socket recv() is not returning in Python

Question

I was writing an echo server but recv() does not return while the sender process is alive. If I use one recv() call instead of my recvall() function, it is returning and working. Please let me know what is wrong with recvall() function..

Server:

import socket
def recvall(skt):
    msg_total = b""
    while True:
        msg = skt.recv(1024)
        if not msg: break
        msg_total += msg
    return msg_total
def main():
    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    s.bind(("localhost",3333))
    s.listen()
    conn,addr = s.accept()
    # data = conn.recv(1024) <= this recv() is not blocking
    data = recvall(conn)
    conn.sendall(data)
main()

Client:

import socket
def main():
    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    s.connect(("localhost",3333))
    msg = ("a" * 10).encode()
    s.sendall(msg)
    rsp = s.recv(1024)
main()