1 files changed, 122 insertions, 0 deletions
diff --git a/pkg/user/mount.go b/pkg/user/mount.go
new file mode 100644
index 0000000..c96e414
--- /dev/null
+++ b/pkg/user/mount.go
@@ -0,0 +1,122 @@
+// Copyright (c) 2022, Sylabs Inc. All rights reserved.
+// This software is licensed under a 3-clause BSD license. Please consult the
+// LICENSE file distributed with the sources of this project regarding your
+// rights to use or distribute this software.
+
+package user
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"os/exec"
+	"path/filepath"
+
+	"github.com/sylabs/sif/v2/pkg/sif"
+)
+
+// mountSquashFS mounts the SquashFS filesystem from path at offset into mountPath.
+func mountSquashFS(ctx context.Context, offset int64, path, mountPath string, mo mountOpts) error {
+	args := []string{
+		"-o", fmt.Sprintf("ro,offset=%d", offset),
+		filepath.Clean(path),
+		filepath.Clean(mountPath),
+	}
+	//nolint:gosec // note (gosec exclusion) - we require callers to be able to specify squashfuse not on PATH
+	cmd := exec.CommandContext(ctx, mo.squashfusePath, args...)
+	cmd.Stdout = mo.stdout
+	cmd.Stderr = mo.stderr
+
+	if err := cmd.Run(); err != nil {
+		return fmt.Errorf("failed to mount: %w", err)
+	}
+
+	return nil
+}
+
+// mountOpts accumulates mount options.
+type mountOpts struct {
+	stdout         io.Writer
+	stderr         io.Writer
+	squashfusePath string
+}
+
+// MountOpt are used to specify mount options.
+type MountOpt func(*mountOpts) error
+
+// OptMountStdout writes standard output to w.
+func OptMountStdout(w io.Writer) MountOpt {
+	return func(mo *mountOpts) error {
+		mo.stdout = w
+		return nil
+	}
+}
+
+// OptMountStderr writes standard error to w.
+func OptMountStderr(w io.Writer) MountOpt {
+	return func(mo *mountOpts) error {
+		mo.stderr = w
+		return nil
+	}
+}
+
+var errSquashfusePathInvalid = errors.New("squashfuse path must be relative or absolute")
+
+// OptMountSquashfusePath sets an explicit path to the squashfuse binary. The path must be an
+// absolute or relative path.
+func OptMountSquashfusePath(path string) MountOpt {
+	return func(mo *mountOpts) error {
+		if filepath.Base(path) == path {
+			return errSquashfusePathInvalid
+		}
+		mo.squashfusePath = path
+		return nil
+	}
+}
+
+var errUnsupportedFSType = errors.New("unrecognized filesystem type")
+
+// Mount mounts the primary system partition of the SIF file at path into mountPath.
+//
+// Mount may start one or more underlying processes. By default, stdout and stderr of these
+// processes is discarded. To modify this behavior, consider using OptMountStdout and/or
+// OptMountStderr.
+//
+// By default, Mount searches for a squashfuse binary in the directories named by the PATH
+// environment variable. To override this behavior, consider using OptMountSquashfusePath().
+func Mount(ctx context.Context, path, mountPath string, opts ...MountOpt) error {
+	mo := mountOpts{
+		squashfusePath: "squashfuse",
+	}
+
+	for _, opt := range opts {
+		if err := opt(&mo); err != nil {
+			return fmt.Errorf("%w", err)
+		}
+	}
+
+	f, err := sif.LoadContainerFromPath(path, sif.OptLoadWithFlag(os.O_RDONLY))
+	if err != nil {
+		return fmt.Errorf("failed to load image: %w", err)
+	}
+	defer func() { _ = f.UnloadContainer() }()
+
+	d, err := f.GetDescriptor(sif.WithPartitionType(sif.PartPrimSys))
+	if err != nil {
+		return fmt.Errorf("failed to get partition descriptor: %w", err)
+	}
+
+	fs, _, _, err := d.PartitionMetadata()
+	if err != nil {
+		return fmt.Errorf("failed to get partition metadata: %w", err)
+	}
+
+	switch fs {
+	case sif.FsSquash:
+		return mountSquashFS(ctx, d.Offset(), path, mountPath, mo)
+	default:
+		return errUnsupportedFSType
+	}
+}