在Python 3中通过套接字发送图像

Question

I am trying to send an image (screenshot) over socket from the client to the server. In Python 2 I was able to use the read() and write() function in order to read and write binary data as well as StringIO . But all of them disappeared in Python 3. I was playing around with PIL , but I can't get the test program running.

CLIENT

image = ImageGrab.grab()
s.send(image.tobytes())

I create a screenshot using GrabImage and save it as image . After that I send the image as binary over the socket to the server.

SERVER

data = conn.recv(4194304)
img = Image.frombytes('RGB', (1366, 768), data)
img.save('screenshot.jpg')

However, If I run the script I get an error message:
ValueError: not enough image data

I think I'm missing something decisive, but I can't figure it out.
Thank you, chrizator.

Answer 1

It's likely that the call to .recv() is returning before all the data is retrieved; the parameter is a maximum size, not an exact size. You'll need to call .recv() in a loop and append the data until the entire image is received. This implies that you'll need some way to know WHEN the entire data is received - common strategies for this are:

• Keep reading until you see some particular terminating character or character sequence. Not directly applicable in this case, since the raw image data could accidentally contain any particular sequence of bytes whatsoever.
• Send the length (perhaps as a decimal number with a terminator, or a fixed-size binary value) ahead of the data; keep reading until you've received that many bytes.
• Close the socket after sending the data; keep reading until you get a zero-byte result.