restmapper + discovery: early return in context-aware APIs

The rationale for explicit cancellation checks is that these functions have
side effects that can be avoided when checking upfront. These side effects can
still occur when cancellation happens while the functions are executing, but
"already canceled" is common enough that it deserves special handling.

Kubernetes-commit: c3f63fc258b73e487da7ca84c40be43fc4c5f4dd

discovery/cached/memory/memcache.go

@@ -169,6 +169,10 @@ func (d *memCacheClient) GroupsAndMaybeResources() (*metav1.APIGroupList, map[sc
 // to resources. The returned groups will never be nil, but the resources map can be nil
 // if there are no cached resources.
 func (d *memCacheClient) GroupsAndMaybeResourcesWithContext(ctx context.Context) (*metav1.APIGroupList, map[schema.GroupVersion]*metav1.APIResourceList, map[schema.GroupVersion]error, error) {
+	if err := ctx.Err(); err != nil {
+		return nil, nil, nil, err
+	}
+
 	d.lock.Lock()
 	defer d.lock.Unlock()
 

discovery/discovery_client.go

@@ -607,6 +607,10 @@ func (d *DiscoveryClient) GroupsAndMaybeResourcesWithContext(ctx context.Context
 	map[schema.GroupVersion]*metav1.APIResourceList,
 	map[schema.GroupVersion]error,
 	error) {
+	if err := ctx.Err(); err != nil {
+		return nil, nil, nil, err
+	}
+
 	// Legacy group ordered first (there is only one -- core/v1 group). Returned groups must
 	// be non-nil, but it could be empty. Returned resources, apiResources map could be nil.
 	groups, resources, failedGVs, err := d.downloadLegacy(ctx)
@@ -887,6 +891,10 @@ func ServerGroupsAndResources(d DiscoveryInterface) ([]*metav1.APIGroup, []*meta
 }
 
 func ServerGroupsAndResourcesWithContext(ctx context.Context, d DiscoveryInterfaceWithContext) ([]*metav1.APIGroup, []*metav1.APIResourceList, error) {
+	if err := ctx.Err(); err != nil {
+		return nil, nil, err
+	}
+
 	var sgs *metav1.APIGroupList
 	var resources []*metav1.APIResourceList
 	var failedGVs map[schema.GroupVersion]error
@@ -960,6 +968,10 @@ func ServerPreferredResources(d DiscoveryInterface) ([]*metav1.APIResourceList,
 
 // ServerPreferredResourcesWithContext uses the provided discovery interface to look up preferred resources
 func ServerPreferredResourcesWithContext(ctx context.Context, d DiscoveryInterfaceWithContext) ([]*metav1.APIResourceList, error) {
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+
 	var serverGroupList *metav1.APIGroupList
 	var failedGroups map[schema.GroupVersion]error
 	var groupVersionResources map[schema.GroupVersion]*metav1.APIResourceList

openapi/cached/client.go

@@ -70,6 +70,10 @@ func (c *Client) Paths() (map[string]openapi.GroupVersion, error) {
 }
 
 func (c *Client) PathsWithContext(ctx context.Context) (map[string]openapi.GroupVersionWithContext, error) {
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+
 	c.once.Do(func() {
 		uncached, err := c.delegate.PathsWithContext(ctx)
 		if err != nil {

openapi/cached/groupversion.go

@@ -55,6 +55,10 @@ func (g *groupversion) Schema(contentType string) ([]byte, error) {
 }
 
 func (g *groupversion) SchemaWithContext(ctx context.Context, contentType string) ([]byte, error) {
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+
 	g.lock.Lock()
 	defer g.lock.Unlock()