Add flag enable-disk

* Adds `enable-disk` flag -> allows to explicitly enable disk, on by default but will turn into off by default from %"14.0"
* When `enable-disk=true` -> serve from either source.Type = file or zip, independently from API response (effectively no change from current behaviour)
* When `enable-disk=false` -> serve 500 if source.Type = file or source.Path.HasPrefix("file://")
* This change is completely independent from -domain-config-source

Changelog: added

4 files changed, 58 insertions, 16 deletions

diff --git a/internal/source/gitlab/factory.go b/internal/source/gitlab/factory.go
index b033a592..77ad63ed 100644
--- a/internal/source/gitlab/factory.go
+++ b/internal/source/gitlab/factory.go
@@ -1,6 +1,9 @@
 package gitlab
 
 import (
+	"errors"
+	"fmt"
+
 	log "github.com/sirupsen/logrus"
 
 	"gitlab.com/gitlab-org/gitlab-pages/internal/serving"
@@ -9,6 +12,10 @@ import (
 	"gitlab.com/gitlab-org/gitlab-pages/internal/source/gitlab/api"
 )
 
+var (
+	errDiskDisabled = errors.New("gitlab: disk access is disabled via enable-disk=false")
+)
+
 // fabricateLookupPath fabricates a serving LookupPath based on the API LookupPath
 // `size` argument is DEPRECATED, see
 // https://gitlab.com/gitlab-org/gitlab-pages/issues/272
@@ -25,14 +32,18 @@ func fabricateLookupPath(size int, lookup api.LookupPath) *serving.LookupPath {
 }
 
 // fabricateServing fabricates serving based on the GitLab API response
-func fabricateServing(lookup api.LookupPath) serving.Serving {
+func (g *Gitlab) fabricateServing(lookup api.LookupPath) (serving.Serving, error) {
 	source := lookup.Source
 
 	switch source.Type {
 	case "file":
-		return local.Instance()
+		if !g.enableDisk {
+			return nil, errDiskDisabled
+		}
+
+		return local.Instance(), nil
 	case "zip":
-		return zip.Instance()
+		return zip.Instance(), nil
 	case "serverless":
 		log.Errorf("attempted to fabricate serverless serving for project %d", lookup.ProjectID)
 
@@ -49,9 +60,5 @@ func fabricateServing(lookup api.LookupPath) serving.Serving {
 		// return serving
 	}
 
-	return defaultServing()
-}
-
-func defaultServing() serving.Serving {
-	return local.Instance()
+	return nil, fmt.Errorf("gitlab: unkown serving source type: %q", source.Type)
 }
diff --git a/internal/source/gitlab/factory_test.go b/internal/source/gitlab/factory_test.go
index 46740d35..43157a5a 100644
--- a/internal/source/gitlab/factory_test.go
+++ b/internal/source/gitlab/factory_test.go
@@ -1,6 +1,7 @@
 package gitlab
 
 import (
+	"fmt"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -32,15 +33,38 @@ func TestFabricateLookupPath(t *testing.T) {
 
 func TestFabricateServing(t *testing.T) {
 	t.Run("when lookup path requires disk serving", func(t *testing.T) {
+		g := Gitlab{
+			enableDisk: true,
+		}
+
 		lookup := api.LookupPath{
 			Prefix: "/",
 			Source: api.Source{Type: "file"},
 		}
+		srv, err := g.fabricateServing(lookup)
+		require.NoError(t, err)
+		require.IsType(t, &disk.Disk{}, srv)
+	})
+
+	t.Run("when lookup path requires disk serving but disk is disabled", func(t *testing.T) {
+		g := Gitlab{
+			enableDisk: false,
+		}
 
-		require.IsType(t, &disk.Disk{}, fabricateServing(lookup))
+		lookup := api.LookupPath{
+			Prefix: "/",
+			Source: api.Source{Type: "file"},
+		}
+		srv, err := g.fabricateServing(lookup)
+		require.EqualError(t, err, errDiskDisabled.Error())
+		require.Nil(t, srv)
 	})
 
 	t.Run("when lookup path requires serverless serving", func(t *testing.T) {
+		g := Gitlab{
+			enableDisk: true,
+		}
+
 		lookup := api.LookupPath{
 			Prefix: "/",
 			Source: api.Source{
@@ -58,8 +82,11 @@ func TestFabricateServing(t *testing.T) {
 			},
 		}
 
+		srv, err := g.fabricateServing(lookup)
+		require.EqualError(t, err, fmt.Sprintf("gitlab: unkown serving source type: %q", lookup.Source.Type))
+
 		// Serverless serving has been deprecated.
 		// require.IsType(t, &serverless.Serverless{}, fabricateServing(lookup))
-		require.IsType(t, &disk.Disk{}, fabricateServing(lookup))
+		require.Nil(t, srv)
 	})
 }
diff --git a/internal/source/gitlab/gitlab.go b/internal/source/gitlab/gitlab.go
index fdcbd88f..14788e1d 100644
--- a/internal/source/gitlab/gitlab.go
+++ b/internal/source/gitlab/gitlab.go
@@ -23,9 +23,11 @@ import (
 // Gitlab source represent a new domains configuration source. We fetch all the
 // information about domains from GitLab instance.
 type Gitlab struct {
-	client  api.Resolver
-	mu      sync.RWMutex
-	isReady bool
+	client           api.Resolver
+	mu               sync.RWMutex
+	isReady          bool
+	useLegacyStorage bool
+	enableDisk       bool
 }
 
 // New returns a new instance of gitlab domain source.
@@ -36,7 +38,8 @@ func New(cfg *config.GitLab) (*Gitlab, error) {
 	}
 
 	g := &Gitlab{
-		client: cache.NewCache(glClient, &cfg.Cache),
+		client:     cache.NewCache(glClient, &cfg.Cache),
+		enableDisk: cfg.EnableDisk,
 	}
 
 	go g.poll(backoff.DefaultInitialInterval, maxPollingTime)
@@ -92,8 +95,13 @@ func (g *Gitlab) Resolve(r *http.Request) (*serving.Request, error) {
 				subPath = strings.TrimPrefix(urlPath, lookup.Prefix)
 			}
 
+			srv, err := g.fabricateServing(lookup)
+			if err != nil {
+				return nil, err
+			}
+
 			return &serving.Request{
-				Serving:    fabricateServing(lookup),
+				Serving:    srv,
 				LookupPath: fabricateLookupPath(size, lookup),
 				SubPath:    subPath}, nil
 		}
diff --git a/internal/source/gitlab/gitlab_test.go b/internal/source/gitlab/gitlab_test.go
index bd6b2171..4a5f1a7b 100644
--- a/internal/source/gitlab/gitlab_test.go
+++ b/internal/source/gitlab/gitlab_test.go
@@ -43,7 +43,7 @@ func TestGetDomain(t *testing.T) {
 
 func TestResolve(t *testing.T) {
 	client := client.StubClient{File: "client/testdata/test.gitlab.io.json"}
-	source := Gitlab{client: client}
+	source := Gitlab{client: client, enableDisk: true}
 
 	t.Run("when requesting nested group project with root path", func(t *testing.T) {
 		target := "https://test.gitlab.io:443/my/pages/project/"