CODEWITHSUNDEEP
c++boost-asio
Christopher Pisz
Christopher Pisz

Reputation: 4010

boost::asio::streambuf::consume - Injects garbage character

When I lose connection, in my server code, I try to reconnect in a loop forever. Once I reconnect, I send a login message to the component I am connected to. That component then sends back a login response that looks like "MyResponse"

The initial connection works fine. After I reconnect, however, I get garbage before the expected message, that looks like: "ýMyResponse"

After googling this. I see many questions on Stack Overflow about the boost::asio::streambuf that is used for async sockets in boost::asio. Particularly about reusing he buffer. I have followed the advice there and called consume upon disconnecting. In other words, I call boost::asio::streambuf::consume after I call shutdown and close on my socket, after being called back with an error on recv in response to a call to recv_until.

I have also used wireshark to make sure that the garbage character is not being sent and it is not.

After much debugging, it appears as though the calls to consume are injecting a character rather than clearing out all characters.

Here is a minimal example:

#include <boost/asio.hpp>

#include <iostream>
#include <sstream>
#include <string>

int main()
{
    boost::asio::streambuf buffer;

    std::cout << "buffer size " << buffer.size() << std::endl;

    buffer.consume(std::numeric_limits<size_t>::max());

    std::cout << "buffer size " << buffer.size() << std::endl;

    std::istream is(&buffer);
    std::string contents;
    is >> contents;

    std::cout << "Contents: "  << contents << std::endl;

    std::cout << "buffer size " << buffer.size() << std::endl;

    return 0;
}

Output:

buffer size 0
buffer size 1
Contents: ²
buffer size 0

Expected Output:

buffer size 0
buffer size 0
Contents:
buffer size 0

If I do not use consume, I get some of the message, previous to disconnect, before the first message after reconnection, in my server code.

If I do use consume, I get a garbage character.

See:

Working with boost::asio::streambuf

Read until a string delimiter in boost::asio::streambuf

boost asio async_read: the read message adds to itself

Upvotes: 3

Views: 830

Answers (1)

Christopher Pisz
Christopher Pisz

Reputation: 4010

boost::asio::streambuf::consume overflows.

Use

buffer.consume(buffer.size());

Rather than

buffer.consume(std::numeric_limits<size_t>::max());

Reporting bug to boost mailing list.

Upvotes: 2

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