Save BIO into char* (from SMIME_write_CMS) - ios

Question

I want to save (pipe/copy) a BIO into a char array.
When I know the size it works, but otherwise not.
For example, I can store the content of my char* into a BIO using this
const unsigned char* data = ...
myBio = BIO_new_mem_buf((void*)data, strlen(data));
But when I try to use SMIME_write_CMS which takes a BIO (what I've created before) for the output it doesn't work.
const int SIZE = 50000;
unsigned char *temp = malloc(SIZE);
memset(temp, 0, SIZE);
out = BIO_new_mem_buf((void*)temp, SIZE);
if (!out) {
NSLog(#"Couldn't create new file!");
assert(false);
}
int finished = SMIME_write_CMS(out, cms, in, flags);
if (!finished) {
NSLog(#"SMIME write CMS didn't succeed!");
assert(false);
}
printf("cms encrypted: %s\n", temp);
NSLog(#"All succeeded!");
The OpenSSL reference uses a direct file output with the BIO.
This works but I can't use BIO_new_file() in objective-c... :-/
out = BIO_new_file("smencr.txt", "w");
if (!out)
goto err;
/* Write out S/MIME message */
if (!SMIME_write_CMS(out, cms, in, flags))
goto err;
Do you guys have any suggestion?

Answer 1

I would suggest trying to use SIZE-1, that way you are guaranteed that it is NULL terminated. Otherwise, it is possible that it is just over running the buffer.
out = BIO_new_mem_buf((void*)temp, SIZE-1);
Let me know if that helps.
Edit:
When using BIO_new_mem_buf() it is a read only buffer, so you cannot write to it. If you want to write to memory use:
BIO *bio = BIO_new(BIO_s_mem());