lib: Use a common helper function to compare checksums

So we get a consistent error message; came up in a PR review.

Closes: #1277
Approved by: jlebon

src/libostree/ostree-core-private.h

@@ -141,6 +141,12 @@ _ostree_validate_bareuseronly_mode_finfo (GFileInfo  *finfo,
   return _ostree_validate_bareuseronly_mode (content_mode, checksum, error);
 }
 
+gboolean
+_ostree_compare_object_checksum (OstreeObjectType objtype,
+                                 const char      *expected,
+                                 const char      *actual,
+                                 GError         **error);
+
 gboolean
 _ostree_parse_delta_name (const char  *delta_name,
                           char        **out_from,

src/libostree/ostree-core.c

@@ -1004,6 +1004,22 @@ ostree_checksum_file_async_finish (GFile          *f,
   return TRUE;
 }
 
+/* Common helper to compare checksums for an object, so we have a consistent
+ * error message.
+ */
+gboolean
+_ostree_compare_object_checksum (OstreeObjectType objtype,
+                                 const char      *expected,
+                                 const char      *actual,
+                                 GError         **error)
+{
+  if (!g_str_equal (expected, actual))
+    return glnx_throw (error, "Corrupted %s object; checksum expected='%s' actual='%s'",
+                       ostree_object_type_to_string (objtype),
+                       expected, actual);
+  return TRUE;
+}
+
 /**
  * ostree_create_directory_metadata:
  * @dir_info: a #GFileInfo containing directory information

src/libostree/ostree-repo-commit.c

@@ -685,10 +685,12 @@ write_content_object (OstreeRepo         *self,
   else
     {
       actual_checksum = actual_checksum_owned = ot_checksum_instream_get_string (checksum_input);
-      if (expected_checksum && strcmp (actual_checksum, expected_checksum) != 0)
-        return glnx_throw (error, "Corrupted %s object %s (actual checksum is %s)",
-                           ostree_object_type_to_string (OSTREE_OBJECT_TYPE_FILE),
-                           expected_checksum, actual_checksum);
+      if (expected_checksum)
+        {
+          if (!_ostree_compare_object_checksum (OSTREE_OBJECT_TYPE_FILE, expected_checksum, actual_checksum,
+                                                error))
+            return FALSE;
+        }
     }
 
   g_assert (actual_checksum != NULL); /* Pacify static analysis */
@@ -954,10 +956,11 @@ write_metadata_object (OstreeRepo         *self,
           return TRUE;
         }
 
-      if (expected_checksum && strcmp (actual_checksum, expected_checksum) != 0)
-        return glnx_throw (error, "Corrupted %s object %s (actual checksum is %s)",
-                           ostree_object_type_to_string (objtype),
-                           expected_checksum, actual_checksum);
+      if (expected_checksum)
+        {
+          if (!_ostree_compare_object_checksum (objtype, expected_checksum, actual_checksum, error))
+            return FALSE;
+        }
     }
 
   /* Ok, checksum is known, let's get the data */

src/libostree/ostree-repo-pull.c

@@ -1005,13 +1005,8 @@ content_fetch_on_write_complete (GObject        *object,
   checksum_obj = ostree_object_to_string (checksum, objtype);
   g_debug ("write of %s complete", checksum_obj);
 
-  if (strcmp (checksum, expected_checksum) != 0)
-    {
-      g_set_error (error, G_IO_ERROR, G_IO_ERROR_FAILED,
-                   "Corrupted content object; checksum expected='%s' actual='%s'",
-                   expected_checksum, checksum);
-      goto out;
-    }
+  if (!_ostree_compare_object_checksum (objtype, expected_checksum, checksum, error))
+    goto out;
 
   pull_data->n_fetched_content++;
   /* Was this a delta fallback? */
@@ -1256,13 +1251,8 @@ meta_fetch_on_complete (GObject           *object,
           char hexdigest[OSTREE_SHA256_STRING_LEN+1];
           ot_checksum_get_hexdigest (&hasher, hexdigest, sizeof (hexdigest));
 
-          if (strcmp (checksum, hexdigest) != 0)
-            {
-              (void) glnx_throw (error, "Corrupted %s object %s (actual checksum is %s)",
-                                 ostree_object_type_to_string (objtype),
-                                 checksum, hexdigest);
-              goto out;
-            }
+          if (!_ostree_compare_object_checksum (objtype, checksum, hexdigest, error))
+            goto out;
 
           /* Do GPG verification. `detached_data` may be NULL if no detached
            * metadata was found during pull; that's handled by