libtracker-sparql: Add private XML serializer task

This object takes care of serializing cursors into
application/sparql-results+xml format.

4 files changed, 299 insertions, 1 deletions

diff --git a/docs/reference/libtracker-sparql/meson.build b/docs/reference/libtracker-sparql/meson.build
index d5817657c..cc9c793a9 100644
--- a/docs/reference/libtracker-sparql/meson.build
+++ b/docs/reference/libtracker-sparql/meson.build
@@ -39,6 +39,7 @@ private_headers = [
     'tracker-private.h',
     'tracker-serializer.h',
     'tracker-serializer-json.h',
+    'tracker-serializer-xml.h',
     'direct',
     'bus',
     'remote',
diff --git a/src/libtracker-sparql/meson.build b/src/libtracker-sparql/meson.build
index 55248ac38..0e6064e67 100644
--- a/src/libtracker-sparql/meson.build
+++ b/src/libtracker-sparql/meson.build
@@ -27,6 +27,7 @@ libtracker_sparql_c_sources = files(
     'tracker-statement.c',
     'tracker-serializer.c',
     'tracker-serializer-json.c',
+    'tracker-serializer-xml.c',
     'tracker-uri.c',
     'tracker-utils.c',
     'tracker-version.c',
@@ -51,7 +52,7 @@ libtracker_sparql_c_public_headers = files(
 libtracker_sparql_intermediate = static_library('tracker-sparql-intermediate',
     enum_types,
     libtracker_sparql_c_sources,
-    dependencies: [tracker_common_dep, json_glib],
+    dependencies: [tracker_common_dep, json_glib, libxml2],
     gnu_symbol_visibility: 'hidden',
 )
 
diff --git a/src/libtracker-sparql/tracker-serializer-xml.c b/src/libtracker-sparql/tracker-serializer-xml.c
new file mode 100644
index 000000000..a28d48c32
--- /dev/null
+++ b/src/libtracker-sparql/tracker-serializer-xml.c
@@ -0,0 +1,260 @@
+/*
+ * Copyright (C) 2020, Red Hat, Inc
+ *
+ * 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 2.1 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., 51 Franklin Street, Fifth Floor,
+ * Boston, MA  02110-1301, USA.
+ *
+ * Author: Carlos Garnacho <carlosg@gnome.org>
+ */
+
+/* Serialization of cursors to the XML format defined at:
+ * https://www.w3.org/TR/2013/REC-rdf-sparql-XMLres-20130321/
+ */
+
+#include "config.h"
+
+#include "tracker-serializer-xml.h"
+
+#include <libxml/xmlwriter.h>
+
+struct _TrackerSerializerXml
+{
+	TrackerSerializer parent_instance;
+	xmlBufferPtr buffer;
+	xmlTextWriterPtr writer;
+	GPtrArray *vars;
+	gssize current_pos;
+
+	guint stream_closed : 1;
+	guint cursor_started : 1;
+	guint cursor_finished : 1;
+	guint head_printed : 1;
+};
+
+G_DEFINE_TYPE (TrackerSerializerXml, tracker_serializer_xml,
+               TRACKER_TYPE_SERIALIZER)
+
+static void
+tracker_serializer_xml_finalize (GObject *object)
+{
+	g_input_stream_close (G_INPUT_STREAM (object), NULL, NULL);
+
+	G_OBJECT_CLASS (tracker_serializer_xml_parent_class)->finalize (object);
+}
+
+static gboolean
+serialize_up_to_position (TrackerSerializerXml  *serializer_xml,
+                          gsize                  pos,
+                          GCancellable          *cancellable,
+                          GError               **error)
+{
+	TrackerSparqlCursor *cursor;
+	GError *inner_error = NULL;
+	gint i;
+
+	if (!serializer_xml->buffer)
+		serializer_xml->buffer = xmlBufferCreate ();
+	if (!serializer_xml->writer)
+		serializer_xml->writer = xmlNewTextWriterMemory (serializer_xml->buffer, 0);
+	if (!serializer_xml->vars)
+		serializer_xml->vars = g_ptr_array_new_with_free_func (g_free);
+
+	cursor = tracker_serializer_get_cursor (TRACKER_SERIALIZER (serializer_xml));
+
+	if (!serializer_xml->head_printed) {
+		xmlTextWriterStartDocument (serializer_xml->writer, "1.0", "UTF-8", NULL);
+		xmlTextWriterStartElement (serializer_xml->writer, "sparql");
+
+		xmlTextWriterStartElement (serializer_xml->writer, "head");
+
+		for (i = 0; i < tracker_sparql_cursor_get_n_columns (cursor); i++) {
+			const gchar *var;
+
+			var = tracker_sparql_cursor_get_variable_name (cursor, i);
+			xmlTextWriterStartElement (serializer_xml->writer, "variable");
+
+			if (var && *var) {
+				g_ptr_array_add (serializer_xml->vars,
+				                 g_strdup (var));
+			} else {
+				g_ptr_array_add (serializer_xml->vars,
+				                 g_strdup_printf ("var%d", i + 1));
+			}
+
+			xmlTextWriterWriteFormatAttribute (serializer_xml->writer,
+			                                   "name",
+			                                   "%s",
+			                                   (gchar *) g_ptr_array_index (serializer_xml->vars, i));
+			xmlTextWriterEndElement (serializer_xml->writer);
+		}
+
+		xmlTextWriterEndElement (serializer_xml->writer);
+		xmlTextWriterStartElement (serializer_xml->writer, "results");
+		serializer_xml->head_printed = TRUE;
+	}
+
+	while (!serializer_xml->cursor_finished &&
+	       xmlBufferLength (serializer_xml->buffer) < pos) {
+		if (!tracker_sparql_cursor_next (cursor, cancellable, &inner_error)) {
+			if (inner_error) {
+				g_propagate_error (error, inner_error);
+				return FALSE;
+			} else {
+				xmlTextWriterEndElement (serializer_xml->writer);
+				xmlTextWriterEndElement (serializer_xml->writer);
+				xmlTextWriterEndDocument (serializer_xml->writer);
+				serializer_xml->cursor_finished = TRUE;
+				break;
+			}
+		} else {
+			serializer_xml->cursor_started = TRUE;
+		}
+
+		xmlTextWriterStartElement (serializer_xml->writer, "result");
+
+		for (i = 0; i < tracker_sparql_cursor_get_n_columns (cursor); i++) {
+			const gchar *var, *str, *type, *datatype = NULL;
+
+			if (tracker_sparql_cursor_get_value_type (cursor, i) == TRACKER_SPARQL_VALUE_TYPE_UNBOUND)
+				continue;
+
+			var = g_ptr_array_index (serializer_xml->vars, i);
+
+			xmlTextWriterStartElement (serializer_xml->writer, "binding");
+			xmlTextWriterWriteFormatAttribute (serializer_xml->writer,
+			                                   "name",
+			                                   "%s",
+			                                   var);
+
+			switch (tracker_sparql_cursor_get_value_type (cursor, i)) {
+			case TRACKER_SPARQL_VALUE_TYPE_URI:
+				type = "uri";
+				break;
+			case TRACKER_SPARQL_VALUE_TYPE_STRING:
+				type = "literal";
+				datatype = TRACKER_PREFIX_XSD "string";
+				break;
+			case TRACKER_SPARQL_VALUE_TYPE_INTEGER:
+			case TRACKER_SPARQL_VALUE_TYPE_BOOLEAN:
+				type = "literal";
+				datatype = TRACKER_PREFIX_XSD "integer";
+				break;
+			case TRACKER_SPARQL_VALUE_TYPE_DOUBLE:
+				type = "literal";
+				datatype = TRACKER_PREFIX_XSD "double";
+				break;
+			case TRACKER_SPARQL_VALUE_TYPE_DATETIME:
+				type = "literal";
+				datatype = TRACKER_PREFIX_XSD "dateTime";
+				break;
+			case TRACKER_SPARQL_VALUE_TYPE_BLANK_NODE:
+				type = "bnode";
+				break;
+			default:
+				g_warn_if_reached ();
+				break;
+			}
+
+			xmlTextWriterStartElement (serializer_xml->writer, type);
+
+			if (datatype) {
+				xmlTextWriterWriteFormatAttribute (serializer_xml->writer,
+				                                   "datatype",
+				                                   "%s",
+				                                   datatype);
+			}
+
+			str = tracker_sparql_cursor_get_string (cursor, i, NULL);
+
+			if (str) {
+				xmlTextWriterWriteRaw (serializer_xml->writer, str);
+			}
+
+			xmlTextWriterEndElement (serializer_xml->writer);
+			xmlTextWriterEndElement (serializer_xml->writer);
+		}
+
+		xmlTextWriterEndElement (serializer_xml->writer);
+	}
+
+	return TRUE;
+}
+
+static gssize
+tracker_serializer_xml_read (GInputStream  *istream,
+                             gpointer       buffer,
+                             gsize          count,
+                             GCancellable  *cancellable,
+                             GError       **error)
+{
+	TrackerSerializerXml *serializer_xml = TRACKER_SERIALIZER_XML (istream);
+	gsize bytes_unflushed, bytes_copied;
+	const xmlChar *xml_buf;
+
+	if (serializer_xml->stream_closed ||
+	    (serializer_xml->cursor_finished &&
+	     serializer_xml->current_pos == xmlBufferLength (serializer_xml->buffer)))
+		return 0;
+
+	if (!serialize_up_to_position (serializer_xml,
+	                               serializer_xml->current_pos + count,
+	                               cancellable,
+	                               error))
+		return -1;
+
+	bytes_unflushed =
+		xmlBufferLength (serializer_xml->buffer) - serializer_xml->current_pos;
+	bytes_copied = MIN (count, bytes_unflushed);
+
+	xml_buf = xmlBufferContent (serializer_xml->buffer);
+
+	memcpy (buffer,
+	        &xml_buf[serializer_xml->current_pos],
+	        bytes_copied);
+	serializer_xml->current_pos += bytes_copied;
+
+	return bytes_copied;
+}
+
+static gboolean
+tracker_serializer_xml_close (GInputStream  *istream,
+                              GCancellable  *cancellable,
+                              GError       **error)
+{
+	TrackerSerializerXml *serializer_xml = TRACKER_SERIALIZER_XML (istream);
+
+	serializer_xml->stream_closed = TRUE;
+	g_clear_pointer (&serializer_xml->buffer, xmlBufferFree);
+	g_clear_pointer (&serializer_xml->writer, xmlFreeTextWriter);
+
+	return TRUE;
+}
+
+static void
+tracker_serializer_xml_class_init (TrackerSerializerXmlClass *klass)
+{
+	GObjectClass *object_class = G_OBJECT_CLASS (klass);
+	GInputStreamClass *istream_class = G_INPUT_STREAM_CLASS (klass);
+
+	object_class->finalize = tracker_serializer_xml_finalize;
+
+	istream_class->read_fn = tracker_serializer_xml_read;
+	istream_class->close_fn = tracker_serializer_xml_close;
+}
+
+static void
+tracker_serializer_xml_init (TrackerSerializerXml *serializer)
+{
+}
diff --git a/src/libtracker-sparql/tracker-serializer-xml.h b/src/libtracker-sparql/tracker-serializer-xml.h
new file mode 100644
index 000000000..d94bf4eb6
--- /dev/null
+++ b/src/libtracker-sparql/tracker-serializer-xml.h
@@ -0,0 +1,36 @@
+/*
+ * Copyright (C) 2020, Red Hat, Inc
+ *
+ * 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 2.1 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., 51 Franklin Street, Fifth Floor,
+ * Boston, MA  02110-1301, USA.
+ *
+ * Author: Carlos Garnacho <carlosg@gnome.org>
+ */
+
+#ifndef TRACKER_SERIALIZER_XML_H
+#define TRACKER_SERIALIZER_XML_H
+
+#include <libtracker-sparql/tracker-sparql.h>
+#include <libtracker-sparql/tracker-private.h>
+#include <libtracker-sparql/tracker-serializer.h>
+
+#define TRACKER_TYPE_SERIALIZER_XML (tracker_serializer_xml_get_type())
+
+G_DECLARE_FINAL_TYPE (TrackerSerializerXml,
+                      tracker_serializer_xml,
+                      TRACKER, SERIALIZER_XML,
+                      TrackerSerializer);
+
+#endif /* TRACKER_SERIALIZER_XML_H */