automatic fallback to http

Signed-off-by: Terry Howe <terrylhowe@gmail.com>

pkg/registry/client.go

@@ -103,25 +103,7 @@ func NewClient(options ...ClientOption) (*Client, error) {
 		client.credentialsFile = helmpath.ConfigPath(CredentialsFileBasename)
 	}
 	if client.httpClient == nil {
-		type cloner[T any] interface {
-			Clone() T
-		}
-
-		// try to copy (clone) the http.DefaultTransport so any mutations we
-		// perform on it (e.g. TLS config) are not reflected globally
-		// follow https://github.com/golang/go/issues/39299 for a more elegant
-		// solution in the future
-		transport := http.DefaultTransport
-		if t, ok := transport.(cloner[*http.Transport]); ok {
-			transport = t.Clone()
-		} else if t, ok := transport.(cloner[http.RoundTripper]); ok {
-			// this branch will not be used with go 1.20, it was added
-			// optimistically to try to clone if the http.DefaultTransport
-			// implementation changes, still the Clone method in that case
-			// might not return http.RoundTripper...
-			transport = t.Clone()
-		}
-
+		transport := newTransport()
 		client.httpClient = &http.Client{
 			Transport: retry.NewTransport(transport),
 		}
@@ -305,6 +287,11 @@ func ensureTLSConfig(client *auth.Client) (*tls.Config, error) {
 		switch t := t.Base.(type) {
 		case *http.Transport:
 			transport = t
+		case *fallbackTransport:
+			switch t := t.Base.(type) {
+			case *http.Transport:
+				transport = t
+			}
 		}
 	}
 

pkg/registry/fallback.go

@@ -0,0 +1,71 @@
+/*
+Copyright The Helm Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package registry
+
+import (
+	"crypto/tls"
+	"net/http"
+	"sync/atomic"
+)
+
+type fallbackTransport struct {
+	Base      http.RoundTripper
+	forceHTTP atomic.Bool
+}
+
+func newTransport() *fallbackTransport {
+	type cloner[T any] interface {
+		Clone() T
+	}
+	// try to copy (clone) the http.DefaultTransport so any mutations we
+	// perform on it (e.g. TLS config) are not reflected globally
+	// follow https://github.com/golang/go/issues/39299 for a more elegant
+	// solution in the future
+	baseTransport := http.DefaultTransport
+	if t, ok := baseTransport.(cloner[*http.Transport]); ok {
+		baseTransport = t.Clone()
+	} else if t, ok := baseTransport.(cloner[http.RoundTripper]); ok {
+		// this branch will not be used with go 1.20, it was added
+		// optimistically to try to clone if the http.DefaultTransport
+		// implementation changes, still the Clone method in that case
+		// might not return http.RoundTripper...
+		baseTransport = t.Clone()
+	}
+
+	return &fallbackTransport{
+		Base: baseTransport,
+	}
+}
+
+// RoundTrip wraps base round trip with conditional insecure retry.
+func (t *fallbackTransport) RoundTrip(req *http.Request) (*http.Response, error) {
+	if ok := t.forceHTTP.Load(); ok {
+		req.URL.Scheme = "http"
+		return t.Base.RoundTrip(req)
+	}
+	resp, err := t.Base.RoundTrip(req)
+	if err != nil && req.URL.Scheme == "https" {
+		if tlsErr, ok := err.(tls.RecordHeaderError); ok {
+			if string(tlsErr.RecordHeader[:]) == "HTTP/" {
+				t.forceHTTP.Store(true)
+				req.URL.Scheme = "http"
+				return t.Base.RoundTrip(req)
+			}
+		}
+	}
+	return resp, err
+}