lib: Move bareuseronly verification into commit/core

Conceptually `ostree-repo-pull.c` should be be written using
just public APIs; we theoretically support building without HTTP
for people who just want to use the object store portion and
do their own fetching.

We have some nontrivial behaviors in the pull layer though; one
of those is the "bareuseronly" verification.  Make a new internal
API that accepts flags, move it into `commit.c`.  This
is prep for further work in changing object import to support
reflinks.

Closes: #1193
Approved by: jlebon

src/libostree/ostree-repo-commit.c

@@ -262,10 +262,8 @@ commit_loose_regfile_object (OstreeRepo        *self,
     }
   else if (self->mode == OSTREE_REPO_MODE_BARE_USER_ONLY)
     {
-      guint32 invalid_modebits = (mode & ~S_IFMT) & ~0775;
-      if (invalid_modebits > 0)
-        return glnx_throw (error, "Invalid mode 0%04o with bits 0%04o in bare-user-only repository",
-                           mode, invalid_modebits);
+      if (!_ostree_validate_bareuseronly_mode (mode, checksum, error))
+        return FALSE;
 
       if (!glnx_fchmod (tmpf->fd, mode, error))
         return FALSE;
@@ -3171,6 +3169,249 @@ G_DEFINE_BOXED_TYPE(OstreeRepoCommitModifier, ostree_repo_commit_modifier,
                     ostree_repo_commit_modifier_ref,
                     ostree_repo_commit_modifier_unref);
 
+/* Special case between bare-user and bare-user-only,
+ * mostly for https://github.com/flatpak/flatpak/issues/845
+ * see below for any more comments.
+ */
+static gboolean
+import_is_bareuser_only_conversion (OstreeRepo *src_repo,
+                                    OstreeRepo *dest_repo,
+                                    OstreeObjectType objtype)
+{
+  return src_repo->mode == OSTREE_REPO_MODE_BARE_USER
+    && dest_repo->mode == OSTREE_REPO_MODE_BARE_USER_ONLY
+    && objtype == OSTREE_OBJECT_TYPE_FILE;
+}
+
+/* Returns TRUE if we can potentially just call link() to copy an object. */
+static gboolean
+import_via_hardlink_is_possible (OstreeRepo *src_repo,
+                                 OstreeRepo *dest_repo,
+                                 OstreeObjectType objtype)
+{
+  /* We need the ability to make hardlinks */
+  if (src_repo->owner_uid != dest_repo->owner_uid)
+    return FALSE;
+  /* Equal modes are always compatible */
+  if (src_repo->mode == dest_repo->mode)
+    return TRUE;
+  /* Metadata is identical between all modes */
+  if (OSTREE_OBJECT_TYPE_IS_META (objtype))
+    return TRUE;
+  /* And now a special case between bare-user and bare-user-only,
+   * mostly for https://github.com/flatpak/flatpak/issues/845
+   */
+  if (import_is_bareuser_only_conversion (src_repo, dest_repo, objtype))
+    return TRUE;
+  return FALSE;
+}
+
+/* Copy the detached metadata for commit @checksum from @source repo
+ * to @self.
+ */
+static gboolean
+copy_detached_metadata (OstreeRepo    *self,
+                        OstreeRepo    *source,
+                        const char   *checksum,
+                        GCancellable  *cancellable,
+                        GError        **error)
+{
+  g_autoptr(GVariant) detached_meta = NULL;
+  if (!ostree_repo_read_commit_detached_metadata (source,
+                                                  checksum, &detached_meta,
+                                                  cancellable, error))
+    return FALSE;
+
+  if (detached_meta)
+    {
+      if (!ostree_repo_write_commit_detached_metadata (self,
+                                                       checksum, detached_meta,
+                                                       cancellable, error))
+        return FALSE;
+    }
+
+  return TRUE;
+}
+
+/* Try to import an object by just calling linkat(); returns
+ * a value in @out_was_supported if we were able to do it or not.
+ */
+static gboolean
+import_one_object_link (OstreeRepo    *self,
+                        OstreeRepo    *source,
+                        const char   *checksum,
+                        OstreeObjectType objtype,
+                        gboolean       *out_was_supported,
+                        GCancellable  *cancellable,
+                        GError        **error)
+{
+  const char *errprefix = glnx_strjoina ("Importing ", checksum, ".",
+                                         ostree_object_type_to_string (objtype));
+  GLNX_AUTO_PREFIX_ERROR (errprefix, error);
+  char loose_path_buf[_OSTREE_LOOSE_PATH_MAX];
+  _ostree_loose_path (loose_path_buf, checksum, objtype, self->mode);
+
+  /* Hardlinking between bare-user → bare-user-only is only possible for regular
+   * files, *not* symlinks, which in bare-user are stored as regular files.  At
+   * this point we need to parse the file to see the difference.
+   */
+  if (import_is_bareuser_only_conversion (source, self, objtype))
+    {
+      struct stat stbuf;
+
+      if (!_ostree_repo_load_file_bare (source, checksum, NULL, &stbuf,
+                                        NULL, NULL, cancellable, error))
+        return FALSE;
+
+      if (S_ISREG (stbuf.st_mode))
+        {
+          /* This is OK, we'll drop through and try a hardlink */
+        }
+      else if (S_ISLNK (stbuf.st_mode))
+        {
+          /* NOTE early return */
+          *out_was_supported = FALSE;
+          return TRUE;
+        }
+      else
+        g_assert_not_reached ();
+    }
+
+  if (!_ostree_repo_ensure_loose_objdir_at (self->objects_dir_fd, loose_path_buf, cancellable, error))
+    return FALSE;
+
+  *out_was_supported = TRUE;
+  if (linkat (source->objects_dir_fd, loose_path_buf, self->objects_dir_fd, loose_path_buf, 0) != 0)
+    {
+      if (errno == EEXIST)
+        return TRUE;
+      else if (errno == EMLINK || errno == EXDEV || errno == EPERM)
+        {
+          /* EMLINK, EXDEV and EPERM shouldn't be fatal; we just can't do the
+           * optimization of hardlinking instead of copying.
+           */
+          *out_was_supported = FALSE;
+          return TRUE;
+        }
+      else
+        return glnx_throw_errno_prefix (error, "linkat");
+    }
+
+  if (objtype == OSTREE_OBJECT_TYPE_COMMIT)
+    {
+      if (!copy_detached_metadata (self, source, checksum, cancellable, error))
+        return FALSE;
+    }
+
+  return TRUE;
+}
+
+/* A version of ostree_repo_import_object_from_with_trust()
+ * with flags; may make this public API later.
+ */
+gboolean
+_ostree_repo_import_object (OstreeRepo           *self,
+                            OstreeRepo           *source,
+                            OstreeObjectType      objtype,
+                            const char           *checksum,
+                            OstreeRepoImportFlags flags,
+                            GCancellable         *cancellable,
+                            GError              **error)
+{
+  const gboolean trusted = (flags & _OSTREE_REPO_IMPORT_FLAGS_TRUSTED) > 0;
+  /* Implements OSTREE_REPO_PULL_FLAGS_BAREUSERONLY_FILES which was designed for flatpak */
+  const gboolean verify_bareuseronly = (flags & _OSTREE_REPO_IMPORT_FLAGS_VERIFY_BAREUSERONLY) > 0;
+
+  /* If we need to do bareuseronly verification, let's dispense with that
+   * first so we don't complicate the rest of the code below.
+   */
+  if (verify_bareuseronly && !OSTREE_OBJECT_TYPE_IS_META (objtype))
+    {
+      g_autoptr(GFileInfo) src_finfo = NULL;
+      if (!ostree_repo_load_file (source, checksum,
+                                  NULL, &src_finfo, NULL,
+                                  cancellable, error))
+        return FALSE;
+
+      if (!_ostree_validate_bareuseronly_mode_finfo (src_finfo, checksum, error))
+        return FALSE;
+    }
+
+   /* We try to import via hardlink. If the remote is explicitly not trusted
+   * (i.e.) their checksums may be incorrect, we skip that. Also, we require the
+   * repository modes to match, as well as the owner uid (since we need to be
+   * able to make hardlinks).
+   */
+  if (trusted && import_via_hardlink_is_possible (source, self, objtype))
+    {
+      gboolean hardlink_was_supported = FALSE;
+
+      if (!import_one_object_link (self, source, checksum, objtype,
+                                   &hardlink_was_supported,
+                                   cancellable, error))
+        return FALSE;
+
+      /* If we hardlinked, we're done! */
+      if (hardlink_was_supported)
+        return TRUE;
+    }
+
+  /* The copy path */
+
+  /* First, do we have the object already? */
+  gboolean has_object;
+  if (!ostree_repo_has_object (self, objtype, checksum, &has_object,
+                               cancellable, error))
+    return FALSE;
+  /* If we have it, we're done */
+  if (has_object)
+    return TRUE;
+
+  if (OSTREE_OBJECT_TYPE_IS_META (objtype))
+    {
+      /* Metadata object */
+      g_autoptr(GVariant) variant = NULL;
+
+      if (objtype == OSTREE_OBJECT_TYPE_COMMIT)
+        {
+          /* FIXME - cleanup detached metadata if copy below fails */
+          if (!copy_detached_metadata (self, source, checksum, cancellable, error))
+            return FALSE;
+        }
+
+      if (!ostree_repo_load_variant (source, objtype, checksum,
+                                     &variant, error))
+        return FALSE;
+
+      g_autofree guchar *real_csum = NULL;
+      if (!ostree_repo_write_metadata (self, objtype,
+                                       checksum, variant,
+                                       trusted ? NULL : &real_csum,
+                                       cancellable, error))
+        return FALSE;
+    }
+  else
+    {
+      /* Content object */
+      guint64 length;
+      g_autoptr(GInputStream) object_stream = NULL;
+
+      if (!ostree_repo_load_object_stream (source, objtype, checksum,
+                                           &object_stream, &length,
+                                           cancellable, error))
+        return FALSE;
+
+      g_autofree guchar *real_csum = NULL;
+      if (!ostree_repo_write_content (self, checksum,
+                                      object_stream, length,
+                                      trusted ? NULL : &real_csum,
+                                      cancellable, error))
+        return FALSE;
+    }
+
+  return TRUE;
+}
+
 static OstreeRepoTransactionStats *
 ostree_repo_transaction_stats_copy (OstreeRepoTransactionStats *stats)
 {