Initial commit

10 files changed, 576 insertions, 0 deletions

diff --git a/src/clock/deps-exe/s6-clockadd b/src/clock/deps-exe/s6-clockadd
new file mode 100644
index 0000000..a11a5f4
--- /dev/null
+++ b/src/clock/deps-exe/s6-clockadd
@@ -0,0 +1,2 @@
+-lskarnet
+${SYSCLOCK_LIB}
diff --git a/src/clock/deps-exe/s6-clockview b/src/clock/deps-exe/s6-clockview
new file mode 100644
index 0000000..a11a5f4
--- /dev/null
+++ b/src/clock/deps-exe/s6-clockview
@@ -0,0 +1,2 @@
+-lskarnet
+${SYSCLOCK_LIB}
diff --git a/src/clock/deps-exe/s6-sntpclock b/src/clock/deps-exe/s6-sntpclock
new file mode 100644
index 0000000..e027835
--- /dev/null
+++ b/src/clock/deps-exe/s6-sntpclock
@@ -0,0 +1,3 @@
+-lskarnet
+${SOCKET_LIB}
+${TAINNOW_LIB}
diff --git a/src/clock/deps-exe/s6-taiclock b/src/clock/deps-exe/s6-taiclock
new file mode 100644
index 0000000..e027835
--- /dev/null
+++ b/src/clock/deps-exe/s6-taiclock
@@ -0,0 +1,3 @@
+-lskarnet
+${SOCKET_LIB}
+${TAINNOW_LIB}
diff --git a/src/clock/deps-exe/s6-taiclockd b/src/clock/deps-exe/s6-taiclockd
new file mode 100644
index 0000000..720fe7d
--- /dev/null
+++ b/src/clock/deps-exe/s6-taiclockd
@@ -0,0 +1,3 @@
+-lskarnet
+${SOCKET_LIB}
+${SYSCLOCK_LIB}
diff --git a/src/clock/s6-clockadd.c b/src/clock/s6-clockadd.c
new file mode 100644
index 0000000..990f3ba
--- /dev/null
+++ b/src/clock/s6-clockadd.c
@@ -0,0 +1,58 @@
+/* ISC license. */
+
+#include <skalibs/sgetopt.h>
+#include <skalibs/uint.h>
+#include <skalibs/allreadwrite.h>
+#include <skalibs/strerr2.h>
+#include <skalibs/tai.h>
+
+#define USAGE "s6-clockadd [ -f ] [ -e errmax ]"
+#define dieusage() strerr_dieusage(100, USAGE)
+
+int main (int argc, char const *const *argv)
+{
+  tain_t now, adj ;
+  unsigned int emax = 2000 ;
+  int flagforce = 0 ;
+  PROG = "s6-clockadd" ;
+  {
+    subgetopt_t l = SUBGETOPT_ZERO ;
+    for (;;)
+    {
+      register int opt = subgetopt_r(argc, argv, "fe:", &l) ;
+      if (opt == -1) break ;
+      switch (opt)
+      {
+        case 'f' : flagforce = 1 ; break ;
+        case 'e' : if (!uint0_scan(l.arg, &emax)) dieusage() ; break ;
+        default : dieusage() ;
+      }
+    }
+    argc -= l.ind ; argv += l.ind ;
+  }
+  {
+    char buf[TAIN_PACK] ;
+    if (allread(0, buf, TAIN_PACK) < TAIN_PACK)
+      strerr_diefu1sys(111, "read 16 bytes from stdin") ;
+    tain_unpack(buf, &adj) ;
+  }
+  tain_from_millisecs(&now, emax) ;
+  if (tain_less(&now, &adj))
+  {
+    tain_t tmp = TAIN_ZERO ;
+    tain_sub(&tmp, &tmp, &adj) ;
+    if (tain_less(&now, &tmp))
+    {
+      char fmt[UINT_FMT] ;
+      fmt[uint_fmt(fmt, emax)] = 0 ;
+      if (flagforce)
+        strerr_warnw3x("time discrepancy bigger than ", fmt, " milliseconds") ;
+      else
+        strerr_dief3x(1, "time discrepancy bigger than ", fmt, " milliseconds") ;
+    }
+  }
+  if (!sysclock_get(&now)) strerr_diefu1sys(111, "sysclock_get") ;
+  tain_add(&now, &now, &adj) ;
+  if (!sysclock_set(&now)) strerr_diefu1sys(111, "sysclock_set") ;
+  return 0 ;
+}
diff --git a/src/clock/s6-clockview.c b/src/clock/s6-clockview.c
new file mode 100644
index 0000000..3600cce
--- /dev/null
+++ b/src/clock/s6-clockview.c
@@ -0,0 +1,31 @@
+/* ISC license. */
+
+#include <skalibs/allreadwrite.h>
+#include <skalibs/buffer.h>
+#include <skalibs/strerr2.h>
+#include <skalibs/tai.h>
+#include <skalibs/djbtime.h>
+
+int main (void)
+{
+  char buf[TAIN_PACK] ;
+  tain_t now, adj ;
+  localtmn_t l ;
+  char fmt[LOCALTMN_FMT] ;
+  PROG = "s6-clockview" ;
+
+  if (allread(0, buf, TAIN_PACK) < TAIN_PACK) strerr_diefu1sys(111, "read from stdin") ;
+  tain_unpack(buf, &adj) ;
+  if (!sysclock_get(&now)) strerr_diefu1sys(111, "sysclock_get") ;
+  if (!localtmn_from_sysclock(&l, &now, 1)) strerr_diefu1sys(111, "localtmn_from_sysclock") ;
+  if (buffer_puts(buffer_1, "before: ") < 0) goto fail ;
+  if (buffer_put(buffer_1, fmt, localtmn_fmt(fmt, &l)) < 0) goto fail ;
+  tain_add(&now, &now, &adj) ;
+  if (!localtmn_from_sysclock(&l, &now, 1)) strerr_diefu1sys(111, "localtmn_from_sysclock") ;
+  if (buffer_puts(buffer_1, "\nafter:  ") < 0) goto fail ;
+  if (buffer_put(buffer_1, fmt, localtmn_fmt(fmt, &l)) < 0) goto fail ;
+  if (buffer_putflush(buffer_1, "\n", 1) < 0) goto fail ;
+  return 0 ;
+ fail:
+  strerr_diefu1sys(111, "write to stdout") ;
+}
diff --git a/src/clock/s6-sntpclock.c b/src/clock/s6-sntpclock.c
new file mode 100644
index 0000000..a7bcc22
--- /dev/null
+++ b/src/clock/s6-sntpclock.c
@@ -0,0 +1,238 @@
+/* ISC license. */
+
+#include <sys/types.h>
+#include <unistd.h>
+#include <errno.h>
+#include <skalibs/error.h>
+#include <skalibs/uint16.h>
+#include <skalibs/uint32.h>
+#include <skalibs/uint.h>
+#include <skalibs/sgetopt.h>
+#include <skalibs/allreadwrite.h>
+#include <skalibs/bytestr.h>
+#include <skalibs/error.h>
+#include <skalibs/strerr2.h>
+#include <skalibs/tai.h>
+#include <skalibs/djbtime.h>
+#include <skalibs/iopause.h>
+#include <skalibs/allreadwrite.h>
+#include <skalibs/socket.h>
+#include <skalibs/ip46.h>
+
+#define USAGE "s6-sntpclock [ -f ] [ -v verbosity ] [ -r roundtrips ] [ -t triptimeout ] [ -h throttle ] [ -T totaltimeout ] [ -e errmax ] [ -p port ] ipaddress"
+#define dieusage() strerr_dieusage(100, USAGE)
+
+static unsigned int verbosity = 1 ;
+
+int ntp_exchange (int s, ip46_t const *ip, uint16 port, tain_t *stamps, tain_t const *deadline)
+{
+  char query[48] = "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0" ;
+  char answer[48] = "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0" ;
+  tain_t starttime ;
+  uint64 ntpstamp ;
+  ip46_t dummyip ;
+  uint16 dummyport ;
+  int r ;
+  tain_copynow(&starttime) ;
+  query[0] = 35 ; /* SNTPv4, client */
+  if (!ntp_from_tain(&ntpstamp, &starttime)) return 0 ;
+  uint64_pack_big(query+24, ntpstamp) ;
+  uint64_pack_big(query+40, ntpstamp) ;
+  if (verbosity >= 3)
+  {
+    char fmtntp[UINT64_XFMT] ;
+    fmtntp[uint64_xfmt(fmtntp, ntpstamp)] = 0 ;
+    strerr_warni2x("NTP stamp[0] sent: ", fmtntp) ;
+  }
+  r = socket_sendnb46_g(s, query, 48, ip, port, deadline) ;
+  if (r < 0) return 0 ;
+  if (r < 48) return (errno = EPIPE, 0) ;
+  r = socket_recvnb46_g(s, answer, 48, &dummyip, &dummyport, deadline) ;
+  if (r < 0) return 0 ;
+  if (r < 48) return (errno = EPROTO, 0) ;
+  if (((answer[0] & 7) != 2) && ((answer[0] & 7) != 4)) return (errno = EPROTO, 0) ;
+  if (!(answer[0] & 56)) return (errno = EPROTO, 0) ;
+  if (byte_diff(query+40, 8, answer+24)) return (errno = EPROTO, 0) ;
+  stamps[0] = starttime ;
+  uint64_unpack_big(answer+32, &ntpstamp) ;
+  tain_from_ntp(stamps+1, ntpstamp) ;
+  if (verbosity >= 3)
+  {
+    char fmtntp[UINT64_XFMT] ;
+    fmtntp[uint64_xfmt(fmtntp, ntpstamp)] = 0 ;
+    strerr_warni2x("NTP stamp[1] received: ", fmtntp) ;
+  }
+  uint64_unpack_big(answer+40, &ntpstamp) ;
+  tain_from_ntp(stamps+2, ntpstamp) ;
+  if (verbosity >= 3)
+  {
+    char fmtntp[UINT64_XFMT] ;
+    fmtntp[uint64_xfmt(fmtntp, ntpstamp)] = 0 ;
+    strerr_warni2x("NTP stamp[2] received: ", fmtntp) ;
+  }
+  tain_copynow(&stamps[3]) ;
+  return 1 ;
+}
+
+int main (int argc, char const *const *argv)
+{
+  tain_t deltamin = TAIN_ZERO ;
+  tain_t deltaoffset ;
+  tain_t deltamax ;
+  tain_t errmax ;
+  tain_t timeouttto, throttletto, globaltto ;
+  tain_t globaldeadline ;
+  unsigned int roundtrips = 10 ;
+  unsigned int i = 0 ;
+  int sock ;
+  int flagforce = 0 ;
+  ip46_t ipremote ;
+  uint16 portremote = 123 ;
+  PROG = "s6-sntpclock" ;
+
+  {
+    unsigned int timeout = 2000 ;
+    unsigned int throttle = 0 ;
+    unsigned int bigtimeout = 10000 ;
+    unsigned int emax = 100 ;
+    subgetopt_t l = SUBGETOPT_ZERO ;
+    for (;;)
+    {
+      register int opt = subgetopt_r(argc, argv, "fv:r:t:h:T:e:p:", &l) ;
+      if (opt == -1) break ;
+      switch (opt)
+      {
+        case 'f' : flagforce = 1 ; break ;
+        case 'v' : if (!uint0_scan(l.arg, &verbosity)) dieusage() ; break ;
+        case 'r' : if (!uint0_scan(l.arg, &roundtrips)) dieusage() ; break ;
+        case 't' : if (!uint0_scan(l.arg, &timeout)) dieusage() ; break ;
+        case 'h' : if (!uint0_scan(l.arg, &throttle)) dieusage() ; break ;
+        case 'T' : if (!uint0_scan(l.arg, &bigtimeout)) dieusage() ; break ;
+        case 'e' : if (!uint0_scan(l.arg, &emax)) dieusage() ; break ;
+        case 'p' : if (!uint160_scan(l.arg, &portremote)) dieusage() ; break ;
+        default : dieusage() ;
+      }
+    }
+    argc -= l.ind ; argv += l.ind ;
+    if (timeout) tain_from_millisecs(&timeouttto, timeout) ;
+    else timeouttto = tain_infinite_relative ;
+    tain_from_millisecs(&throttletto, throttle) ;
+    if (bigtimeout) tain_from_millisecs(&globaltto, bigtimeout) ;
+    else globaltto = tain_infinite_relative ;
+    tain_from_millisecs(&errmax, emax) ;
+  }
+  if (!argc) dieusage() ;
+  if (!ip46_scan(argv[0], &ipremote)) dieusage() ;
+
+  sock = socket_udp46(ip46_is6(&ipremote)) ;
+  if (sock < 0) strerr_diefu1sys(111, "socket_udp") ;
+
+  tain_uint(&deltaoffset, 1072224000U) ; /* about 34 years, which is the best we can do with NTP */
+  tain_add(&deltamax, &deltaoffset, &deltaoffset) ;
+  tain_now_g() ;
+  tain_add_g(&globaldeadline, &globaltto) ;
+  if (!socket_deadlineconnstamp46_g(sock, &ipremote, portremote, &globaldeadline))
+    strerr_diefu1sys(111, "socket_deadlineconnstamp") ;
+
+  for (; i < roundtrips ; i++)
+  {
+    tain_t stamps[4] ;
+    tain_t deadline ;
+    tain_add_g(&deadline, &timeouttto) ;
+    if (tain_less(&globaldeadline, &deadline)) deadline = globaldeadline ;
+    if (verbosity >= 3)
+    {
+      char fmt[UINT_FMT] ;
+      char fmtr[UINT_FMT] ;
+      fmt[uint_fmt(fmt, i+1)] = 0 ;
+      fmtr[uint_fmt(fmtr, roundtrips)] = 0 ;
+      strerr_warni4x("NTP round-trip ", fmt, "/", fmtr) ;
+    }
+    if (!ntp_exchange(sock, &ipremote, portremote, stamps, &deadline))
+    {
+      if (verbosity >= 2)
+      {
+        char fmt[UINT_FMT] ;
+        char fmtr[UINT_FMT] ;
+        fmt[uint_fmt(fmt, i+1)] = 0 ;
+        fmtr[uint_fmt(fmtr, roundtrips)] = 0 ;
+        strerr_warni5sys("NTP round-trip ", fmt, "/", fmtr, " failed") ;
+      }
+    }
+    else
+    {
+      tain_t cur, min, max ;
+      if (verbosity >= 3)
+      {
+        unsigned int j = 0 ;
+        for (; j < 4 ; j++)
+        {
+          uint64 ntp ;
+          localtmn_t l ;
+          char fmt[UINT_FMT] ;
+          char fmtntp[UINT64_XFMT] ;
+          char fmttaia[TAIN_FMT] ;
+          char fmtlocal[LOCALTMN_FMT] ;
+          ntp_from_tain(&ntp, &stamps[j]) ;
+          localtmn_from_tain(&l, &stamps[j], 1) ;
+          fmt[uint_fmt(fmt, j)] = 0 ;
+          fmttaia[tain_fmt(fmttaia, &stamps[j])] = 0 ;
+          fmtntp[uint64_xfmt(fmtntp, ntp)] = 0 ;
+          fmtlocal[localtmn_fmt(fmtlocal, &l)] = 0 ;
+          strerr_warni6x("stamp[", fmt, "] : taia: ", fmttaia, ", ntp: ", fmtntp) ;
+          strerr_warni2x("localdate: ", fmtlocal) ;
+        }
+      }
+      tain_add(&cur, &stamps[1], &deltaoffset) ;
+      tain_add(&min, &stamps[0], &deltamin) ;
+      tain_add(&max, &stamps[0], &deltamax) ;
+      if (tain_less(&cur, &max) && !tain_less(&cur, &min))
+        tain_sub(&deltamax, &cur, &stamps[0]) ;
+      tain_add(&cur, &stamps[2], &deltaoffset) ;
+      tain_add(&min, &stamps[3], &deltamin) ;
+      tain_add(&max, &stamps[3], &deltamax) ;
+      if (tain_less(&cur, &max) && !tain_less(&cur, &min))
+        tain_sub(&deltamin, &cur, &stamps[3]) ;
+    }
+
+    tain_add_g(&deadline, &throttletto) ;
+    if (tain_less(&globaldeadline, &deadline)) deadline = globaldeadline ;
+    deepsleepuntil_g(&deadline) ;
+    if (!tain_future(&globaldeadline))
+    {
+      if (verbosity)
+      {
+        errno = ETIMEDOUT ;
+        strerr_diefu1sys(1, "complete series of SNTP exchanges") ;
+      }
+      else return 1 ;
+    }
+  }
+
+  {
+    char adj[TAIN_PACK] ;
+    tain_t delta ;
+    if (tain_less(&deltamax, &deltamin)) tain_sub(&delta, &deltamin, &deltamax) ;
+    else tain_sub(&delta, &deltamax, &deltamin) ;
+    if (tain_less(&errmax, &delta))
+    {
+      if (verbosity)
+      {
+        char fmtd[TAIN_FMT] ;
+        char fmte[TAIN_FMT] ;
+        fmtd[tain_fmt(fmtd, &delta)] = 0 ;
+        fmte[tain_fmt(fmte, &errmax)] = 0 ;
+        strerr_warnw2x("maximum acceptable uncertainty: ", fmte) ;
+        strerr_warnw2x("current calculated uncertainty: ", fmtd) ;
+      }
+      if (!flagforce) strerr_dief1x(111, "time uncertainty too large") ;
+    }
+
+    tain_add(&delta, &deltamax, &deltamin) ;
+    tain_half(&delta, &delta) ;
+    tain_sub(&delta, &delta, &deltaoffset) ;
+    tain_pack(adj, &delta) ;
+    if (allwrite(1, adj, TAIN_PACK) < TAIN_PACK) strerr_diefu1sys(111, "write to stdout") ;
+  }
+  return 0 ;
+}
diff --git a/src/clock/s6-taiclock.c b/src/clock/s6-taiclock.c
new file mode 100644
index 0000000..99150b5
--- /dev/null
+++ b/src/clock/s6-taiclock.c
@@ -0,0 +1,182 @@
+/* ISC license. */
+
+#include <sys/types.h>
+#include <unistd.h>
+#include <errno.h>
+#include <skalibs/error.h>
+#include <skalibs/uint16.h>
+#include <skalibs/uint32.h>
+#include <skalibs/uint.h>
+#include <skalibs/sgetopt.h>
+#include <skalibs/allreadwrite.h>
+#include <skalibs/bytestr.h>
+#include <skalibs/strerr2.h>
+#include <skalibs/tai.h>
+#include <skalibs/djbtime.h>
+#include <skalibs/iopause.h>
+#include <skalibs/allreadwrite.h>
+#include <skalibs/socket.h>
+#include <skalibs/ip46.h>
+#include <skalibs/random.h>
+
+#define USAGE "s6-taiclock [ -f ] [ -v verbosity ] [ -r roundtrips ] [ -t triptimeout ] [ -h throttle ] [ -T totaltimeout ] [ -e errmax ] [ -p port ] ipaddress"
+#define dieusage() strerr_dieusage(100, USAGE)
+
+static unsigned int verbosity = 1 ;
+
+#define N 28
+
+int tain_exchange (int s, ip46_t const *ip, uint16 port, tain_t *serversays, tain_t const *deadline)
+{
+  char query[N] = "ctai" ;
+  char answer[N] ;
+  ip46_t dummyip ;
+  int r ;
+  uint16 dummyport ;
+  tain_pack(query+4, &STAMP) ;
+  if (badrandom_string(query+20, N-20) < N-20) return 0 ; /* cookie */
+  r = socket_sendnb46_g(s, query, N, ip, port, deadline) ;
+  if (r < 0) return 0 ;
+  if (r < N) return (errno = EPIPE, 0) ;
+  r = socket_recvnb46_g(s, answer, N, &dummyip, &dummyport, deadline) ;
+  if (r < 0) return 0 ;
+  if (r < N) return (errno = EPROTO, 0) ;
+  if (byte_diff(answer, 4, "stai")) return (errno = EPROTO, 0) ;
+  if (byte_diff(query+20, N-20, answer+20)) return (errno = EPROTO, 0) ;
+  tain_unpack(answer+4, serversays) ;
+  return 1 ;
+}
+
+int main (int argc, char const *const *argv)
+{
+  tain_t deltamin = TAIN_ZERO ;
+  tain_t deltaoffset ;
+  tain_t deltamax ;
+  tain_t errmax ;
+  tain_t timeouttto, throttletto, globaltto ;
+  tain_t globaldeadline ;
+  unsigned int roundtrips = 10 ;
+  unsigned int i = 0 ;
+  ip46_t ipremote ;
+  int sock ;
+  int flagforce = 0 ;
+  uint16 portremote = 4014 ;
+  PROG = "s6-taiclock" ;
+
+  {
+    unsigned int timeout = 2000 ;
+    unsigned int throttle = 0 ;
+    unsigned int bigtimeout = 10000 ;
+    unsigned int emax = 100 ;
+    subgetopt_t l = SUBGETOPT_ZERO ;
+    for (;;)
+    {
+      register int opt = subgetopt_r(argc, argv, "fv:r:t:h:T:e:p:", &l) ;
+      if (opt == -1) break ;
+      switch (opt)
+      {
+        case 'f' : flagforce = 1 ; break ;
+        case 'v' : if (!uint0_scan(l.arg, &verbosity)) dieusage() ; break ;
+        case 'r' : if (!uint0_scan(l.arg, &roundtrips)) dieusage() ; break ;
+        case 't' : if (!uint0_scan(l.arg, &timeout)) dieusage() ; break ;
+        case 'h' : if (!uint0_scan(l.arg, &throttle)) dieusage() ; break ;
+        case 'T' : if (!uint0_scan(l.arg, &bigtimeout)) dieusage() ; break ;
+        case 'e' : if (!uint0_scan(l.arg, &emax)) dieusage() ; break ;
+        case 'p' : if (!uint160_scan(l.arg, &portremote)) dieusage() ; break ;
+        default : dieusage() ;
+      }
+    }
+    argc -= l.ind ; argv += l.ind ;
+    if (timeout) tain_from_millisecs(&timeouttto, timeout) ;
+    else timeouttto = tain_infinite_relative ;
+    tain_from_millisecs(&throttletto, throttle) ;
+    if (bigtimeout) tain_from_millisecs(&globaltto, bigtimeout) ;
+    else globaltto = tain_infinite_relative ;
+    tain_from_millisecs(&errmax, emax) ;
+  }
+  if (!argc) dieusage() ;
+  if (!ip46_scan(argv[0], &ipremote)) dieusage() ;
+
+  sock = socket_udp46(ip46_is6(&ipremote)) ;
+  if (sock < 0) strerr_diefu1sys(111, "socket_udp") ;
+
+  tain_uint(&deltaoffset, 0xffffffffU) ;
+  tain_add(&deltaoffset, &deltaoffset, &deltaoffset) ; /* about 136 years */
+  tain_add(&deltamax, &deltaoffset, &deltaoffset) ;
+  tain_now_g() ;
+  tain_add_g(&globaldeadline, &globaltto) ;
+  if (!socket_deadlineconnstamp46_g(sock, &ipremote, portremote, &globaldeadline))
+    strerr_diefu1sys(111, "socket_deadlineconnstamp") ;
+
+  for (; i < roundtrips ; i++)
+  {
+    tain_t deadline, before, serversays ;
+    tain_add_g(&deadline, &timeouttto) ;
+    if (tain_less(&globaldeadline, &deadline)) deadline = globaldeadline ;
+    tain_copynow(&before) ;
+    if (!tain_exchange(sock, &ipremote, portremote, &serversays, &deadline))
+    {
+      if (verbosity >= 2)
+      {
+        char fmt[UINT_FMT] ;
+        char fmtr[UINT_FMT] ;
+        fmt[uint_fmt(fmt, i+1)] = 0 ;
+        fmtr[uint_fmt(fmtr, roundtrips)] = 0 ;
+        strerr_warni5sys("TAIA round-trip ", fmt, "/", fmtr, " failed") ;
+      }
+    }
+    else
+    {
+      tain_t cur, min, max ;
+      tain_add(&cur, &serversays, &deltaoffset) ;
+      tain_add(&min, &before, &deltamin) ;
+      tain_add(&max, &before, &deltamax) ;
+      if (tain_less(&cur, &max) && !tain_less(&cur, &min))
+        tain_sub(&deltamax, &cur, &before) ;
+      tain_add_g(&min, &deltamin) ;
+      tain_add_g(&max, &deltamax) ;
+      if (tain_less(&cur, &max) && !tain_less(&cur, &min))
+        tain_sub(&deltamin, &cur, &STAMP) ;
+    }
+
+    tain_add_g(&deadline, &throttletto) ;
+    if (tain_less(&globaldeadline, &deadline)) deadline = globaldeadline ;
+    deepsleepuntil_g(&deadline) ;
+    if (!tain_future(&globaldeadline))
+    {
+      if (verbosity)
+      {
+        errno = ETIMEDOUT ;
+        strerr_diefu1sys(1, "complete series of TAIA exchanges") ;
+      }
+      else return 1 ;
+    }
+  }
+
+  {
+    char adj[TAIN_PACK] ;
+    tain_t delta ;
+    if (tain_less(&deltamax, &deltamin)) tain_sub(&delta, &deltamin, &deltamax) ;
+    else tain_sub(&delta, &deltamax, &deltamin) ;
+    if (tain_less(&errmax, &delta))
+    {
+      if (verbosity)
+      {
+        char fmtd[TAIN_FMT] ;
+        char fmte[TAIN_FMT] ;
+        fmtd[tain_fmt(fmtd, &delta)] = 0 ;
+        fmte[tain_fmt(fmte, &errmax)] = 0 ;
+        strerr_warnw2x("maximum acceptable uncertainty: ", fmte) ;
+        strerr_warnw2x("current calculated uncertainty: ", fmtd) ;
+      }
+      if (!flagforce) strerr_dief1x(111, "time uncertainty too large") ;
+    }
+
+    tain_add(&delta, &deltamax, &deltamin) ;
+    tain_half(&delta, &delta) ;
+    tain_sub(&delta, &delta, &deltaoffset) ;
+    tain_pack(adj, &delta) ;
+    if (allwrite(1, adj, TAIN_PACK) < TAIN_PACK) strerr_diefu1sys(111, "write to stdout") ;
+  }
+  return 0 ;
+}
diff --git a/src/clock/s6-taiclockd.c b/src/clock/s6-taiclockd.c
new file mode 100644
index 0000000..b206400
--- /dev/null
+++ b/src/clock/s6-taiclockd.c
@@ -0,0 +1,54 @@
+/* ISC license. */
+
+#include <skalibs/bytestr.h>
+#include <skalibs/sgetopt.h>
+#include <skalibs/strerr2.h>
+#include <skalibs/fmtscan.h>
+#include <skalibs/djbunix.h>
+#include <skalibs/socket.h>
+#include <skalibs/tai.h>
+#include <skalibs/ip46.h>
+
+#define USAGE "s6-taiclockd [ -i ip ] [ -p port ]"
+#define dieusage() strerr_dieusage(100, USAGE)
+
+int main (int argc, char const *const *argv)
+{
+  int s ;
+  ip46_t ip = IP46_ZERO ;
+  uint16 port = 4014 ;
+  subgetopt_t l = SUBGETOPT_ZERO ;
+  PROG = "s6-taiclockd" ;
+  for (;;)
+  {
+    register int opt = subgetopt_r(argc, argv, "i:p:", &l) ;
+    if (opt == -1) break ;
+    switch (opt)
+    {
+      case 'i' : if (!ip46_scan(l.arg, &ip)) dieusage() ; break ;
+      case 'p' : if (!uint160_scan(l.arg, &port)) dieusage() ; break ;
+      default : dieusage() ;
+    }
+  }
+  argc -= l.ind ; argv += l.ind ;
+  s = socket_udp46(ip46_is6(&ip)) ;
+  if (s < 0) strerr_diefu1sys(111, "socket_udp") ;
+  if (ndelay_off(s) < 0) strerr_diefu1sys(111, "ndelay_off") ;
+  if (socket_bind46_reuse(s, &ip, port) < 0)
+    strerr_diefu1sys(111, "socket_bind_reuse") ;
+
+  for (;;)
+  {
+    char packet[256] ;
+    register int r = socket_recv46(s, packet, 256, &ip, &port) ;
+    if ((r >= 20) && !byte_diff(packet, 4, "ctai"))
+    {
+      tain_t now ;
+      packet[0] = 's' ;
+      if (!tain_sysclock(&now)) strerr_diefu1sys(111, "tain_sysclock") ;
+      tain_pack(packet + 4, &now) ;
+      if (socket_send46(s, packet, r, &ip, port) < 0)
+        strerr_warnwu1sys("socket_send") ;
+    }
+  }
+}