Add a json_c_visit() function to provide a way to iterate over a tree…

… of json-c objects.
shinae-woo · Oct 29, 2016 · ecdc14f · ecdc14f
1 parent 7e12b9f
commit ecdc14f
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Showing 8 changed files with 410 additions and 4 deletions.
diff --git a/.gitignore b/.gitignore
@@ -22,18 +22,19 @@
 /tests/test4
 /tests/testReplaceExisting
 /tests/testSubDir
-/tests/test_parse_int64
-/tests/test_parse
 /tests/test_cast
 /tests/test_charcase
+/tests/test_compare
 /tests/test_double_serializer
 /tests/test_locale
 /tests/test_null
+/tests/test_parse
+/tests/test_parse_int64
 /tests/test_printbuf
 /tests/test_set_serializer
-/tests/test_compare
-/tests/test_util_file
 /tests/test_set_value
+/tests/test_util_file
+/tests/test_visit
 /tests/*.vg.out
 /tests/*.log
 /tests/*.trs

diff --git a/Makefile.am b/Makefile.am
@@ -28,6 +28,7 @@ libjson_cinclude_HEADERS = \
 	json_object_private.h \
 	json_tokener.h \
 	json_util.h \
+	json_visit.h \
 	linkhash.h \
 	math_compat.h \
 	printbuf.h \
@@ -43,6 +44,7 @@ libjson_c_la_SOURCES = \
 	json_object_iterator.c \
 	json_tokener.c \
 	json_util.c \
+	json_visit.c \
 	linkhash.c \
 	printbuf.c \
 	random_seed.c

diff --git a/json_visit.c b/json_visit.c
@@ -0,0 +1,133 @@
+/*
+ * Copyright (c) 2016 Eric Haszlakiewicz
+ *
+ * This is free software; you can redistribute it and/or modify
+ * it under the terms of the MIT license. See COPYING for details.
+ */
+
+#include <stdio.h>
+
+#include "config.h"
+#include "json_inttypes.h"
+#include "json_object.h"
+#include "json_visit.h"
+#include "linkhash.h"
+
+static int _json_c_visit(json_object *jso, json_object *parent_jso,
+                         const char *jso_key, size_t *jso_index,
+                         json_c_visit_userfunc userfunc, void *userarg);
+
+int json_c_visit(json_object *jso, int future_flags,
+                 json_c_visit_userfunc userfunc, void *userarg)
+{
+	int ret = _json_c_visit(jso, NULL, NULL, NULL, userfunc, userarg);
+	switch(ret)
+	{
+	case JSON_C_VISIT_RETURN_CONTINUE:
+	case JSON_C_VISIT_RETURN_SKIP:
+	case JSON_C_VISIT_RETURN_POP:
+	case JSON_C_VISIT_RETURN_STOP:
+		return 0;
+	default:
+		return JSON_C_VISIT_RETURN_ERROR;
+	}
+}
+static int _json_c_visit(json_object *jso, json_object *parent_jso,
+                         const char *jso_key, size_t *jso_index,
+                         json_c_visit_userfunc userfunc, void *userarg)
+{
+	int userret = userfunc(jso, 0, parent_jso, jso_key, jso_index, userarg);
+	switch(userret)
+	{
+	case JSON_C_VISIT_RETURN_CONTINUE:
+		break;
+	case JSON_C_VISIT_RETURN_SKIP:
+	case JSON_C_VISIT_RETURN_POP:
+	case JSON_C_VISIT_RETURN_STOP:
+	case JSON_C_VISIT_RETURN_ERROR:
+		return userret;
+	default:
+		fprintf(stderr, "ERROR: invalid return value from json_c_visit userfunc: %d\n", userret);
+		return JSON_C_VISIT_RETURN_ERROR;
+	}
+
+	switch(json_object_get_type(jso))
+	{
+	case json_type_null:
+	case json_type_boolean:
+	case json_type_double:
+	case json_type_int:
+	case json_type_string:
+		// we already called userfunc above, move on to the next object
+		return JSON_C_VISIT_RETURN_CONTINUE;
+
+	case json_type_object:
+	{
+		json_object_object_foreach(jso, key, child)
+		{
+			userret = _json_c_visit(child, jso, key, NULL, userfunc, userarg);
+			if (userret == JSON_C_VISIT_RETURN_POP)
+				break;
+			if (userret == JSON_C_VISIT_RETURN_STOP ||
+				userret == JSON_C_VISIT_RETURN_ERROR)
+				return userret;
+			if (userret != JSON_C_VISIT_RETURN_CONTINUE &&
+				userret != JSON_C_VISIT_RETURN_SKIP)
+			{
+				fprintf(stderr, "INTERNAL ERROR: _json_c_visit returned %d\n", userret);
+				return JSON_C_VISIT_RETURN_ERROR;
+			}
+		}
+		break;
+	}
+	case json_type_array:
+	{
+		size_t array_len = json_object_array_length(jso);
+		size_t ii;
+		for (ii = 0; ii < array_len; ii++)
+		{
+			json_object *child = json_object_array_get_idx(jso, ii);
+			userret = _json_c_visit(child, jso, NULL, &ii, userfunc, userarg);
+			if (userret == JSON_C_VISIT_RETURN_POP)
+				break;
+			if (userret == JSON_C_VISIT_RETURN_STOP ||
+				userret == JSON_C_VISIT_RETURN_ERROR)
+				return userret;
+			if (userret != JSON_C_VISIT_RETURN_CONTINUE &&
+				userret != JSON_C_VISIT_RETURN_SKIP)
+			{
+				fprintf(stderr, "INTERNAL ERROR: _json_c_visit returned %d\n", userret);
+				return JSON_C_VISIT_RETURN_ERROR;
+			}
+		}
+		break;
+	}
+	default:
+		fprintf(stderr, "INTERNAL ERROR: _json_c_visit found object of unknown type: %d\n", json_object_get_type(jso));
+		return JSON_C_VISIT_RETURN_ERROR;
+	}
+
+	// Call userfunc for the second type on container types, after all
+	//  members of the container have been visited.
+	// Non-container types will have already returned before this point.
+
+	userret = userfunc(jso, JSON_C_VISIT_SECOND, parent_jso, jso_key, jso_index, userarg);
+	switch(userret)
+	{
+	case JSON_C_VISIT_RETURN_SKIP:
+	case JSON_C_VISIT_RETURN_POP:
+		// These are not really sensible during JSON_C_VISIT_SECOND, 
+		// but map them to JSON_C_VISIT_CONTINUE anyway.
+		// FALLTHROUGH
+	case JSON_C_VISIT_RETURN_CONTINUE:
+		return JSON_C_VISIT_RETURN_CONTINUE;
+	case JSON_C_VISIT_RETURN_STOP:
+	case JSON_C_VISIT_RETURN_ERROR:
+		return userret;
+	default:
+		fprintf(stderr, "ERROR: invalid return value from json_c_visit userfunc: %d\n", userret);
+		return JSON_C_VISIT_RETURN_ERROR;
+	}
+	// NOTREACHED
+}
+
diff --git a/json_visit.h b/json_visit.h
@@ -0,0 +1,91 @@
+
+#ifndef _json_c_json_visit_h_
+#define _json_c_json_visit_h_
+
+#include "json_object.h"
+
+typedef int (json_c_visit_userfunc)(json_object *jso, int flags,
+                                     json_object *parent_jso,                                                        const char *jso_key,
+                                     size_t *jso_index, void *userarg);
+
+/**
+ * Visit each object in the JSON hierarchy starting at jso.
+ * For each object, userfunc is called, passing the object and userarg.
+ * If the object has a parent (i.e. anything other than jso itself)
+ * its parent will be passed as parent_jso, and either jso_key or jso_index
+ * will be set, depending on whether the parent is an object or an array.
+ *
+ * Nodes will be visited depth first, but containers (arrays and objects)
+ * will be visited twice, the second time with JSON_C_VISIT_SECOND set in
+ * flags.
+ *
+ * userfunc must return one of the defined return values, to indicate
+ * whether and how to continue visiting nodes, or one of various ways to stop.
+ *
+ * Returns 0 if nodes were visited successfully, even if some were 
+ *  intentionally skipped due to what userfunc returned.
+ * Returns <0 if an error occurred during iteration, including if
+ *  userfunc returned JSON_C_VISIT_RETURN_ERROR.
+ */
+int json_c_visit(json_object *jso, int future_flags,
+                 json_c_visit_userfunc userfunc, void *userarg);
+
+/**
+ * Passed to json_c_visit_userfunc as one of the flags values to indicate
+ * that this is the second time a container (array or object) is being
+ * called, after all of it's members have been iterated over.
+ */
+#define JSON_C_VISIT_SECOND  0x02
+
+/**
+ * This json_c_visit_userfunc return value indicates that iteration
+ * should proceed normally.
+ */
+#define JSON_C_VISIT_RETURN_CONTINUE 0
+
+
+/**
+ * This json_c_visit_userfunc return value indicates that iteration
+ * over the members of the current object should be skipped.
+ * If the current object isn't a container (array or object), this
+ * is no different than JSON_C_VISIT_RETURN_CONTINUE.
+ */
+#define JSON_C_VISIT_RETURN_SKIP 7547
+
+/**
+ * This json_c_visit_userfunc return value indicates that iteration
+ * of the fields/elements of the <b>containing</b> object should stop
+ * and continue "popped up" a level of the object hierarchy.
+ * For example, returning this when handling arg will result in 
+ * arg3 and any other fields being skipped.   The next call to userfunc
+ * will be the JSON_C_VISIT_SECOND call on "foo", followed by a userfunc
+ * call on "bar".
+ * <pre>
+ * {
+ *   "foo": {
+ *     "arg1": 1,
+ *     "arg2": 2,
+ *     "arg3": 3,
+ *     ...
+ *   },
+ *   "bar": {
+ *     ...
+ *   }
+ * }
+ * </pre>
+ */
+#define JSON_C_VISIT_RETURN_POP 767
+
+/**
+ * This json_c_visit_userfunc return value indicates that iteration
+ * should stop immediately, and cause json_c_visit to return success.
+ */
+#define JSON_C_VISIT_RETURN_STOP 7867
+
+/**
+ * This json_c_visit_userfunc return value indicates that iteration
+ * should stop immediately, and cause json_c_visit to return an error.
+ */
+#define JSON_C_VISIT_RETURN_ERROR -1
+
+#endif /* _json_c_json_visit_h_ */
diff --git a/tests/Makefile.am b/tests/Makefile.am
@@ -22,6 +22,7 @@ TESTS+= test_printbuf.test
 TESTS+= test_set_serializer.test
 TESTS+= test_compare.test
 TESTS+= test_set_value.test
+TESTS+= test_visit.test
 
 check_PROGRAMS=
 check_PROGRAMS += $(TESTS:.test=)

diff --git a/tests/test_visit.c b/tests/test_visit.c
@@ -0,0 +1,111 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stddef.h>
+#include <string.h>
+#include <assert.h>
+
+#include "json.h"
+#include "json_tokener.h"
+#include "json_visit.h"
+
+static json_c_visit_userfunc emit_object;
+static json_c_visit_userfunc skip_arrays;
+static json_c_visit_userfunc pop_and_stop;
+static json_c_visit_userfunc err_on_subobj2;
+
+int main(void)
+{
+	MC_SET_DEBUG(1);
+
+	const char *input = "{\
+		\"obj1\": 123,\
+		\"obj2\": {\
+			\"subobj1\": \"aaa\",\
+			\"subobj2\": \"bbb\",\
+			\"subobj3\": [ \"elem1\", \"elem2\", true ],\
+		},\
+		\"obj3\": 1.234,\
+		\"obj4\": [ true, false, null ]\
+	}";
+
+	json_object *jso = json_tokener_parse(input);
+	printf("jso.to_string()=%s\n", json_object_to_json_string(jso));
+
+	int rv;
+	rv = json_c_visit(jso, 0, emit_object, NULL);
+	printf("json_c_visit(emit_object)=%d\n", rv);
+	printf("================================\n\n");
+
+	rv = json_c_visit(jso, 0, skip_arrays, NULL);
+	printf("json_c_visit(skip_arrays)=%d\n", rv);
+	printf("================================\n\n");
+
+	rv = json_c_visit(jso, 0, pop_and_stop, NULL);
+	printf("json_c_visit(pop_and_stop)=%d\n", rv);
+	printf("================================\n\n");
+
+	rv = json_c_visit(jso, 0, err_on_subobj2, NULL);
+	printf("json_c_visit(err_on_subobj2)=%d\n", rv);
+	printf("================================\n\n");
+
+	json_object_put(jso);
+}
+
+
+static int emit_object(json_object *jso, int flags,
+                     json_object *parent_jso,
+                     const char *jso_key,
+                     size_t *jso_index, void *userarg)
+{
+	printf("flags: 0x%x, key: %s, index: %ld, value: %s\n",
+	       flags,
+	       (jso_key ? jso_key : "(null)"),
+	       (jso_index ? (long)*jso_index : -1L),
+	       json_object_to_json_string(jso));
+	return JSON_C_VISIT_RETURN_CONTINUE;
+}
+
+static int skip_arrays(json_object *jso, int flags,
+                     json_object *parent_jso,
+                     const char *jso_key,
+                     size_t *jso_index, void *userarg)
+{
+	(void)emit_object(jso, flags, parent_jso, jso_key, jso_index, userarg);
+	if (json_object_get_type(jso) == json_type_array)
+		return JSON_C_VISIT_RETURN_SKIP;
+	return JSON_C_VISIT_RETURN_CONTINUE;
+}
+
+static int pop_and_stop(json_object *jso, int flags,
+                     json_object *parent_jso,
+                     const char *jso_key,
+                     size_t *jso_index, void *userarg)
+{
+	(void)emit_object(jso, flags, parent_jso, jso_key, jso_index, userarg);
+	if (jso_key != NULL && strcmp(jso_key, "subobj1") == 0)
+	{
+		printf("POP after handling subobj1\n");
+		return JSON_C_VISIT_RETURN_POP;
+	}
+	if (jso_key != NULL && strcmp(jso_key, "obj3") == 0)
+	{
+		printf("STOP after handling obj3\n");
+		return JSON_C_VISIT_RETURN_STOP;
+	}
+	return JSON_C_VISIT_RETURN_CONTINUE;
+}
+
+static int err_on_subobj2(json_object *jso, int flags,
+                     json_object *parent_jso,
+                     const char *jso_key,
+                     size_t *jso_index, void *userarg)
+{
+	(void)emit_object(jso, flags, parent_jso, jso_key, jso_index, userarg);
+	if (jso_key != NULL && strcmp(jso_key, "subobj2") == 0)
+	{
+		printf("ERROR after handling subobj1\n");
+		return JSON_C_VISIT_RETURN_ERROR;
+	}
+	return JSON_C_VISIT_RETURN_CONTINUE;
+}
+