From 2f0a241a3e37b44307df82bf9812aeff2952acc2 Mon Sep 17 00:00:00 2001
From: Thayne McCombs <astrothayne@gmail.com>
Date: Wed, 28 Dec 2022 22:55:51 -0700
Subject: [PATCH] Support forwarding structured data to log implementation

See: #328
---
 kv.rs  | 100 +++++++++++++++++++++++++++++++++++++++++++++++++++++++--
 lib.rs |  23 +++++++------
 2 files changed, 111 insertions(+), 12 deletions(-)

diff --git a/kv.rs b/kv.rs
index 2172843..3af2fa8 100644
--- a/kv.rs
+++ b/kv.rs
@@ -1,4 +1,6 @@
-use slog::{Record, Serializer};
+use slog::{Record, Serializer, KV};
+
+use std::fmt::Arguments;
 
 pub(crate) struct Visitor {
     kvs: Vec<(String, String)>,
@@ -25,7 +27,7 @@ impl<'kvs, 'a> log::kv::Visitor<'kvs> for Visitor {
     }
 }
 
-impl slog::KV for Visitor {
+impl KV for Visitor {
     fn serialize(&self, _record: &Record, serializer: &mut dyn Serializer) -> slog::Result {
         for (key, val) in &self.kvs {
             serializer.emit_str(key.to_owned().into(), val.as_str())?;
@@ -33,3 +35,97 @@ impl slog::KV for Visitor {
         Ok(())
     }
 }
+
+/// Create a [`log::kv::Source`] for the key-value pairs for a slog record.
+pub(crate) fn get_kv_source<'a>(
+    record: &'a slog::Record<'a>,
+    logger_kv: &'a slog::OwnedKVList,
+) -> std::io::Result<Vec<(String, OwnedValue)>> {
+    let mut serialized_source = LogSerializer(vec![]);
+
+    record.kv().serialize(record, &mut serialized_source)?;
+    logger_kv.serialize(record, &mut serialized_source)?;
+    Ok(serialized_source.0)
+}
+
+/// A wrapper around [`log::kv::Value`], that owns the data included.
+///
+/// In particular this is necessary for strings, and large integers (u128, and i128), because the
+/// `Value` type itself only supports references, which must survive for the lifetime of the
+/// visitor.
+pub(crate) enum OwnedValue {
+    Value(log::kv::Value<'static>),
+    Str(String),
+    U128(Box<u128>),
+    I128(Box<i128>),
+}
+
+impl log::kv::value::ToValue for OwnedValue {
+    fn to_value(&self) -> log::kv::Value<'_> {
+        use OwnedValue::*;
+
+        match self {
+            Value(v) => v.to_value(),
+            Str(s) => s.to_value(),
+            U128(v) => v.to_value(),
+            I128(v) => v.to_value(),
+        }
+    }
+}
+
+struct LogSerializer(Vec<(String, OwnedValue)>);
+
+impl LogSerializer {
+    fn add(&mut self, key: slog::Key, val: OwnedValue) -> slog::Result {
+        self.0.push((key.into(), val));
+        Ok(())
+    }
+}
+
+macro_rules! emit_to_value {
+    ($f:ident : $t:ty) => {
+        fn $f(&mut self, key: slog::Key, val: $t) -> slog::Result {
+            self.add(key, OwnedValue::Value(val.into()))
+        }
+    };
+}
+
+impl Serializer for LogSerializer {
+    fn emit_arguments(&mut self, key: slog::Key, val: &Arguments<'_>) -> slog::Result {
+        self.add(key, OwnedValue::Str(val.to_string()))
+    }
+
+    emit_to_value!(emit_usize: usize);
+    emit_to_value!(emit_isize: isize);
+    emit_to_value!(emit_bool: bool);
+    emit_to_value!(emit_char: char);
+    emit_to_value!(emit_u8: u8);
+    emit_to_value!(emit_i8: i8);
+    emit_to_value!(emit_u16: u16);
+    emit_to_value!(emit_i16: i16);
+    emit_to_value!(emit_u32: u32);
+    emit_to_value!(emit_i32: i32);
+    emit_to_value!(emit_f32: f32);
+    emit_to_value!(emit_f64: f64);
+
+    fn emit_u128(&mut self, key: slog::Key, val: u128) -> slog::Result {
+        self.add(key, OwnedValue::U128(Box::new(val)))
+    }
+
+    fn emit_i128(&mut self, key: slog::Key, val: i128) -> slog::Result {
+        self.add(key, OwnedValue::I128(Box::new(val)))
+    }
+
+    fn emit_str(&mut self, key: slog::Key, val: &str) -> slog::Result {
+        self.add(key, OwnedValue::Str(val.to_string()))
+    }
+
+    fn emit_unit(&mut self, key: slog::Key) -> slog::Result {
+        use log::kv::ToValue;
+        self.add(key, OwnedValue::Value(().to_value()))
+    }
+
+    fn emit_none(&mut self, key: slog::Key) -> slog::Result {
+        self.emit_unit(key)
+    }
+}
diff --git a/lib.rs b/lib.rs
index 4b9f8e9..4cedb2f 100644
--- a/lib.rs
+++ b/lib.rs
@@ -266,16 +266,19 @@ impl slog::Drain for StdLog {
          * This avoids using the private log::__private_api_log api function,
          * which is just a thin wrapper around a `RecordBuilder`.
          */
-        log::logger().log(
-            &log::Record::builder()
-                .args(format_args!("{}", lazy))
-                .level(level)
-                .target(target)
-                .module_path_static(Some(info.module()))
-                .file_static(Some(info.file()))
-                .line(Some(info.line()))
-                .build(),
-        );
+        let mut record_builder = log::Record::builder();
+        record_builder
+            .level(level)
+            .target(target)
+            .module_path_static(Some(info.module()))
+            .file_static(Some(info.file()))
+            .line(Some(info.line()));
+        #[cfg(feature = "kv_unstable")]
+        let source = kv::get_kv_source(info, logger_values)?;
+        #[cfg(feature = "kv_unstable")]
+        record_builder.key_values(&source);
+
+        log::logger().log(&record_builder.args(format_args!("{}", lazy)).build());
 
         Ok(())
     }