Added configurable CDN endpoint (#214)

* added configurable cdn endpoint

pkg/config/env/cdn.go

@@ -0,0 +1,23 @@
+package env
+
+import (
+	"net/url"
+
+	"github.com/gobuffalo/envy"
+)
+
+// CDNEndpointWithDefault returns CDN endpoint if set
+// if not it should default to clouds default blob storage endpoint e.g
+func CDNEndpointWithDefault(value *url.URL) *url.URL {
+	rawURI, err := envy.MustGet("CDN_ENDPOINT")
+	if err != nil {
+		return value
+	}
+
+	uri, err := url.Parse(rawURI)
+	if err != nil {
+		return value
+	}
+
+	return uri
+}

pkg/storage/azurecdn/storage.go

@@ -37,7 +37,7 @@ func New(accountName, accountKey string) (*Storage, error) {
 //
 //	<meta name="go-import" content="gomods.com/athens mod BaseURL()">
 func (s Storage) BaseURL() *url.URL {
-	return s.accountURL
+	return env.CDNEndpointWithDefault(s.accountURL)
 }
 
 // Save implements the (github.com/gomods/athens/pkg/storage).Saver interface.

pkg/storage/gcp/saver.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"io"
 	"log"
+	"net/url"
 	"time"
 
 	"cloud.google.com/go/storage"
@@ -18,7 +19,8 @@ import (
 // Storage implements the Saver interface
 // (./pkg/storage).Saver
 type Storage struct {
-	bucket *storage.BucketHandle
+	bucket  *storage.BucketHandle
+	baseURI *url.URL
 }
 
 // New returns a new Storage instance authenticated using the provided
@@ -37,7 +39,23 @@ func New(ctx context.Context, cred option.ClientOption) (*Storage, error) {
 		return nil, err
 	}
 	bkt := client.Bucket(bucketname)
-	return &Storage{bucket: bkt}, nil
+
+	u, err := url.Parse(fmt.Sprintf("https://storage.googleapis.com/%s", bucketname))
+	if err != nil {
+		return nil, err
+	}
+
+	return &Storage{bucket: bkt, baseURI: u}, nil
+}
+
+// BaseURL returns the base URL that stores all modules. It can be used
+// in the "meta" tag redirect response to vgo.
+//
+// For example:
+//
+//	<meta name="go-import" content="gomods.com/athens mod BaseURL()">
+func (s *Storage) BaseURL() *url.URL {
+	return env.CDNEndpointWithDefault(s.baseURI)
 }
 
 // Save uploads the module .mod, .zip and .info files for a given version.

pkg/storage/s3/storage.go

@@ -73,7 +73,7 @@ func NewWithClient(bucketName string, client s3iface.S3API) (*Storage, error) {
 //
 //	<meta name="go-import" content="gomods.com/athens mod BaseURL()">
 func (s Storage) BaseURL() *url.URL {
-	return s.baseURI
+	return env.CDNEndpointWithDefault(s.baseURI)
 }
 
 // Save implements the (github.com/gomods/athens/pkg/storage).Saver interface.