Rewrite sntp in Lua with only a little C

Author: nwf

app/modules/sntppkt.c

@@ -0,0 +1,388 @@
+/*
+ * Copyright 2015 Dius Computing Pty Ltd. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ * - Redistributions in binary form must reproduce the above copyright
+ *   notice, this list of conditions and the following disclaimer in the
+ *   documentation and/or other materials provided with the
+ *   distribution.
+ * - Neither the name of the copyright holders nor the names of
+ *   its contributors may be used to endorse or promote products derived
+ *   from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL
+ * THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
+ * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * @author Johny Mattsson <[email protected]>
+ * @author Nathaniel Wesley Filardo <[email protected]>
+ */
+
+// Module for Simple Network Time Protocol (SNTP) packet processing;
+// see lua_modules/sntp/sntp.lua for the user-friendly bits of this.
+
+#include "module.h"
+#include "lauxlib.h"
+#include "lmem.h"
+#include "os_type.h"
+#include "osapi.h"
+#include "lwip/udp.h"
+#include <stdlib.h>
+#include "user_modules.h"
+#include "lwip/dns.h"
+#include "task/task.h"
+#include "user_interface.h"
+
+#define max(a,b) ((a < b) ? b : a)
+
+#define NTP_PORT 123
+#define NTP_ANYCAST_ADDR(dst)  IP4_ADDR(dst, 224, 0, 1, 1)
+
+#if 0
+# define sntppkt_dbg(...) dbg_printf(__VA_ARGS__)
+#else
+# define sntppkt_dbg(...)
+#endif
+
+typedef struct
+{
+  uint32_t sec;
+  uint32_t frac;
+} ntp_timestamp_t;
+
+static const uint32_t NTP_TO_UNIX_EPOCH = 2208988800ul;
+
+typedef struct
+{
+  uint8_t mode : 3;
+  uint8_t ver : 3;
+  uint8_t LI : 2;
+  uint8_t stratum;
+  uint8_t poll;
+  uint8_t precision;
+  uint32_t delta_r;
+  uint32_t epsilon_r;
+  uint32_t refid;
+  ntp_timestamp_t ref;
+  ntp_timestamp_t origin;
+  ntp_timestamp_t recv;
+  ntp_timestamp_t xmit;
+} __attribute__((packed)) ntp_frame_t;
+
+#define NTP_RESPONSE_METATABLE  "sntppkt.resp"
+typedef struct {
+    /* Copied from incoming packet */
+    uint32_t  delta_r;
+    uint32_t  epsilon_r;
+    uint8_t   LI;
+    uint8_t   stratum;
+
+    /* Computed as per RFC 5905; units are 2^(-32) seconds */
+    int64_t   theta;
+    int64_t   delta;
+
+    /* Local computation */
+    uint32_t  rx_s;
+    uint32_t  rx_us;
+    uint32_t  cached_delta;
+} ntp_response_t;
+
+static uint64_t
+sntppkt_div1m(uint64_t n) {
+  uint64_t q1 = (n >> 5) + (n >> 10);
+  uint64_t q2 = (n >> 12) + (q1 >> 1);
+  uint64_t q3 = (q2 >> 11) - (q2 >> 23);
+
+  uint64_t q = n + q1 + q2 - q3;
+
+  q = q >> 20;
+
+  // Ignore the error term -- it is measured in pico seconds
+  return q;
+}
+
+static uint32_t
+sntppkt_us_to_frac(uint64_t us) {
+  return sntppkt_div1m(us << 32);
+}
+
+static const uint32_t MICROSECONDS      = 1000000;
+
+static uint32_t
+sntppkt_frac16_to_us(uint64_t frac) {
+  return (frac * MICROSECONDS) >> 16;
+}
+
+/*
+ * Convert sec/usec to a Lua string suitable for depositing into a SNTP packet
+ * buffer.  This is a little gross, but it's not the worst thing a C
+ * programmer's ever done, I'm sure.
+ */
+static int
+sntppkt_make_ts(lua_State *L) {
+  ntp_timestamp_t ts;
+  uint32_t usec;
+
+  ts.sec  = htonl(luaL_checkinteger(L, 1) + NTP_TO_UNIX_EPOCH) ;
+  usec    =       luaL_checkinteger(L, 2)  ;
+  ts.frac = htonl(sntppkt_us_to_frac(usec));
+
+  lua_pushlstring(L, (const char *)&ts, sizeof(ts));
+  return 1;
+}
+
+/*
+ * Process a SNTP packet as contained in a Lua string, given a cookie timestamp
+ * and local clock second*usecond pair.  Generates a ntp_response_t userdata
+ * for later processing or a string if the server is telling us to go away.
+ *
+ * :: string (packet)
+ * -> string (cookie)
+ * -> int (local clock, sec component)
+ * -> int (local clock, usec component)
+ * -> sntppkt.resp
+ *
+ */
+static int
+sntppkt_proc_pkt(lua_State *L) {
+  const char  *pkts;
+  size_t       pkts_len;
+
+  uint32_t     now_sec;
+  uint32_t     now_usec;
+
+  ntp_timestamp_t *cookie;
+  size_t           cookie_len;
+
+  ntp_response_t *ntpr;
+
+  // make sure we have an aligned copy to work from
+  // XXX nwf: is this necessary?
+  ntp_frame_t  pktb;
+
+  now_usec = luaL_checkinteger(L, 4);
+  now_sec  = luaL_checkinteger(L, 3);
+
+  luaL_checktype(L, 2, LUA_TSTRING);
+  cookie   = (ntp_timestamp_t*) lua_tolstring(L, 2, &cookie_len);
+  if (cookie_len != sizeof(*cookie)) {
+    luaL_error(L, "Bad expected cookie");
+  }
+
+  luaL_checktype(L, 1, LUA_TSTRING);
+  pkts = lua_tolstring(L, 1, &pkts_len);
+  if (pkts_len != sizeof(pktb)) {
+    luaL_error(L, "Bad packet length");
+  }
+  os_memcpy (&pktb, pkts, sizeof(pktb));
+
+  if (memcmp((const char *)cookie, (const char *)&pktb.origin, sizeof (*cookie))) {
+    /* bad cookie; return nil */
+    return 0;
+  }
+
+  /* KOD? */
+  if (pktb.LI == 3) {
+    lua_pushlstring(L, (const char *)&pktb.refid, 4);
+    return 1;
+  }
+
+  ntpr = lua_newuserdata(L, sizeof(ntp_response_t));
+  luaL_getmetatable(L, NTP_RESPONSE_METATABLE);
+  lua_setmetatable(L, -2);
+
+  ntpr->rx_s      = now_sec;
+  ntpr->rx_us     = now_usec;
+  ntpr->LI        = pktb.LI;
+  ntpr->stratum   = pktb.stratum;
+
+  // NTP Short Format: 16 bit seconds, 16 bit fraction
+  ntpr->delta_r   = ntohl(pktb.delta_r);
+  ntpr->epsilon_r = ntohl(pktb.epsilon_r);
+
+  /* Heavy time lifting time */
+
+  // NTP Long Format: 32 bit seconds, 32 bit fraction
+  pktb.origin.sec  = ntohl(pktb.origin.sec);
+  pktb.origin.frac = ntohl(pktb.origin.frac);
+  pktb.recv.sec    = ntohl(pktb.recv.sec);
+  pktb.recv.frac   = ntohl(pktb.recv.frac);
+  pktb.xmit.sec    = ntohl(pktb.xmit.sec);
+  pktb.xmit.frac   = ntohl(pktb.xmit.frac);
+
+  // When we sent it (our clock)
+  uint64_t ntp_origin = (((uint64_t) pktb.origin.sec             ) << 32)
+                        + pktb.origin.frac;
+  // When they got it (their clock)
+  uint64_t ntp_recv   = (((uint64_t) pktb.recv.sec               ) << 32)
+                        + pktb.recv.frac;
+  // When they replied (their clock)
+  uint64_t ntp_xmit   = (((uint64_t) pktb.xmit.sec               ) << 32)
+                        + pktb.xmit.frac;
+  // When we got it back (our clock)
+  uint64_t ntp_dest   = (((uint64_t) now_sec + NTP_TO_UNIX_EPOCH ) << 32)
+                        + sntppkt_us_to_frac(now_usec);
+
+              // |       outgoing offset           |   |        incoming offset         |
+  ntpr->theta = (int64_t)(ntp_recv - ntp_origin) / 2 + (int64_t)(ntp_xmit - ntp_dest) / 2;
+
+              // |       our clock delta           |   |       their clock delta        |
+  ntpr->delta = (int64_t)(ntp_dest - ntp_origin) / 2 + (int64_t)(ntp_xmit - ntp_recv) / 2;
+
+  ntpr->cached_delta = ntpr->delta_r + (ntpr->delta >> 17);
+
+  sntppkt_dbg("SNTPPKT PROC n_r=%llx n_o=%llx n_x=%llx n_d=%llx th=%llx "
+    "d=%llx + %lx = cd=%lx\n",
+    ntp_recv, ntp_origin, ntp_xmit, ntp_dest, ntpr->theta,
+    ntpr->delta, ntpr->delta_r, ntpr->cached_delta);
+
+  return 1;
+}
+
+/*
+ * Left-biased selector of a "preferred" NTP response.  Note that preference
+ * is rather subjective!
+ *
+ * Returns true iff we'd prefer the second response to the first.
+ *
+ * :: sntppkt.resp -> sntppkt.resp -> boolean
+ */
+
+static int
+sntppkt_resp_pick(lua_State *L) {
+
+  ntp_response_t *a = luaL_checkudata(L, 1, NTP_RESPONSE_METATABLE);
+  ntp_response_t *b = luaL_checkudata(L, 2, NTP_RESPONSE_METATABLE);
+  int biased = 0;
+
+  biased = lua_toboolean(L, 3);
+
+  /*
+   * If we're "biased", prefer the second structure if the delay less than
+   * 3/4ths of the delay in the first.  An unbiased comparison just uses
+   * the raw delay values.
+   */
+  if (biased) {
+    lua_pushboolean(L, a->cached_delta * 3 > b->cached_delta * 4);
+  } else {
+    lua_pushboolean(L, a->cached_delta     > b->cached_delta    );
+  }
+  return 1;
+}
+
+static void
+field_from_number(lua_State *L, const char * field_name, lua_Number value) {
+  lua_pushnumber(L, value);
+  lua_setfield(L, -2, field_name);
+}
+
+/*
+ * Inflate a NTP response into a Lua table
+ *
+ * :: sntppkt.resp -> { }
+ */
+static int
+sntppkt_resp_totable(lua_State *L) {
+  ntp_response_t *r = luaL_checkudata(L, 1, NTP_RESPONSE_METATABLE);
+
+  lua_createtable(L, 0, 6);
+
+  sntppkt_dbg("SNTPPKT READ th=%llx\n", r->theta);
+
+  field_from_number(L, "theta_s", r->theta >> 32);
+  field_from_number(L, "theta_us", ((r->theta & 0xFFFFFFFF) * MICROSECONDS) >> 32);
+
+  field_from_number(L, "delta", r->delta >> 16);
+  field_from_number(L, "delta_r", r->delta_r);
+  field_from_number(L, "epsilon_r", r->epsilon_r);
+
+  field_from_number(L, "leapind", r->LI);
+  field_from_number(L, "stratum", r->stratum);
+  field_from_number(L, "rx_s"   , r->rx_s);
+  field_from_number(L, "rx_us"  , r->rx_us);
+
+  return 1;
+}
+
+/*
+ * Compute local RTC drift rate given a SNTP response, previous sample time,
+ * and error integral value.  Returns new rate and integral value.
+ *
+ * Results are only sensible if resp->theta is sufficiently small (i.e., less
+ * than a second) and the inter-sample duration must, of course, be positive.
+ *
+ * :: sntppkt.resp
+ * -> int (prior sample time, seconds component)
+ * -> int (prior sample time, microseconds component)
+ * -> int (integral)
+ * -> int (rate), int (integral)
+ *
+ */
+static int
+sntppkt_resp_drift_compensate(lua_State *L) {
+  ntp_response_t *resp = luaL_checkudata(L, 1, NTP_RESPONSE_METATABLE);
+
+  int32_t theta32 = resp->theta >> 32;
+  if (theta32 != 0 && theta32 != -1) {
+    return luaL_error(L, "Large deviation");
+  }
+
+  uint32_t prior_s  = luaL_checkinteger(L, 2);
+  uint32_t prior_us = luaL_checkinteger(L, 3);
+  int32_t  err_int  = luaL_checkinteger(L, 4);
+
+  uint64_t prior    = ((uint64_t)prior_s    << 32) + sntppkt_us_to_frac(   prior_us);
+  uint64_t rx       = ((uint64_t)resp->rx_s << 32) + sntppkt_us_to_frac(resp->rx_us);
+
+  int64_t  isdur    = rx - prior;
+  if (isdur <= 0) {
+    return luaL_error(L, "Negative time base");
+  }
+
+  /* Compute our drift rate over 2 */
+  int32_t drift2 = ((resp->theta << 31) / isdur) >> 32;
+
+  int32_t newrate = drift2 * 2 + err_int;
+  err_int += drift2 >> 1;
+
+  lua_pushnumber(L, newrate);
+  lua_pushnumber(L, err_int);
+  return 2;
+}
+
+LROT_BEGIN(sntppkt_resp)
+  LROT_FUNCENTRY( pick, sntppkt_resp_pick )
+  LROT_FUNCENTRY( totable, sntppkt_resp_totable )
+  LROT_FUNCENTRY( drift_compensate, sntppkt_resp_drift_compensate )
+
+  LROT_TABENTRY( __index, sntppkt_resp )
+LROT_END(sntppkt_resp, sntppkt_resp, 0)
+
+static int
+sntppkt_init(lua_State *L)
+{
+  luaL_rometatable(L, NTP_RESPONSE_METATABLE, LROT_TABLEREF(sntppkt_resp));
+  return 0;
+}
+
+// Module function map
+LROT_BEGIN(sntppkt)
+  LROT_FUNCENTRY( make_ts  , sntppkt_make_ts   )
+  LROT_FUNCENTRY( proc_pkt , sntppkt_proc_pkt  )
+LROT_END( sntppkt, NULL, 0 )
+
+NODEMCU_MODULE(SNTPPKT, "sntppkt", sntppkt, sntppkt_init);