Convert "binary string" to "const char*" for send (web server)

Question

I want send binary data with function send()

functions:

void ssend(const char* data){
    send(socket_fd, data, strlen(data), 0);
}

bool readFile(const char* path){
    std::ifstream ifile(path);
    if(ifile){
        if(!ifile.is_open()){
            ErrorPage("403");
            return true;
        }
        std::string sLine;

        std::string Header = "HTTP/1.1 200 OK\nConnection: Keep-Alive\nKeep-Alive: timeout=5, max=100\nServer: BrcontainerSimpleServer/0.0.1 (Win32) (Whitout Compiler code)\n\n";
        ssend(Header.c_str());

        while(!ifile.eof()){
            getline(ifile, sLine);
            cout << "String: " << sLine << endl;
            cout << "const char*: " << sLine.c_str() << endl;

            ssend(sLine.c_str());
        }
        return true;
    }
    return false;
}

Test:

...
while (1) {
    socket_fd = accept(listen_fd, (struct sockaddr *)&client_addr,&client_addr_length);
    readFile( httpPath );
    recv(socket_fd, request, 32768, 0);
    closesocket(socket_fd);
}
...

When converting to binary string with .c_str(), data disappear. How to solve this problem?

how to send binary data with the function send()?

Jonathan Wood · Accepted Answer · 2013-01-03 00:15:14Z

3

In C and C++, strings are terminated with a character with the value of zero ('\0'). So when you say "binary string", you are mixing things that don't go together since binary data is not the same as a string.

Instead of a string, use a BYTE array and pass the length as an additional argument so you know how many bytes to send.

Your use of strlen() will stop counting as soon as it encounters the string terminator.

answered Jan 3, 2013 at 0:15

Jonathan Wood

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4 Comments

Guy Sirton Over a year ago

std::string can hold binary data so if the OP doesn't convert to a C string he can make that work... (or vector<char>)

Jonathan Wood Over a year ago

Yes, I didn't mean to suggest that it couldn't be made to work but I don't consider it ideal. Aside from the null-terminator issue, there is also the issue of Unicode. So, I don't know what his send() method does, but I kind of think it should send bytes.

Guy Sirton Over a year ago

I think his send() is sockets API.

Korvo Over a year ago

Thanks, Jonathan, I used <vector>, +1 for you

Guy Sirton · Accepted Answer · 2013-01-03 01:51:58Z

1

You could:

void ssend(const std::string& data)
{
  send(socket_fd, data.data(), data.length(), 0);
}

or:

ssend(const std::vector<char>& data)
{
  send(socket_fd, &data[0], data.size(), 0);
}

If you are reading binary data from the file you will need to deal with that as well (e.g. open the file with ios::binary, use read() rather than getline()). You probably want to use some sort of encoding to send binary data out from a web server though.

answered Jan 3, 2013 at 1:51

Guy Sirton

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