static cJSON_bool print_value(const cJSON * const item, printbuffer * const output_buffer)

[GitHub-LHD]

The print_value() very absurd!!!
eg:
(1) if output_buffer->buffer is global, the function is very danger!!!
(2) struct{
int flag;
char buf[];
}
if output_buffer->buffer point to buf[] and buf[] realloced, oh mg god!!!

[Alanscut]

Hi @mengxiangren , function print_value and struct printbuffer is not exposed to users, and the memory allocation of the print_buffer is performed inside the static function. Where do you find that the output_buffer->buffer becomes global?

[GitHub-LHD]

Thanks for your reply, please see example.c

…

------------------ 原始邮件 ------------------ 发件人: "DaveGamble/cJSON" <notifications@github.com&gt;; 发送时间:&nbsp;2020年8月5日(星期三) 上午10:08 收件人:&nbsp;"DaveGamble/cJSON"<cJSON@noreply.github.com&gt;; 抄送:&nbsp;"孟乡人"<775924562@qq.com&gt;;"Mention"<mention@noreply.github.com&gt;; 主题:&nbsp;Re: [DaveGamble/cJSON] static cJSON_bool print_value(const cJSON * const item, printbuffer * const output_buffer) (#492) Hi @mengxiangren , function print_value and struct printbuffer is not exposed to users, and the memory allocation of the print_buffer is performed inside the static function. Where do you find that the output_buffer-&gt;buffer becomes global? — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub, or unsubscribe.

[GitHub-LHD]

Explame one:

static buf[100];
cJSON root;

cJSON_PrintPreallocated(root, buf, 100, 1)
{
printbuffer p = { 0, 0, 0, 0, 0, 0, { 0, 0, 0 } };
...
print_value(item, &p)
{
...
ensure(output_buffer, 1000); //if reallocte buf, it is error
....
}
}

Explame two:

static struct fa{
int flag;
char *buf[];
};
static struct fa *flexible_array;
cJSON root;

flexible_array = molloc(sizeof(struct fa) + 100);

cJSON_PrintPreallocated(root, flexible_array->buf, 100, 1)
{
printbuffer p = { 0, 0, 0, 0, 0, 0, { 0, 0, 0 } };
...
print_value(item, &p)
{
...
ensure(output_buffer, 1000); //if reallocte buf, it is error
....
}
}

printf("%s", flexible_array->buf);//if reallocte buf, it is error

[Alanscut]

realloc the output_buffer->buffer won't report error, realloc the buf just change the size of memory block pointed by buf. Have you ever tested your snippet? what error has your program reported? I compiled your example one with valgrind, and it didn't detect any memory errors.

[GitHub-LHD]

realloc the output_buffer->buffer won't report error, realloc the buf just change the size of memory block pointed by buf. Have you ever tested your snippet? what error has your program reported? I compiled your example one with valgrind, and it didn't detect any memory errors.

Use you code, now set buf[2],then run again
static char buf[2]
cJSON_PrintPreallocated(root, buf, 2, 1);

[Alanscut]

then the cJSON_PrintPreallocated will return 0, namely failed to print root to buf, still no error.

[Alanscut]

I suggest you test it in your server and post the error logs, in case I mishandle something.

[GitHub-LHD]

then the cJSON_PrintPreallocated will return 0, namely failed to print root to buf, still no error.

I means, the buf(static) shouldn't reallocate, becase the buf is global

[GitHub-LHD]

then the cJSON_PrintPreallocated will return 0, namely failed to print root to buf, still no error.

I means, the buf(static) shouldn't reallocate, becase the buf is global

if static buf[100], the realloc(50), it is right
if static buf[50], the realloc(100), it is error

[Alanscut]

I suggest you test it in your server and post the error logs, in case I mishandle something.

are you test example two?
yes, example two certainly reported an error, because cJSON_PrintPreallocated can't accept a char * buf[], but a char *

static struct fa{
int flag;
char *buf[]; // this is a char **
};

[GitHub-LHD]

I suggest you test it in your server and post the error logs, in case I mishandle something.

are you test example two?
yes, example two certainly reported an error, because cJSON_PrintPreallocated can't accept a char * buf[], but a char *

static struct fa{
int flag;
char *buf[]; // this is a char **
};

sorry,it should
static struct fa{
int flag;
char buf[];
};

[GitHub-LHD]

I suggest you test it in your server and post the error logs, in case I mishandle something.

are you test example two?
yes, example two certainly reported an error, because cJSON_PrintPreallocated can't accept a char * buf[], but a char *

static struct fa{
int flag;
char *buf[]; // this is a char **
};

sorry,it should
static struct fa{
int flag;
char buf[];
};

struct fa is contiguous memory address, if reallocate fa.buf, then struct fa will not contiguous memory address

[Alanscut]

realloc function won't invoked in the cJSON_PrintPreallocated function.

cJSON/cJSON.c

Lines 1286 to 1303 in cf97c6f

	CJSON_PUBLIC(cJSON_bool) cJSON_PrintPreallocated(cJSON *item, char *buffer, const int length, const cJSON_bool format)
	{
	printbuffer p = { 0, 0, 0, 0, 0, 0, { 0, 0, 0 } };
	if ((length < 0) || (buffer == NULL))
	{
	return false;
	}
	p.buffer = (unsigned char*)buffer;
	p.length = (size_t)length;
	p.offset = 0;
	p.noalloc = true;
	p.format = format;
	p.hooks = global_hooks;
	return print_value(item, &p);
	}

if the length of buffer is smaller than needed, then it will return NULL in line464.

cJSON/cJSON.c

Lines 434 to 465 in cf97c6f

	/* realloc printbuffer if necessary to have at least "needed" bytes more */
	static unsigned char* ensure(printbuffer * const p, size_t needed)
	{
	unsigned char *newbuffer = NULL;
	size_t newsize = 0;
	if ((p == NULL) || (p->buffer == NULL))
	{
	return NULL;
	}
	if ((p->length > 0) && (p->offset >= p->length))
	{
	/* make sure that offset is valid */
	return NULL;
	}
	if (needed > INT_MAX)
	{
	/* sizes bigger than INT_MAX are currently not supported */
	return NULL;
	}
	needed += p->offset + 1;
	if (needed <= p->length)
	{
	return p->buffer + p->offset;
	}
	if (p->noalloc) {
	return NULL;
	}

[GitHub-LHD]

realloc function won't invoked in the cJSON_PrintPreallocated function.

cJSON/cJSON.c

Lines 1286 to 1303 in cf97c6f

	CJSON_PUBLIC(cJSON_bool) cJSON_PrintPreallocated(cJSON *item, char *buffer, const int length, const cJSON_bool format)
	{
	printbuffer p = { 0, 0, 0, 0, 0, 0, { 0, 0, 0 } };
	if ((length < 0) || (buffer == NULL))
	{
	return false;
	}
	p.buffer = (unsigned char*)buffer;
	p.length = (size_t)length;
	p.offset = 0;
	p.noalloc = true;
	p.format = format;
	p.hooks = global_hooks;
	return print_value(item, &p);
	}

if the length of buffer is smaller than needed, then it will return NULL in line464.

cJSON/cJSON.c

Lines 434 to 465 in cf97c6f

	/* realloc printbuffer if necessary to have at least "needed" bytes more */
	static unsigned char* ensure(printbuffer * const p, size_t needed)
	{
	unsigned char *newbuffer = NULL;
	size_t newsize = 0;
	if ((p == NULL) || (p->buffer == NULL))
	{
	return NULL;
	}
	if ((p->length > 0) && (p->offset >= p->length))
	{
	/* make sure that offset is valid */
	return NULL;
	}
	if (needed > INT_MAX)
	{
	/* sizes bigger than INT_MAX are currently not supported */
	return NULL;
	}
	needed += p->offset + 1;
	if (needed <= p->length)
	{
	return p->buffer + p->offset;
	}
	if (p->noalloc) {
	return NULL;
	}

Sorry, i misunderstood

[GitHub-LHD]

realloc function won't invoked in the cJSON_PrintPreallocated function.

cJSON/cJSON.c

Lines 1286 to 1303 in cf97c6f

	CJSON_PUBLIC(cJSON_bool) cJSON_PrintPreallocated(cJSON *item, char *buffer, const int length, const cJSON_bool format)
	{
	printbuffer p = { 0, 0, 0, 0, 0, 0, { 0, 0, 0 } };
	if ((length < 0) || (buffer == NULL))
	{
	return false;
	}
	p.buffer = (unsigned char*)buffer;
	p.length = (size_t)length;
	p.offset = 0;
	p.noalloc = true;
	p.format = format;
	p.hooks = global_hooks;
	return print_value(item, &p);
	}

if the length of buffer is smaller than needed, then it will return NULL in line464.

cJSON/cJSON.c

Lines 434 to 465 in cf97c6f

	/* realloc printbuffer if necessary to have at least "needed" bytes more */
	static unsigned char* ensure(printbuffer * const p, size_t needed)
	{
	unsigned char *newbuffer = NULL;
	size_t newsize = 0;
	if ((p == NULL) || (p->buffer == NULL))
	{
	return NULL;
	}
	if ((p->length > 0) && (p->offset >= p->length))
	{
	/* make sure that offset is valid */
	return NULL;
	}
	if (needed > INT_MAX)
	{
	/* sizes bigger than INT_MAX are currently not supported */
	return NULL;
	}
	needed += p->offset + 1;
	if (needed <= p->length)
	{
	return p->buffer + p->offset;
	}
	if (p->noalloc) {
	return NULL;
	}

I have another question, in print_value()

static cJSON_bool print_value(const cJSON * const item, printbuffer * const output_buffer)
{
...
output = ensure(output_buffer, 5); //5 = strlen("null") + strlen("");
if (output == NULL)
{
return false;
}
strcpy((char*)output, "null");
...
}
static unsigned char* ensure(printbuffer * const p, size_t needed)
{
...
needed += p->offset + 1; //why does needed + 1?
if (needed <= p->length) //if length= 5, print_value() will return false, but it should have return "null"
{ //so, it should be "output = ensure(output_buffer, 4)"?
return p->buffer + p->offset;
}
if (p->noalloc)
{
return NULL;
}
...
}