",
+    "examples/logs-basic",
     "examples/traceresponse",
     "examples/tracing-grpc",
     "examples/jaeger-remote-sampler",

examples/logs-basic/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "logs-basic"
+version = "0.1.0"
+edition = "2021"
+publish = false
+
+[dependencies]
+opentelemetry_api = { path = "../../opentelemetry-api", features = ["logs"] }
+opentelemetry_sdk = { path = "../../opentelemetry-sdk", features = ["logs"] }
+opentelemetry-stdout = { path = "../../opentelemetry-stdout", features = ["logs"]}
+opentelemetry-appender-log = { path = "../../opentelemetry-appender-log"}
+log = {version = "0.4.17"}

examples/logs-basic/README.md

@@ -0,0 +1,16 @@
+# Log Appender for API -  Example
+
+This example shows how to use the opentelemetry-appender-log crate, which is a
+[logging appender](https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/glossary.md#log-appender--bridge) that bridges logs from the [log crate](https://docs.rs/log/latest/log/) to OpenTelemetry.
+The example setups a LoggerProvider with stdout exporter, so logs are emitted to stdout.
+
+## Usage
+
+Run the following, and Logs emitted using [log](https://docs.rs/log/latest/log/) will be written out to stdout.
+
+```shell
+$ cargo run
+```
+
+
+

examples/logs-basic/src/main.rs

@@ -0,0 +1,28 @@
+use log::{error, Level};
+use opentelemetry_api::KeyValue;
+use opentelemetry_appender_log::OpenTelemetryLogBridge;
+use opentelemetry_sdk::logs::{Config, LoggerProvider};
+use opentelemetry_sdk::Resource;
+
+fn main() {
+    // Setup LoggerProvider with a stdout exporter
+    let exporter = opentelemetry_stdout::LogExporter::default();
+    let logger_provider = LoggerProvider::builder()
+        .with_config(
+            Config::default().with_resource(Resource::new(vec![KeyValue::new(
+                "service.name",
+                "logs-basic-example",
+            )])),
+        )
+        .with_simple_exporter(exporter)
+        .build();
+
+    // Setup Log Appender for the log crate.
+    let otel_log_appender = OpenTelemetryLogBridge::new(&logger_provider);
+    log::set_boxed_logger(Box::new(otel_log_appender)).unwrap();
+    log::set_max_level(Level::Error.to_level_filter());
+
+    // Emit logs using macros from the log crate.
+    // These logs gets piped through OpenTelemetry bridge and gets exported to stdout.
+    error!(target: "my-target", "hello from {}. My price is {}", "apple", 2.99);
+}

opentelemetry-appender-log/CHANGELOG.md

@@ -0,0 +1,2 @@
+# Changelog
+

opentelemetry-appender-log/CODEOWNERS

@@ -0,0 +1,5 @@
+# Code owners file.
+# This file controls who is tagged for review for any given pull request.
+
+# For anything not explicitly taken by someone else:
+*  @open-telemetry/rust-approvers

opentelemetry-appender-log/Cargo.toml

@@ -0,0 +1,17 @@
+[package]
+name = "opentelemetry-appender-log"
+version = "0.1.0"
+edition = "2021"
+description = "An OpenTelemetry appender for the log crate"
+homepage = "https://github.com/open-telemetry/opentelemetry-rust/tree/main/opentelemetry-appender-log"
+repository = "https://github.com/open-telemetry/opentelemetry-rust/tree/main/opentelemetry-appender-log"
+readme = "README.md"
+keywords = ["opentelemetry", "log", "logs"]
+license = "Apache-2.0"
+rust-version = "1.60"
+
+[dependencies]
+opentelemetry_api = { version = "0.19", path = "../opentelemetry-api", features = ["logs"]}
+opentelemetry_sdk = { version = "0.19", path = "../opentelemetry-sdk", features = ["logs"]}
+log = {version = "0.4.17", features = ["kv_unstable", "std"]}
+

opentelemetry-appender-log/LICENSE

@@ -0,0 +1,201 @@
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opentelemetry-appender-log/README.md

@@ -0,0 +1,23 @@
+![OpenTelemetry — An observability framework for cloud-native software.][splash]
+
+[splash]: https://raw.githubusercontent.com/open-telemetry/opentelemetry-rust/main/assets/logo-text.png
+
+# OpenTelemetry Log Appender
+
+A [Log Appender](https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/glossary.md#log-appender--bridge) that bridges logs from the [log crate](https://docs.rs/log/latest/log/) to OpenTelemetry.
+
+[![Crates.io: opentelemetry-appender-log](https://img.shields.io/crates/v/opentelemetry-appender-log.svg)](https://crates.io/crates/opentelemetry-appender-log)
+[![Documentation](https://docs.rs/opentelemetry-appender-log/badge.svg)](https://docs.rs/opentelemetry-appender-log)
+[![LICENSE](https://img.shields.io/crates/l/opentelemetry-appender-log)](./LICENSE)
+[![GitHub Actions CI](https://github.com/open-telemetry/opentelemetry-rust/workflows/CI/badge.svg)](https://github.com/open-telemetry/opentelemetry-rust/actions?query=workflow%3ACI+branch%3Amain)
+[![Slack](https://img.shields.io/badge/slack-@cncf/otel/rust-brightgreen.svg?logo=slack)](https://cloud-native.slack.com/archives/C03GDP0H023)
+
+## Overview
+
+[`OpenTelemetry`] is a collection of tools, APIs, and SDKs used to instrument,
+generate, collect, and export telemetry data (metrics, logs, and traces) for
+analysis in order to understand your software's performance and behavior. This
+crate provides additional propagators and exporters for sending telemetry data
+to vendors or using experimental propagators like `base64`.
+
+[`OpenTelemetry`]: https://crates.io/crates/opentelemetry

opentelemetry-appender-log/src/lib.rs

@@ -0,0 +1,59 @@
+use log::{Level, Metadata, Record};
+use opentelemetry_api::logs::{AnyValue, LogRecordBuilder, Logger, LoggerProvider, Severity};
+
+pub struct OpenTelemetryLogBridge<P, L>
+where
+    P: LoggerProvider<Logger = L> + Send + Sync,
+    L: Logger + Send + Sync,
+{
+    logger: L,
+    _phantom: std::marker::PhantomData<P>, // P is not used in this struct
+}
+
+impl<P, L> log::Log for OpenTelemetryLogBridge<P, L>
+where
+    P: LoggerProvider<Logger = L> + Send + Sync,
+    L: Logger + Send + Sync,
+{
+    fn enabled(&self, _metadata: &Metadata) -> bool {
+        // TODO: This should be dynamic instead of the current hardcoded value.
+        true
+    }
+
+    fn log(&self, record: &Record) {
+        if self.enabled(record.metadata()) {
+            self.logger.emit(
+                LogRecordBuilder::new()
+                    .with_severity_number(map_severity_to_otel_severity(record.level()))
+                    .with_severity_text(record.level().as_str())
+                    .with_body(AnyValue::from(record.args().to_string()))
+                    .build(),
+            );
+        }
+    }
+
+    fn flush(&self) {}
+}
+
+impl<P, L> OpenTelemetryLogBridge<P, L>
+where
+    P: LoggerProvider<Logger = L> + Send + Sync,
+    L: Logger + Send + Sync,
+{
+    pub fn new(provider: &P) -> Self {
+        OpenTelemetryLogBridge {
+            logger: provider.logger("opentelemetry-log-appender"),
+            _phantom: Default::default(),
+        }
+    }
+}
+
+fn map_severity_to_otel_severity(level: Level) -> Severity {
+    match level {
+        Level::Error => Severity::Error,
+        Level::Warn => Severity::Warn,
+        Level::Info => Severity::Info,
+        Level::Debug => Severity::Debug,
+        Level::Trace => Severity::Trace,
+    }
+}