Add a json_set_serializer() function to allow the string output of a json_object to be customized.

.gitignore

@@ -35,6 +35,7 @@
 /tests/test_cast
 /tests/test_null
 /tests/test_printbuf
+/tests/test_set_serializer
 /Debug
 /Release
 *.lo

json_object.c

@@ -46,6 +46,13 @@ const char *json_hex_chars = "0123456789abcdefABCDEF";
 static void json_object_generic_delete(struct json_object* jso);
 static struct json_object* json_object_new(enum json_type o_type);
 
+static json_object_to_json_string_fn json_object_object_to_json_string;
+static json_object_to_json_string_fn json_object_boolean_to_json_string;
+static json_object_to_json_string_fn json_object_int_to_json_string;
+static json_object_to_json_string_fn json_object_double_to_json_string;
+static json_object_to_json_string_fn json_object_string_to_json_string;
+static json_object_to_json_string_fn json_object_array_to_json_string;
+
 
 /* ref count debugging */
 
@@ -134,10 +141,16 @@ extern struct json_object* json_object_get(struct json_object *jso)
 
 extern void json_object_put(struct json_object *jso)
 {
-  if(jso) {
-    jso->_ref_count--;
-    if(!jso->_ref_count) jso->_delete(jso);
-  }
+	if(jso)
+	{
+		jso->_ref_count--;
+		if(!jso->_ref_count)
+		{
+			if (jso->_user_delete)
+				jso->_user_delete(jso, jso->_userdata);
+			jso->_delete(jso);
+		}
+	}
 }
 
 
@@ -187,6 +200,57 @@ enum json_type json_object_get_type(struct json_object *jso)
   return jso->o_type;
 }
 
+/* set a custom conversion to string */
+
+void json_object_set_serializer(json_object *jso,
+	json_object_to_json_string_fn to_string_func,
+	void *userdata,
+	json_object_delete_fn *user_delete)
+{
+	// First, clean up any previously existing user info
+	if (jso->_user_delete)
+	{
+		jso->_user_delete(jso, jso->_userdata);
+	}
+	jso->_userdata = NULL;
+	jso->_user_delete = NULL;
+
+	if (to_string_func == NULL)
+	{
+		// Reset to the standard serialization function
+		switch(jso->o_type)
+		{
+		case json_type_null:
+			jso->_to_json_string = NULL;
+			break;
+		case json_type_boolean:
+			jso->_to_json_string = &json_object_boolean_to_json_string;
+			break;
+		case json_type_double:
+			jso->_to_json_string = &json_object_double_to_json_string;
+			break;
+		case json_type_int:
+			jso->_to_json_string = &json_object_int_to_json_string;
+			break;
+		case json_type_object:
+			jso->_to_json_string = &json_object_object_to_json_string;
+			break;
+		case json_type_array:
+			jso->_to_json_string = &json_object_array_to_json_string;
+			break;
+		case json_type_string:
+			jso->_to_json_string = &json_object_string_to_json_string;
+			break;
+		}
+		return;
+	}
+
+	jso->_to_json_string = to_string_func;
+	jso->_userdata = userdata;
+	jso->_user_delete = user_delete;
+}
+
+
 /* extended conversion to string */
 
 const char* json_object_to_json_string_ext(struct json_object *jso, int flags)

json_object.h

@@ -70,6 +70,19 @@ typedef struct json_object json_object;
 typedef struct json_object_iter json_object_iter;
 typedef struct json_tokener json_tokener;
 
+/**
+ * Type of custom user delete functions.  See json_object_set_serializer.
+ */
+typedef void (json_object_delete_fn)(struct json_object *jso, void *userdata);
+
+/**
+ * Type of a custom serialization function.  See json_object_set_serializer.
+ */
+typedef int (json_object_to_json_string_fn)(struct json_object *jso,
+						struct printbuf *pb,
+						int level,
+						int flags);
+
 /* supported object types */
 
 typedef enum json_type {
@@ -149,6 +162,38 @@ extern const char* json_object_to_json_string(struct json_object *obj);
 extern const char* json_object_to_json_string_ext(struct json_object *obj, int
 flags);
 
+/**
+ * Set a custom serialization function to be used when this particular object
+ * is converted to a string by json_object_to_json_string.
+ *
+ * If a custom serializer is already set on this object, any existing 
+ * user_delete function is called before the new one is set.
+ *
+ * If to_string_func is NULL, the other parameters are ignored
+ * and the default behaviour is reset.
+ *
+ * The userdata parameter is optional and may be passed as NULL.  If provided,
+ * it is passed to to_string_func as-is.  This parameter may be NULL even
+ * if user_delete is non-NULL.
+ *
+ * The user_delete parameter is optional and may be passed as NULL, even if
+ * the userdata parameter is non-NULL.  It will be called just before the
+ * json_object is deleted, after it's reference count goes to zero
+ * (see json_object_put()).
+ * If this is not provided, it is up to the caller to free the userdata at
+ * an appropriate time. (i.e. after the json_object is deleted)
+ *
+ * @param jso the object to customize
+ * @param to_string_func the custom serialization function
+ * @param userdata an optional opaque cookie
+ * @param user_delete an optional function from freeing userdata
+ */
+void json_object_set_serializer(json_object *jso,
+	json_object_to_json_string_fn to_string_func,
+	void *userdata,
+	json_object_delete_fn *user_delete);
+
+
 
 /* object type methods */
 

json_object_private.h

@@ -16,16 +16,12 @@
 extern "C" {
 #endif
 
-typedef void (json_object_delete_fn)(struct json_object *o);
-typedef int (json_object_to_json_string_fn)(struct json_object *o,
-						struct printbuf *pb,
-						int level,
-						int flags);
+typedef void (json_object_private_delete_fn)(struct json_object *o);
 
 struct json_object
 {
   enum json_type o_type;
-  json_object_delete_fn *_delete;
+  json_object_private_delete_fn *_delete;
   json_object_to_json_string_fn *_to_json_string;
   int _ref_count;
   struct printbuf *_pb;
@@ -40,6 +36,8 @@ struct json_object
         int len;
     } c_string;
   } o;
+  json_object_delete_fn *_user_delete;
+  void *_userdata;
 };
 
 #ifdef __cplusplus

tests/Makefile.am

@@ -42,6 +42,10 @@ TESTS+= test_printbuf.test
 check_PROGRAMS+=test_printbuf
 test_printbuf_LDADD = $(LIBJSON_LA)
 
+TESTS+= test_set_serializer.test
+check_PROGRAMS += test_set_serializer
+test_set_serializer_LDADD = $(LIBJSON_LA)
+
 EXTRA_DIST=
 EXTRA_DIST += $(TESTS)
 

tests/test_set_serializer.c

@@ -0,0 +1,71 @@
+#include <assert.h>
+#include <stdio.h>
+#include <string.h>
+
+#include "json.h"
+#include "printbuf.h"
+
+struct myinfo {
+	int value;
+};
+
+static int freeit_was_called = 0;
+static void freeit(json_object *jso, void *userdata)
+{
+	struct myinfo *info = userdata;
+	printf("freeit, value=%d\n", info->value);
+	// Don't actually free anything here, the userdata is stack allocated.
+	freeit_was_called = 1;
+}
+static int custom_serializer(struct json_object *o,
+					struct printbuf *pb,
+					int level,
+					int flags)
+{
+	sprintbuf(pb, "Custom Output");
+	return 0;
+}
+
+int main(int argc, char **argv)
+{
+	json_object *my_object;
+
+	MC_SET_DEBUG(1);
+
+	printf("Test setting, then resetting a custom serializer:\n");
+	my_object = json_object_new_object();
+	json_object_object_add(my_object, "abc", json_object_new_int(12));
+	json_object_object_add(my_object, "foo", json_object_new_string("bar"));
+
+	printf("my_object.to_string(standard)=%s\n", json_object_to_json_string(my_object));
+
+	struct myinfo userdata = { .value = 123 };
+	json_object_set_serializer(my_object, custom_serializer, &userdata, freeit);
+
+	printf("my_object.to_string(custom serializer)=%s\n", json_object_to_json_string(my_object));
+
+	printf("Next line of output should be from the custom freeit function:\n");
+	freeit_was_called = 0;
+	json_object_set_serializer(my_object, NULL, NULL, NULL);
+	assert(freeit_was_called);
+
+	printf("my_object.to_string(standard)=%s\n", json_object_to_json_string(my_object));
+
+	json_object_put(my_object);
+
+	// ============================================
+
+	my_object = json_object_new_object();
+	printf("Check that the custom serializer isn't free'd until the last json_object_put:\n");
+	json_object_set_serializer(my_object, custom_serializer, &userdata, freeit);
+	json_object_get(my_object);
+	json_object_put(my_object);
+	printf("my_object.to_string(custom serializer)=%s\n", json_object_to_json_string(my_object));
+	printf("Next line of output should be from the custom freeit function:\n");
+
+	freeit_was_called = 0;	
+	json_object_put(my_object);
+	assert(freeit_was_called);
+
+	return 0;
+}

tests/test_set_serializer.expected

@@ -0,0 +1,9 @@
+my_object.to_string(standard)={ "abc": 12, "foo": "bar" }
+my_object.to_string(custom serializer)=Custom Output
+Next line of output should be from the custom freeit function:
+freeit, value=123
+my_object.to_string(standard)={ "abc": 12, "foo": "bar" }
+Check that the custom serializer isn't free'd until the last json_object_put:
+my_object.to_string(custom serializer)=Custom Output
+Next line of output should be from the custom freeit function:
+freeit, value=123

tests/test_set_serializer.test

@@ -0,0 +1,12 @@
+#!/bin/sh
+
+# Common definitions
+if test -z "$srcdir"; then
+    srcdir="${0%/*}"
+    test "$srcdir" = "$0" && srcdir=.
+    test -z "$srcdir" && srcdir=.
+fi
+. "$srcdir/test-defs.sh"
+
+run_output_test test_set_serializer
+exit $?