_fileobject.readline() from Python's standard-library socket.py

gistfile1.py

    def readline(self, size=-1):
        buf = self._rbuf
        buf.seek(0, 2)  # seek end
        if buf.tell() > 0:
            # check if we already have it in our buffer
            buf.seek(0)
            bline = buf.readline(size)
            if bline.endswith('\n') or len(bline) == size:
                self._rbuf = StringIO()
                self._rbuf.write(buf.read())
                return bline
            del bline
        if size < 0:
            # Read until \n or EOF, whichever comes first
            if self._rbufsize <= 1:
                # Speed up unbuffered case
                buf.seek(0)
                buffers = [buf.read()]
                self._rbuf = StringIO()  # reset _rbuf.  we consume it via buf.
                data = None
                recv = self._sock.recv
                while True:
                    try:
                        while data != "\n":
                            data = recv(1)
                            if not data:
                                break
                            buffers.append(data)
                    except error, e:
                        # The try..except to catch EINTR was moved outside the
                        # recv loop to avoid the per byte overhead.
                        if e.args[0] == EINTR:
                            continue
                        raise
                    break
                return "".join(buffers)

            buf.seek(0, 2)  # seek end
            self._rbuf = StringIO()  # reset _rbuf.  we consume it via buf.
            while True:
                try:
                    data = self._sock.recv(self._rbufsize)
                except error, e:
                    if e.args[0] == EINTR:
                        continue
                    raise
                if not data:
                    break
                nl = data.find('\n')
                if nl >= 0:
                    nl += 1
                    buf.write(data[:nl])
                    self._rbuf.write(data[nl:])
                    del data
                    break
                buf.write(data)
            return buf.getvalue()
        else:
            # Read until size bytes or \n or EOF seen, whichever comes first
            buf.seek(0, 2)  # seek end
            buf_len = buf.tell()
            if buf_len >= size:
                buf.seek(0)
                rv = buf.read(size)
                self._rbuf = StringIO()
                self._rbuf.write(buf.read())
                return rv
            self._rbuf = StringIO()  # reset _rbuf.  we consume it via buf.
            while True:
                try:
                    data = self._sock.recv(self._rbufsize)
                except error, e:
                    if e.args[0] == EINTR:
                        continue
                    raise
                if not data:
                    break
                left = size - buf_len
                # did we just receive a newline?
                nl = data.find('\n', 0, left)
                if nl >= 0:
                    nl += 1
                    # save the excess data to _rbuf
                    self._rbuf.write(data[nl:])
                    if buf_len:
                        buf.write(data[:nl])
                        break
                    else:
                        # Shortcut.  Avoid data copy through buf when returning
                        # a substring of our first recv().
                        return data[:nl]
                n = len(data)
                if n == size and not buf_len:
                    # Shortcut.  Avoid data copy through buf when
                    # returning exactly all of our first recv().
                    return data
                if n >= left:
                    buf.write(data[:left])
                    self._rbuf.write(data[left:])
                    break
                buf.write(data)
                buf_len += n
                #assert buf_len == buf.tell()
            return buf.getvalue()