messages/codec.h
#ifndef URMS_CODEC_H
#define URMS_CODEC_H
#include <stddef.h>
#include <stdint.h>
#include <string.h>
#define URMS_SUBPROTOCOL 4096
#define URMS_MAX_FRAME 4112
typedef struct {
uint8_t kind;
uint64_t id;
const uint8_t *text;
size_t length;
} urms_frame;
/* Validate Unicode scalars: reject overlong encodings, surrogates and
* >U+10FFFF. */
static int urms_utf8(const uint8_t *p, size_t n) {
for (size_t i = 0; i < n;) {
uint32_t c = p[i++], min = 0;
unsigned more = 0;
if (c < 0x80)
continue;
if (c >= 0xc2 && c <= 0xdf) {
c &= 0x1f;
more = 1;
min = 0x80;
} else if (c >= 0xe0 && c <= 0xef) {
c &= 15;
more = 2;
min = 0x800;
} else if (c >= 0xf0 && c <= 0xf4) {
c &= 7;
more = 3;
min = 0x10000;
} else
return 0;
if (n - i < more)
return 0;
while (more--) {
uint8_t v = p[i++];
if ((v & 0xc0) != 0x80)
return 0;
c = (c << 6) | (v & 0x3f);
}
if (c < min || c > 0x10ffff || (c >= 0xd800 && c <= 0xdfff))
return 0;
}
return 1;
}
static size_t urms_encode(uint8_t *out, size_t capacity, uint8_t kind,
uint64_t id, const uint8_t *text, size_t n) {
if (!id || (kind != 1 && kind != 2) || n > 4096 || (kind == 2 && n) ||
capacity < 16 + n || !urms_utf8(text, n))
return 0;
memcpy(out, "URMS", 4);
out[4] = 1;
out[5] = kind;
out[6] = (uint8_t)(n >> 8);
out[7] = (uint8_t)n;
for (unsigned i = 0; i < 8; i++)
out[8 + i] = (uint8_t)(id >> (56 - 8 * i));
if (n)
memcpy(out + 16, text, n);
return 16 + n;
}
static int urms_decode(const uint8_t *b, size_t n, urms_frame *f) {
if (n < 16 || n > URMS_MAX_FRAME || memcmp(b, "URMS", 4) || b[4] != 1 ||
(b[5] != 1 && b[5] != 2) || (((size_t)b[6] << 8) | b[7]) != n - 16 ||
(b[5] == 2 && n != 16) || !urms_utf8(b + 16, n - 16))
return 0;
uint64_t id = 0;
for (unsigned i = 8; i < 16; i++)
id = (id << 8) | b[i];
if (!id)
return 0;
f->kind = b[5];
f->id = id;
f->text = b + 16;
f->length = n - 16;
return 1;
}
static inline int urms_self_test(void) {
const uint8_t golden[] = {0x55, 0x52, 0x4d, 0x53, 1, 1, 0, 2, 0,
0, 0, 0, 0, 0, 0, 1, 0x68, 0x69};
const uint8_t ack[] = {0x55, 0x52, 0x4d, 0x53, 1, 2, 0, 0,
0, 0, 0, 0, 0, 0, 0, 1};
uint8_t b[URMS_MAX_FRAME + 1], text[4097];
urms_frame f;
if (urms_encode(b, sizeof(b), 1, 1, (const uint8_t *)"hi", 2) !=
sizeof(golden) ||
memcmp(b, golden, sizeof(golden)))
return 1;
if (!urms_decode(golden, sizeof(golden), &f) || f.kind != 1 || f.id != 1 ||
f.length != 2)
return 1;
if (urms_encode(b, sizeof(b), 2, 1, NULL, 0) != sizeof(ack) ||
memcmp(b, ack, sizeof(ack)) || !urms_decode(ack, sizeof(ack), &f))
return 1;
memset(text, 'x', sizeof(text));
size_t n = urms_encode(b, sizeof(b), 1, UINT64_MAX, text, 4096);
if (n != URMS_MAX_FRAME || !urms_decode(b, n, &f) || f.id != UINT64_MAX)
return 1;
b[n] = 0;
if (urms_decode(b, n + 1, &f))
return 1;
const uint8_t unicode[] = {0xc3, 0xa9, 0xf0, 0x9f, 0x99, 0x82, 0};
n = urms_encode(b, sizeof(b), 1, 7, unicode, sizeof(unicode));
if (!n || !urms_decode(b, n, &f) || f.length != sizeof(unicode))
return 1;
n = urms_encode(b, sizeof(b), 1, 1, NULL, 0);
if (!n || !urms_decode(b, n, &f))
return 1;
for (size_t i = 0; i < sizeof(golden); i++)
if (urms_decode(golden, i, &f))
return 1;
const unsigned edits[][2] = {{0, 0}, {4, 2}, {5, 3}, {5, 2},
{6, 16}, {7, 1}, {15, 0}};
for (size_t i = 0; i < sizeof(edits) / sizeof(*edits); i++) {
memcpy(b, golden, sizeof(golden));
b[edits[i][0]] = (uint8_t)edits[i][1];
if (urms_decode(b, sizeof(golden), &f))
return 1;
}
memcpy(b, golden, sizeof(golden));
b[18] = 0;
if (urms_decode(b, 19, &f))
return 1;
b[16] = 0xc0;
b[17] = 0xaf;
if (urms_decode(b, 18, &f))
return 1;
const uint8_t bad[][4] = {{0xed, 0xa0, 0x80, 0},
{0xf4, 0x90, 0x80, 0x80},
{0xe2, 0x82, 0, 0},
{0x80, 0, 0, 0}};
for (size_t i = 0; i < 4; i++)
if (urms_encode(b, sizeof(b), 1, 1, bad[i], 4))
return 1;
if (urms_encode(b, sizeof(b), 1, 0, NULL, 0) ||
urms_encode(b, sizeof(b), 2, 1, text, 1) ||
urms_encode(b, sizeof(b), 3, 1, NULL, 0) ||
urms_encode(b, sizeof(b), 1, 1, text, 4097))
return 1;
return 0;
}
#endif
