feat: Add basic support for OpenCensus tracing (resolvers only) (#70)

* feat: Add basic support for OpenCensus tracing (resolvers only)

* chore: add dep to go.mod

go.mod

@@ -8,6 +8,7 @@ require (
 	github.com/99designs/gqlgen v0.17.34
 	github.com/spf13/cobra v1.7.0
 	github.com/vektah/gqlparser/v2 v2.5.6
+	go.opencensus.io v0.24.0
 )
 
 require (
@@ -45,7 +46,6 @@ require (
 	github.com/spf13/pflag v1.0.5 // indirect
 	github.com/uber/jaeger-client-go v2.25.0+incompatible // indirect
 	github.com/zemirco/memorystore v0.0.0-20160308183530-ecd57e5134f6 // indirect
-	go.opencensus.io v0.24.0 // indirect
 	go.uber.org/atomic v1.7.0 // indirect
 	go.uber.org/automaxprocs v1.5.1 // indirect
 	go.uber.org/multierr v1.6.0 // indirect

module.go

@@ -37,21 +37,25 @@ func (*Module) Configure(injector *dingo.Injector) {
 type routes struct {
 	exec                 graphql.ExecutableSchema
 	reverseRouter        web.ReverseRouter
-	origins              flamingoConfig.Slice
-	introspectionEnabled bool
-	uploadMaxSize        int64
 	operationMiddlewares []graphql.OperationMiddleware
+
+	// configs
+	origins                  flamingoConfig.Slice
+	openCensusTracingEnabled bool
+	introspectionEnabled     bool
+	uploadMaxSize            int64
 }
 
 // Inject executable schema
 func (r *routes) Inject(
 	reverseRouter web.ReverseRouter,
 	config *struct {
-		Exec                 graphql.ExecutableSchema      `inject:",optional"`
-		OperationMiddlewares []graphql.OperationMiddleware `inject:",optional"`
-		Origins              flamingoConfig.Slice          `inject:"config:graphql.cors.origins"`
-		IntrospectionEnabled bool                          `inject:"config:graphql.introspectionEnabled,optional"`
-		UploadMaxSize        int64                         `inject:"config:graphql.multipartForm.uploadMaxSize,optional"`
+		Exec                     graphql.ExecutableSchema      `inject:",optional"`
+		OperationMiddlewares     []graphql.OperationMiddleware `inject:",optional"`
+		Origins                  flamingoConfig.Slice          `inject:"config:graphql.cors.origins"`
+		IntrospectionEnabled     bool                          `inject:"config:graphql.introspectionEnabled,optional"`
+		OpenCensusTracingEnabled bool                          `inject:"config:graphql.openCensusTracingEnabled,optional"`
+		UploadMaxSize            int64                         `inject:"config:graphql.multipartForm.uploadMaxSize,optional"`
 	},
 ) {
 	r.reverseRouter = reverseRouter
@@ -61,6 +65,7 @@ func (r *routes) Inject(
 		r.introspectionEnabled = config.IntrospectionEnabled
 		r.uploadMaxSize = config.UploadMaxSize
 		r.operationMiddlewares = config.OperationMiddlewares
+		r.openCensusTracingEnabled = config.OpenCensusTracingEnabled
 	}
 }
 
@@ -96,6 +101,10 @@ func (r *routes) Routes(registry *web.RouterRegistry) {
 			Cache: lru.New(100),
 		})
 
+		if r.openCensusTracingEnabled {
+			srv.Use(&OpenCensusTracingExtension{})
+		}
+
 		return srv
 	}(r.exec)
 
@@ -122,6 +131,7 @@ func (m *Module) CueConfig() string {
 	return `
 graphql: {
 	introspectionEnabled: bool | *false
+	openCensusTracingEnabled: bool | *true
 	multipartForm: {
 		uploadMaxSize: (int | *1.5M) & > 0
 	}

opencensus_tracing.go

@@ -0,0 +1,52 @@
+package graphql
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/99designs/gqlgen/graphql"
+	"go.opencensus.io/trace"
+)
+
+var _ graphql.HandlerExtension = &OpenCensusTracingExtension{}
+var _ graphql.ResponseInterceptor = &OpenCensusTracingExtension{}
+var _ graphql.FieldInterceptor = &OpenCensusTracingExtension{}
+var _ graphql.OperationInterceptor = &OpenCensusTracingExtension{}
+
+type OpenCensusTracingExtension struct{}
+
+func (o *OpenCensusTracingExtension) ExtensionName() string {
+	return "OpenCensusTracing"
+}
+
+func (o *OpenCensusTracingExtension) InterceptField(ctx context.Context, next graphql.Resolver) (res interface{}, err error) {
+	fieldContext := graphql.GetFieldContext(ctx)
+
+	// for now, we only trace resolvers
+	if !fieldContext.IsResolver {
+		return next(ctx)
+	}
+
+	spanName := fmt.Sprintf("graphql/resolver/%s", fieldContext.Field.Name)
+	if fieldContext.Object != "Query" && fieldContext.Object != "Mutation" {
+		// enrich information if the resolver is registered on a graphql subtype, e.g. resolver that resolves `sortedList` on type `Users_Result`
+		spanName = fmt.Sprintf("graphql/resolver/%s/%s", fieldContext.Object, fieldContext.Field.Name)
+	}
+
+	ctx, span := trace.StartSpan(ctx, spanName)
+	defer span.End()
+
+	return next(ctx)
+}
+
+func (o *OpenCensusTracingExtension) InterceptOperation(ctx context.Context, next graphql.OperationHandler) graphql.ResponseHandler {
+	return next(ctx)
+}
+
+func (o *OpenCensusTracingExtension) InterceptResponse(ctx context.Context, next graphql.ResponseHandler) *graphql.Response {
+	return next(ctx)
+}
+
+func (o *OpenCensusTracingExtension) Validate(_ graphql.ExecutableSchema) error {
+	return nil
+}