CONTRIB: opentracing: add the OpenTracing filter

This commit adds the OpenTracing filter (hereinafter we will use the
abbreviated name 'the OT filter') to the contrib tree.

The OT filter adds native support for using distributed tracing in HAProxy.
This is enabled by sending an OpenTracing compliant request to one of the
supported tracers; such as Datadog, Jaeger, Lightstep and Zipkin tracers.
Please note: tracers are not listed by any preference, but alphabetically.

The OT filter is a standard HAProxy filter, so what applies to others also
applies to this one (of course, by that I mean what is described in the
documentation, more precisely in the doc/internals/filters.txt file).

The OT filter activation is done explicitly by specifying it in the HAProxy
configuration.  If this is not done, the OT filter in no way participates
in the work of HAProxy.

As for the impact on HAProxy speed, this is documented with several tests
located in the test directory, and the result is found in the README-speed-*
files.  In short, the speed of operation depends on the way it is used and
the complexity of the configuration, from an almost immeasurable impact to
a significant deceleration (5x and more).  I think that in some normal use
the speed of HAProxy with the filter on will be quite satisfactory with a
slowdown of less than 4%.

The OT filter allows intensive use of ACLs, which can be defined anywhere in
the configuration.  Thus, it is possible to use the filter only for those
connections that are of interest to us.

More detailed documentation related to the operation, configuration and use
of the filter can be found in the contrib/opentracing directory.

To make the OpenTracing filter easier to configure and compile, several
entries have been added to the Makefile.  When running the make utility,
it is possible to use several new arguments:

  USE_OT=1     : enable the OpenTracing filter
  OT_DEBUG=1   : compile the OpenTracing filter in debug mode
  OT_INC=path  : force the include path to libopentracing-c-wrapper
  OT_LIB=path  : force the lib path to libopentracing-c-wrapper
  OT_RUNPATH=1 : add libopentracing-c-wrapper RUNPATH to haproxy executable

If USE_OT is set, then an additional Makefile from the contrib/opentracing
directory is included in the compilation process.
diff --git a/contrib/opentracing/src/opentracing.c b/contrib/opentracing/src/opentracing.c
new file mode 100644
index 0000000..b79b90a
--- /dev/null
+++ b/contrib/opentracing/src/opentracing.c
@@ -0,0 +1,1035 @@
+/***
+ * Copyright 2020 HAProxy Technologies
+ *
+ * This file is part of the HAProxy OpenTracing filter.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ */
+#include "include.h"
+
+
+static struct pool_head *pool_head_ot_span_context = NULL;
+
+#ifdef USE_POOL_OT_SPAN_CONTEXT
+REGISTER_POOL(&pool_head_ot_span_context, "ot_span_context", MAX(sizeof(struct otc_span), sizeof(struct otc_span_context)));
+#endif
+
+
+#ifdef DEBUG_OT
+
+/***
+ * NAME
+ *   ot_text_map_show -
+ *
+ * ARGUMENTS
+ *   text_map -
+ *
+ * DESCRIPTION
+ *   -
+ *
+ * RETURN VALUE
+ *   This function does not return a value.
+ */
+void ot_text_map_show(const struct otc_text_map *text_map)
+{
+	FLT_OT_FUNC("%p", text_map);
+
+	if (text_map == NULL)
+		FLT_OT_RETURN();
+
+	FLT_OT_DBG_TEXT_MAP(text_map);
+
+	if ((text_map->key != NULL) && (text_map->value != NULL) && (text_map->count > 0)) {
+		size_t i;
+
+		for (i = 0; i < text_map->count; i++)
+			FLT_OT_DBG(3, "  \"%s\" -> \"%s\"", text_map->key[i], text_map->value[i]);
+	}
+
+	FLT_OT_RETURN();
+}
+
+
+/***
+ * NAME
+ *   ot_debug -
+ *
+ * ARGUMENTS
+ *   This function takes no arguments.
+ *
+ * DESCRIPTION
+ *   -
+ *
+ * RETURN VALUE
+ *   This function does not return a value.
+ */
+void ot_debug(void)
+{
+	char buffer[BUFSIZ];
+
+	FLT_OT_FUNC("");
+
+	otc_statistics(buffer, sizeof(buffer));
+	FLT_OT_DBG(0, "%s", buffer);
+
+	FLT_OT_RETURN();
+}
+
+#endif /* DEBUG_OT */
+
+
+/***
+ * NAME
+ *   ot_mem_malloc -
+ *
+ * ARGUMENTS
+ *   func -
+ *   line -
+ *   size -
+ *
+ * DESCRIPTION
+ *   -
+ *
+ * RETURN VALUE
+ *   -
+ */
+static void *ot_mem_malloc(FLT_OT_DBG_ARGS(const char *func, int line, ) size_t size)
+{
+	return flt_ot_pool_alloc(pool_head_ot_span_context, size, 1, NULL);
+}
+
+
+/***
+ * NAME
+ *   ot_mem_free -
+ *
+ * ARGUMENTS
+ *   func -
+ *   line -
+ *   ptr  -
+ *
+ * DESCRIPTION
+ *   -
+ *
+ * RETURN VALUE
+ *   This function does not return a value.
+ */
+static void ot_mem_free(FLT_OT_DBG_ARGS(const char *func, int line, ) void *ptr)
+{
+	flt_ot_pool_free(pool_head_ot_span_context, &ptr);
+}
+
+
+/***
+ * NAME
+ *   ot_init -
+ *
+ * ARGUMENTS
+ *   tracer -
+ *   config -
+ *   plugin -
+ *   err    -
+ *
+ * DESCRIPTION
+ *   -
+ *
+ * RETURN VALUE
+ *   -
+ */
+int ot_init(struct otc_tracer **tracer, const char *config, const char *plugin, char **err)
+{
+	char cwd[PATH_MAX], path[PATH_MAX], errbuf[BUFSIZ] = "";
+	int  rc, retval = -1;
+
+	FLT_OT_FUNC("%p:%p \"%s\", \"%s\", %p:%p", FLT_OT_DPTR_ARGS(tracer), config, plugin, FLT_OT_DPTR_ARGS(err));
+
+	flt_ot_pools_info();
+#ifdef USE_POOL_OT_SPAN_CONTEXT
+	FLT_OT_DBG(2, "sizeof_pool(ot_span_context) = %u", pool_head_ot_span_context->size);
+#endif
+
+	if (getcwd(cwd, sizeof(cwd)) == NULL) {
+		FLT_OT_ERR("failed to get current working directory");
+
+		FLT_OT_RETURN(retval);
+	}
+	rc = snprintf(path, sizeof(path), "%s/%s", cwd, plugin);
+	if ((rc == -1) || (rc >= sizeof(path))) {
+		FLT_OT_ERR("failed to construct the OpenTracing plugin path");
+
+		FLT_OT_RETURN(retval);
+	}
+
+	*tracer = otc_tracer_init(path, config, NULL, errbuf, sizeof(errbuf));
+	if (*tracer == NULL) {
+		FLT_OT_ERR("%s", (*errbuf == '\0') ? "failed to initialize tracing library" : errbuf);
+	} else {
+		otc_ext_init(ot_mem_malloc, ot_mem_free);
+
+		retval = 0;
+	}
+
+	FLT_OT_RETURN(retval);
+}
+
+
+/***
+ * NAME
+ *   ot_close -
+ *
+ * ARGUMENTS
+ *   tracer -
+ *
+ * DESCRIPTION
+ *   -
+ *
+ * RETURN VALUE
+ *   This function does not return a value.
+ */
+void ot_close(struct otc_tracer **tracer)
+{
+	FLT_OT_FUNC("%p:%p", FLT_OT_DPTR_ARGS(tracer));
+
+	if ((tracer == NULL) || (*tracer == NULL))
+		FLT_OT_RETURN();
+
+	(*tracer)->close(*tracer);
+
+	*tracer = NULL;
+
+	FLT_OT_RETURN();
+}
+
+
+/***
+ * NAME
+ *   ot_span_init -
+ *
+ * ARGUMENTS
+ *   tracer         -
+ *   operation_name -
+ *   ts_steady      -
+ *   ts_system      -
+ *   ref_type       -
+ *   ref_ctx_idx    -
+ *   ref_span       -
+ *   tags           -
+ *   num_tags       -
+ *   err            -
+ *
+ * DESCRIPTION
+ *   -
+ *
+ * RETURN VALUE
+ *   -
+ */
+struct otc_span *ot_span_init(struct otc_tracer *tracer, const char *operation_name, const struct timespec *ts_steady, const struct timespec *ts_system, int ref_type, int ref_ctx_idx, const struct otc_span *ref_span, const struct otc_tag *tags, int num_tags, char **err)
+{
+	struct otc_start_span_options  options;
+	struct otc_span_context        context = { .idx = ref_ctx_idx, .span = ref_span };
+	struct otc_span_reference      references = { ref_type, &context };
+	struct otc_span               *retptr = NULL;
+
+	FLT_OT_FUNC("%p, \"%s\", %p, %p, %d, %d, %p, %p, %d, %p:%p", tracer, operation_name, ts_steady, ts_system, ref_type, ref_ctx_idx, ref_span, tags, num_tags, FLT_OT_DPTR_ARGS(err));
+
+	if (operation_name == NULL)
+		FLT_OT_RETURN(retptr);
+	else if (tracer == NULL)
+		FLT_OT_RETURN(retptr);
+
+	(void)memset(&options, 0, sizeof(options));
+
+	if (ts_steady != NULL)
+		(void)memcpy(&(options.start_time_steady.value), ts_steady, sizeof(options.start_time_steady.value));
+
+	if (ts_system != NULL)
+		(void)memcpy(&(options.start_time_system.value), ts_system, sizeof(options.start_time_system.value));
+
+	if (FLT_OT_IN_RANGE(ref_type, otc_span_reference_child_of, otc_span_reference_follows_from)) {
+		options.references     = &references;
+		options.num_references = 1;
+	}
+
+	options.tags     = tags;
+	options.num_tags = num_tags;
+
+	retptr = tracer->start_span_with_options(tracer, operation_name, &options);
+	if (retptr == NULL)
+		FLT_OT_ERR("failed to init new span");
+	else
+		FLT_OT_DBG(2, "span %p:%zd initialized", retptr, retptr->idx);
+
+	FLT_OT_RETURN(retptr);
+}
+
+
+/***
+ * NAME
+ *   ot_span_init_va -
+ *
+ * ARGUMENTS
+ *   tracer         -
+ *   operation_name -
+ *   ts_steady      -
+ *   ts_system      -
+ *   ref_type       -
+ *   ref_ctx_idx    -
+ *   ref_span       -
+ *   err            -
+ *   tag_key        -
+ *   tag_value      -
+ *
+ * DESCRIPTION
+ *   -
+ *
+ * RETURN VALUE
+ *   -
+ */
+struct otc_span *ot_span_init_va(struct otc_tracer *tracer, const char *operation_name, const struct timespec *ts_steady, const struct timespec *ts_system, int ref_type, int ref_ctx_idx, const struct otc_span *ref_span, char **err, const char *tag_key, const char *tag_value, ...)
+{
+	struct otc_tag   tags[FLT_OT_MAXTAGS];
+	int              num_tags = 0;
+	struct otc_span *retptr;
+
+	FLT_OT_FUNC("%p, \"%s\", %p, %p, %d, %d, %p, %p:%p, \"%s\", \"%s\", ...", tracer, operation_name, ts_steady, ts_system, ref_type, ref_ctx_idx, ref_span, FLT_OT_DPTR_ARGS(err), tag_key, tag_value);
+
+	if (tag_key != NULL) {
+		va_list ap;
+
+		va_start(ap, tag_value);
+		for (num_tags = 0; (num_tags < FLT_OT_TABLESIZE(tags)) && (tag_key != NULL) && (tag_value != NULL); num_tags++) {
+			tags[num_tags].key = (char *)tag_key;
+			FLT_OT_VSET(&(tags[num_tags].value), string, tag_value);
+
+			tag_key = va_arg(ap, typeof(tag_key));
+			if (tag_key != NULL)
+				tag_value = va_arg(ap, typeof(tag_value));
+		}
+		va_end(ap);
+	}
+
+	retptr = ot_span_init(tracer, operation_name, ts_steady, ts_system, ref_type, ref_ctx_idx, ref_span, tags, num_tags, err);
+
+	FLT_OT_RETURN(retptr);
+}
+
+
+/***
+ * NAME
+ *   ot_span_tag -
+ *
+ * ARGUMENTS
+ *   span     -
+ *   tags     -
+ *   num_tags -
+ *
+ * DESCRIPTION
+ *   -
+ *
+ * RETURN VALUE
+ *   -
+ */
+int ot_span_tag(struct otc_span *span, const struct otc_tag *tags, int num_tags)
+{
+	int retval = -1;
+
+	FLT_OT_FUNC("%p, %p, %d", span, tags, num_tags);
+
+	if ((span == NULL) || (tags == NULL))
+		FLT_OT_RETURN(retval);
+
+	for (retval = 0; retval < num_tags; retval++)
+		span->set_tag(span, tags[retval].key, &(tags[retval].value));
+
+	FLT_OT_RETURN(retval);
+}
+
+
+/***
+ * NAME
+ *   ot_span_tag_va -
+ *
+ * ARGUMENTS
+ *   span  -
+ *   key   -
+ *   type  -
+ *   value -
+ *
+ * DESCRIPTION
+ *   -
+ *
+ * RETURN VALUE
+ *   -
+ */
+int ot_span_tag_va(struct otc_span *span, const char *key, int type, ...)
+{
+	va_list          ap;
+	struct otc_value ot_value;
+	int              retval = -1;
+
+	FLT_OT_FUNC("%p, \"%s\", %d, ...", span, key, type);
+
+	if ((span == NULL) || (key == NULL))
+		FLT_OT_RETURN(retval);
+
+	va_start(ap, type);
+	for (retval = 0; (key != NULL) && FLT_OT_IN_RANGE(type, otc_value_bool, otc_value_null); retval++) {
+		ot_value.type = type;
+		if (type == otc_value_bool)
+			ot_value.value.bool_value = va_arg(ap, typeof(ot_value.value.bool_value));
+		else if (type == otc_value_double)
+			ot_value.value.double_value = va_arg(ap, typeof(ot_value.value.double_value));
+		else if (type == otc_value_int64)
+			ot_value.value.int64_value = va_arg(ap, typeof(ot_value.value.int64_value));
+		else if (type == otc_value_uint64)
+			ot_value.value.uint64_value = va_arg(ap, typeof(ot_value.value.uint64_value));
+		else if (type == otc_value_string)
+			ot_value.value.string_value = va_arg(ap, typeof(ot_value.value.string_value));
+		else if (type == otc_value_null)
+			ot_value.value.string_value = va_arg(ap, typeof(ot_value.value.string_value));
+		span->set_tag(span, key, &ot_value);
+
+		key = va_arg(ap, typeof(key));
+		if (key != NULL)
+			type = va_arg(ap, typeof(type));
+	}
+	va_end(ap);
+
+	FLT_OT_RETURN(retval);
+}
+
+
+/***
+ * NAME
+ *   ot_span_log -
+ *
+ * ARGUMENTS
+ *   span       -
+ *   log_fields -
+ *   num_fields -
+ *
+ * DESCRIPTION
+ *   -
+ *
+ * RETURN VALUE
+ *   -
+ */
+int ot_span_log(struct otc_span *span, const struct otc_log_field *log_fields, int num_fields)
+{
+	int retval = -1;
+
+	FLT_OT_FUNC("%p, %p, %d", span, log_fields, num_fields);
+
+	if ((span == NULL) || (log_fields == NULL))
+		FLT_OT_RETURN(retval);
+
+	retval = MIN(OTC_MAXLOGFIELDS, num_fields);
+
+	span->log_fields(span, log_fields, retval);
+
+	FLT_OT_RETURN(retval);
+}
+
+
+/***
+ * NAME
+ *   ot_span_log_va -
+ *
+ * ARGUMENTS
+ *   span  -
+ *   key   -
+ *   value -
+ *
+ * DESCRIPTION
+ *   -
+ *
+ * RETURN VALUE
+ *   -
+ */
+int ot_span_log_va(struct otc_span *span, const char *key, const char *value, ...)
+{
+	va_list              ap;
+	struct otc_log_field log_field[OTC_MAXLOGFIELDS];
+	int                  retval = -1;
+
+	FLT_OT_FUNC("%p, \"%s\", \"%s\", ...", span, key, value);
+
+	if ((span == NULL) || (key == NULL) || (value == NULL))
+		FLT_OT_RETURN(retval);
+
+	va_start(ap, value);
+	for (retval = 0; (retval < FLT_OT_TABLESIZE(log_field)) && (key != NULL); retval++) {
+		log_field[retval].key                      = key;
+		log_field[retval].value.type               = otc_value_string;
+		log_field[retval].value.value.string_value = value;
+
+		key = va_arg(ap, typeof(key));
+		if (key != NULL)
+			value = va_arg(ap, typeof(value));
+	}
+	va_end(ap);
+
+	span->log_fields(span, log_field, retval);
+
+	FLT_OT_RETURN(retval);
+}
+
+
+/***
+ * NAME
+ *   ot_span_log_fmt -
+ *
+ * ARGUMENTS
+ *   span   -
+ *   key    -
+ *   format -
+ *
+ * DESCRIPTION
+ *   -
+ *
+ * RETURN VALUE
+ *   -
+ */
+int ot_span_log_fmt(struct otc_span *span, const char *key, const char *format, ...)
+{
+	va_list ap;
+	char    value[BUFSIZ];
+	int     n;
+
+	FLT_OT_FUNC("%p, \"%s\", \"%s\", ...", span, key, format);
+
+	if ((span == NULL) || (key == NULL) || (format == NULL))
+		FLT_OT_RETURN(-1);
+
+	va_start(ap, format);
+	n = vsnprintf(value, sizeof(value), format, ap);
+	if (!FLT_OT_IN_RANGE(n, 0, sizeof(value) - 1)) {
+		FLT_OT_DBG(2, "WARNING: log buffer too small (%d > %zu)", n, sizeof(value));
+
+		FLT_OT_STR_ELLIPSIS(value, sizeof(value));
+	}
+	va_end(ap);
+
+	FLT_OT_RETURN(ot_span_log_va(span, key, value, NULL));
+}
+
+
+/***
+ * NAME
+ *   ot_span_set_baggage -
+ *
+ * ARGUMENTS
+ *   span    -
+ *   baggage -
+ *
+ * DESCRIPTION
+ *   -
+ *
+ * RETURN VALUE
+ *   -
+ */
+int ot_span_set_baggage(struct otc_span *span, const struct otc_text_map *baggage)
+{
+	size_t i;
+	int    retval = -1;
+
+	FLT_OT_FUNC("%p, %p", span, baggage);
+
+	if ((span == NULL) || (baggage == NULL))
+		FLT_OT_RETURN(retval);
+
+	if ((baggage->key == NULL) || (baggage->value == NULL))
+		FLT_OT_RETURN(retval);
+
+	for (retval = i = 0; i < baggage->count; i++) {
+		FLT_OT_DBG(3, "set baggage: \"%s\" -> \"%s\"", baggage->key[i], baggage->value[i]);
+
+		if ((baggage->key[i] != NULL) && (baggage->value[i] != NULL)) {
+			span->set_baggage_item(span, baggage->key[i], baggage->value[i]);
+
+			retval++;
+		}
+	}
+
+	FLT_OT_RETURN(retval);
+}
+
+
+/***
+ * NAME
+ *   ot_span_set_baggage_va -
+ *
+ * ARGUMENTS
+ *   span  -
+ *   key   -
+ *   value -
+ *
+ * DESCRIPTION
+ *   -
+ *
+ * RETURN VALUE
+ *   -
+ */
+int ot_span_set_baggage_va(struct otc_span *span, const char *key, const char *value, ...)
+{
+	va_list ap;
+	int     retval = -1;
+
+	FLT_OT_FUNC("%p, \"%s\", \"%s\", ...", span, key, value);
+
+	if ((span == NULL) || (key == NULL) || (value == NULL))
+		FLT_OT_RETURN(retval);
+
+	va_start(ap, value);
+	for (retval = 0; (key != NULL); retval++) {
+		FLT_OT_DBG(3, "set baggage: \"%s\" -> \"%s\"", key, value);
+
+		span->set_baggage_item(span, key, value);
+
+		key = va_arg(ap, typeof(key));
+		if (key != NULL)
+			value = va_arg(ap, typeof(value));
+	}
+	va_end(ap);
+
+	FLT_OT_RETURN(retval);
+}
+
+
+/***
+ * NAME
+ *   ot_span_baggage_va -
+ *
+ * ARGUMENTS
+ *   span -
+ *   key  -
+ *
+ * DESCRIPTION
+ *   -
+ *
+ * RETURN VALUE
+ *   -
+ */
+struct otc_text_map *ot_span_baggage_va(const struct otc_span *span, const char *key, ...)
+{
+	va_list              ap;
+	struct otc_text_map *retptr = NULL;
+	int                  i, n;
+
+	FLT_OT_FUNC("%p, \"%s\", ...", span, key);
+
+	if ((span == NULL) || (key == NULL))
+		FLT_OT_RETURN(retptr);
+
+	va_start(ap, key);
+	for (n = 1; va_arg(ap, typeof(key)) != NULL; n++);
+	va_end(ap);
+
+	retptr = otc_text_map_new(NULL, n);
+	if (retptr == NULL)
+		FLT_OT_RETURN(retptr);
+
+	va_start(ap, key);
+	for (i = 0; (i < n) && (key != NULL); i++) {
+		char *value = (char *)span->baggage_item(span, key);
+
+		if (value != NULL) {
+			(void)otc_text_map_add(retptr, key, 0, value, 0, OTC_TEXT_MAP_DUP_KEY | OTC_TEXT_MAP_DUP_VALUE);
+
+			FLT_OT_DBG(3, "get baggage[%d]: \"%s\" -> \"%s\"", i, retptr->key[i], retptr->value[i]);
+		} else {
+			FLT_OT_DBG(3, "get baggage[%d]: \"%s\" -> invalid key", i, key);
+		}
+
+		key = va_arg(ap, typeof(key));
+	}
+	va_end(ap);
+
+	FLT_OT_RETURN(retptr);
+}
+
+
+/***
+ * NAME
+ *   ot_inject_text_map -
+ *
+ * ARGUMENTS
+ *   tracer  -
+ *   span    -
+ *   carrier -
+ *
+ * DESCRIPTION
+ *   -
+ *
+ * RETURN VALUE
+ *   -
+ */
+struct otc_span_context *ot_inject_text_map(struct otc_tracer *tracer, const struct otc_span *span, struct otc_text_map_writer *carrier)
+{
+	struct otc_span_context *retptr = NULL;
+	int                      rc;
+
+	FLT_OT_FUNC("%p, %p, %p", tracer, span, carrier);
+
+	if ((span == NULL) || (carrier == NULL))
+		FLT_OT_RETURN(retptr);
+	else if (tracer == NULL)
+		FLT_OT_RETURN(retptr);
+
+	retptr = span->span_context((struct otc_span *)span);
+	if (retptr == NULL)
+		FLT_OT_RETURN(retptr);
+
+	(void)memset(carrier, 0, sizeof(*carrier));
+
+	rc = tracer->inject_text_map(tracer, carrier, retptr);
+	if (rc != otc_propagation_error_code_success) {
+		FLT_OT_FREE_CLEAR(retptr);
+	} else {
+#ifdef DEBUG_OT
+		FLT_OT_DBG_TEXT_CARRIER(carrier, set);
+		ot_text_map_show(&(carrier->text_map));
+		FLT_OT_DBG_SPAN_CONTEXT(retptr);
+#endif
+	}
+
+	FLT_OT_RETURN(retptr);
+}
+
+
+/***
+ * NAME
+ *   ot_inject_http_headers -
+ *
+ * ARGUMENTS
+ *   tracer  -
+ *   span    -
+ *   carrier -
+ *   err     -
+ *
+ * DESCRIPTION
+ *   -
+ *
+ * RETURN VALUE
+ *   -
+ */
+struct otc_span_context *ot_inject_http_headers(struct otc_tracer *tracer, const struct otc_span *span, struct otc_http_headers_writer *carrier, char **err)
+{
+	struct otc_span_context *retptr = NULL;
+	int                      rc;
+
+	FLT_OT_FUNC("%p, %p, %p, %p:%p", tracer, span, carrier, FLT_OT_DPTR_ARGS(err));
+
+	if ((span == NULL) || (carrier == NULL))
+		FLT_OT_RETURN(retptr);
+	else if (tracer == NULL)
+		FLT_OT_RETURN(retptr);
+
+	retptr = span->span_context((struct otc_span *)span);
+	if (retptr == NULL) {
+		FLT_OT_ERR("failed to create span context");
+
+		FLT_OT_RETURN(retptr);
+	}
+
+	(void)memset(carrier, 0, sizeof(*carrier));
+
+	rc = tracer->inject_http_headers(tracer, carrier, retptr);
+	if (rc != otc_propagation_error_code_success) {
+		FLT_OT_ERR("failed to inject HTTP headers data");
+
+		FLT_OT_FREE_CLEAR(retptr);
+	} else {
+#ifdef DEBUG_OT
+		FLT_OT_DBG_TEXT_CARRIER(carrier, set);
+		ot_text_map_show(&(carrier->text_map));
+		FLT_OT_DBG_SPAN_CONTEXT(retptr);
+#endif
+	}
+
+	FLT_OT_RETURN(retptr);
+}
+
+
+/***
+ * NAME
+ *   ot_inject_binary -
+ *
+ * ARGUMENTS
+ *   tracer  -
+ *   span    -
+ *   carrier -
+ *
+ * DESCRIPTION
+ *   -
+ *
+ * RETURN VALUE
+ *   -
+ */
+struct otc_span_context *ot_inject_binary(struct otc_tracer *tracer, const struct otc_span *span, struct otc_custom_carrier_writer *carrier)
+{
+	struct otc_span_context *retptr = NULL;
+	int                      rc;
+
+	FLT_OT_FUNC("%p, %p, %p", tracer, span, carrier);
+
+	if ((span == NULL) || (carrier == NULL))
+		FLT_OT_RETURN(retptr);
+	else if (tracer == NULL)
+		FLT_OT_RETURN(retptr);
+
+	retptr = span->span_context((struct otc_span *)span);
+	if (retptr == NULL)
+		FLT_OT_RETURN(retptr);
+
+	(void)memset(carrier, 0, sizeof(*carrier));
+
+	rc = tracer->inject_binary(tracer, carrier, retptr);
+	if (rc != otc_propagation_error_code_success) {
+		FLT_OT_FREE_CLEAR(retptr);
+	} else {
+#ifdef DEBUG_OT
+		struct otc_jaeger_trace_context *ctx = carrier->binary_data.data;
+
+		FLT_OT_DBG_CUSTOM_CARRIER(carrier, inject);
+		FLT_OT_DBG(3, "trace context: %016" PRIx64 "%016" PRIx64 ":%016" PRIx64 ":%016" PRIx64 ":%02hhx <%s> <%s>",
+		           ctx->trace_id[0], ctx->trace_id[1], ctx->span_id, ctx->parent_span_id, ctx->flags,
+		           flt_ot_str_hex(ctx->baggage, carrier->binary_data.size - sizeof(*ctx)),
+		           flt_ot_str_ctrl(ctx->baggage, carrier->binary_data.size - sizeof(*ctx)));
+		FLT_OT_DBG_SPAN_CONTEXT(retptr);
+#endif
+	}
+
+	FLT_OT_RETURN(retptr);
+}
+
+
+/***
+ * NAME
+ *   ot_extract_text_map -
+ *
+ * ARGUMENTS
+ *   tracer   -
+ *   carrier  -
+ *   text_map -
+ *
+ * DESCRIPTION
+ *   -
+ *
+ * RETURN VALUE
+ *   -
+ */
+struct otc_span_context *ot_extract_text_map(struct otc_tracer *tracer, struct otc_text_map_reader *carrier, const struct otc_text_map *text_map)
+{
+	struct otc_span_context *retptr = NULL;
+	int                      rc;
+
+	FLT_OT_FUNC("%p, %p, %p", tracer, carrier, text_map);
+
+	if (carrier == NULL)
+		FLT_OT_RETURN(retptr);
+	else if (tracer == NULL)
+		FLT_OT_RETURN(retptr);
+
+	if (text_map != NULL) {
+		(void)memset(carrier, 0, sizeof(*carrier));
+		(void)memcpy(&(carrier->text_map), text_map, sizeof(carrier->text_map));
+
+		FLT_OT_DBG_TEXT_CARRIER(carrier, foreach_key);
+	}
+
+	rc = tracer->extract_text_map(tracer, carrier, &retptr);
+	if (rc != otc_propagation_error_code_success)
+		FLT_OT_FREE_CLEAR(retptr);
+	else if (retptr != NULL)
+		FLT_OT_DBG_SPAN_CONTEXT(retptr);
+
+	FLT_OT_RETURN(retptr);
+}
+
+
+/***
+ * NAME
+ *   ot_extract_http_headers -
+ *
+ * ARGUMENTS
+ *   tracer   -
+ *   carrier  -
+ *   text_map -
+ *   err      -
+ *
+ * DESCRIPTION
+ *   -
+ *
+ * RETURN VALUE
+ *   -
+ */
+struct otc_span_context *ot_extract_http_headers(struct otc_tracer *tracer, struct otc_http_headers_reader *carrier, const struct otc_text_map *text_map, char **err)
+{
+	struct otc_span_context *retptr = NULL;
+	int                      rc;
+
+	FLT_OT_FUNC("%p, %p, %p, %p:%p", tracer, carrier, text_map, FLT_OT_DPTR_ARGS(err));
+
+	if (carrier == NULL)
+		FLT_OT_RETURN(retptr);
+	else if (tracer == NULL)
+		FLT_OT_RETURN(retptr);
+
+	if (text_map != NULL) {
+		(void)memset(carrier, 0, sizeof(*carrier));
+		(void)memcpy(&(carrier->text_map), text_map, sizeof(carrier->text_map));
+
+		FLT_OT_DBG_TEXT_CARRIER(carrier, foreach_key);
+	}
+
+	rc = tracer->extract_http_headers(tracer, carrier, &retptr);
+	if (rc != otc_propagation_error_code_success) {
+		FLT_OT_ERR("failed to extract HTTP headers data");
+
+		FLT_OT_FREE_CLEAR(retptr);
+	}
+	else if (retptr != NULL)
+		FLT_OT_DBG_SPAN_CONTEXT(retptr);
+
+	FLT_OT_RETURN(retptr);
+}
+
+
+/***
+ * NAME
+ *   ot_extract_binary -
+ *
+ * ARGUMENTS
+ *   tracer      -
+ *   carrier     -
+ *   binary_data -
+ *
+ * DESCRIPTION
+ *   -
+ *
+ * RETURN VALUE
+ *   -
+ */
+struct otc_span_context *ot_extract_binary(struct otc_tracer *tracer, struct otc_custom_carrier_reader *carrier, const struct otc_binary_data *binary_data)
+{
+	struct otc_span_context *retptr = NULL;
+	int                      rc;
+
+	FLT_OT_FUNC("%p, %p, %p", tracer, carrier, binary_data);
+
+	if (carrier == NULL)
+		FLT_OT_RETURN(retptr);
+	else if (tracer == NULL)
+		FLT_OT_RETURN(retptr);
+
+	if ((FLT_OT_DEREF(binary_data, data, NULL) != NULL) && (binary_data->size > 0)) {
+		(void)memset(carrier, 0, sizeof(*carrier));
+		(void)memcpy(&(carrier->binary_data), binary_data, sizeof(carrier->binary_data));
+
+		FLT_OT_DBG_CUSTOM_CARRIER(carrier, extract);
+	}
+
+	rc = tracer->extract_binary(tracer, carrier, &retptr);
+	if (rc != otc_propagation_error_code_success)
+		FLT_OT_FREE_CLEAR(retptr);
+	else if (retptr != NULL)
+		FLT_OT_DBG_SPAN_CONTEXT(retptr);
+
+	FLT_OT_RETURN(retptr);
+}
+
+
+/***
+ * NAME
+ *   ot_span_finish -
+ *
+ * ARGUMENTS
+ *   span      -
+ *   ts_finish -
+ *   log_ts    -
+ *   log_key   -
+ *   log_value -
+ *
+ * DESCRIPTION
+ *   -
+ *
+ * RETURN VALUE
+ *   This function does not return a value.
+ */
+void ot_span_finish(struct otc_span **span, const struct timespec *ts_finish, const struct timespec *log_ts, const char *log_key, const char *log_value, ...)
+{
+	struct otc_finish_span_options options;
+	struct otc_log_field           log_field[OTC_MAXLOGFIELDS];
+	struct otc_log_record          log_records = { .fields = log_field, .num_fields = 0 };
+#ifdef DEBUG_OT
+	typeof((*span)->idx)           idx = FLT_OT_DDEREF(span, idx, 0);
+#endif
+
+	FLT_OT_FUNC("%p:%p, %p, %p, \"%s\", \"%s\", ...", FLT_OT_DPTR_ARGS(span), ts_finish, log_ts, log_key, log_value);
+
+	if ((span == NULL) || (*span == NULL))
+		FLT_OT_RETURN();
+
+	(void)memset(&options, 0, sizeof(options));
+
+	if (ts_finish != NULL)
+		(void)memcpy(&(options.finish_time.value), ts_finish, sizeof(options.finish_time.value));
+
+	if (log_key != NULL) {
+		va_list ap;
+		int     i;
+
+		if (log_ts != NULL)
+			(void)memcpy(&(log_records.timestamp.value), log_ts, sizeof(log_records.timestamp.value));
+
+		va_start(ap, log_value);
+		for (i = 0; (i < FLT_OT_TABLESIZE(log_field)) && (log_key != NULL); i++) {
+			log_field[i].key                      = log_key;
+			log_field[i].value.type               = otc_value_string;
+			log_field[i].value.value.string_value = log_value;
+
+			log_key = va_arg(ap, typeof(log_key));
+			if (log_key != NULL)
+				log_value = va_arg(ap, typeof(log_value));
+		}
+		va_end(ap);
+
+		log_records.num_fields  = i;
+		options.log_records     = &log_records;
+		options.num_log_records = 1;
+	}
+
+	/*
+	 * Caution: memory allocated for the span is released
+	 *          in the function finish_with_options().
+	 */
+	(*span)->finish_with_options(*span, &options);
+
+	FLT_OT_DBG(2, "span %p:%zu finished", *span, idx);
+
+	*span = NULL;
+
+	FLT_OT_RETURN();
+}
+
+/*
+ * Local variables:
+ *  c-indent-level: 8
+ *  c-basic-offset: 8
+ * End:
+ *
+ * vi: noexpandtab shiftwidth=8 tabstop=8
+ */