loader: allow overwrite of URL hostname again

This adds back the support for overwriting the host name a chart is
downloaded from (again) using the `SOURCE_CONTROLLER_LOCALHOST`
environment variable.

Signed-off-by: Hidde Beydals <hidde@hhh.computer>

internal/loader/artifact_url.go

@@ -24,6 +24,8 @@ import (
 	"fmt"
 	"io"
 	"net/http"
+	"net/url"
+	"os"
 
 	"github.com/hashicorp/go-retryablehttp"
 	digestlib "github.com/opencontainers/go-digest"
@@ -32,6 +34,13 @@ import (
 	"helm.sh/helm/v3/pkg/chart/loader"
 )
 
+const (
+	// envSourceControllerLocalhost is the name of the environment variable
+	// used to override the hostname of the source-controller from which
+	// the chart is usually downloaded.
+	envSourceControllerLocalhost = "SOURCE_CONTROLLER_LOCALHOST"
+)
+
 var (
 	// ErrFileNotFound is an error type used to signal 404 HTTP status code responses.
 	ErrFileNotFound = errors.New("file not found")
@@ -45,6 +54,11 @@ var (
 // digest before loading the chart. It returns the loaded chart.Chart, or an
 // error. The error may be of type ErrIntegrity if the integrity check fails.
 func SecureLoadChartFromURL(client *retryablehttp.Client, URL, digest string) (*chart.Chart, error) {
+	URL, err := overwriteHostname(URL, os.Getenv(envSourceControllerLocalhost))
+	if err != nil {
+		return nil, err
+	}
+
 	req, err := retryablehttp.NewRequest(http.MethodGet, URL, nil)
 	if err != nil {
 		return nil, err
@@ -94,3 +108,18 @@ func copyAndVerify(digest string, reader io.Reader, writer io.Writer) error {
 	}
 	return nil
 }
+
+// overwriteHostname overwrites the hostname of the given URL with the given
+// hostname. If the hostname is empty, the URL is returned unmodified.
+func overwriteHostname(URL, hostname string) (string, error) {
+	if hostname == "" {
+		return URL, nil
+	}
+
+	u, err := url.Parse(URL)
+	if err != nil {
+		return "", fmt.Errorf("failed to parse URL to overwrite hostname: %w", err)
+	}
+	u.Host = hostname
+	return u.String(), nil
+}

internal/loader/artifact_url_test.go

@@ -23,6 +23,7 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"os"
+	"strings"
 	"testing"
 
 	"github.com/hashicorp/go-retryablehttp"
@@ -72,6 +73,19 @@ func TestSecureLoadChartFromURL(t *testing.T) {
 		g.Expect(got.Metadata.Version).To(Equal("0.1.0"))
 	})
 
+	t.Run("overwrites hostname", func(t *testing.T) {
+		g := NewWithT(t)
+
+		t.Setenv(envSourceControllerLocalhost, strings.TrimPrefix(server.URL, "http://"))
+		wrongHostnameURL := "http://invalid.com" + chartPath
+
+		got, err := SecureLoadChartFromURL(client, wrongHostnameURL, digest.String())
+		g.Expect(err).ToNot(HaveOccurred())
+		g.Expect(got).ToNot(BeNil())
+		g.Expect(got.Name()).To(Equal("chart"))
+		g.Expect(got.Metadata.Version).To(Equal("0.1.0"))
+	})
+
 	t.Run("error on chart data digest mismatch", func(t *testing.T) {
 		g := NewWithT(t)
 
@@ -162,3 +176,44 @@ func Test_copyAndVerify(t *testing.T) {
 		})
 	}
 }
+
+func Test_overwriteHostname(t *testing.T) {
+	tests := []struct {
+		name     string
+		URL      string
+		hostname string
+		want     string
+		wantErr  bool
+	}{
+		{
+			name:     "overwrite hostname",
+			URL:      "http://example.com",
+			hostname: "localhost",
+			want:     "http://localhost",
+		},
+		{
+			name:     "overwrite hostname with port",
+			URL:      "http://example.com",
+			hostname: "localhost:9090",
+			want:     "http://localhost:9090",
+		},
+		{
+			name:     "no hostname",
+			URL:      "http://example.com",
+			hostname: "",
+			want:     "http://example.com",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := overwriteHostname(tt.URL, tt.hostname)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("overwriteHostname() error = %v, wantErr %v", err, tt.wantErr)
+				return
+			}
+			if got != tt.want {
+				t.Errorf("overwriteHostname() got = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}