msgpack packing char array in C - c

Question

How do I work with msgpack_pack_raw and msgpack_pack_raw_body to send an unsigned char array to more importantly, how to retrieve (unpack) it?
What I have done is as follows:
msgpack_sbuffer* buffer = msgpack_sbuffer_new();
msgpack_packer* pk = msgpack_packer_new(buffer, msgpack_sbuffer_write);
msgpack_sbuffer_clear(buffer);
msgpack_pack_array(pk, 10);
unsigned char a[10] = "0123456789";
msgpack_pack_raw(pk, 10);
msgpack_pack_raw_body(pk,a,10);
and in the receiver part I have:
msgpack_unpacked msg;
msgpack_unpacked_init(&msg);
msgpack_unpack_next(&msg, buffer->data, buffer->size, NULL);
msgpack_object obj = msg.data;
msgpack_object* p = obj.via.array.ptr;
int length = (*p).via.raw.size;
IDPRINT(length);
unsigned char* b = (unsigned char*) malloc(length);
memcpy(b,(*p).via.raw.ptr,length);
But it throws seg fault when executing "int length = (*p).via.raw.size;".
Any idea why?

Answer 1

Any idea why?
This is because msgpack_pack_array(pk, 10); is not required here, since you pack your data as a raw buffer of a given size. In other words msgpack_pack_raw and msgpack_pack_raw_body are sufficient.
At unpack time, you must access its fields as follow:
length: obj.via.raw.size
data: obj.via.raw.ptr
see: msgpack_object_raw in object.h.
Here's a recap of how to proceed:
#include <stdio.h>
#include <assert.h>
#include <msgpack.h>
int main(void) {
unsigned char a[10] = "0123456789";
char *buf = NULL;
int size;
/* -- PACK -- */
msgpack_sbuffer sbuf;
msgpack_sbuffer_init(&sbuf);
msgpack_packer pck;
msgpack_packer_init(&pck, &sbuf, msgpack_sbuffer_write);
msgpack_pack_raw(&pck, 10);
msgpack_pack_raw_body(&pck, a, 10);
size = sbuf.size;
buf = malloc(sbuf.size);
memcpy(buf, sbuf.data, sbuf.size);
msgpack_sbuffer_destroy(&sbuf);
/* -- UNPACK -- */
unsigned char *b = NULL;
int bsize = -1;
msgpack_unpacked msg;
msgpack_unpacked_init(&msg);
if (msgpack_unpack_next(&msg, buf, size, NULL)) {
msgpack_object root = msg.data;
if (root.type == MSGPACK_OBJECT_RAW) {
bsize = root.via.raw.size;
b = malloc(bsize);
memcpy(b, root.via.raw.ptr, bsize);
}
}
/* -- CHECK -- */
assert(bsize == 10);
assert(b != NULL);
for (int i = 0; i < bsize; i++)
assert(b[i] == a[i]);
printf("ok\n");
free(buf);
free(b);
return 0;
}