Add mode support to open()

rt/include/python/builtins.hpp

@@ -184,17 +184,55 @@ struct {
 using PyFile = decltype(file)::type;
 //}
 
-typon::Task<typon::PyFile> open(const PyStr &path, std::string_view mode) {
+typon::Task<PyFile> open(const PyStr &path, std::string_view mode) {
   const char *path_c = path.c_str();
+  size_t len = 0;
   struct statx statxbuf;
-  if (int err = co_await typon::io::statx(AT_FDCWD, path_c, 0, STATX_SIZE, &statxbuf)) {
-    system_error(-err, "statx()");
+  if (int err = co_await typon::io::statx(AT_FDCWD, path_c, 0, STATX_SIZE,
+                                          &statxbuf)) {
+    // new file
+  } else {
+    len = statxbuf.stx_size;
   }
-  int fd = co_await typon::io::openat(AT_FDCWD, path_c, O_RDONLY, 0);
+  int flags = 0;
+  bool created = false, writable = false, readable = false;
+
+  if (mode.find('x') != std::string_view::npos) {
+    created = true;
+    writable = true;
+    flags = O_EXCL | O_CREAT;
+  } else if (mode.find('r') != std::string_view::npos) {
+    readable = true;
+    flags = 0;
+  } else if (mode.find('w') != std::string_view::npos) {
+    writable = true;
+    flags = O_CREAT | O_TRUNC;
+  } else if (mode.find('a') != std::string_view::npos) {
+    writable = true;
+    flags = O_APPEND | O_CREAT;
+  }
+
+  if (mode.find('+') != std::string_view::npos) {
+    readable = true;
+    writable = true;
+  }
+
+  if (readable && writable) {
+    flags |= O_RDWR;
+  } else if (readable) {
+    flags |= O_RDONLY;
+  } else {
+    flags |= O_WRONLY;
+  }
+
+  flags |= O_CLOEXEC;
+
+  int fd = co_await typon::io::openat(AT_FDCWD, path_c, flags, 0666);
   if (fd < 0) {
+    std::cerr << path << "," << flags << std::endl;
     system_error(-fd, "openat()");
   }
-  co_return typon::PyFile(fd, statxbuf.stx_size);
+  co_return PyFile(fd, len);
 }
 
 #include "../typon/generator.hpp"