Add support for Key-Value pairs

Cargo.toml

@@ -1,7 +1,10 @@
 [package]
 name = "log4rs"
 version = "1.3.0"
-authors = ["Steven Fackler <sfackler@gmail.com>", "Evan Simmons <esims89@gmail.com>"]
+authors = [
+    "Steven Fackler <sfackler@gmail.com>",
+    "Evan Simmons <esims89@gmail.com>",
+]
 description = "A highly configurable multi-output logging implementation for the `log` facade"
 license = "MIT OR Apache-2.0"
 repository = "https://github.com/estk/log4rs"
@@ -13,7 +16,13 @@ rust-version = "1.69"
 [features]
 default = ["all_components", "config_parsing", "yaml_format"]
 
-config_parsing = ["humantime", "serde", "serde-value", "typemap-ors", "log/serde"]
+config_parsing = [
+    "humantime",
+    "serde",
+    "serde-value",
+    "typemap-ors",
+    "log/serde",
+]
 yaml_format = ["serde_yaml"]
 json_format = ["serde_json"]
 toml_format = ["toml"]
@@ -27,13 +36,21 @@ fixed_window_roller = []
 size_trigger = []
 time_trigger = ["rand"]
 onstartup_trigger = []
-json_encoder = ["serde", "serde_json", "chrono", "log-mdc", "log/serde", "thread-id"]
+json_encoder = [
+    "serde",
+    "serde_json",
+    "chrono",
+    "log-mdc",
+    "log/serde",
+    "thread-id",
+]
 pattern_encoder = ["chrono", "log-mdc", "thread-id"]
 ansi_writer = []
 console_writer = ["ansi_writer", "libc", "winapi"]
 simple_writer = []
 threshold_filter = []
 background_rotation = []
+log_kv = ["log/kv"]
 
 all_components = [
     "console_appender",
@@ -47,7 +64,7 @@ all_components = [
     "onstartup_trigger",
     "json_encoder",
     "pattern_encoder",
-    "threshold_filter"
+    "threshold_filter",
 ]
 
 gzip = ["flate2"]
@@ -58,11 +75,13 @@ harness = false
 
 [dependencies]
 arc-swap = "1.6"
-chrono = { version = "0.4.23", optional = true, features = ["clock"], default-features = false }
+chrono = { version = "0.4.23", optional = true, features = [
+    "clock",
+], default-features = false }
 flate2 = { version = "1.0", optional = true }
 fnv = "1.0"
 humantime = { version = "2.1", optional = true }
-log = { version = "0.4.20", features = ["std"] }
+log = { version = "0.4.21", features = ["std"] }
 log-mdc = { version = "0.1", optional = true }
 serde = { version = "1.0.196", optional = true, features = ["derive"] }
 serde-value = { version = "0.7", optional = true }
@@ -72,14 +91,20 @@ serde_json = { version = "1.0", optional = true }
 serde_yaml = { version = "0.9", optional = true }
 toml = { version = "<0.8.10", optional = true }
 parking_lot = { version = "0.12.0", optional = true }
-rand = { version = "0.8", optional = true}
+rand = { version = "0.8", optional = true }
 thiserror = "1.0.15"
 anyhow = "1.0.28"
 derivative = "2.2"
 once_cell = "1.17.1"
 
 [target.'cfg(windows)'.dependencies]
-winapi = { version = "0.3", optional = true, features = ["handleapi", "minwindef", "processenv", "winbase", "wincon"] }
+winapi = { version = "0.3", optional = true, features = [
+    "handleapi",
+    "minwindef",
+    "processenv",
+    "winbase",
+    "wincon",
+] }
 
 [target.'cfg(not(windows))'.dependencies]
 libc = { version = "0.2", optional = true }
@@ -98,7 +123,11 @@ required-features = ["json_encoder", "console_appender"]
 
 [[example]]
 name = "log_to_file"
-required-features = ["console_appender", "file_appender", "rolling_file_appender"]
+required-features = [
+    "console_appender",
+    "file_appender",
+    "rolling_file_appender",
+]
 
 [[example]]
 name = "compile_time_config"

src/encode/json.rs

@@ -24,6 +24,11 @@
 //!     }
 //! }
 //! ```
+//! If the `log_kv` feature is enabled, an additional `attributes` field will
+//! contain a map of the record's [log::kv][log_kv] structured logging
+//! attributes.
+//!
+//! [log_kv]: https://docs.rs/log/latest/log/kv/index.html
 
 use chrono::{
     format::{DelayedFormat, Fixed, Item},
@@ -76,6 +81,8 @@ impl JsonEncoder {
             thread: thread.name(),
             thread_id: thread_id::get(),
             mdc: Mdc,
+            #[cfg(feature = "log_kv")]
+            attributes: kv::get_attributes(record.key_values())?,
         };
         message.serialize(&mut serde_json::Serializer::new(&mut *w))?;
         w.write_all(NEWLINE.as_bytes())?;
@@ -106,6 +113,8 @@ struct Message<'a> {
     thread: Option<&'a str>,
     thread_id: usize,
     mdc: Mdc,
+    #[cfg(feature = "log_kv")]
+    attributes: kv::Map,
 }
 
 fn ser_display<T, S>(v: &T, s: S) -> Result<S::Ok, S::Error>
@@ -162,6 +171,34 @@ impl Deserialize for JsonEncoderDeserializer {
         Ok(Box::<JsonEncoder>::default())
     }
 }
+#[cfg(feature = "log_kv")]
+mod kv {
+    use log::kv::VisitSource;
+    use std::collections::BTreeMap;
+
+    pub(crate) type Map = BTreeMap<String, String>;
+
+    pub(crate) fn get_attributes(source: &dyn log::kv::Source) -> anyhow::Result<Map> {
+        struct Visitor {
+            inner: Map,
+        }
+        impl<'kvs> VisitSource<'kvs> for Visitor {
+            fn visit_pair(
+                &mut self,
+                key: log::kv::Key<'kvs>,
+                value: log::kv::Value<'kvs>,
+            ) -> Result<(), log::kv::Error> {
+                self.inner.insert(format!("{key}"), format!("{value}"));
+                Ok(())
+            }
+        }
+        let mut visitor = Visitor {
+            inner: BTreeMap::new(),
+        };
+        source.visit(&mut visitor)?;
+        Ok(visitor.inner)
+    }
+}
 
 #[cfg(test)]
 #[cfg(feature = "simple_writer")]
@@ -189,26 +226,35 @@ mod test {
 
         let encoder = JsonEncoder::new();
 
+        let mut record_builder = Record::builder();
+        record_builder
+            .level(level)
+            .target(target)
+            .module_path(Some(module_path))
+            .file(Some(file))
+            .line(Some(line));
+
+        #[cfg(feature = "log_kv")]
+        record_builder.key_values(&[("log_foo", "log_bar")]);
+
         let mut buf = vec![];
         encoder
             .encode_inner(
                 &mut SimpleWriter(&mut buf),
                 time,
-                &Record::builder()
-                    .level(level)
-                    .target(target)
-                    .module_path(Some(module_path))
-                    .file(Some(file))
-                    .line(Some(line))
-                    .args(format_args!("{}", message))
-                    .build(),
+                &record_builder.args(format_args!("{}", message)).build(),
             )
             .unwrap();
 
+        #[cfg(feature = "log_kv")]
+        let expected_attributes = ",\"attributes\":{\"log_foo\":\"log_bar\"}";
+        #[cfg(not(feature = "log_kv"))]
+        let expected_attributes = "";
+
         let expected = format!(
             "{{\"time\":\"{}\",\"level\":\"{}\",\"message\":\"{}\",\"module_path\":\"{}\",\
             \"file\":\"{}\",\"line\":{},\"target\":\"{}\",\
-            \"thread\":\"{}\",\"thread_id\":{},\"mdc\":{{\"foo\":\"bar\"}}}}",
+            \"thread\":\"{}\",\"thread_id\":{},\"mdc\":{{\"foo\":\"bar\"}}{}}}",
             time.to_rfc3339(),
             level,
             message,
@@ -218,6 +264,7 @@ mod test {
             target,
             thread,
             thread_id::get(),
+            expected_attributes
         );
         assert_eq!(expected, String::from_utf8(buf).unwrap().trim());
     }