Consider the following struct and functions
typedef struct __attribute__((__packed__)) req_file {
uint32_t start_pos;
uint32_t byte_count;
uint16_t name_len;
} req_file;
void req_file_hton(req_file *d){
d->name_len = htons(d->name_len);
d->start_pos = htonl(d->start_pos);
d->byte_count = htonl(d->byte_count);
}
void req_file_ntoh(req_file *d){
d->name_len = ntohs(d->name_len);
d->start_pos = ntohl(d->start_pos);
d->byte_count = ntohl(d->byte_count);
}
The above code is tedious to write for a lot of structs with many fields. I would like to configure the name and the fields of the struct once, and have the functions struct_name_hton
and struct_name_ntoh
generated for me. I have tried to play with x macros a little but had bad luck. A portable C preprocessor solution will be highly appreciated (not C++).
Well, that's easy.
#include <stdint.h>
#include <arpa/inet.h>
/* the NETSTRUCT library ------------------------------- */
// for uint32_t
#define NETSTRUCT_dec_uint32_t(n) uint32_t n;
#define NETSTRUCT_hton_uint32_t(n) t->n = htonl(t->n);
#define NETSTRUCT_ntoh_uint32_t(n) t->n = ntohl(t->n);
// for uint16_t
#define NETSTRUCT_dec_uint16_t(n) uint16_t n;
#define NETSTRUCT_hton_uint16_t(n) t->n = htons(t->n);
#define NETSTRUCT_ntoh_uint16_t(n) t->n = ntohs(t->n);
// dec hton ntoh switch
#define NETSTRUCT_dec(type, name) NETSTRUCT_dec_##type(name)
#define NETSTRUCT_hton(type, name) NETSTRUCT_hton_##type(name)
#define NETSTRUCT_ntoh(type, name) NETSTRUCT_ntoh_##type(name)
// calls NETSTRUCT_mod
#define NETSTRUCT1(mod, a) NETSTRUCT_##mod a
#define NETSTRUCT2(mod, a, ...) NETSTRUCT1(mod, a) NETSTRUCT1(mod, __VA_ARGS__)
#define NETSTRUCT3(mod, a, ...) NETSTRUCT1(mod, a) NETSTRUCT2(mod, __VA_ARGS__)
#define NETSTRUCT4(mod, a, ...) NETSTRUCT1(mod, a) NETSTRUCT3(mod, __VA_ARGS__)
// TO DO: all up to NETSTRUCT64
// variadic macro overload
#define NETSTRUCT_GET(_1,_2,_3,_4,NAME,...) NAME
// Overlads VA_ARGS with specified mod
#define NETSTRUCT_IN(mod, ...) \
NETSTRUCT_GET(__VA_ARGS__, NETSTRUCT4, NETSTRUCT3, NETSTRUCT2, NETSTRUCT1) \
(mod, __VA_ARGS__)
// entrypoint of out library
#define NETSTRUCT(name, ...) \
\
struct name { \
NETSTRUCT_IN(dec, __VA_ARGS__) \
} __attribute__((__packed__)); \
\
void name##_hton(struct name *t) { \
NETSTRUCT_IN(hton, __VA_ARGS__) \
} \
\
void name##_ntoh(struct name *t) { \
NETSTRUCT_IN(ntoh, __VA_ARGS__) \
}
/* -------------------------------------------------------- */
// adding custom type
#define NETSTRUCT_dec_uint8_t_arr_8(n) uint8_t n[8];
#define NETSTRUCT_hton_uint8_t_arr_8(n) do{}while(0);
#define NETSTRUCT_ntoh_uint8_t_arr_8(n) do{}while(0);
NETSTRUCT(reg_file,
(uint32_t, start_pos),
(uint32_t, byte_count),
(uint16_t, name_len),
(uint8_t_arr_8, example_custom_array)
);
int main() {
struct reg_file t;
reg_file_hton(&t);
reg_file_ntoh(&t);
}
I have written the mactos so it's easy to add another function, most probably void name##serialize(char *in)
and void name##deserialize(const char *out)
. The design can be slightly refactored so that type callbacks NETSTRUCT_dec_*
take two or even unknown number of arguments with ex. NETSTRUCT(name, (type_callback_suffix, (arguments, arguments2)))
.
@edit added custom array type example and some lines order changing.