Add recv_into method

[tekktrik]

Addresses Issue #55 by adding the recv_into() method. Tested with Adafruit CircuitPython 7.1.0-beta.0 on 2021-11-12; Adafruit Feather M4 Express with samd51j19 with AirLift FeatherWing, with a modified version of the esp32spi_tcp_client.py example!

[anecdata]

I believe for CPython compatibility, recv_into would return the number of bytes rather than the supplied buffer itself:
https://docs.python.org/3/library/socket.html#socket.socket.recv_into

Tested on:
Adafruit CircuitPython 7.1.0 on 2021-12-28; Adafruit PyPortal with samd51j20
with this code:

import time
from secrets import secrets  # pylint: disable=no-name-in-module
import board
from digitalio import DigitalInOut
from adafruit_esp32spi import adafruit_esp32spi
import adafruit_esp32spi.adafruit_esp32spi_socket as socket


TIMEOUT = 5
# edit host and port to match server
HOST = "wifitest.adafruit.com"
PORT = 80
MAXBUF = 512
INTERVAL = 5

# PyPortal or similar; edit pins as needed
spi = board.SPI()
esp32_cs = DigitalInOut(board.ESP_CS)
esp32_ready = DigitalInOut(board.ESP_BUSY)
esp32_reset = DigitalInOut(board.ESP_RESET)
esp = adafruit_esp32spi.ESP_SPIcontrol(spi, esp32_cs, esp32_ready, esp32_reset)

# connect to wifi AP
print("Connecting to wifi...")
esp.connect(secrets)

# create the socket
socket.set_interface(esp)
socketaddr = socket.getaddrinfo(HOST, PORT)[0][4]
s = socket.socket()
s.settimeout(TIMEOUT)

buf = bytearray(MAXBUF)
while True:
    print("Connecting to socket...")
    # s.connect((HOST, PORT))
    s.connect(socketaddr)

    s.send(b"GET /testwifi/index.html HTTP/1.0\r\n\r\n")
    print("Sent")

    # size = s.recv_into(buf)
    ret_buf = s.recv_into(buf)
    # print('Received', buf[:size])
    print('Received:\n', buf[:len(buf)].decode(), "\n?=\n", ret_buf[:len(ret_buf)].decode())

    s.close()

    time.sleep(INTERVAL)

[tekktrik]

Thanks @anecdata, good catch! Changed the return to the number of bytes read!

[anecdata]

Re-tested, size and buf are as expected. LGTM!

Since it's a new feature, there's little risk, but maybe one of the library devs want to look at it.