create library for using locationd in python using ffi (#20711)

* create library for using locationd in python using ffi

* lib is not required in release

* cleanup

* dont build liblocationd on release

* add check on buffer size
old-commit-hash: e08a570a13

selfdrive/locationd/SConscript

@@ -10,9 +10,13 @@ if GetOption('kaitai'):
 
 env.Program("ubloxd", ["ubloxd.cc", "ublox_msg.cc", "generated/ubx.cpp", "generated/gps.cpp"], LIBS=loc_libs)
 
-ekf_sym_cc = env.Object("#rednose/helpers/ekf_sym.cc")
+ekf_sym_cc = env.SharedObject("#rednose/helpers/ekf_sym.cc")
+locationd_sources = ["locationd.cc", "models/live_kf.cc", ekf_sym_cc]
 lenv = env.Clone()
 lenv["_LIBFLAGS"] += f' {libkf[0].get_labspath()}'
-locationd = lenv.Program("locationd", ["locationd.cc", "models/live_kf.cc", ekf_sym_cc],
-                         LIBS=loc_libs + transformations)
+locationd = lenv.Program("locationd", locationd_sources, LIBS=loc_libs + transformations)
 lenv.Depends(locationd, libkf)
+
+if File("liblocationd.cc").exists():
+  liblocationd = lenv.SharedLibrary("liblocationd", ["liblocationd.cc"] + locationd_sources, LIBS=loc_libs + transformations)
+  lenv.Depends(liblocationd, libkf)

selfdrive/locationd/liblocationd.cc

@@ -0,0 +1,22 @@
+#include "locationd.h"
+
+extern "C" {
+  typedef Localizer* Localizer_t;
+
+  Localizer *localizer_init() {
+    return new Localizer();
+  }
+
+  void localizer_get_message_bytes(Localizer *localizer, uint64_t logMonoTime,
+    bool inputsOK, bool sensorsOK, bool gpsOK, char *buff, size_t buff_size)
+  {
+    MessageBuilder msg_builder;
+    kj::ArrayPtr<char> arr = localizer->get_message_bytes(msg_builder, logMonoTime, inputsOK, sensorsOK, gpsOK).asChars();
+    assert(buff_size >= arr.size());
+    memcpy(buff, arr.begin(), arr.size());
+  }
+
+  void localizer_handle_msg_bytes(Localizer *localizer, const char *data, size_t size) {
+    localizer->handle_msg_bytes(data, size);
+  }
+}