create db links if not exist for all configured repos

internal/cache/cache.go

@@ -6,6 +6,7 @@ import (
 	"net"
 	"net/http"
 	"os"
+	"path/filepath"
 	"sync"
 	"sync/atomic"
 	"time"
@@ -59,6 +60,10 @@ func NewCache(cacheRoot string, mirrorURLs []string, mirroredRepos []string) (*C
 		return nil, err
 	}
 
+	if err := checkSymLinks(cr, mirroredRepos); err != nil {
+		return nil, err
+	}
+
 	return &Cache{
 		cfg: cfg,
 		cr:  cr,
@@ -80,3 +85,21 @@ type UpstreamError struct {
 func (e *UpstreamError) Error() string {
 	return fmt.Sprintf("upstream returned %d", e.StatusCode)
 }
+
+func checkSymLinks(cr *os.Root, repos []string) error {
+	for _, repo := range repos {
+		dirPath := filepath.Join(repo, "os/x86_64")
+		if err := cr.MkdirAll(dirPath, 0750); err != nil {
+			return err
+		}
+		lnPath := filepath.Join(dirPath, repo+".db")
+		srcPath := filepath.Join(dirPath, repo+".db.tar.gz")
+		if _, err := cr.Lstat(lnPath); err == nil {
+			continue // link exists
+		}
+		if err := cr.Symlink(srcPath, lnPath); err != nil {
+			return err
+		}
+	}
+	return nil
+}

internal/cache/cache_test.go

@@ -7,6 +7,8 @@ import (
 	"io"
 	"net/http"
 	"net/http/httptest"
+	"os"
+	"path/filepath"
 	"testing"
 	"time"
 )
@@ -206,3 +208,28 @@ func TestFetchRetryNonExist(t *testing.T) {
 		t.Errorf("expected 404 got %d", upstreamErr.StatusCode)
 	}
 }
+
+func TestCreateSymlinks(t *testing.T) {
+	repos := []string{"core", "extra"}
+	tmp := t.TempDir()
+	cr, err := os.OpenRoot(tmp)
+	if err != nil {
+		t.Fatalf("unable to create tmp dir: %v", err)
+	}
+
+	if err := checkSymLinks(cr, repos); err != nil {
+		t.Fatalf("error creating links: %v", err)
+	}
+
+	for _, repo := range repos {
+		lnfile := filepath.Join(repo, "os/x86_64", repo+".db")
+		expected := lnfile + ".tar.gz"
+		lnval, err := cr.Readlink(lnfile)
+		if err != nil {
+			t.Errorf("%s has no link: %v", repo, err)
+		}
+		if lnval != expected {
+			t.Errorf("expected %s got %s", expected, lnval)
+		}
+	}
+}