重用Python Bytearray / Memoryview

Question

I am attempting to receive a series of protobufs via a socket; I won't know the amount of data in advance. I'm sending a fair amount of them, and need to buffer the messages as I receive them (to ensure that I get all messages). I would like to make use of the bytearray/memoryview available in Python to eliminate an unnecessary copy.

I'm currently using a string and appending the data as I receive it. This is easy and I can "shift" down the "buffer" by doing something like:

# Create the buffer
str_buffer = []

# Get some data and add it to our "buffer"
str_buffer += "Hello World"

# Do something with the data . . .

# "shift"/offset the message by the data we processed
str_buffer = str_buffer[6:]

Is it possible to do something similar using a bytearray/memoryview?

# Create the buffer/memoryarray 
buffer = bytearray(1024)
view   = memoryview(buffer)

# I can set a single byte
view[0] = 'a'

# I can "offset" the view by the data we processed, but doing this 
# shrinks the view by 3 bytes. Doing this multiple times eventually shrinks
# the view to 0.
view = view[3:]

The problem arises when I try to add more data to the end. If I ever "offset" the existing view, the size of the view "shrinks*" and I can add less and less data. Is there anyway to reuse the existing memoryview and just shift the data to the left?

*Based on the documentation, I know I can't resize the array. I think the illusion of shrinking is a misunderstanding on my part.

Answer 1

you really, honestly don't need to know in advance how much data to expect, just keep reading until you don't get any more data:

import socket, sys

HOST = 'localhost'        # The remote host
PORT = 50007              # The same port as used by the server

recvbuff = bytearray(16)
recvview = memoryview(recvbuff)

size = 0

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((HOST, PORT))
while True:
    nbytes = s.recv_into(recvview)
    if not nbytes:
        break
    size += nbytes
    recvview = recvview[nbytes:]
    if not len(recvview):
        print "filled a chunk", recvbuff
        recvview = memoryview(recvbuff)

print 'end of data', recvbuff[:len(recvview)], size

s.close()