read_line

This function reads a complete newline-terminated line from the stream and returns it in allocated memory.

The trailing newline (and carriage return if any) are not included in the returned string.

Parameters:

this	a StreamBuffer object
cancellable	optional Cancellable object, or null

Returns:

the line read, which the caller must free when done with, or null on eof. If an error occurs, throws will be set.