Add support for querying the available built-in transports

Because the list of supported built-in transports depends on the
availability of external libraries (libusb, hidapi) and the operating
system, the application needs some mechanism to retrieve this
information at runtime. Therefore, a new dc_context_get_transports()
function is added, which returns a bitmask with all the available
built-in transports.

include/libdivecomputer/context.h

@@ -53,6 +53,9 @@ dc_context_set_loglevel (dc_context_t *context, dc_loglevel_t loglevel);
 dc_status_t
 dc_context_set_logfunc (dc_context_t *context, dc_logfunc_t logfunc, void *userdata);
 
+unsigned int
+dc_context_get_transports (dc_context_t *context);
+
 #ifdef __cplusplus
 }
 #endif /* __cplusplus */

src/context.c

@@ -19,6 +19,10 @@
  * MA 02110-1301 USA
  */
 
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
 #include <stdlib.h>
 #include <stdio.h>
 #include <stdarg.h>
@@ -313,3 +317,35 @@ dc_context_hexdump (dc_context_t *context, dc_loglevel_t loglevel, const char *f
 
 	return DC_STATUS_SUCCESS;
 }
+
+unsigned int
+dc_context_get_transports (dc_context_t *context)
+{
+	UNUSED(context);
+
+	return DC_TRANSPORT_SERIAL
+#if defined(HAVE_LIBUSB)
+		| DC_TRANSPORT_USB
+#endif
+#if defined(HAVE_HIDAPI)
+		| DC_TRANSPORT_USBHID
+#elif defined(HAVE_LIBUSB) && !defined(__APPLE__)
+		| DC_TRANSPORT_USBHID
+#endif
+#ifdef _WIN32
+#ifdef HAVE_AF_IRDA_H
+		| DC_TRANSPORT_IRDA
+#endif
+#ifdef HAVE_WS2BTH_H
+		| DC_TRANSPORT_BLUETOOTH
+#endif
+#else /* _WIN32 */
+#ifdef HAVE_LINUX_IRDA_H
+		| DC_TRANSPORT_IRDA
+#endif
+#ifdef HAVE_BLUEZ
+		| DC_TRANSPORT_BLUETOOTH
+#endif
+#endif /* _WIN32 */
+	;
+}

src/libdivecomputer.symbols

@@ -21,6 +21,7 @@ dc_context_new
 dc_context_free
 dc_context_set_loglevel
 dc_context_set_logfunc
+dc_context_get_transports
 
 dc_iterator_next
 dc_iterator_free