From abe224371883209d4db1bc8e099750a5b7d8ebb5 Mon Sep 17 00:00:00 2001
From: Bhautik Pipaliya <56270044+bhautikpip@users.noreply.github.com>
Date: Thu, 22 Jul 2021 11:39:27 -0700
Subject: [PATCH] API: create new linked span from current context (#2115)

* API: create new linked span from current context

* ran make precommit

* Update trace/trace.go

* Updated CHANGELOG

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>
---
 CHANGELOG.md        |  1 +
 trace/trace.go      |  8 ++++++++
 trace/trace_test.go | 18 ++++++++++++++++++
 3 files changed, 27 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 00cc68b561f..6ebf2fcb081 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,6 +12,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 - Added `WithOSDescription` resource configuration option to set OS (Operating System) description resource attribute (`os.description`). (#1840)
 - Added `WithOS` resource configuration option to set all OS (Operating System) resource attributes at once. (#1840)
+- Added API `LinkFromContext` to return Link which encapsulates SpanContext from provided context and also encapsulates attributes. (#2115)
 
 ### Changed
 
diff --git a/trace/trace.go b/trace/trace.go
index 15eb4673b41..8564cb9dfe6 100644
--- a/trace/trace.go
+++ b/trace/trace.go
@@ -408,6 +408,14 @@ type Link struct {
 	DroppedAttributeCount int
 }
 
+// LinkFromContext returns a link encapsulating the SpanContext in the provided ctx.
+func LinkFromContext(ctx context.Context, attrs ...attribute.KeyValue) Link {
+	return Link{
+		SpanContext: SpanContextFromContext(ctx),
+		Attributes:  attrs,
+	}
+}
+
 // SpanKind is the role a Span plays in a Trace.
 type SpanKind int
 
diff --git a/trace/trace_test.go b/trace/trace_test.go
index 2a32270b27b..d6115f286b9 100644
--- a/trace/trace_test.go
+++ b/trace/trace_test.go
@@ -16,8 +16,13 @@ package trace
 
 import (
 	"bytes"
+	"context"
 	"testing"
 
+	"github.com/stretchr/testify/assert"
+
+	"go.opentelemetry.io/otel/attribute"
+
 	"github.com/google/go-cmp/cmp"
 )
 
@@ -643,3 +648,16 @@ func TestSpanContextDerivation(t *testing.T) {
 		t.Fatalf("WithTraceState: Unexpected context created: %s", cmp.Diff(modified, to))
 	}
 }
+
+func TestLinkFromContext(t *testing.T) {
+	k1v1 := attribute.String("key1", "value1")
+	spanCtx := SpanContext{traceID: TraceID([16]byte{1}), remote: true}
+
+	receiverCtx := ContextWithRemoteSpanContext(context.Background(), spanCtx)
+	link := LinkFromContext(receiverCtx, k1v1)
+
+	if !assertSpanContextEqual(link.SpanContext, spanCtx) {
+		t.Fatalf("LinkFromContext: Unexpected context created: %s", cmp.Diff(link.SpanContext, spanCtx))
+	}
+	assert.Equal(t, link.Attributes[0], k1v1)
+}