libotutil: Add ot_gpgme_ctx_tmp_home_dir()

Currently used for signature verification, will also be used for
importing GPG keys.

src/libotutil/ot-gpg-utils.c

@@ -22,6 +22,10 @@
 
 #include "ot-gpg-utils.h"
 
+#include <stdlib.h>
+
+#include "libglnx.h"
+
 void
 ot_gpgme_error_to_gio_error (gpgme_error_t   gpg_error,
                              GError        **error)
@@ -55,3 +59,82 @@ ot_gpgme_error_to_gio_error (gpgme_error_t   gpg_error,
                gpgme_strsource (gpg_error),
                gpgme_strerror (gpg_error));
 }
+
+gboolean
+ot_gpgme_ctx_tmp_home_dir (gpgme_ctx_t     gpgme_ctx,
+                           const char     *tmp_dir,
+                           char          **out_tmp_home_dir,
+                           GOutputStream **out_pubring_stream,
+                           GCancellable   *cancellable,
+                           GError        **error)
+{
+  g_autoptr(GFile) pubring_file = NULL;
+  g_autoptr(GOutputStream) target_stream = NULL;
+  g_autofree char *pubring_path = NULL;
+  g_autofree char *tmp_home_dir = NULL;
+  gpgme_error_t gpg_error;
+  gboolean ret = FALSE;
+
+  g_return_val_if_fail (gpgme_ctx != NULL, FALSE);
+
+  /* GPGME has no API for using multiple keyrings (aka, gpg --keyring),
+   * so we create a temporary directory and tell GPGME to use it as the
+   * home directory.  Then (optionally) create a pubring.gpg file there
+   * and hand the caller an open output stream to concatenate necessary
+   * keyring files. */
+
+  if (tmp_dir == NULL)
+    tmp_dir = g_get_tmp_dir ();
+
+  tmp_home_dir = g_build_filename (tmp_dir, "ostree-gpg-XXXXXX", NULL);
+
+  if (mkdtemp (tmp_home_dir) == NULL)
+    {
+      glnx_set_error_from_errno (error);
+      goto out;
+    }
+
+  /* Not documented, but gpgme_ctx_set_engine_info() accepts NULL for
+   * the executable file name, which leaves the old setting unchanged. */
+  gpg_error = gpgme_ctx_set_engine_info (gpgme_ctx,
+                                         GPGME_PROTOCOL_OpenPGP,
+                                         NULL, tmp_home_dir);
+  if (gpg_error != GPG_ERR_NO_ERROR)
+    {
+      ot_gpgme_error_to_gio_error (gpg_error, error);
+      goto out;
+    }
+
+  if (out_pubring_stream != NULL)
+    {
+      GFileOutputStream *pubring_stream;
+      glnx_unref_object GFile *pubring_file = NULL;
+      g_autofree char *pubring_path = NULL;
+
+      pubring_path = g_build_filename (tmp_home_dir, "pubring.gpg", NULL);
+      pubring_file = g_file_new_for_path (pubring_path);
+
+      pubring_stream = g_file_create (pubring_file,
+                                      G_FILE_CREATE_NONE,
+                                      cancellable, error);
+      if (pubring_stream == NULL)
+        goto out;
+
+      /* Sneaky cast from GFileOutputStream to GOutputStream. */
+      *out_pubring_stream = g_steal_pointer (&pubring_stream);
+    }
+
+  if (out_tmp_home_dir != NULL)
+    *out_tmp_home_dir = g_steal_pointer (&tmp_home_dir);
+
+  ret = TRUE;
+
+out:
+  if (!ret)
+    {
+      /* Clean up our mess on error. */
+      (void) glnx_shutil_rm_rf_at (AT_FDCWD, tmp_home_dir, NULL, NULL);
+    }
+
+  return ret;
+}

src/libotutil/ot-gpg-utils.h

@@ -27,4 +27,11 @@ G_BEGIN_DECLS
 
 void ot_gpgme_error_to_gio_error (gpgme_error_t gpg_error, GError **error);
 
+gboolean ot_gpgme_ctx_tmp_home_dir (gpgme_ctx_t     gpgme_ctx,
+                                    const char     *tmp_dir,
+                                    char          **out_tmp_home_dir,
+                                    GOutputStream **out_pubring_stream,
+                                    GCancellable   *cancellable,
+                                    GError        **error);
+
 G_END_DECLS