[tracker/wip/carlosg/sparql1.1: 51/145] libtracker-data: Add "service" virtual table

[Carlos Garnacho <carlosg src gnome org>]

commit 6d605789cfe4241705b8f2e103d294a0de5f6a3c
Author: Carlos Garnacho <carlosg gnome org>
Date:   Thu May 30 11:58:46 2019 +0200

    libtracker-data: Add "service" virtual table
    
    This virtual table will be used as the base for SERVICE{} syntax,
    and allows querying remote sparql endpoints as if it were part of
    the local data.
    
    This virtual table takes 3 parameters:
    - service: the uri of the remote service to query
    - query: the sparql query to issue on that remote service
    - silent: whether errors are fatal or not

 src/libtracker-data/meson.build            |   1 +
 src/libtracker-data/tracker-vtab-service.c | 348 +++++++++++++++++++++++++++++
 src/libtracker-data/tracker-vtab-service.h |  30 +++
 3 files changed, 379 insertions(+)
---
diff --git a/src/libtracker-data/meson.build b/src/libtracker-data/meson.build
index c59fdb6ad..4f40c1fcc 100644
--- a/src/libtracker-data/meson.build
+++ b/src/libtracker-data/meson.build
@@ -57,6 +57,7 @@ libtracker_data = library('tracker-data',
     'tracker-sparql-types.c',
     'tracker-sparql.c',
     'tracker-uuid.c',
+    'tracker-vtab-service.c',
     'tracker-vtab-triples.c',
     tracker_common_enum_header,
     tracker_data_enums[0],
diff --git a/src/libtracker-data/tracker-vtab-service.c b/src/libtracker-data/tracker-vtab-service.c
new file mode 100644
index 000000000..4a5cda2f2
--- /dev/null
+++ b/src/libtracker-data/tracker-vtab-service.c
@@ -0,0 +1,348 @@
+/*
+ * Copyright (C) 2019, 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>
+ */
+#include "config.h"
+
+#include "tracker-vtab-service.h"
+#include <libtracker-sparql/tracker-sparql.h>
+
+#define N_VIRTUAL_COLUMNS 100
+#define COL_SERVICE 101
+#define COL_QUERY 102
+#define COL_SILENT 103
+
+typedef struct {
+       sqlite3 *db;
+} TrackerServiceModule;
+
+typedef struct {
+       struct sqlite3_vtab parent;
+       TrackerServiceModule *module;
+       GList *cursors;
+} TrackerServiceVTab;
+
+typedef struct {
+       struct sqlite3_vtab_cursor parent;
+       TrackerServiceVTab *vtab;
+       TrackerSparqlConnection *conn;
+       TrackerSparqlCursor *sparql_cursor;
+       gchar *service;
+       gchar *query;
+       guint64 rowid;
+       guint silent   : 1;
+       guint finished : 1;
+} TrackerServiceCursor;
+
+typedef struct {
+       int column;
+       int op;
+} ConstraintData;
+
+static void
+tracker_service_module_free (gpointer data)
+{
+       TrackerServiceModule *module = data;
+
+       g_free (module);
+}
+
+static void
+tracker_service_vtab_free (gpointer data)
+{
+       TrackerServiceVTab *vtab = data;
+
+       g_list_free (vtab->cursors);
+       g_free (vtab);
+}
+
+static void
+tracker_service_cursor_free (gpointer data)
+{
+       TrackerServiceCursor *cursor = data;
+
+       g_free (cursor->service);
+       g_free (cursor->query);
+       g_clear_object (&cursor->conn);
+       g_clear_object (&cursor->sparql_cursor);
+
+       g_free (cursor);
+}
+
+static int
+service_create (sqlite3            *db,
+               gpointer            data,
+               int                 argc,
+               const char *const  *argv,
+               sqlite3_vtab      **vtab_out,
+               char              **err_out)
+{
+       TrackerServiceModule *module = data;
+       TrackerServiceVTab *vtab;
+       GString *str;
+       gint i, rc;
+
+       vtab = g_new0 (TrackerServiceVTab, 1);
+       vtab->module = module;
+
+       str = g_string_new ("CREATE TABLE x(\n");
+
+       for (i = 0; i <= N_VIRTUAL_COLUMNS; i++)
+               g_string_append_printf (str, "col%d TEXT, ", i);
+
+       g_string_append (str,
+                        "service TEXT HIDDEN, "
+                        "query TEXT HIDDEN, "
+                        "silent INTEGER HIDDEN)");
+       rc = sqlite3_declare_vtab (module->db, str->str);
+       g_string_free (str, TRUE);
+
+       if (rc == SQLITE_OK)
+               *vtab_out = &vtab->parent;
+       else
+               g_free (vtab);
+
+       return rc;
+}
+
+static int
+service_best_index (sqlite3_vtab       *vtab,
+                   sqlite3_index_info *info)
+{
+       int i, argv_idx = 1;
+       ConstraintData *data;
+
+       data = sqlite3_malloc (sizeof (ConstraintData) * info->nConstraint);
+       bzero (data, sizeof (ConstraintData) * info->nConstraint);
+
+       for (i = 0; i < info->nConstraint; i++) {
+               if (!info->aConstraint[i].usable)
+                       continue;
+
+               if (info->aConstraint[i].iColumn != COL_SERVICE &&
+                   info->aConstraint[i].iColumn != COL_QUERY &&
+                   info->aConstraint[i].iColumn != COL_SILENT) {
+                       info->aConstraintUsage[i].argvIndex = -1;
+                       continue;
+               }
+
+               if (info->aConstraint[i].op != SQLITE_INDEX_CONSTRAINT_EQ)
+                       goto error;
+
+               data[i].column = info->aConstraint[i].iColumn;
+               data[i].op = info->aConstraint[i].op;
+
+               info->aConstraintUsage[i].argvIndex = argv_idx;
+               info->aConstraintUsage[i].omit = FALSE;
+               argv_idx++;
+       }
+
+       info->orderByConsumed = FALSE;
+       info->idxStr = (char *) data;
+       info->needToFreeIdxStr = TRUE;
+
+       return SQLITE_OK;
+
+error:
+       sqlite3_free (data);
+       return SQLITE_ERROR;
+}
+
+static int
+service_destroy (sqlite3_vtab *vtab)
+{
+       tracker_service_vtab_free (vtab);
+       return SQLITE_OK;
+}
+
+static int
+service_open (sqlite3_vtab         *vtab_sqlite,
+             sqlite3_vtab_cursor **cursor_ret)
+{
+       TrackerServiceVTab *vtab = (TrackerServiceVTab *) vtab_sqlite;
+       TrackerServiceCursor *cursor;
+
+       cursor = g_new0 (TrackerServiceCursor, 1);
+       cursor->vtab = vtab;
+
+       vtab->cursors = g_list_prepend (vtab->cursors, cursor);
+       *cursor_ret = (sqlite3_vtab_cursor *) cursor;
+
+       return SQLITE_OK;
+}
+
+static int
+service_close (sqlite3_vtab_cursor *vtab_cursor)
+{
+       TrackerServiceCursor *cursor = (TrackerServiceCursor *) vtab_cursor;
+       TrackerServiceVTab *vtab = cursor->vtab;
+
+       vtab->cursors = g_list_remove (vtab->cursors, cursor);
+       tracker_service_cursor_free (cursor);
+       return SQLITE_OK;
+}
+
+static int
+service_filter (sqlite3_vtab_cursor  *vtab_cursor,
+               int                   idx,
+               const char           *idx_str,
+               int                   argc,
+               sqlite3_value       **argv)
+{
+       TrackerServiceCursor *cursor = (TrackerServiceCursor *) vtab_cursor;
+       const ConstraintData *constraints = (const ConstraintData *) idx_str;
+       GError *error = NULL;
+       gint i;
+
+       cursor->finished = FALSE;
+       cursor->rowid = 0;
+
+       for (i = 0; i < argc; i++) {
+               if (constraints[i].column == COL_SERVICE)
+                       cursor->service = g_strdup (sqlite3_value_text (argv[i]));
+               if (constraints[i].column == COL_QUERY)
+                       cursor->query = g_strdup (sqlite3_value_text (argv[i]));
+               if (constraints[i].column == COL_SILENT)
+                       cursor->silent = !!sqlite3_value_int (argv[i]);
+       }
+
+       if (!cursor->service || !cursor->query)
+               return SQLITE_ERROR;
+
+       cursor->conn = tracker_sparql_connection_remote_new (cursor->service);
+       cursor->sparql_cursor = tracker_sparql_connection_query (cursor->conn,
+                                                                cursor->query,
+                                                                NULL, &error);
+       if (error)
+               goto fail;
+
+       cursor->finished =
+               !tracker_sparql_cursor_next (cursor->sparql_cursor, NULL, &error);
+
+       if (error)
+               goto fail;
+
+       return SQLITE_OK;
+
+fail:
+       if (cursor->silent) {
+               cursor->finished = TRUE;
+               g_error_free (error);
+               return SQLITE_OK;
+       } else {
+               g_warning ("Could not create remote cursor: %s\n", error->message);
+               g_error_free (error);
+               return SQLITE_ERROR;
+       }
+}
+
+static int
+service_next (sqlite3_vtab_cursor *vtab_cursor)
+{
+       TrackerServiceCursor *cursor = (TrackerServiceCursor *) vtab_cursor;
+
+       if (!cursor->sparql_cursor)
+               return SQLITE_ERROR;
+
+       cursor->finished =
+               !tracker_sparql_cursor_next (cursor->sparql_cursor, NULL, NULL);
+
+       cursor->rowid++;
+       return SQLITE_OK;
+}
+
+static int
+service_eof (sqlite3_vtab_cursor *vtab_cursor)
+{
+       TrackerServiceCursor *cursor = (TrackerServiceCursor *) vtab_cursor;
+
+       return cursor->finished;
+}
+
+static int
+service_column (sqlite3_vtab_cursor *vtab_cursor,
+               sqlite3_context     *context,
+               int                  n_col)
+{
+       TrackerServiceCursor *cursor = (TrackerServiceCursor *) vtab_cursor;
+       const gchar *str;
+
+       if (n_col == COL_SERVICE) {
+               sqlite3_result_text (context, cursor->service, -1, NULL);
+       } else if (n_col == COL_QUERY) {
+               sqlite3_result_text (context, cursor->query, -1, NULL);
+       } else if (n_col == COL_SILENT) {
+               sqlite3_result_int (context, cursor->silent);
+       } else if (n_col < tracker_sparql_cursor_get_n_columns (cursor->sparql_cursor)) {
+               /* FIXME: Handle other types better */
+               str = tracker_sparql_cursor_get_string (cursor->sparql_cursor, n_col, NULL);
+               sqlite3_result_text (context, g_strdup (str), -1, g_free);
+       } else {
+               sqlite3_result_null (context);
+       }
+
+       return SQLITE_OK;
+}
+
+static int
+service_rowid (sqlite3_vtab_cursor *vtab_cursor,
+              sqlite_int64        *rowid_out)
+{
+       TrackerServiceCursor *cursor = (TrackerServiceCursor *) vtab_cursor;
+
+       *rowid_out = cursor->rowid;
+       return SQLITE_OK;
+}
+
+void
+tracker_vtab_service_init (sqlite3           *db,
+                          TrackerOntologies *ontologies)
+{
+       TrackerServiceModule *module;
+       static const sqlite3_module service_module = {
+               2, /* version */
+               service_create,
+               service_create,
+               service_best_index,
+               service_destroy,
+               service_destroy,
+               service_open,
+               service_close,
+               service_filter,
+               service_next,
+               service_eof,
+               service_column,
+               service_rowid,
+               NULL, /* update */
+               NULL, /* begin */
+               NULL, /* sync */
+               NULL, /* commit */
+               NULL, /* rollback */
+               NULL, /* find function */
+               NULL, /* rename */
+               NULL, /* savepoint */
+               NULL, /* release */
+               NULL, /* rollback to */
+       };
+
+       module = g_new0 (TrackerServiceModule, 1);
+       module->db = db;
+       sqlite3_create_module_v2 (db, "tracker_service", &service_module,
+                                 module, tracker_service_module_free);
+}
diff --git a/src/libtracker-data/tracker-vtab-service.h b/src/libtracker-data/tracker-vtab-service.h
new file mode 100644
index 000000000..9b85f29c7
--- /dev/null
+++ b/src/libtracker-data/tracker-vtab-service.h
@@ -0,0 +1,30 @@
+/*
+ * Copyright (C) 2019, 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>
+ */
+#include <sqlite3.h>
+#include "tracker-ontologies.h"
+
+#ifndef __TRACKER_VTAB_SERVICE_H__
+#define __TRACKER_VTAB_SERVICE_H__
+
+void tracker_vtab_service_init (sqlite3           *db,
+                               TrackerOntologies *ontologies);
+
+#endif /* __TRACKER_VTAB_SERVICE_H__ */