MicroPython socket-only file download routine with cert pinning and hashing

download.py

#DESIGNED FOR MICROPYTHON

server_dict = [{"address": "test.com","fingerprints":[bytearray('adlfasdfekre3r2309234902302lqkejroi23ro239842342304')]}] #list of possible servers and accepted keys

def download_file(server_dir,filename,server_index=0,block_size=512): #Boneless file downloader
    #typical socket stuff
    s = socket.socket()
    s.settimeout(60)
    ai = socket.getaddrinfo(server_dict[server_index]['address'], 443) #FIXME: This will probably do a dns lookup every time - probably shouldn't.
    addr = ai[0][-1]
    s.connect(addr)
    s = ssl.wrap_socket(s)
    #get the hash and compare
    certHash = binascii.hexlify(hashlib.sha256(s.getpeercert(True)).digest())
    print("Certificate Hash: " + str(certHash))
    print("Accepted Hashes:")
    for i in server_dict[server_index]['fingerprints']:
        print(str(i))
    if not bytearray(certHash) in server_dict[server_index]['fingerprints']:
        print("Certificate doesn't match.")
        s.close()
        return False
    #tell the server what you wnat
    http_headers = "POST " + server_dir + " HTTP/1.1\r\nConnection: Keep-Alive\r\nAccept: */*\r\nHost: " + server_dict[server_index]['address'] + "\r\nUser-Agent: Seldon\r\nContent-Type: application/x-www-form-urlencoded\r\nContent-Length: 0\r\n\r\n"
    s.write(http_headers)
    #Extract the content_length from the response header
    response_header = s.read(1)
    while not '\r\n\r\n' in response_header:
        response_header += s.read(1)
    response_header = str(response_header).split('\\r\\n')
    content_length = int([x for x in response_header if 'Content-Length' in x][0].replace('Content-Length: ',""))
    #Actually write to file now
    f = open(filename,'wb+')
    page_count = 0
    hash_obj = hashlib.sha256()
    while(True):
        if(content_length-(page_count*block_size) < block_size):
            response = s.read(content_length%block_size)
            f.write(response)
            hash_obj.update(response)
            print('Wrote ' + str(content_length%block_size))
            break
        else:
            response = s.read(block_size)
            f.write(response)
            hash_obj.update(response)
            page_count+=1
            print('Wrote full block')
    f.close()
    s.close()
    print("Final file size: ")
    print(os.stat(filename)[6])
    #return the hex digest
    return base64.b64encode(hash_obj.digest())