garbage send from python3 client to cpp server

Question

I have a CPP server and python3 client but when I'm sending data I'm getting garbage values (wrong numbers and \0 in the middle of the string) i tried to use this answer and also C++ TCP socket garbage value.

the client code (python3):

MESSAGE = "HELLO WORLD"
def send_via_socket(message):
    print(len(message))
    s.send(bytes([len(message)]))
    data = pack('<Q%ds' % len(message), len(message), message.encode())
    s.send(data)
    return True

SERVER_IP = "127.0.0.1"
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
# Create a socket object
ans = s.connect((SERVER_IP, PORT))
if ans is None:
     write_to_log('connection to server establish')
     send_via_socket(MESSAGE)
else:
     write_to_log('connection failed')
     message = s.recv(1024)
     write_to_log(str(message, 'utf-8'))
     res = res
except socket.error as err:
    message = f"socket creation failed with error %s" % err
    write_to_log(message)
    return res

and the read function in the server (cpp)

int Server::readString(int fd, std::string &str)
{
    size_t len;
    char *buf;

    auto bytesReceived =read(fd, &len, sizeof(len));
    if(bytesReceived == -1)
    {
        return bytesReceived;
    }
    buf = new char[len];
    bytesReceived = read(fd, buf, len);
    if(bytesReceived == -1)
    {
        return bytesReceived;
    }

    str.assign(buf, len);
    delete []buf;
    return bytesReceived;
}

I also have a CPP client and its work fine

yaodav · Accepted Answer · 2020-01-05 15:41:44Z

1

the answer that I found at the end was using Oleguer Canal functions

its solves all the garbage problome

answered Jan 5, 2020 at 15:41

yaodav

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1 Comment

Oleguer Over a year ago

Holly shit, just saw you linked my repo! Happy to be useful :)

lenik · Accepted Answer · 2019-12-29 14:38:28Z

0

This might fail, once the length of the encoded message is not equal to the length of the original message -- happens a lot, once you start sending UTF-8 or anything besides plain ASCII:

data = pack('<Q%ds' % len(message), len(message), message.encode())

You might be better off using protobuf or something like ZeroMQ for sending your data. Easy to implement in any language, and you don't have to count bytes anymore.

answered Dec 29, 2019 at 14:38

lenik

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Comments

Jeff Garrett · Accepted Answer · 2019-12-29 16:46:02Z

0

s.send(bytes([len(message)]))

Sends the length as a single byte.

auto bytesReceived =read(fd, &len, sizeof(len));

Reads the length as a size_t, which is more than a single byte.

answered Dec 29, 2019 at 16:46

Jeff Garrett

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