ssize_t Pair::prepareRead()

in gloo/transport/tcp/pair.cc [449:515]
48 lines of code
9 McCabe index (conditional complexity)

ssize_t Pair::prepareRead(
    Op& op,
    NonOwningPtr<UnboundBuffer>& buf,
    struct iovec& iov) {
  iov.iov_base = nullptr;
  iov.iov_len = 0;

  // Read preamble
  if (op.nread < sizeof(op.preamble)) {
    iov.iov_base = ((char*)&op.preamble) + op.nread;
    iov.iov_len = sizeof(op.preamble) - op.nread;
    return iov.iov_len;
  }

  auto opcode = op.getOpcode();
  auto offset = op.nread - sizeof(op.preamble);

  // Remote side is sending data to a buffer; read payload
  if (opcode == Op::SEND_BUFFER) {
    if (op.buf == nullptr) {
      op.buf = getBuffer(op.preamble.slot);
      // Buffer not (yet) registered, leave it for next loop iteration
      if (op.buf == nullptr) {
        return -1;
      }
    }

    iov.iov_base = ((char*)op.buf->ptr_) + offset + op.preamble.roffset;
    iov.iov_len = op.preamble.length - offset;

    // Bytes read must be in bounds for target buffer
    GLOO_ENFORCE_LE(op.preamble.roffset + op.preamble.length, op.buf->size_);
    return iov.iov_len;
  }

  // Remote side is sending data to an unbound buffer; read payload
  if (opcode == Op::SEND_UNBOUND_BUFFER) {
    if (!op.ubuf) {
      auto it = localPendingRecv_.find(op.preamble.slot);
      GLOO_ENFORCE(it != localPendingRecv_.end());
      std::deque<UnboundBufferOp>& queue = it->second;
      GLOO_ENFORCE(!queue.empty());
      std::tie(op.ubuf, op.offset, op.nbytes) = queue.front();
      queue.pop_front();
      if (queue.empty()) {
        localPendingRecv_.erase(it);
      }
    }

    // Acquire short lived pointer to unbound buffer.
    // This is a stack allocated variable in the read function
    // which is destructed upon that function returning.
    buf = NonOwningPtr<UnboundBuffer>(op.ubuf);
    if (!buf) {
      return -1;
    }

    iov.iov_base = ((char*)buf->ptr) + op.offset + offset;
    iov.iov_len = op.preamble.length - offset;

    // Bytes read must be in bounds for target buffer
    GLOO_ENFORCE_LE(op.preamble.length, op.nbytes);
    return iov.iov_len;
  }

  return 0;
}