How to Resolve \"Invalid Argument\" Error When Setting Up an HTTP Server on a TCP Socket in Go?

HTTP Server over TCP Socket in Go: Resolving Invalid Argument Error

In Go, creating a TCP socket, binding it to a specific device (VRF interface), and setting up an HTTP server on it can be a cumbersome task. This article addresses the common error "accept tcp 127.0.0.1:80: accept: invalid argument" that can arise during this process.

The Problem

The provided code snippet shows an attempt to establish a TCP socket, bind it to a VRF interface, and start an HTTP server on that interface. However, the HTTP server fails to start, resulting in the aforementioned error.

The Solution

The incorrect socket configuration is the root cause of this error. To rectify it, we employ a net.ListenConfig to inject the desired socket options before the syscall.Bind step. This configuration ensures the socket setup is handled appropriately and aligns with the expectations of the net package.

Injecting Options with ListenConfig

net.ListenConfig offers a Control method that allows us to introduce customized socket options. It provides access to the raw file descriptor used in the socket configuration through a closure.

The code below demonstrates how to inject the SO_BINDTODEVICE option using the ListenConfig.Control function:

<code class="go">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>

By placing this code in the Control field of ListenConfig and using it to listen on a TCP address, we can inject our custom socket option before binding the socket:

<code class="go">lc := net.ListenConfig{Control: controlOnConnSetup}
ln, err := lc.Listen(context.Background(), "tcp", "127.0.0.1:80")</code>

This approach ensures that the socket is configured correctly and avoids the "invalid argument" error.

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