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Implement Variadic Object Traversal #688

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Implement Variadic Object Traversal #688

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950d928
added Variadic object finder
ChiragH25 Apr 17, 2024
14950bd
fixed root array issues
ChiragH25 Apr 17, 2024
e5c9735
removed type checking to attempt to resolve Visual Studio Errors
ChiragH25 Apr 17, 2024
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7 changes: 7 additions & 0 deletions doc/apiref.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -648,6 +648,13 @@ allowed in object keys.
Get a value corresponding to *key* from *object*. Returns *NULL* if
*key* is not found and on error.

.. function:: json_t *json_object_get_path(const json_t* object, size_t depth, ...)

.. refcounting:: borrow

Get a value corresponding to the path from *object*. Returns *NULL* if
the object is not found and on error.

.. function:: json_t *json_object_getn(const json_t *object, const char *key, size_t key_len)

.. refcounting:: borrow
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1 change: 1 addition & 0 deletions src/jansson.def
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Expand Up @@ -35,6 +35,7 @@ EXPORTS
json_object_size
json_object_get
json_object_getn
json_object_get_path
json_object_set_new
json_object_setn_new
json_object_set_new_nocheck
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1 change: 1 addition & 0 deletions src/jansson.h
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Expand Up @@ -188,6 +188,7 @@ void json_object_seed(size_t seed);
size_t json_object_size(const json_t *object);
json_t *json_object_get(const json_t *object, const char *key)
JANSSON_ATTRS((warn_unused_result));
json_t *json_object_get_path(const json_t* object, size_t depth, ...);
json_t *json_object_getn(const json_t *object, const char *key, size_t key_len)
JANSSON_ATTRS((warn_unused_result));
int json_object_set_new(json_t *object, const char *key, json_t *value);
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25 changes: 25 additions & 0 deletions src/value.c
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Expand Up @@ -103,6 +103,31 @@ json_t *json_object_get(const json_t *json, const char *key) {
return json_object_getn(json, key, strlen(key));
}

json_t *json_object_get_path(json_t* object, size_t depth, ...){
va_list path;
size_t i = 0;

va_start(path, depth);

for (i = 0; i < depth; i++){
if(object->type == JSON_ARRAY){
object = json_array_get(object, va_arg(path, size_t));
if(!object){
return NULL;
}
continue;
}
object = json_object_get(object, va_arg(path, const char*));
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Hi, thanks for the PR!

It seems to me that the function is quite dangerous: if the json structure differs from the expected one, then the passed array index can be used as a pointer to a string.

In this case, we have no way to return an error to the user, since va args is not typed in any way.

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That is true, though that seems inherent to a variadic approach. printf and other functions I've found tend to have this issue regardless. I considered an approach of using a pointer array to a specific struct with appropriate typechecking but it defeated the purpose of making a convenient interface.

I largely created this function as a way of simplifying getting parts of a JSON object from a known JSON structure and thought it might be useful for other people as well. the variadic approach handles object traversal well and in my exeprience using this in my own project, I've found that if I ever mess up the location of an index in the path, I just get a null return since it's extremely unlikely that such a space in memory would have a char pointer with a value that's also a key in the object that is being queried.

And even if it did, the worst case result is that it returns an unintended child of the JSON which is still relatively safe.

I've also passed a char* as an index and just had null returns since it's unlikely that the array in question is large enough that the pointer in question is a valid index.

Since any inputs to this function are never edited or copied, simply read from the impact on other parts of the memory should be effectively null.

Granted this is obviously not intended for any application where the path is passed in by a user or some outside source, since that might allow a bad actor to pass in something specifically malicious. (though it would be quite unweildy to work with regardless in this scenario as far as I'm aware)

But in the bounds of standard development where this may be used, I figure that it fails in a sufficiently safe manner even if the path is incorrect.

Beyond that if this still seems too unsafe, I'm not too concerned about it and just wanted to pass along a tool that I made since I thought it might be useful, and I'll just retain it for my own use. Thank you for your time in that case, and if you have any reccomendations on how to make it safer given the goal of this function, please let me know as I'm more than happy to learn.

if(!object){
return NULL;
}
}

va_end(path);

return object;
}

json_t *json_object_getn(const json_t *json, const char *key, size_t key_len) {
json_object_t *object;

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4 changes: 3 additions & 1 deletion test/suites/api/Makefile.am
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Expand Up @@ -18,7 +18,8 @@ check_PROGRAMS = \
test_simple \
test_sprintf \
test_unpack \
test_version
test_version \
test_get_path

test_array_SOURCES = test_array.c util.h
test_chaos_SOURCES = test_chaos.c util.h
Expand All @@ -36,6 +37,7 @@ test_simple_SOURCES = test_simple.c util.h
test_sprintf_SOURCES = test_sprintf.c util.h
test_unpack_SOURCES = test_unpack.c util.h
test_version_SOURCES = test_version.c util.h
test_get_path_SOURCES = test_get_path.c util.h

AM_CPPFLAGS = -I$(top_builddir)/src -I$(top_srcdir)/src
LDFLAGS = -static # for speed and Valgrind
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153 changes: 153 additions & 0 deletions test/suites/api/test_get_path.c
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@@ -0,0 +1,153 @@
#include "util.h"
#include <jansson.h>
#include <string.h>

static void run_tests() {
json_error_t *error;

json_t *json = json_pack(
"{s:{s:[{}[]sifbbn],s:s,s:i,s:f,s:b,s:b,s:n,s:{s:{s:{}}}}}",
"base",
"array",
"string 1",
1,
2.2,
1,
0,
"string2",
"string3",
"integer",
3,
"real",
4.4,
"true",
1,
"false",
0,
"null",
"nest 1",
"nest 2",
"nest 3"
);

json_t* value = json_object_get_path(json, 1, "A");
if(value) fail("should not have found object");

value = json_object_get_path(json, 1, "A");
if(value) fail("should not have found array");

value = json_object_get_path(json, 1, "A");
if(value) fail("should not have found string");

value = json_object_get_path(json, 1, "A");
if(value) fail("should not have found integer");

value = json_object_get_path(json, 1, "A");
if(value) fail("should not have found true");

value = json_object_get_path(json, 1, "A");
if(value) fail("should not have found false");

value = json_object_get_path(json, 1, "A");
if(value) fail("should not have found null");

value = json_object_get_path(json, 1, "base");
if(!value) fail("did not find object");

value = json_object_get_path(json, 2, "base", "array");
if(!value) fail("did not find array");

value = json_object_get_path(json, 3, "base", "array", (size_t) 0);
if(!value) fail("did not find array element");
if(value->type != JSON_OBJECT) fail("did not find object in array");

value = json_object_get_path(json, 3, "base", "array", (size_t) 1);
if(!value) fail("did not find array element");
if(value->type != JSON_ARRAY) fail("did not find array in array");

value = json_object_get_path(json, 3, "base", "array", (size_t) 2);
if(!value) fail("did not find array element");
if(value->type != JSON_STRING) fail("did not find string in array");

value = json_object_get_path(json, 3, "base", "array", (size_t) 3);
if(!value) fail("did not find array element");
if(value->type != JSON_INTEGER) fail("did not find integer in array");

value = json_object_get_path(json, 3, "base", "array", (size_t) 4);
if(!value) fail("did not find array element");
if(value->type != JSON_REAL) fail("did not find real in array");

value = json_object_get_path(json, 3, "base", "array", (size_t) 5);
if(!value) fail("did not find array element");
if(value->type != JSON_TRUE) fail("did not find real in array");

value = json_object_get_path(json, 3, "base", "array", (size_t) 6);
if(!value) fail("did not find array element");
if(value->type != JSON_FALSE) fail("did not find real in array");

value = json_object_get_path(json, 3, "base", "array", (size_t) 7);
if(!value) fail("did not find array element");
if(value->type != JSON_NULL) fail("did not find real in array");

value = json_object_get_path(json, 3, "base", "array", (size_t) 8);
if(value) fail("should not have found array element");

value = json_object_get_path(json, 2, "base", "string2");
if(!value) fail("did not find string in object");
if(value->type != JSON_STRING) fail("did not find string in object");
if(strcmp(json_string_value(value), "string3")) fail("did not get appropriate string value");

value = json_object_get_path(json, 2, "base", "integer");
if(!value) fail("did not find integer in object");
if(value->type != JSON_INTEGER) fail("did not find integer in object");
if(json_integer_value(value) != 3) fail("did not get appropriate integer value");

value = json_object_get_path(json, 2, "base", "real");
if(!value) fail("did not find real in object");
if(value->type != JSON_REAL) fail("did not find real in object");
if(json_real_value(value)!= 4.4) fail("did not get appropriate real value");

value = json_object_get_path(json, 2, "base", "true");
if(!value) fail("did not find true in object");
if(value->type != JSON_TRUE) fail("did not find true in object");
if(!json_is_true(value)) fail("did not get appropriate true value");

value = json_object_get_path(json, 2, "base", "false");
if(!value) fail("did not find false in object");
if(value->type != JSON_FALSE) fail("did not find false in object");
if(!json_is_false(value)) fail("did not get appropriate false value");

value = json_object_get_path(json, 2, "base", "null");
if(!value) fail("did not find null in object");
if(value->type != JSON_NULL) fail("did not find null in object");

value = json_object_get_path(json, 2, "base", "null", "nest 1", "nest 2", "nest 3");
if(!value) fail("did not ignore garbage arguments");

value = json_object_get_path(json, 3, "base", "nest 1", "nest 2");
if(!value) fail("did not find nested object");

value = json_object_get_path(json, 4, "base", "nest 1", "nest 2", "nest 3");
if(!value) fail("did not find nested object");

json = json_pack(
"[sss]",
"base",
"array",
"string 1"
);

value = json_object_get_path(json, 1, (size_t) 0);
if(!value) fail("did not find object in list");
if(strcmp(json_string_value(value), "base")) fail("did not get appropriate string value");

value = json_object_get_path(json, 1, (size_t) 1);
if(!value) fail("did not find object in list");
if(strcmp(json_string_value(value), "array")) fail("did not get appropriate string value");

value = json_object_get_path(json, 1, (size_t) 2);
if(!value) fail("did not find object in list");
if(strcmp(json_string_value(value), "string 1")) fail("did not get appropriate string value");

json_decref(json);
}