repo: Add ostree_repo_write_regfile

This API is push rather than pull, which makes it much more
suitable to use cases like parsing a tar file from external
code.

Now, we have a large mess in this area internally because
the original file writing code was pull based, but static
deltas hit the same problem of wanting a push API, so I added
this special `OstreeRepoBareContent` just for writing regular
files from a push API.

Eventually...I'd like to deprecate the pull based API,
and rework things so that for regular files the push API
is the default, and then `write_content_object()` would
be split up into archive/bare cases.

In this world the `ostree_repo_write_content()` API would
then need to hackily bridge pull to push and it'd be
less efficient.

Anyways for now due to this bifurcation, this API only
works on non-archive repositories, but that's fine for
now because that's what I want for the `ostree-ext-container`
bits.

src/libostree/ostree-content-writer.c

@@ -0,0 +1,144 @@
+/* 
+ * SPDX-License-Identifier: LGPL-2.0+
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General
+ * Public License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place, Suite 330,
+ * Boston, MA 02111-1307, USA.
+ */
+
+#include "config.h"
+
+#include "ostree-content-writer.h"
+#include "ostree-repo-private.h"
+#include "ostree-autocleanups.h"
+
+struct _OstreeContentWriter
+{
+  GOutputStream parent_instance;
+
+  OstreeRepo *repo;
+  OstreeRepoBareContent output;
+};
+
+G_DEFINE_TYPE (OstreeContentWriter, ostree_content_writer, G_TYPE_OUTPUT_STREAM)
+
+static void     ostree_content_writer_finalize     (GObject *object);
+static gssize   ostree_content_writer_write         (GOutputStream         *stream,
+                                                     const void                 *buffer,
+                                                     gsize                 count,
+                                                     GCancellable         *cancellable,
+                                                     GError              **error);
+static gboolean ostree_content_writer_close        (GOutputStream         *stream,
+                                                    GCancellable         *cancellable,
+                                                    GError              **error);
+
+static void
+ostree_content_writer_class_init (OstreeContentWriterClass *klass)
+{
+  GObjectClass *gobject_class = G_OBJECT_CLASS (klass);
+  GOutputStreamClass *stream_class = G_OUTPUT_STREAM_CLASS (klass);
+  
+  gobject_class->finalize     = ostree_content_writer_finalize;
+
+  stream_class->write_fn = ostree_content_writer_write;
+  stream_class->close_fn = ostree_content_writer_close;
+}
+
+static void
+ostree_content_writer_finalize (GObject *object)
+{
+  OstreeContentWriter *stream;
+
+  stream = (OstreeContentWriter*)(object);
+
+  g_clear_object (&stream->repo);
+  _ostree_repo_bare_content_cleanup (&stream->output);
+
+  G_OBJECT_CLASS (ostree_content_writer_parent_class)->finalize (object);
+}
+
+static void
+ostree_content_writer_init (OstreeContentWriter *self)
+{
+  self->output.initialized = FALSE;
+ }
+
+OstreeContentWriter *
+_ostree_content_writer_new (OstreeRepo           *repo,
+                           const char            *checksum,
+                           guint                  uid,
+                           guint                  gid,
+                           guint                  mode,
+                           guint64                content_len,
+                           GVariant              *xattrs,
+                           GError               **error)
+{
+  g_autoptr(OstreeContentWriter) stream = g_object_new (OSTREE_TYPE_CONTENT_WRITER, NULL);
+  stream->repo = g_object_ref (repo);
+  if (!_ostree_repo_bare_content_open (stream->repo, checksum, content_len, uid, gid, mode, xattrs,
+                                       &stream->output, NULL, error))
+    return NULL;
+  return g_steal_pointer (&stream);
+}
+
+static gssize
+ostree_content_writer_write (GOutputStream  *stream,
+                             const void    *buffer,
+                             gsize          count,
+                             GCancellable  *cancellable,
+                             GError       **error)
+{
+  OstreeContentWriter *self = (OstreeContentWriter*) stream;
+
+  if (g_cancellable_set_error_if_cancelled (cancellable, error))
+    return -1;
+
+  if (!_ostree_repo_bare_content_write (self->repo, &self->output,
+                                        buffer, count, cancellable, error))
+    return -1;
+  return count;
+}
+
+static gboolean
+ostree_content_writer_close (GOutputStream        *stream,
+                             GCancellable         *cancellable,
+                             GError              **error)
+{
+  /* We don't expect people to invoke close() - they need to call finish()
+   * to get the checksum.  We'll clean up in finalize anyways if need be.
+   */
+  return TRUE;
+}
+
+/**
+ * ostree_content_writer_finish:
+ * @self: Writer
+ * @cancellable: Cancellable
+ * @error: Error
+ *
+ * Complete the object write and return the checksum.
+ * Returns: (transfer full): Checksum, or %NULL on error
+ */
+char *
+ostree_content_writer_finish (OstreeContentWriter  *self,
+                              GCancellable         *cancellable,
+                              GError              **error)
+{
+  char actual_checksum[OSTREE_SHA256_STRING_LEN+1];
+  if (!_ostree_repo_bare_content_commit (self->repo, &self->output, actual_checksum,
+                                         sizeof (actual_checksum), cancellable, error))
+    return NULL;
+
+  return g_strdup (actual_checksum);
+}