Method communicate

cpp-subprocess/subprocess.hpp:2027–2090

  }

  inline std::pair<OutBuffer, ErrBuffer>
  Communication::communicate(const char* msg, size_t length)
  {
    // Optimization from subprocess.py
    // If we are using one pipe, or no pipe
    // at all, using select() or threads is unnecessary.
    auto hndls = {stream_->input(), stream_->output(), stream_->error()};
    int count = std::count(std::begin(hndls), std::end(hndls), nullptr);
    const int len_conv = length;

    if (count >= 2) {
      OutBuffer obuf;
      ErrBuffer ebuf;
      if (stream_->input()) {
        if (msg) {
          int wbytes = std::fwrite(msg, sizeof(char), length, stream_->input());
          if (wbytes < len_conv) {
            if (errno != EPIPE && errno != EINVAL) {
              throw OSError("fwrite error", errno);
            }
          }
        }
        // Close the input stream
        stream_->input_.reset();
      } else if (stream_->output()) {
        // Read till EOF
        // ATTN: This could be blocking, if the process
        // at the other end screws up, we get screwed as well
        obuf.add_cap(out_buf_cap_);

        int rbytes = util::read_all(
                            stream_->output(),
                            obuf.buf);

        if (rbytes == -1) {
          throw OSError("read to obuf failed", errno);
        }

        obuf.length = rbytes;
        // Close the output stream
        stream_->output_.reset();

      } else if (stream_->error()) {
        // Same screwness applies here as well
        ebuf.add_cap(err_buf_cap_);

        int rbytes = util::read_atmost_n(
                                  stream_->error(),
                                  ebuf.buf.data(),
                                  ebuf.buf.size());

        if (rbytes == -1) {
          throw OSError("read to ebuf failed", errno);
        }

        ebuf.length = rbytes;
        // Close the error stream
        stream_->error_.reset();