examples/: Add cat.cpp

rt/examples/cat.cpp

+#include <typon/typon.hpp>
+
+#include <cstdio>
+#include <string>
+
+using namespace typon;
+
+Task<int> cat(const char * path) {
+  struct statx statxbuf;
+  if (int err = co_await io::statx(AT_FDCWD, path, 0, STATX_SIZE, &statxbuf))
+  {
+    co_return err;
+  }
+  int fd = co_await io::openat(AT_FDCWD, path, O_RDONLY, 0);
+  if (fd < 0) {
+    co_return fd;
+  }
+
+  auto size = statxbuf.stx_size;
+  std::string buf(size, '\0');
+  int nbytes = co_await io::read(fd, buf.data(), size);
+
+  co_await io::close(fd);
+
+  if (nbytes < 0) {
+    co_return nbytes;
+  }
+
+  co_return co_await io::write(1, buf);
+}
+
+
+Root root(int argc, char * argv[]) {
+  if (argc < 2) {
+    fprintf(stderr, "Usage: %s [file name] <[file name] ...>\n", argv[0]);
+  }
+
+  for (int i = 1; i < argc; i++) {
+    int res = co_await cat(argv[i]);
+    if (res < 0) {
+      fprintf(stderr, "Failed to cat %s\n", argv[i]);
+    }
+  }
+}
+
+int main(int argc, char * argv[]) {
+  root(argc, argv).call();
+}