Use C code from pgsql-hackers

pg_uuidv7.c

@@ -16,35 +16,107 @@ PG_MODULE_MAGIC;
 
 PG_FUNCTION_INFO_V1(uuid_generate_v7);
 
+#define UUID_RND_CACHE_LEN 64
+int rnd_cache_ptr = UUID_RND_CACHE_LEN;
+unsigned char random_cache[UUID_RND_CACHE_LEN];
+
+static bool
+cached_strong_random(void *buf, size_t len)
+{
+	if (len + rnd_cache_ptr >= UUID_RND_CACHE_LEN)
+	{
+		if (!pg_strong_random(random_cache, UUID_RND_CACHE_LEN))
+			return false;
+		rnd_cache_ptr = 0;
+	}
+	memcpy(buf, &random_cache[rnd_cache_ptr], len);
+	rnd_cache_ptr += len;
+	return true;
+}
+
+static uint32_t sequence_counter;
+static uint64_t previous_timestamp = 0;
+
 Datum uuid_generate_v7(PG_FUNCTION_ARGS)
 {
-	pg_uuid_t *uuid = palloc(UUID_LEN);
-	struct timespec ts;
+	pg_uuid_t  *uuid = palloc(UUID_LEN);
 	uint64_t tms;
+	struct timespec ts;
 
-	if (!pg_strong_random(uuid, UUID_LEN))
-		ereport(ERROR,
-				(errcode(ERRCODE_INTERNAL_ERROR),
-				 errmsg("could not generate random values")));
-
-	/*
-	 * Set first 48 bits to unix epoch timestamp
-	 */
 	if (clock_gettime(CLOCK_REALTIME, &ts) != 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_INTERNAL_ERROR),
 				 errmsg("could not get CLOCK_REALTIME")));
 
 	tms = ((uint64_t)ts.tv_sec * 1000) + ((uint64_t)ts.tv_nsec / 1000000);
-	tms = pg_hton64(tms << 16);
-	memcpy(&uuid->data[0], &tms, 6);
+
+	if (tms <= previous_timestamp)
+	{
+		/* Time did not increment from the previous generation, we must increment counter */
+		++sequence_counter;
+		if (sequence_counter > 0x3ffff)
+		{
+			/* We only have 18-bit counter */
+			sequence_counter = 0;
+			previous_timestamp++;
+		}
+
+		/* protection from leap backward */
+		tms = previous_timestamp;
+
+		/* fill everything after the timestamp and counter with random bytes */
+		if (!cached_strong_random(&uuid->data[8], UUID_LEN - 8))
+			ereport(ERROR,
+					(errcode(ERRCODE_INTERNAL_ERROR),
+					errmsg("could not generate random values")));
+
+		/* most significant 4 bits of 18-bit counter */
+		uuid->data[6] = (unsigned char)(sequence_counter >> 14);
+		/* next 8 bits */
+		uuid->data[7] = (unsigned char)(sequence_counter >> 6);
+		/* least significant 6 bits */
+		uuid->data[8] = (unsigned char)(sequence_counter);
+	}
+	else
+	{
+		/* fill everything after the timestamp with random bytes */
+		if (!cached_strong_random(&uuid->data[6], UUID_LEN - 6))
+			ereport(ERROR,
+					(errcode(ERRCODE_INTERNAL_ERROR),
+					errmsg("could not generate random values")));
+
+		/*
+		 * Left-most counter bits are initialized as zero for the sole purpose
+		 * of guarding against counter rollovers.
+		 * See section "Fixed-Length Dedicated Counter Seeding"
+		 * https://datatracker.ietf.org/doc/html/draft-ietf-uuidrev-rfc4122bis-09#monotonicity_counters
+		 */
+		uuid->data[6] = (uuid->data[6] & 0xf7);
+
+		sequence_counter = ((uint32_t)uuid->data[8] & 0x3f) +
+							(((uint32_t)uuid->data[7]) << 6) +
+							(((uint32_t)uuid->data[6] & 0x0f) << 14);
+
+		previous_timestamp = tms;
+	}
+
+	/* Fill in time part */
+	uuid->data[0] = (unsigned char)(tms >> 40);
+	uuid->data[1] = (unsigned char)(tms >> 32);
+	uuid->data[2] = (unsigned char)(tms >> 24);
+	uuid->data[3] = (unsigned char)(tms >> 16);
+	uuid->data[4] = (unsigned char)(tms >> 8);
+	uuid->data[5] = (unsigned char)tms;
 
 	/*
-	 * Set magic numbers for a "version 7" UUID, see
-	 * https://www.ietf.org/archive/id/draft-ietf-uuidrev-rfc4122bis-00.html#name-uuid-version-7
+	 * Set magic numbers for a "version 7" (pseudorandom) UUID, see
+	 * http://tools.ietf.org/html/rfc ???
+	 * https://datatracker.ietf.org/doc/html/draft-peabody-dispatch-new-uuid-format#name-creating-a-uuidv7-value
 	 */
-	uuid->data[6] = (uuid->data[6] & 0x0f) | 0x70; /* 4 bit version [0111] */
-	uuid->data[8] = (uuid->data[8] & 0x3f) | 0x80; /* 2 bit variant [10]   */
+	/* set version field, top four bits are 0, 1, 1, 1 */
+	uuid->data[6] = (uuid->data[6] & 0x0f) | 0x70;
+	/* set variant field, top two bits are 1, 0 */
+	uuid->data[8] = (uuid->data[8] & 0x3f) | 0x80;
 
 	PG_RETURN_UUID_P(uuid);
 }