Move wrapper internally since its not top level relevant

util/wrapper/wrapper.go

@@ -0,0 +1,57 @@
+package wrapper
+
+import (
+	"context"
+
+	"github.com/micro/go-micro/client"
+	"github.com/micro/go-micro/metadata"
+)
+
+type clientWrapper struct {
+	client.Client
+	headers metadata.Metadata
+}
+
+var (
+	HeaderPrefix = "Micro-"
+)
+
+func (c *clientWrapper) setHeaders(ctx context.Context) context.Context {
+	// copy metadata
+	mda, _ := metadata.FromContext(ctx)
+	md := metadata.Copy(mda)
+
+	// set headers
+	for k, v := range c.headers {
+		if _, ok := md[k]; !ok {
+			md[k] = v
+		}
+	}
+
+	return metadata.NewContext(ctx, md)
+}
+
+func (c *clientWrapper) Call(ctx context.Context, req client.Request, rsp interface{}, opts ...client.CallOption) error {
+	ctx = c.setHeaders(ctx)
+	return c.Client.Call(ctx, req, rsp, opts...)
+}
+
+func (c *clientWrapper) Stream(ctx context.Context, req client.Request, opts ...client.CallOption) (client.Stream, error) {
+	ctx = c.setHeaders(ctx)
+	return c.Client.Stream(ctx, req, opts...)
+}
+
+func (c *clientWrapper) Publish(ctx context.Context, p client.Message, opts ...client.PublishOption) error {
+	ctx = c.setHeaders(ctx)
+	return c.Client.Publish(ctx, p, opts...)
+}
+
+// FromService wraps a client to inject From-Service header into metadata
+func FromService(name string, c client.Client) client.Client {
+	return &clientWrapper{
+                c,
+                metadata.Metadata{
+                        HeaderPrefix + "From-Service": name,
+                },
+        }
+}

util/wrapper/wrapper_test.go

@@ -0,0 +1,53 @@
+package wrapper
+
+import (
+	"context"
+	"testing"
+
+	"github.com/micro/go-micro/metadata"
+)
+
+func TestWrapper(t *testing.T) {
+	testData := []struct {
+		existing  metadata.Metadata
+		headers   metadata.Metadata
+		overwrite bool
+	}{
+		{
+			existing: metadata.Metadata{},
+			headers: metadata.Metadata{
+				"foo": "bar",
+			},
+			overwrite: true,
+		},
+		{
+			existing: metadata.Metadata{
+				"foo": "bar",
+			},
+			headers: metadata.Metadata{
+				"foo": "baz",
+			},
+			overwrite: false,
+		},
+	}
+
+	for _, d := range testData {
+		c := &clientWrapper{
+			headers: d.headers,
+		}
+
+		ctx := metadata.NewContext(context.Background(), d.existing)
+		ctx = c.setHeaders(ctx)
+		md, _ := metadata.FromContext(ctx)
+
+		for k, v := range d.headers {
+			if d.overwrite && md[k] != v {
+				t.Fatalf("Expected %s=%s got %s=%s", k, v, k, md[k])
+			}
+			if !d.overwrite && md[k] != d.existing[k] {
+				t.Fatalf("Expected %s=%s got %s=%s", k, d.existing[k], k, md[k])
+			}
+		}
+	}
+
+}