diff --git a/SConstruct b/SConstruct
index 9df0893..9ca8549 100644
--- a/SConstruct
+++ b/SConstruct
@@ -848,6 +848,7 @@ libgpsd_sources = [
     "driver_tsip.c",
     "driver_ubx.c",
     "driver_zodiac.c",
+    "callbacks.c",
 ]
 
 # Cope with scons's failure to set SONAME in its builtins.
@@ -1013,7 +1014,7 @@ gpsd = gpsd_env.Program('gpsd', gpsd_sources,
                         parse_flags = gpsdlibs + dbus_libs)
 env.Depends(gpsd, [compiled_gpsdlib, compiled_gpslib])
 
-gpsdecode = env.Program('gpsdecode', ['gpsdecode.c'], parse_flags=gpsdlibs)
+gpsdecode = env.Program('gpsdecode', ['gpsdecode.c', 'callbacks.c'], parse_flags=gpsdlibs)
 env.Depends(gpsdecode, [compiled_gpsdlib, compiled_gpslib])
 
 gpsctl = env.Program('gpsctl', ['gpsctl.c'], parse_flags=gpsdlibs)
@@ -1080,8 +1081,20 @@ else:
     # Build Python binding
     #
     python_extensions = {
-        "gps" + os.sep + "packet" : ["gpspacket.c", "packet.c", "isgps.c",
-                                        "driver_rtcm2.c", "strl.c", "hex.c", "crc24q.c"],
+        "gps" + os.sep + "packet" : ["gpspacket.c", "packet.c", "isgps.c", "callbacks.c",
+                                     "driver_rtcm2.c", "strl.c", "hex.c", "crc24q.c", "subframe.c",
+                                     "serial.c", "libgps_core.c", "libgps_sock.c", "json.c",
+                                     "bits.c", "libgps_json.c", "shared_json.c", "libgps_shm.c",
+                                     "gpsutils.c", "timebase.c", "rtcm3_json.c", "libgpsd_core.c",
+                                     "drivers.c", "driver_ais.c", "driver_nmea0183.c", "driver_nmea2000.c",
+                                     "driver_garmin_txt.c", "driver_evermore.c", "driver_garmin.c",
+                                     "driver_geostar.c", "driver_italk.c", "driver_oncore.c",
+                                     "driver_navcom.c", "driver_sirf.c", "driver_superstar2.c",
+                                     "driver_tsip.c", "driver_ubx.c", "driver_zodiac.c",
+                                     "net_dgpsip.c", "net_gnss_dispatch.c", "net_ntrip.c",
+                                     "netlib.c", "ais_json.c", "geoid.c", "bsd_base64.c",
+                                     "pseudoais.c", "pseudonmea.c", "rtcm2_json.c",
+                                     "gps_maskdump.c", "driver_rtcm3.c"],
         "gps" + os.sep + "clienthelpers" : ["gpsclient.c", "geoid.c", "gpsdclient.c", "strl.c"]
     }
 
diff --git a/gpsctl.c b/gpsctl.c
index b3c1142..c7c76b2 100644
--- a/gpsctl.c
+++ b/gpsctl.c
@@ -30,29 +30,16 @@ static unsigned int timeout = 0;	/* no timeout */
 static struct gps_context_t context;
 static bool hunting = true;
 
-ssize_t gpsd_write(struct gps_device_t *session,
-		   const char *buf,
-		   const size_t len)
-/* pass low-level data to devices straight through */
-{
-    return gpsd_serial_write(session, buf, len);
-}
-
 /*
  * Set this as high or higher than the maximum number of subtype
  * probes in drivers.c.
  */
 #define REDIRECT_SNIFF	15
 
-void gpsd_report(const int debuglevel, const int errlevel,
-		 const char *fmt, ...)
+static void gpsctl_report(const int debuglevel, const int errlevel,
+		 const char *fmt, va_list ap)
 {
-    va_list ap;
-
-    va_start(ap, fmt);
     gpsd_labeled_report(debuglevel, errlevel, "gpsctl:", fmt, ap);
-    va_end(ap);
-			
 }
 
 static void settle(struct gps_device_t *session)
@@ -214,6 +201,8 @@ int main(int argc, char **argv)
     ssize_t cooklen = 0;
 #endif /* RECONFIGURE_ENABLE */
 
+    gpsd_set_report_callback(gpsctl_report);
+
 #define USAGE	"usage: gpsctl [-l] [-b | -n | -r] [-D n] [-s speed] [-c rate] [-T timeout] [-V] [-t devtype] [-x control] [-e] <device>\n"
     while ((option = getopt(argc, argv, "bec:fhlnrs:t:x:D:T:V")) != -1) {
 	switch (option) {
diff --git a/gpsd.c b/gpsd.c
index dbda5a8..7df8927 100644
--- a/gpsd.c
+++ b/gpsd.c
@@ -165,25 +165,6 @@ static void onsig(int sig)
     signalled = (sig_atomic_t) sig;
 }
 
-ssize_t gpsd_write(struct gps_device_t *session,
-		   const char *buf,
-		   const size_t len)
-/* pass low-level data to devices straight through */
-{
-    return gpsd_serial_write(session, buf, len);
-}
-
-void gpsd_report(const int debuglevel, const int errlevel,
-		 const char *fmt, ...)
-{
-    va_list ap;
-
-    va_start(ap, fmt);
-    gpsd_labeled_report(debuglevel, errlevel, "gpsd:", fmt, ap);
-    va_end(ap);
-			
-}
-
 static void typelist(void)
 /* list installed drivers and enabled features */
 {
diff --git a/gpsd.h-tail b/gpsd.h-tail
index 5090e22..9e60544 100644
--- a/gpsd.h-tail
+++ b/gpsd.h-tail
@@ -990,6 +990,12 @@ __attribute__((__format__(__printf__, 3, 4))) void gpsd_report(const int, const
 void gpsd_report(const int, const int, const char *, ...);
 #endif
 
+/* over-ridable callouts from core library to application code */
+typedef void (*report_callback_t)(const int, const int, const char *, va_list);
+void gpsd_set_report_callback(report_callback_t);
+typedef ssize_t (*write_callback_t)(struct gps_device_t *, const char *, const size_t);
+void gpsd_set_write_callback(write_callback_t);
+
 #ifdef S_SPLINT_S
 extern struct protoent *getprotobyname(const char *);
 extern /address@hidden@*/char *strptime(const char *,const char *tp,/address@hidden@*/struct tm *)/address@hidden address@hidden/;
diff --git a/gpsdecode.c b/gpsdecode.c
index 2223881..2906a06 100644
--- a/gpsdecode.c
+++ b/gpsdecode.c
@@ -27,23 +27,10 @@ static unsigned int typelist[32];
  *
  **************************************************************************/
 
-ssize_t gpsd_write(struct gps_device_t *session,
-		   const char *buf,
-		   const size_t len)
-/* pass low-level data to devices straight through */
+static void gpsdecode_report(const int debuglevel, const int errlevel,
+		 const char *fmt, va_list ap)
 {
-    return gpsd_serial_write(session, buf, len);
-}
-
-void gpsd_report(const int debuglevel, const int errlevel,
-		 const char *fmt, ...)
-{
-    va_list ap;
-
-    va_start(ap, fmt);
     gpsd_labeled_report(debuglevel, errlevel, "gpsdecode:", fmt, ap);
-    va_end(ap);
-			
 }
 
 #ifdef AIVDM_ENABLE
@@ -644,6 +631,8 @@ int main(int argc, char **argv)
     enum
     { doencode, dodecode } mode = dodecode;
 
+    gpsd_set_report_callback(gpsdecode_report);
+
     while ((c = getopt(argc, argv, "cdejpst:uvVD:")) != EOF) {
 	switch (c) {
 	case 'c':
diff --git a/gpsmon.c b/gpsmon.c
index e6d57c8..c746ddc 100644
--- a/gpsmon.c
+++ b/gpsmon.c
@@ -588,7 +588,7 @@ static void packet_log(const char *fmt, ...)
 }
 #endif /* PPS_ENABLE */
 
-void gpsd_report(const int debuglevel, const int errlevel, const char *fmt, ...)
+static void gpsmon_report(const int debuglevel, const int errlevel, const char *fmt, va_list ap)
 /* our version of the logger */
 {
     char buf[BUFSIZ]; 
@@ -632,14 +632,11 @@ void gpsd_report(const int debuglevel, const int errlevel, const char *fmt, ...)
     (void)strlcpy(buf, "gpsmon:", BUFSIZ);
     (void)strncat(buf, err_str, BUFSIZ - strlen(buf));
     if (errlevel <= debuglevel) {
-	va_list ap;
-	va_start(ap, fmt);
 	packet_vlog(buf, sizeof(buf), fmt, ap);
-	va_end(ap);
     }
 }
 
-ssize_t gpsd_write(struct gps_device_t *session,
+static ssize_t gpsmon_write(struct gps_device_t *session,
 		   const char *buf,
 		   const size_t len)
 /* pass low-level data to devices, echoing it to the log window */
@@ -1087,6 +1084,9 @@ int main(int argc, char **argv)
     char inbuf[80];
     volatile bool nocurses = false;
 
+    gpsd_set_report_callback(gpsmon_report);
+    gpsd_set_write_callback(gpsmon_write);
+
     /*@ -observertrans @*/
     (void)putenv("TZ=UTC");	// for ctime()
     /*@ +observertrans @*/
diff --git a/gpspacket.c b/gpspacket.c
index cb85140..b63074b 100644
--- a/gpspacket.c
+++ b/gpspacket.c
@@ -14,11 +14,10 @@ static PyObject *ErrorObject = NULL;
 
 static PyObject *report_callback = NULL;
 
-void gpsd_report(int unused UNUSED, int errlevel, const char *fmt, ... )
+static void gpspacket_report(int unused UNUSED, int errlevel, const char *fmt, va_list ap)
 {
     char buf[BUFSIZ];
     PyObject *args;
-    va_list ap;
 
     if (!report_callback)   /* no callback defined, exit early */
 	return;
@@ -28,9 +27,7 @@ void gpsd_report(int unused UNUSED, int errlevel, const char *fmt, ... )
 	return;
     }
 
-    va_start(ap, fmt);
     (void)vsnprintf(buf, sizeof(buf), fmt, ap);
-    va_end(ap);
 
     args = Py_BuildValue("(is)", errlevel, buf);
     if (!args)
@@ -55,6 +52,7 @@ newLexerObject(PyObject *arg UNUSED)
     if (self == NULL)
 	return NULL;
     memset(&self->lexer, 0, sizeof(struct gps_packet_t));
+    gpsd_set_report_callback(gpspacket_report);
     packet_reset(&self->lexer);
     return self;
 }
diff --git a/test_geoid.c b/test_geoid.c
index 2392b1a..32f2d45 100644
--- a/test_geoid.c
+++ b/test_geoid.c
@@ -10,29 +10,18 @@
 
 #include "gpsd.h"
 
-ssize_t gpsd_write(struct gps_device_t *session,
-		   const char *buf,
-		   const size_t len)
-/* pass low-level data to devices straight through */
+static void test_geoid_report(const int debuglevel, const int errlevel,
+		 const char *fmt, va_list ap)
 {
-    return gpsd_serial_write(session, buf, len);
-}
-
-void gpsd_report(const int debuglevel, const int errlevel,
-		 const char *fmt, ...)
-{
-    va_list ap;
-
-    va_start(ap, fmt);
     gpsd_labeled_report(debuglevel, errlevel, "geoid:", fmt, ap);
-    va_end(ap);
-			
 }
 
 int main(int argc, char **argv)
 {
     double lat, lon;
 
+    gpsd_set_report_callback(test_geoid_report);
+
     if (argc != 3) {
 	fprintf(stderr, "Usage: %s lat lon\n", argv[0]);
 	return 1;
diff --git a/test_packet.c b/test_packet.c
index 2228ddb..5b61b30 100644
--- a/test_packet.c
+++ b/test_packet.c
@@ -17,27 +17,14 @@
 
 static int verbose = 0;
 
-ssize_t gpsd_write(struct gps_device_t *session,
-		   const char *buf,
-		   const size_t len)
-/* pass low-level data to devices straight through */
-{
-    return gpsd_serial_write(session, buf, len);
-}
-
-void gpsd_report(int debuglevel, int errlevel, const char *fmt, ...)
+static void test_packet_report(int debuglevel, int errlevel, const char *fmt, va_list ap)
 /* assemble command in printf(3) style, use stderr or syslog */
 {
     if (errlevel <= debuglevel) {
 	char buf[BUFSIZ];
-	va_list ap;
-
 	buf[0] = '\0';
-	va_start(ap, fmt);
 	(void)vsnprintf(buf + strlen(buf), sizeof(buf) - strlen(buf), fmt,
 			ap);
-	va_end(ap);
-
 	(void)fputs(buf, stderr);
     }
 }
@@ -400,6 +387,8 @@ int main(int argc, char *argv[])
     int failcount = 0;
     int option, singletest = 0;
 
+    gpsd_set_report_callback(test_packet_report);
+
     verbose = 0;
     while ((option = getopt(argc, argv, "ce:t:v:")) != -1) {
 	switch (option) {