How to Resolve \'Invalid Argument\' Error when Creating an HTTP Server on a Custom TCP Socket in Go?

HTTP Server from TCP Socket (in Go)

Problem:

Creating an HTTP server on a specific VRF interface using a custom TCP socket results in the error "accept tcp 127.0.0.1:80: accept: invalid argument."

Solution:

Injection of Socket Options Using net.ListenConfig:

To resolve this issue, use a net.ListenConfig to inject the desired socket options before calling syscall.Bind. This ensures that the socket setup is performed according to the specifications of the net package.

Steps:

1. Define a net.ListenConfig with a Control function to manipulate the raw file descriptor.
2. Use the Control function to call syscall.SetsockoptString to set the VRF interface binding.
3. Create a listener using the ListenConfig and serve HTTP requests.

Code Sample:

<code class="go">func main() {
    lc := net.ListenConfig{Control: controlOnConnSetup}

    ln, err := lc.Listen(context.Background(), "tcp", "127.0.0.1:80")
    if err != nil {
        log.Fatal(err)
    }
    ln.Close()
}

func controlOnConnSetup(network string, address string, c syscall.RawConn) error {
    var operr error
    fn := func(fd uintptr) {
        operr = syscall.SetsockoptString(int(fd), syscall.SOL_SOCKET, syscall.SO_BINDTODEVICE, "vrfiface")
    }
    if err := c.Control(fn); err != nil {
        return err
    }
    if operr != nil {
        return operr
    }
    return nil
}</code>

This approach allows for the addition of custom socket options before binding the socket to an IP address and port, resolving the issue encountered when creating an HTTP server on a specific VRF interface.

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