Add initial JSONPath implementation

JSONPath is a JSON query syntax similar to what XPath does for XML;
using JSONPath it's possible to address a specific node (or set of
nodes) inside a JSON document.

The JsonPath class is a simple implementation of part of the JSONPath
proposal, as formalised by Stefan Gössner here:

  http://goessner.net/articles/JsonPath/

The covered operators are:

  • root, or '$';
  • child, both using the dot-notation and the bracket notation;
  • recursive descent, or '..';
  • subscript, or '[]';
  • set, or '[,]';
  • slice, or '[start:end:step]'.

The only missing operators are the filter, or '?()' and the script,
or '()', because implementing a JavaScript interpreter inside JSON-GLib
is not one of my greatest aspirations. It should be possible, though,
to parse and evaluate simple arithmetic conditions, in the future.

The JsonPath methods are pretty straightforward: a JsonPath instance
should be created and used to compile an expression; the compilation
might result in a syntax error or not. Then, the JsonPath instance can
be used to match any JSON tree. Like the other JSONPath implementations,
JsonPath returns a JSON array of matching nodes.

A simple, one-off static method called json_path_query() is also
provided; the method wraps the JsonPath creation, the expression
compilation, and the matching, as well as disposing the JsonPath
instance once done.

For the time being, only positive testing is provided; negative testing
for the expression compilation will follow.

2 files changed, 144 insertions, 0 deletions

diff --git a/json-glib/tests/Makefile.am b/json-glib/tests/Makefile.am
index fea656d..5e21412 100644
--- a/json-glib/tests/Makefile.am
+++ b/json-glib/tests/Makefile.am
@@ -26,6 +26,7 @@ TEST_PROGS += \
 	builder-test		\
 	reader-test		\
 	gvariant-test		\
+	path-test		\
 	boxed			\
 	serialize-simple	\
 	serialize-complex	\
diff --git a/json-glib/tests/path-test.c b/json-glib/tests/path-test.c
new file mode 100644
index 0000000..3a5e41c
--- /dev/null
+++ b/json-glib/tests/path-test.c
@@ -0,0 +1,143 @@
+#include <string.h>
+#include <glib.h>
+#include <json-glib/json-glib.h>
+
+static const char *test_json =
+"{ \"store\": {"
+"    \"book\": [ "
+"      { \"category\": \"reference\","
+"        \"author\": \"Nigel Rees\","
+"        \"title\": \"Sayings of the Century\","
+"        \"price\": \"8.95\""
+"      },"
+"      { \"category\": \"fiction\","
+"        \"author\": \"Evelyn Waugh\","
+"        \"title\": \"Sword of Honour\","
+"        \"price\": \"12.99\""
+"      },"
+"      { \"category\": \"fiction\","
+"        \"author\": \"Herman Melville\","
+"        \"title\": \"Moby Dick\","
+"        \"isbn\": \"0-553-21311-3\","
+"        \"price\": \"8.99\""
+"      },"
+"      { \"category\": \"fiction\","
+"        \"author\": \"J. R. R. Tolkien\","
+"        \"title\": \"The Lord of the Rings\","
+"        \"isbn\": \"0-395-19395-8\","
+"        \"price\": \"22.99\""
+"      }"
+"    ],"
+"    \"bicycle\": {"
+"      \"color\": \"red\","
+"      \"price\": \"19.95\""
+"    }"
+"  }"
+"}";
+
+static const char *test_expressions[] = {
+  "$.store.book[0].title",
+  "$['store']['book'][0]['title']",
+  "$.store.book[*].author",
+  "$..author",
+  "$.store.*",
+  "$.store..price",
+  "$..book[2]",
+  "$..book[-1:]",
+  "$..book[0,1]",
+  "$..book[:2]",
+};
+
+static const char *test_results[] = {
+  "[\"Sayings of the Century\"]",
+  "[\"Sayings of the Century\"]",
+  "[\"Nigel Rees\",\"Evelyn Waugh\",\"Herman Melville\",\"J. R. R. Tolkien\"]",
+  "[\"Nigel Rees\",\"Evelyn Waugh\",\"Herman Melville\",\"J. R. R. Tolkien\"]",
+  NULL,
+  "[\"8.95\",\"12.99\",\"8.99\",\"22.99\",\"19.95\"]",
+  "[{\"category\":\"fiction\",\"author\":\"Herman Melville\",\"title\":\"Moby Dick\",\"isbn\":\"0-553-21311-3\",\"price\":\"8.99\"}]",
+  "[{\"category\":\"fiction\",\"author\":\"J. R. R. Tolkien\",\"title\":\"The Lord of the Rings\",\"isbn\":\"0-395-19395-8\",\"price\":\"22.99\"}]",
+  "[{\"category\":\"reference\",\"author\":\"Nigel Rees\",\"title\":\"Sayings of the Century\",\"price\":\"8.95\"},{\"category\":\"fiction\",\"author\":\"Evelyn Waugh\",\"title\":\"Sword of Honour\",\"price\":\"12.99\"}]",
+  "[{\"category\":\"reference\",\"author\":\"Nigel Rees\",\"title\":\"Sayings of the Century\",\"price\":\"8.95\"},{\"category\":\"fiction\",\"author\":\"Evelyn Waugh\",\"title\":\"Sword of Honour\",\"price\":\"12.99\"}]",
+};
+
+static void
+test_expression (void)
+{
+  JsonPath *path = json_path_new ();
+  int i;
+
+  for (i = 0; i < G_N_ELEMENTS (test_expressions); i++)
+    {
+      const char *expr = test_expressions[i];
+      GError *error = NULL;
+
+      g_assert (json_path_compile (path, expr, &error));
+      g_assert_no_error (error);
+    }
+
+  g_object_unref (path);
+}
+
+static void
+test_match (void)
+{
+  JsonParser *parser = json_parser_new ();
+  JsonGenerator *gen = json_generator_new ();
+  JsonPath *path = json_path_new ();
+  JsonNode *root;
+  int i;
+
+  json_parser_load_from_data (parser, test_json, -1, NULL);
+  root = json_parser_get_root (parser);
+
+  for (i = 0; i < G_N_ELEMENTS (test_expressions); i++)
+    {
+      const char *expr = test_expressions[i];
+      const char *res = test_results[i];
+      JsonNode *matches;
+      char *str;
+
+      if (res == NULL || *res == '\0')
+        continue;
+
+      g_assert (json_path_compile (path, expr, NULL));
+
+      matches = json_path_match (path, root);
+      g_assert (JSON_NODE_HOLDS_ARRAY (matches));
+
+      json_generator_set_root (gen, matches);
+      str = json_generator_to_data (gen, NULL);
+
+      if (g_test_verbose ())
+        {
+          g_print ("* expr[%02d]: '%s' =>\n"
+                   "- result:   %s\n"
+                   "- expected: %s\n",
+                   i, expr, str, res);
+        }
+
+      g_assert_cmpstr (str, ==, res);
+
+      g_free (str);
+      json_node_free (matches);
+    }
+
+  g_object_unref (parser);
+  g_object_unref (path);
+  g_object_unref (gen);
+}
+
+int
+main (int   argc,
+      char *argv[])
+{
+  g_type_init ();
+  g_test_init (&argc, &argv, NULL);
+  g_test_bug_base ("http://bugzilla.gnome.org/show_bug.cgi?id=");
+
+  g_test_add_func ("/path/expressions", test_expression);
+  g_test_add_func ("/path/match", test_match);
+
+  return g_test_run ();
+}