From 77f989a478b63c4ef61d642a0f407801647508a2 Mon Sep 17 00:00:00 2001
From: Samuel Berthe <dev@samuel-berthe.fr>
Date: Fri, 26 Apr 2024 01:57:27 +0200
Subject: [PATCH] feat: load attributes from context

---
 README.md  | 37 +++++++++++++++++++++++++++++++++++++
 go.mod     |  2 +-
 go.sum     |  4 ++--
 handler.go |  9 ++++++++-
 4 files changed, 48 insertions(+), 4 deletions(-)

diff --git a/README.md b/README.md
index 593b299..5d909ee 100644
--- a/README.md
+++ b/README.md
@@ -80,6 +80,8 @@ type Option struct {
 
 	// optional: customize Kafka event builder
 	Converter Converter
+	// optional: fetch attributes from context
+	AttrFromContext []func(ctx context.Context) []slog.Attr
 
 	// optional: see slog.HandlerOptions
 	AddSource   bool
@@ -216,6 +218,41 @@ Kafka message:
 }
 ```
 
+### Tracing
+
+Import the samber/slog-otel library.
+
+```go
+import (
+	slogkafka "github.com/samber/slog-kafka"
+	slogotel "github.com/samber/slog-otel"
+	"go.opentelemetry.io/otel/sdk/trace"
+)
+
+func main() {
+	tp := trace.NewTracerProvider(
+		trace.WithSampler(trace.AlwaysSample()),
+	)
+	tracer := tp.Tracer("hello/world")
+
+	ctx, span := tracer.Start(context.Background(), "foo")
+	defer span.End()
+
+	span.AddEvent("bar")
+
+	logger := slog.New(
+		slogkafka.Option{
+			// ...
+			AttrFromContext: []func(ctx context.Context) []slog.Attr{
+				slogotel.ExtractOtelAttrFromContext([]string{"tracing"}, "trace_id", "span_id"),
+			},
+		}.NewKafkaHandler(),
+	)
+
+	logger.ErrorContext(ctx, "a message")
+}
+```
+
 ## 🤝 Contributing
 
 - Ping me on twitter [@samuelberthe](https://twitter.com/samuelberthe) (DMs, mentions, whatever :))
diff --git a/go.mod b/go.mod
index ba0ad01..52e4d87 100644
--- a/go.mod
+++ b/go.mod
@@ -3,7 +3,7 @@ module github.com/samber/slog-kafka/v2
 go 1.21
 
 require (
-	github.com/samber/slog-common v0.15.2
+	github.com/samber/slog-common v0.16.0
 	github.com/segmentio/kafka-go v0.4.39
 	go.uber.org/goleak v1.2.1
 )
diff --git a/go.sum b/go.sum
index 5c7cf56..b88409e 100644
--- a/go.sum
+++ b/go.sum
@@ -9,8 +9,8 @@ github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZb
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/samber/lo v1.38.1 h1:j2XEAqXKb09Am4ebOg31SpvzUTTs6EN3VfgeLUhPdXM=
 github.com/samber/lo v1.38.1/go.mod h1:+m/ZKRl6ClXCE2Lgf3MsQlWfh4bn1bz6CXEOxnEXnEA=
-github.com/samber/slog-common v0.15.2 h1:jQQK2MzJ1kfEsUyxI/mpwkqB2xI0qCo9Ne1D1yziuP0=
-github.com/samber/slog-common v0.15.2/go.mod h1:Qjrfhwk79XiCIhBj8+jTq1Cr0u9rlWbjawh3dWXzaHk=
+github.com/samber/slog-common v0.16.0 h1:2/t1EcFd1Ru77mh2ab+8B6NBHnEXsBBHtOJc7PSH0aI=
+github.com/samber/slog-common v0.16.0/go.mod h1:Qjrfhwk79XiCIhBj8+jTq1Cr0u9rlWbjawh3dWXzaHk=
 github.com/segmentio/kafka-go v0.4.39 h1:75smaomhvkYRwtuOwqLsdhgCG30B82NsbdkdDfFbvrw=
 github.com/segmentio/kafka-go v0.4.39/go.mod h1:T0MLgygYvmqmBvC+s8aCcbVNfJN4znVne5j0Pzowp/Q=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
diff --git a/handler.go b/handler.go
index 9bfa3fe..9a18660 100644
--- a/handler.go
+++ b/handler.go
@@ -21,6 +21,8 @@ type Option struct {
 
 	// optional: customize Kafka event builder
 	Converter Converter
+	// optional: fetch attributes from context
+	AttrFromContext []func(ctx context.Context) []slog.Attr
 
 	// optional: see slog.HandlerOptions
 	AddSource   bool
@@ -44,6 +46,10 @@ func (o Option) NewKafkaHandler() slog.Handler {
 		o.Converter = DefaultConverter
 	}
 
+	if o.AttrFromContext == nil {
+		o.AttrFromContext = []func(ctx context.Context) []slog.Attr{}
+	}
+
 	return &KafkaHandler{
 		option: o,
 		attrs:  []slog.Attr{},
@@ -64,7 +70,8 @@ func (h *KafkaHandler) Enabled(_ context.Context, level slog.Level) bool {
 }
 
 func (h *KafkaHandler) Handle(ctx context.Context, record slog.Record) error {
-	payload := h.option.Converter(h.option.AddSource, h.option.ReplaceAttr, h.attrs, h.groups, &record)
+	fromContext := slogcommon.ContextExtractor(ctx, h.option.AttrFromContext)
+	payload := h.option.Converter(h.option.AddSource, h.option.ReplaceAttr, append(h.attrs, fromContext...), h.groups, &record)
 
 	return h.publish(record.Time, payload)
 }