[Metrics Rewrite] attribute to label mapping (#243)

[Metrics Rewrite] attribute to label mapping

exporter/collector/breaking-changes.md

@@ -0,0 +1,13 @@
+# Breaking changes vs old googlecloud exporter
+
+The new pdata based exporter has some breaking changes from the original OpenCensus stackdriver
+based `googlecloud` exporter:
+
+## Labels
+
+Original label key mapping code is
+[here](https://github.com/census-ecosystem/opencensus-go-exporter-stackdriver/blob/42e7e58efdb937e8477f827d3fba022212335dbc/sanitize.go#L26).
+The new code does not:
+
+- truncate label keys longer than 100 characters.
+- prepend `key` when the first character is `_`.

exporter/collector/metricsexporter.go

@@ -19,6 +19,8 @@ package collector
 
 import (
 	"context"
+	"strings"
+	"unicode"
 
 	monitoring "cloud.google.com/go/monitoring/apiv3/v2"
 	"go.opentelemetry.io/collector/component"
@@ -173,7 +175,35 @@ func attributesToLabels(
 	attrs pdata.AttributeMap,
 ) labels {
 	// TODO
-	return nil
+	ls := make(labels, attrs.Len())
+	attrs.Range(func(k string, v pdata.AttributeValue) bool {
+		ls[sanitizeKey(k)] = v.AsString()
+		return true
+	})
+	return ls
+}
+
+// Replaces non-alphanumeric characters to underscores. Note, this does not truncate label keys
+// longer than 100 characters or prepend "key" when the first character is "_" like OpenCensus
+// did.
+func sanitizeKey(s string) string {
+	if len(s) == 0 {
+		return s
+	}
+	s = strings.Map(sanitizeRune, s)
+	if unicode.IsDigit(rune(s[0])) {
+		s = "key_" + s
+	}
+	return s
+}
+
+// converts anything that is not a letter or digit to an underscore
+func sanitizeRune(r rune) rune {
+	if unicode.IsLetter(r) || unicode.IsDigit(r) {
+		return r
+	}
+	// Everything else turns into an underscore
+	return '_'
 }
 
 func mergeLabels(mergeInto labels, others ...labels) labels {

exporter/collector/metricsexporter_test.go

@@ -65,3 +65,65 @@ func TestMergeLabels(t *testing.T) {
 		"Should merge intersecting labels, keeping the last value",
 	)
 }
+
+func TestAttributesToLabels(t *testing.T) {
+	// string to string
+	assert.Equal(
+		t,
+		attributesToLabels(pdata.NewAttributeMapFromMap(map[string]pdata.AttributeValue{
+			"foo": pdata.NewAttributeValueString("bar"),
+			"bar": pdata.NewAttributeValueString("baz"),
+		})),
+		labels{"foo": "bar", "bar": "baz"},
+	)
+
+	// various key special cases
+	assert.Equal(
+		t,
+		attributesToLabels(pdata.NewAttributeMapFromMap(map[string]pdata.AttributeValue{
+			"foo.bar":   pdata.NewAttributeValueString("bar"),
+			"_foo":      pdata.NewAttributeValueString("bar"),
+			"123.hello": pdata.NewAttributeValueString("bar"),
+			"":          pdata.NewAttributeValueString("bar"),
+		})),
+		labels{
+			"foo_bar":       "bar",
+			"_foo":          "bar",
+			"key_123_hello": "bar",
+			"":              "bar",
+		},
+	)
+
+	attribSlice := pdata.NewAttributeValueArray()
+	attribSlice.SliceVal().AppendEmpty().SetStringVal("x")
+	attribSlice.SliceVal().AppendEmpty()
+	attribSlice.SliceVal().AppendEmpty().SetStringVal("y")
+
+	attribMap := pdata.NewAttributeValueMap()
+	attribMap.MapVal().InsertString("a", "b")
+
+	// value special cases
+	assert.Equal(
+		t,
+		attributesToLabels(pdata.NewAttributeMapFromMap(map[string]pdata.AttributeValue{
+			"a": pdata.NewAttributeValueBool(true),
+			"b": pdata.NewAttributeValueBool(false),
+			"c": pdata.NewAttributeValueInt(12),
+			"d": pdata.NewAttributeValueDouble(12.3),
+			"e": pdata.NewAttributeValueEmpty(),
+			"f": pdata.NewAttributeValueBytes([]byte{0xde, 0xad, 0xbe, 0xef}),
+			"g": attribSlice,
+			"h": attribMap,
+		})),
+		labels{
+			"a": "true",
+			"b": "false",
+			"c": "12",
+			"d": "12.3",
+			"e": "",
+			"f": "3q2+7w==",
+			"g": `["x",null,"y"]`,
+			"h": `{"a":"b"}`,
+		},
+	)
+}