Move content length out of basic attributes (#1031)

* Move content length out of basic attributes

semconv.httpBasicAttributesFromHTTPRequest() was including the request's content length,
which is a high-cardinality label.  It ended up in metric labels through the use of that function
by semconv.HTTPServerMetricAttributesFromHTTPRequest().

* Add CHANGELOG entry

Co-authored-by: Tyler Yahn <[email protected]>

Author: Aneurysm9

CHANGELOG.md

@@ -12,6 +12,10 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 - Renamed `go.opentelemetry.io/otel/api/standard` package to `go.opentelemetry.io/otel/semconv` to avoid the ambiguous and generic name `standard` and better describe the package as containing OpenTelemetry semantic conventions. (#1016)
 
+### Fixed
+
+- The `semconv.HTTPServerMetricAttributesFromHTTPRequest()` function no longer generates the high-cardinality `http.request.content.length` label. (#1031)
+
 ## [0.10.0] - 2020-07-29
 
 This release migrates the default OpenTelemetry SDK into its own Go module, decoupling the SDK from the API and reducing dependencies for instrumentation packages.

semconv/http.go

@@ -151,11 +151,15 @@ func httpCommonAttributesFromHTTPRequest(request *http.Request) []kv.KeyValue {
 	if ua := request.UserAgent(); ua != "" {
 		attrs = append(attrs, HTTPUserAgentKey.String(ua))
 	}
+	if request.ContentLength > 0 {
+		attrs = append(attrs, HTTPRequestContentLengthKey.Int64(request.ContentLength))
+	}
 
 	return append(attrs, httpBasicAttributesFromHTTPRequest(request)...)
 }
 
 func httpBasicAttributesFromHTTPRequest(request *http.Request) []kv.KeyValue {
+	// as these attributes are used by HTTPServerMetricAttributesFromHTTPRequest, they should be low-cardinality
 	attrs := []kv.KeyValue{}
 
 	if request.TLS != nil {
@@ -177,9 +181,6 @@ func httpBasicAttributesFromHTTPRequest(request *http.Request) []kv.KeyValue {
 	if flavor != "" {
 		attrs = append(attrs, HTTPFlavorKey.String(flavor))
 	}
-	if request.ContentLength > 0 {
-		attrs = append(attrs, HTTPRequestContentLengthKey.Int64(request.ContentLength))
-	}
 
 	return attrs
 }