Major updates/cleanup.

src/internal/io/input.cc

@@ -16,9 +16,11 @@ std::pair<std::string, bool> IO::read_pipe() {
       continue;
     }
     if (n == 0) {
+      if (pipe_input.empty())
+        return {"", true};
       std::string line = std::move(pipe_input);
       pipe_input.clear();
-      return {line, true};
+      return {line, false};
     }
     if (errno == EINTR)
       continue;