add tracing package (forgot to commit)

tracing/tracing.go

@@ -0,0 +1,53 @@
+package tracing
+
+import "context"
+
+type tracingContextKey int
+
+const (
+	CallerContext tracingContextKey = 1 + iota
+)
+
+type jobSubtree struct {
+	jobid string
+}
+
+type ctx struct {
+	parent *ctx
+	job    *jobSubtree
+	ident  string
+}
+
+var root = &ctx{nil, nil, ""}
+
+func getParentOrRoot(c context.Context) *ctx {
+	parent, ok := c.Value(CallerContext).(*ctx)
+	if !ok {
+		parent = root
+	}
+	return parent
+}
+
+func makeChild(c context.Context, child *ctx) context.Context {
+	if child.parent == nil {
+		panic(child)
+	}
+	return context.WithValue(c, CallerContext, child)
+}
+
+func Child(c context.Context, ident string) context.Context {
+	parent := getParentOrRoot(c)
+	return makeChild(c, &ctx{parent: parent, ident: ident})
+}
+
+func GetStack(c context.Context) (idents []string) {
+	ct, ok := c.Value(CallerContext).(*ctx)
+	if !ok {
+		return idents
+	}
+	for ct.parent != nil {
+		idents = append(idents, ct.ident)
+		ct = ct.parent
+	}
+	return idents
+}

tracing/tracing_test.go

@@ -0,0 +1,21 @@
+package tracing
+
+import (
+	"context"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestIt(t *testing.T) {
+	ctx := context.Background()
+
+	ctx = Child(ctx, "a")
+	ctx = Child(ctx, "b")
+	ctx = Child(ctx, "c")
+	ctx = Child(ctx, "d")
+
+	assert.Equal(t, "dcba", strings.Join(GetStack(ctx), ""))
+
+}