Fix content type fallback when a client defaults to CBOR.

With the ClientsAllowCBOR client-go feature gate enabled, a 415 response to a CBOR-encoded REST
causes all subsequent requests from the client to fall back to a JSON request encoding. This
mechanism had only worked as intended when CBOR was explicitly configured in the
ClientContentConfig. When both ClientsAllowCBOR and ClientsPreferCBOR are enabled, an
unconfigured (empty) content type defaults to CBOR instead of JSON. Both ways of configuring a
client to use the CBOR request encoding are now subject to the same fallback mechanism.

Kubernetes-commit: a77f4c7ba2e761461daaf115a38903fc91916dd6

Author: benluddy

rest/client.go

@@ -238,7 +238,8 @@ func (c *RESTClient) Delete() *Request {
 
 // APIVersion returns the APIVersion this RESTClient is expected to use.
 func (c *RESTClient) APIVersion() schema.GroupVersion {
-	return c.content.GetClientContentConfig().GroupVersion
+	config, _ := c.content.GetClientContentConfig()
+	return config.GroupVersion
 }
 
 // requestClientContentConfigProvider observes HTTP 415 (Unsupported Media Type) responses to detect
@@ -257,25 +258,35 @@ type requestClientContentConfigProvider struct {
 }
 
 // GetClientContentConfig returns the ClientContentConfig that should be used for new requests by
-// this client.
-func (p *requestClientContentConfigProvider) GetClientContentConfig() ClientContentConfig {
+// this client and true if the request ContentType was selected by default.
+func (p *requestClientContentConfigProvider) GetClientContentConfig() (ClientContentConfig, bool) {
+	config := p.base
+
+	defaulted := config.ContentType == ""
+	if defaulted {
+		config.ContentType = "application/json"
+	}
+
 	if !clientfeatures.FeatureGates().Enabled(clientfeatures.ClientsAllowCBOR) {
-		return p.base
+		return config, defaulted
+	}
+
+	if defaulted && clientfeatures.FeatureGates().Enabled(clientfeatures.ClientsPreferCBOR) {
+		config.ContentType = "application/cbor"
 	}
 
 	if sawUnsupportedMediaTypeForCBOR := p.sawUnsupportedMediaTypeForCBOR.Load(); !sawUnsupportedMediaTypeForCBOR {
-		return p.base
+		return config, defaulted
 	}
 
-	if mediaType, _, _ := mime.ParseMediaType(p.base.ContentType); mediaType != runtime.ContentTypeCBOR {
-		return p.base
+	if mediaType, _, _ := mime.ParseMediaType(config.ContentType); mediaType != runtime.ContentTypeCBOR {
+		return config, defaulted
 	}
 
-	config := p.base
-	// The default ClientContentConfig sets ContentType to CBOR and the client has previously
-	// received an HTTP 415 in response to a CBOR request. Override ContentType to JSON.
+	// The effective ContentType is CBOR and the client has previously received an HTTP 415 in
+	// response to a CBOR request. Override ContentType to JSON.
 	config.ContentType = runtime.ContentTypeJSON
-	return config
+	return config, defaulted
 }
 
 // UnsupportedMediaType reports that the server has responded to a request with HTTP 415 Unsupported

rest/request.go

@@ -156,14 +156,10 @@ func NewRequest(c *RESTClient) *Request {
 		timeout = c.Client.Timeout
 	}
 
-	contentConfig := c.content.GetClientContentConfig()
-	contentTypeNotSet := len(contentConfig.ContentType) == 0
-	if contentTypeNotSet {
-		contentConfig.ContentType = "application/json"
-		if clientfeatures.FeatureGates().Enabled(clientfeatures.ClientsAllowCBOR) && clientfeatures.FeatureGates().Enabled(clientfeatures.ClientsPreferCBOR) {
-			contentConfig.ContentType = "application/cbor"
-		}
-	}
+	// A request needs to know whether the content type was explicitly configured or selected by
+	// default in order to support the per-request Protobuf override used by clients generated
+	// with --prefers-protobuf.
+	contentConfig, contentTypeDefaulted := c.content.GetClientContentConfig()
 
 	r := &Request{
 		c:              c,
@@ -176,7 +172,7 @@ func NewRequest(c *RESTClient) *Request {
 		warningHandler: c.warningHandler,
 
 		contentConfig:     contentConfig,
-		contentTypeNotSet: contentTypeNotSet,
+		contentTypeNotSet: contentTypeDefaulted,
 	}
 
 	r.setAcceptHeader()