DNM: WIP: Rewrite sntp in Lua with only a little C

Currently known defects:

* Lots of print() debugging still present
* No real handling of LI
* No RTC rate support
* Docs light, and none for sntppkt

Doubtless plenty of others, too.

Author: nwf

app/modules/sntppkt.c

@@ -0,0 +1,315 @@
+/*
+ * 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 "c_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 root_delay;
+  uint32_t root_dispersion;
+  uint32_t refid;
+  ntp_timestamp_t ref;
+  ntp_timestamp_t origin;
+  ntp_timestamp_t recv;
+  ntp_timestamp_t xmit;
+} __attribute__((packed)) ntp_frame_t;
+
+typedef struct {
+    int64_t   delta;
+    uint32_t  cached_delay;
+    uint32_t  txsec;
+    uint32_t  delay_frac;
+    uint32_t  root_delay;
+    uint32_t  root_dispersion;
+    uint8_t   LI;
+    uint8_t   stratum;
+} 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.
+ */
+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 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, "sntppkt.resp");
+  lua_setmetatable(L, -2);
+
+  ntpr->LI              = pktb.LI;
+  ntpr->stratum         = pktb.stratum;
+  ntpr->root_delay      = ntohl(pktb.root_delay);
+  ntpr->root_dispersion = ntohl(pktb.root_dispersion);
+
+  /* Heavy time lifting time */
+
+  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);
+
+  ntpr->txsec = pktb.xmit.sec - NTP_TO_UNIX_EPOCH;
+
+  uint64_t ntp_recv   = (((uint64_t) pktb.recv.sec               ) << 32)
+                        + pktb.recv.frac;
+  uint64_t ntp_origin = (((uint64_t) pktb.origin.sec             ) << 32)
+                        + pktb.origin.frac;
+  uint64_t ntp_xmit   = (((uint64_t) pktb.xmit.sec               ) << 32)
+                        + pktb.xmit.frac;
+  uint64_t ntp_dest   = (((uint64_t) now_sec + NTP_TO_UNIX_EPOCH ) << 32)
+                        + sntppkt_us_to_frac(now_usec);
+
+  ntpr->delta = ((int64_t) ntp_recv - ntp_origin) / 2
+              + ((int64_t) ntp_xmit - ntp_dest  ) / 2;
+
+  ntpr->delay_frac = ((int64_t)ntp_dest - ntp_origin - ntp_xmit + ntp_recv) >> 16;
+
+  ntpr->cached_delay    = ntpr->root_delay * 2 + ntpr->delay_frac;
+
+  return 1;
+}
+
+/*
+ * Left-biased selector of a "preferred" NTP response.  Note that preference
+ * is rather subjective!
+ *
+ * Lua does not make it straightforward to return an existing userdata
+ * object, so instead we merely return a boolean indicating whether the
+ * second argument is superior to the first.
+ */
+
+static int
+sntppkt_pick_resp(lua_State *L) {
+
+  ntp_response_t *a = luaL_checkudata(L, 1, "sntppkt.resp");
+  ntp_response_t *b = luaL_checkudata(L, 2, "sntppkt.resp");
+  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_delay * 3 > b->cached_delay * 4);
+  } else {
+    lua_pushboolean(L, a->cached_delay     > b->cached_delay    );
+  }
+  return 1;
+}
+
+/*
+ * Inflate a NTP response into a Lua table
+ */
+static int
+sntppkt_read_resp(lua_State *L) {
+  ntp_response_t *r = luaL_checkudata(L, 1, "sntppkt.resp");
+
+  lua_createtable(L, 0, 6);
+
+  /* For large corrections, don't bother exposing fine values */
+  int d40 = r->delta >> 40;
+  if (d40 != 0 && d40 != -1) {
+    lua_pushnumber(L, r->delta >> 32);
+    lua_setfield(L, -2, "offset_s");
+  } else {
+    lua_pushnumber(L, (r->delta * MICROSECONDS) >> 32);
+    lua_setfield(L, -2, "offset_us");
+  }
+
+  lua_pushnumber(L, sntppkt_frac16_to_us(r->delay_frac));
+  lua_setfield(L, -2, "delay_us");
+
+  lua_pushnumber(L, sntppkt_frac16_to_us(r->root_delay));
+  lua_setfield(L, -2, "root_delay_us");
+
+  lua_pushnumber(L, r->root_dispersion);
+  lua_setfield(L, -2, "root_dispersion");
+
+  lua_pushnumber(L, r->LI);
+  lua_setfield(L, -2, "leapind");
+
+  lua_pushnumber(L, r->stratum);
+  lua_setfield(L, -2, "stratum");
+
+  return 1;
+}
+
+LROT_BEGIN(sntppkt_resp)
+LROT_END(sntppkt_resp, sntppkt_resp, 0)
+
+static int
+sntppkt_init(lua_State *L)
+{
+  luaL_rometatable(L, "sntppkt.resp"   , 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_FUNCENTRY( pick_resp, sntppkt_pick_resp )
+  LROT_FUNCENTRY( read_resp, sntppkt_read_resp )
+LROT_END( sntppkt, NULL, 0 )
+
+NODEMCU_MODULE(SNTPPKT, "sntppkt", sntppkt, sntppkt_init);