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Added a function to print to pre-allocated buffer #72

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Added a function to print to pre-allocated buffer #72

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2387d9d
added Print function call for pre-allocated buffer
Nov 25, 2016
1193d24
fixed "make test" on Mac (clang)
Nov 25, 2016
df093c3
fix shared utils library to also include cjson object
Nov 25, 2016
42496b2
changed to cJSON_PrintPreallocated, added flag in printbuffer
Nov 25, 2016
4150c30
change noalloc struct item to cjbool
Nov 28, 2016
6ce0915
check print_value return
Nov 28, 2016
6e1b4ba
function to print and compare to preallocated buffer
Nov 28, 2016
652bb77
use print_preallocated function to test printout of JSON
Nov 28, 2016
e559516
change buffer length to to int
Nov 28, 2016
e3e7726
more concise return
Nov 28, 2016
32f3316
forgot to add 0, -1 return values
Nov 28, 2016
7083240
fix flags
Nov 28, 2016
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15 changes: 9 additions & 6 deletions Makefile
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,9 @@ UTILS_LIBNAME = libcjson_utils
CJSON_TEST = cJSON_test
UTILS_TEST = cJSON_test_utils

CJSON_TEST_SRC = cJSON.c test.c
UTILS_TEST_SRC = cJSON.c cJSON_Utils.c test_utils.c

LDLIBS = -lm

LIBVERSION = 1.0.2
Expand Down Expand Up @@ -66,11 +69,11 @@ test: tests

#tests
#cJSON
$(CJSON_TEST): cJSON.c cJSON.h test.c
$(CC) $^ -o $@ $(LDLIBS) -I.
$(CJSON_TEST): $(CJSON_TEST_SRC) cJSON.h
$(CC) $(CJSON_TEST_SRC) -o $@ $(LDLIBS) -I.
#cJSON_Utils
$(UTILS_TEST): cJSON.c cJSON.h test.c
$(CC) $^ -o $@ $(LDLIBS) -I.
$(UTILS_TEST): $(UTILS_TEST_SRC) cJSON.h cJSON_Utils.h
$(CC) $(UTILS_TEST_SRC) -o $@ $(LDLIBS) -I.

#static libraries
#cJSON
Expand All @@ -85,8 +88,8 @@ $(UTILS_STATIC): $(UTILS_OBJ)
$(CJSON_SHARED_VERSION): $(CJSON_OBJ)
$(CC) -shared -o $@ $< $(LDFLAGS)
#cJSON_Utils
$(UTILS_SHARED_VERSION): $(UTILS_OBJ)
$(CC) -shared -o $@ $< $(LDFLAGS)
$(UTILS_SHARED_VERSION): $(UTILS_OBJ) $(CJSON_OBJ)
$(CC) -shared -o $@ $< $(CJSON_OBJ) $(LDFLAGS)

#objects
#cJSON
Expand Down
25 changes: 24 additions & 1 deletion cJSON.c
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Expand Up @@ -244,8 +244,10 @@ typedef struct
char *buffer;
int length;
int offset;
int noalloc;
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Please use cjbool and use true and false when assigning to it.

} printbuffer;


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Don't add random whitespace.

/* realloc printbuffer if necessary to have at least "needed" bytes more */
static char* ensure(printbuffer *p, int needed)
{
Expand All @@ -261,12 +263,17 @@ static char* ensure(printbuffer *p, int needed)
return p->buffer + p->offset;
}

if (p->noalloc) {
return NULL;
}

newsize = pow2gt(needed);
newbuffer = (char*)cJSON_malloc(newsize);
if (!newbuffer)
{
cJSON_free(p->buffer);
p->length = 0;
p->noalloc = 0;
p->buffer = NULL;

return NULL;
Expand Down Expand Up @@ -882,10 +889,22 @@ char *cJSON_PrintBuffered(const cJSON *item, int prebuffer, cjbool fmt)
}
p.length = prebuffer;
p.offset = 0;
p.noalloc = 0;

return print_value(item, 0, fmt, &p);
}

int cJSON_PrintPreallocated(cJSON *item,char *buf, const size_t len, const cjbool fmt)
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About the size_t. I agree that size_t should be used everywhere instead of int, and it will be in v2, but currently ensure and printbuffer and all the other internal functions use int for sizes, so using size_t can create the illusion that numbers exceeding the integer range are supported, but they're not.

So please change to int 😢.

{
char *out;
printbuffer p;
p.buffer = buf;
p.length = len;
p.offset = 0;
p.noalloc = 1;
out = print_value(item,0,fmt,&p);
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By doing this you risk crashes, because print_value will try to reallocate the printbuffer when it is too short.

return (out != buf ? -1 : 0);
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This should return out like the other print functions. It will be NULL if it failed.

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If this function returns a char pointer (effectively providing an alias to the input char *buf or a NULL pointer), it might falsely imply a new dynamically allocated string was created. Do you think it might be more intuitive to use the pointer to char* buf after the function is called if no error was returned, or is consistency of return values with all the cJSON_Print functions more important?

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Hm. Good point. Considering this, your way of returning true or false might actually be better. An API should be hard to misuse in a dangerous way (like having a double free because of the alias).
The question is how far one is willing to protect the users from themselves.

This will then not allow the use of cJSON_PrintPreallocated as an argument to another function (do_something(cJSON_PrintPreallocated(...)))

If you do it the way you suggested, you can just return print_value(...) != NULL;

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That would be more concise. Made the change.

}

/* Parser core - when encountering text, process appropriately. */
static const char *parse_value(cJSON *item, const char *value, const char **ep)
Expand Down Expand Up @@ -1137,7 +1156,11 @@ static char *print_array(const cJSON *item, int depth, cjbool fmt, printbuffer *
child = item->child;
while (child && !fail)
{
print_value(child, depth + 1, fmt, p);
ptr = print_value(child, depth + 1, fmt, p);
if (!ptr)
{
return NULL;
}
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Change this to:

if (!print_value(child, depth + 1, fmt, p))
{
    return NULL;
}

Thank you for finding this problem btw. after that I was taking a closer look to the rest of the library and there are quite some cases where out of memory errors are not handled properly.

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I will also fix these other cases in the next release.

p->offset = update(p);
if (child->next)
{
Expand Down
2 changes: 2 additions & 0 deletions cJSON.h
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Expand Up @@ -83,6 +83,8 @@ extern char *cJSON_Print(const cJSON *item);
extern char *cJSON_PrintUnformatted(const cJSON *item);
/* Render a cJSON entity to text using a buffered strategy. prebuffer is a guess at the final size. guessing well reduces reallocation. fmt=0 gives unformatted, =1 gives formatted */
extern char *cJSON_PrintBuffered(const cJSON *item, int prebuffer, int fmt);
/* Render a cJSON entity to text using a buffer already allocated in memory with length buf_len */
extern int cJSON_PrintPreallocated(cJSON *item, char *buf, const size_t len, const int fmt);
/* Delete a cJSON entity and all subentities. */
extern void cJSON_Delete(cJSON *c);

Expand Down
49 changes: 47 additions & 2 deletions test.c
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Expand Up @@ -22,6 +22,7 @@

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "cJSON.h"

/* Parse text to JSON, then render back to text, and print! */
Expand Down Expand Up @@ -219,16 +220,60 @@ void create_objects(void)
/* cJSON_ReplaceItemInObject(cJSON_GetArrayItem(root, 1), "City", cJSON_CreateIntArray(ids, 4)); */

out = cJSON_Print(root);
cJSON_Delete(root);
printf("%s\n", out);

printf("Test cJSON_PrintPreallocated:\n");
/* create buffer */
size_t len = strlen(out) + 1;
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It is not allowed to mix code and declarations in C89. I have a bug in the Makefile and CMakelists.txt so that the compiler option is not enforced, sorry for that.

I suggest you create a new function just for testing preallocated printing and call it from main (you can pass one of the texts to it).

char *buf = malloc(len);

/* create buffer to fail */
size_t len_fail = strlen(out);
char *buf_fail = malloc(len_fail);

free(out);

/* Print to buffer */
if (cJSON_PrintPreallocated(root, buf, len, 1) != 0) {
printf("cJSON_PrintPreallocated failed (but it should not have!)\n");
free(buf_fail);
free(buf);
exit(EXIT_FAILURE);
} else {
printf("cJSON_PrintPreallocated:\n%s\n", buf);
}

/* unformatted output */
if (cJSON_PrintPreallocated(root, buf, len, 0) != 0) {
printf("cJSON_PrintPreallocated failed (but it should not have!)\n");
free(buf_fail);
free(buf);
exit(EXIT_FAILURE);
} else {
printf("cJSON_PrintPreallocated (unformatted):\n%s\n", buf);
}

free(buf);

/* force it to fail */
if (cJSON_PrintPreallocated(root, buf_fail, len_fail, 1) != 0) {
printf("cJSON_PrintPreallocated failed (as expected)\n");
} else {
printf("cJSON_PrintPreallocated worked (but it should have failed!)\n");
printf("cJSON_PrintPreallocated:\n%s\n", buf_fail);
}

free(buf_fail);
cJSON_Delete(root);

root = cJSON_CreateObject();
cJSON_AddNumberToObject(root, "number", 1.0 / zero);
out = cJSON_Print(root);
cJSON_Delete(root);
printf("%s\n", out);
cJSON_Delete(root);

free(out);

}

int main(void)
Expand Down