[libgdata] documents: Fix error handling for unknown formats for document downloads

[Philip Withnall <pwithnall src gnome org>]

commit dc9d85d323a740216e4525d82f1f43239a310f04
Author: Philip Withnall <philip tecnocode co uk>
Date:   Sun Dec 20 19:19:02 2015 +0000

    documents: Fix error handling for unknown formats for document downloads
    
    https://bugzilla.gnome.org/show_bug.cgi?id=759180

 .../services/documents/gdata-documents-document.c  |   13 ++++++++++++-
 1 files changed, 12 insertions(+), 1 deletions(-)
---
diff --git a/gdata/services/documents/gdata-documents-document.c 
b/gdata/services/documents/gdata-documents-document.c
index efaeb2a..dbd825e 100644
--- a/gdata/services/documents/gdata-documents-document.c
+++ b/gdata/services/documents/gdata-documents-document.c
@@ -355,6 +355,8 @@ gdata_documents_document_new (const gchar *id)
  * #GInputStream operations on the #GDataDownloadStream will not cancel the entire download; merely the read 
or close operation in question. See the
  * #GDataDownloadStream:cancellable for more details.
  *
+ * If the given @export_format is unrecognised or not supported for this document, 
%GDATA_SERVICE_ERROR_NOT_FOUND will be returned.
+ *
  * If @service isn't authenticated, a %GDATA_SERVICE_ERROR_AUTHENTICATION_REQUIRED will be returned.
  *
  * If there is an error getting the document, a %GDATA_SERVICE_ERROR_PROTOCOL_ERROR error will be returned.
@@ -393,6 +395,13 @@ gdata_documents_document_download (GDataDocumentsDocument *self, GDataDocumentsS
 
        /* Get the download URI and create a stream for it */
        download_uri = gdata_documents_document_get_download_uri (self, export_format);
+
+       if (download_uri == NULL) {
+               g_set_error (error, GDATA_SERVICE_ERROR, GDATA_SERVICE_ERROR_NOT_FOUND,
+                            _("Unknown or unsupported document export format ‘%s’."), export_format);
+               return NULL;
+       }
+
        download_stream = GDATA_DOWNLOAD_STREAM (gdata_download_stream_new (GDATA_SERVICE (service), domain, 
download_uri, cancellable));
        g_free (download_uri);
 
@@ -411,7 +420,9 @@ gdata_documents_document_download (GDataDocumentsDocument *self, GDataDocumentsS
  * @export_format should be the file extension of the desired output format for the document, from the list 
accepted by Google Documents. For example:
  * %GDATA_DOCUMENTS_PRESENTATION_PDF, %GDATA_DOCUMENTS_SPREADSHEET_ODS or %GDATA_DOCUMENTS_TEXT_ODT.
  *
- * Return value: the download URI; free with g_free()
+ * If the @export_format is not recognised or not supported for this document, %NULL is returned.
+ *
+ * Return value: (nullable): the download URI, or %NULL; free with g_free()
  *
  * Since: 0.7.0
  **/