c()</code> call, and ahead of each subsequent burst of non-blockingly-available bytes as well. If it returns <code>true</code>, then the operation is canceled; the target buffer (if it has even been determined) is not written to further; and <code>on_rcvd_or_error()</code> is never invoked. Note that <code>should_interrupt_func()</code> may be called ages after whatever outside interrupt-causing condition has occurred; typically your impl would merely check for that condition being the case (e.g., "have we 