Custom Instrumentation

On this page you will learn how to manually propagate trace information into and out of your Native application.

To obtain trace headers from a transaction, use sentry_transaction_iter_headers(). For a span, use sentry_span_iter_headers(). Pass the returned value to the downstream service. If communication happens over HTTP, we recommend you attach all headers to the outgoing HTTP request.

Continuing a trace from an upstream service requires using sentry_transaction_context_update_from_header(). Before starting a transaction, pass its transaction context into the previous function along with the sentry-trace header. The transaction started with the transaction context will contain everything needed to continue the trace.

To obtain headers from a transaction so it can be continued from a downstream service, define a function which merges the headers into some aggregate object. Use the function in sentry_transaction_iter_headers() as a callback. The following example uses sentry_value_t as the aggregate object:

static void
copy_headers_to(const char *key, const char *value, void *userdata)
{
    sentry_value_t *headers
        = (sentry_value_t *)userdata;
    sentry_value_set_by_key(*headers, key, value);
}

int main(int argc, char **argv) {
  ...
	// Transaction to continue off of
	sentry_transaction_context_t *tx_ctx = sentry_transaction_context_new(
        "honk",
        NULL,
    );
    sentry_transaction_t *tx = sentry_transaction_start(tx_ctx, sentry_value_new_null());

	sentry_value_t *headers = sentry_value_new_object();
	sentry_transaction_iter_headers(tx, copy_headers_to, (void *)headers);
}

To create a transaction as a continuation of a trace retrieved from an upstream service, pass an iterator of the incoming headers to the transaction context:

	sentry_transaction_context_t *tx_ctx = sentry_transaction_context_new(
        "honk",
        NULL,
    );
    sentry_transaction_context_update_from_header(
        tx_ctx,
        "sentry-trace",
        "atraceid-aspanid-issampled",
    );